Gravity Field Discussion Forum
Dear ICGEM User,
Welcome to the Gravity Field Discussion Forum! This platform has been created to assist scientists, students, and anyone who is interested in using ICGEM service and its products.
Please post your questions, comments or critics here and ICGEM team will try to respond as soon as possible.
Moreover, other users are very welcome to actively join the discussion or answer the questions as well. Discussions of general interest can help many others and we make all inputs
available upon a confirmation by our system.
Before submitting your question, please take a look at our Frequently Asked Questions (FAQs) since your question might have already been asked and answered by our team.
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You may also contact us per email.
273 
Sinem

Tuesday, November 06. 2018 09:18:32 UTC 
Dear Reza,
It should be possible to get the ps files as well. Are you receiving errors? Could you please send us a screenshot at icgem@gfzpotsdam.de, then we can try to understand what the problem is.
Best regards,
Sinem 
272 
Reza

Wednesday, October 31. 2018 22:00:02 UTC 
Is it possible to get ps files like before? 
271 
Sinem

Wednesday, October 24. 2018 07:03:02 UTC 
Dear Mustafa Yilmaz,
Thank you for using the ICGEM service and for your question. I was wondering whether you meant Bouguer gravity anomalies. If yes, then we certainly expect a considerable difference between the two. If not, then please feel free to reach us at icgem@gfzpotsdam.de and we can exchange emails.
Best regards,
Sinem 
270 
MUSTAFA YILMAZ

Monday, October 22. 2018 17:20:49 UTC 
Dear ICGEM Editor,
Is it appropriate to compare the (spherical) gravity anomalies calculated from ICGEM calculation service (e.g. based on EIGEN6C4) with the (planar) terrestrial gravity anomalies?
How can the topography parameter be fixed?
Kind regards, 
269 
Sinem

Monday, October 01. 2018 09:08:57 UTC 
Dear Trinanda,
Could you please provide us more details what you meant by past data? All the models we have received as far are available on our service website. We do not remove the past data from our service. Once they are published, they are continuously available. Therefore, you can access to any (past) gravity models.
Best regards,
Sinem 
268 
Trinanda

Sunday, September 30. 2018 20:26:46 UTC 
Is it possible to download past data? 
267 
David Avalos

Tuesday, August 07. 2018 21:39:47 UTC 
True, it is there. I think knowing the Wo associated and choosing GM is just fine. Sorry for not seeing it before. Then if a different surface is wanted, like the geoid associated to a specific Wo (standard or personal choice) then one should make the correction by adding the appropriate constant. Cheers. 
266 
Franz Barthelmes

Tuesday, August 07. 2018 13:50:41 UTC 
Dear David,
the user selects the potential value (U0 = W0) for which the geoid is computed implicitely by choosing the reference system. The resulting value for U0 is in the header of the computed grid. You can also select the parameters of the ref. system separately (R, GM, flattening, omega). Do you think it would be better the user could choose the potential value U0 instead of GM?
Best regards
Franz 
265 
David Avalos

Monday, August 06. 2018 20:57:34 UTC 
Thanks to the ICGEM for maintaining a great service.
May I suggest indicating the value of potential to be modeled when we compute geoidal heights? It would be useful to see this number displayed in the description when selecting the functional "geoid" for calculation (or perhaps a chance to select a specific one). This helps interpreting the geoidal heights obtained. Cheers! 
264 
Sinem

Thursday, July 19. 2018 12:03:51 UTC 
Dear Bing Cheng,
Thank you for your message and welcome to the ICGEM service.
I will try to answer your questions here:
1) When you click on the link, it should open the page http://icgem.gfzpotsdam.de/tom_longtime , it is the table or more precisely the list of the models.
2) I am not sure which exact EGM official format you are familiar with. The format of ICGEM is widely used and all the gravity field models included in our service have the same self explanatory format. Please see also http://icgem.gfzpotsdam.de/ICGEMFormat2011.pdf for more information.
3)You could use our Calculation Service (http://icgem.gfzpotsdam.de/calc) with the grid step defined as 2.5 degree and compute the geoid model with the model of your interest.
4) Are you asking for the official download link for EGM2008? Then the following link may help.
http://earthinfo.nga.mil/GandG/wgs84/gravitymod/egm2008/index.html
Hope these answer your questions. Please do not hesitate to contact us if further information is needed.
Best regards,
Sinem 
263 
Bing Cheng

Thursday, July 19. 2018 01:07:27 UTC 
Dear ICGEM Professors,
As a newcomer to use ICGEM service and EGM gravity model,I have some questions:
(1) I did not find the download links referencing to question #8 in FAQs,there is not a table on the webpage when I click“table of models”in homepage.
(2)so called ICGEMformat has some different from the EGM official format?
(3)is there a 2.5*2.5 geoid grid file in ICGEM service？
(4)do you know a NGA offical download link?
thanks a lot! 
262 
Sinem

Thursday, May 31. 2018 06:46:00 UTC 
Dear Davy Raeder Brandão,
Thank you for using our service and your question. Just to clarify, are we talking about the value of the longitude in the output file? If yes, do you think it may be related to the representation of the value (East or West) based on the prime meridian? For example 42 degree west of the prime meridian (which is also represented as 42 degree) would correspond to 318 degree east of the prime meridian. You could simply add/subtract 360 degrees to represent the value the way you like it. Hope this solves your problem, if not please do not hesitate to send us another message.
Best regards,
Sinem 
261 
Davy Raeder Brandão

Wednesday, May 30. 2018 16:29:02 UTC 
first of all thanks ICGEM team for the opportunity to add knowlodge to my master research.
Now, as a beginner at the gravity research, i have a dummy question.
Why when i download the grid the geographic LONG table field is different from model figure created by the Calculation Service?
The expect number should be around 42 degrees, but it cames around +315. The LAT number look like ok, which is around 21.
How to fix it? 
260 
Branislav Glavatovic

Sunday, May 06. 2018 07:05:17 UTC 
The complete content and the way you offered the data on Earth's gravity field is really of great help for any research activity related to that field.
Thank you for you great effort ! 
259 
Elmas Sinem Ince

Wednesday, April 18. 2018 13:43:41 UTC 
Dear Zhouzhibo,
Thank you for using our service and also for your question. We realized that the calculation of Equivalent Water Height in our service may be confusing for other users too. Therefore, we will try here to clarify this topic by answering your question into two parts.
Equivalent Water Height (EWH) is a mathematical definition. In order to relate the EWH and gravity field functionals, we could start with the definition of the geoid. Geoid undulations are the undulations w.r.t. the ellipsoid, i.e., w.r.t. the equipotential surface of the ellipsoidal normal potential. The positive values refer to the undulations above ellipsoidal surface, whereas the negative values represent the undulations below the ellipsoidal surface. In order to simplify the thinking behind the EWH, we could start asking the following question for the longterm models.
1) If the geoid undulations are produced by water (density=1 g/cm3) only, how thick would this water layer be (and how would this thickness height of the water columns vary)?
Water here should not confuse you as it is used conventionally. It would have been possible to use another density and describe another type of column (e.g., rock column). As you experienced already, when you compute the EWH using any of the longterm models or GRACE monthly solutions you will see large numbers of an average of about 600 metre EWH values. These values represent how many metres of water column is needed to create “this much” geoid undulation.
Therefore, we believe nothing is wrong with the number “393 m” you received from the calculation service. To be precise, the negative sign here also represents the negative sign of the geoid undulation. Now, you can imagine for the static models this definition may not be very useful but in the following paragraph you will read how we use this information to monitor the variation of the gravity field.
Now, we can refer to the Equivalent Water Height variations which is more commonly used and sometimes shortly addressed as EWH only which leads confusions.
We must not forget that the main idea of the definition of the EWH is based on the variations of the monthly GRACE solutions. These variations can be in terms of disturbing potential, geoid undulations or any other functional of gravity field. In general, these variations are caused by mass redistributions. Most of the effects causing the mass redistributions are wellknown (e.g., tides) and can be modelled and accordingly removed from the measurements. The residual differences between the monthly solutions are assumed to be mainly caused by water redistribution (that is why it is called as water column but not rock!). So now the question can be modified into:
2) How much of a water column variation can cause or is needed to create “that much” geoid undulation variation between the monthly solutions?
If you take the difference of two or more subsequent monthly solutions in terms of EWH, you will see the values are much smaller which correspond to much smaller geoid variations between the solutions. This can also be computed using the differences of the spherical harmonic coefficients of subsequent monthly solutions directly.
Lastly, for your information, the calculation of the functional “water_column” provided in our service from a gravity field model, we consider the elastic deformation of the Earth due to load of the water layer. The exact formulations can be found in the following references:
Wahr, J., Molenaar, M., & Bryan, F. (1998). Time variability of the Earth's gravity field: Hydrological and oceanic effects and their possible detection using GRACE. Journal of Geophysical Research: Solid Earth, 103(B12), 3020530229.
Wahr, J. (2007). Timevariable gravity from satellites. Treatise on geophysics, 3, 213237.
Hope this helps.
Best regards,
Sinem 
258 
zhouzhibo

Saturday, April 14. 2018 01:56:15 UTC 
Hello，this is the first time for me to ask a question on this site which is very helpful. I am a senior undergraduate and my dissertation is related to satellite gravity，could you tell me the water column in the Calculation Serve? For example，393m，is it right？I think this number is too big. 
257 
Sinem

Friday, January 26. 2018 11:20:08 UTC 
Dear Bryan Andres,
The geoid values are computed on grid points using spherical harmonic coefficients. Therefore no interpolation is introduced at this point. Please do not hesitate to email us back if this does not answer your question.
Best regards,
Sinem 
256 
Andres

Wednesday, January 24. 2018 22:28:47 UTC 
Dear ICGEM EDITOR
I have an important question that its requierd for my University,
what model of interpolation is used in the geoid calculate? 
255 
Sinem

Wednesday, January 17. 2018 13:37:09 UTC 
Dear Mustafa Yilmaz,
Thank you for using our service and your question on the isostatic gravity anomalies. Please see below our answer.
Is there any functional selection in the Calculation Service (ICGEM) for computing "freeair gravity anomaly" and "isostatic gravity anomaly"?
We offer “gravity_anomaly_cl” which is defined as the magnitude of the gradient of the downward continued potential on the geoid minus the magnitude of the gradient of the normal potential on the ellipsoid. Therefore this is technically the free air gravity anomaly defined on the geoidal surface.
We do not offer the calculation of the isostatic gravity anomalies in our service. However, we offer the calculation of the functionals using topography related models which might be useful for this purpose. For more information, the authors of the topography related models can be contacted.
Is the "gravity_anomaly_bg" of the Calculation Service (ICGEM) "refined" or "simple" according to terrain correction?
 The Bouguer gravity anomaly we offer in the Calculation Service is defined based on the description of the simple Bouguer gravity anomaly since only the attraction of the Bouguer plate (2πGρH ) is removed. It is calculated by the spherical approximation of the classical gravity anomaly minus 2πGρH (eqs. 107 and 126 of Technical Report STR09/02). The topographic heights H(λ,φ) are calculated from the spherical harmonic model DTM2006 used up to the same maximum degree as the gravity field model. (For H ≥ 0 (rock) → ρ = 2670 kg/m3, and for H < 0 (water) → ρ = (2670−1025) kg/m3 is used.)
I will be pleased if you give information about the reduction steps of "gravity_earth" to the "gravity_ell" (freeair, bouguer, isostatic, etc.). Which functional(s) of the Calculation Service (ICGEM) can be used in this reduction?
In our calculation service, we use spherical harmonic coefficients that are harmonic outside of the masses. Therefore, we assume that we know the complete information concerning the gravity field. When we compute the gravity functionals at different points (e.g., at the Earth surface or on the geoidal surface), we use the same field information (spherical harmonic coefficients) assuming that the masses are pushed and condensed under the surface that the computation point is referred to. Therefore, we perform the computations at the exact point without applying any reduction. During the calculation process, the mass is already assumed to be condensed and no masses are left outside of the computation point. Based on this, we could tell this is close the definition of the free air reduction as we use a different height in the calculations.
Hope it helps.
Best regards,
Sinem 
254 
Mustafa YILMAZ

Wednesday, January 17. 2018 13:30:07 UTC 
Dear ICGEM Editor,
I am updating my entry (253).
Is there any functional selection in the Calculation Service for computing "isostatic gravity anomaly" with respect to longtime models (EGM08 etc.)?
Can "gravity anomaly_cl" be accepted as "freeair" (approximately)?
Kind regards? 
253 
Mustafa YILMAZ

Sunday, January 14. 2018 08:45:08 UTC 
Dear ICGEM Editor,
Is there any functional selection in the Calculation Service for computing "freeair gravity anomaly" and "isostatic gravity anomaly"?
Is the "gravity_anomaly_bg" of the Calculation Service "refined" or "simple", according to the terrain correction?
I will be pleased if you give information about the reduction of the "gravity_earth" to the "gravity_ell". Which of the functionals of the Calculation Service can be used in this reduction?
Kind regards, 
252 
Sinem

Tuesday, January 02. 2018 07:44:01 UTC 
Dear Luo,
Please refer to question #8 in our collected FAQs at icgem.gfzpotsdam.de/icgem_faq.pdf.
Best regards,
Sinem 
251 
luo

Saturday, December 30. 2017 02:47:54 UTC 
Dear ICGEM editor：
Where I should be how to download satellite gravity data (*.gbf), I haven't found the data in many places (about satellite gravity data).in this i hope for you help.thank you!
best regards
luo 
250 
Sinem

Friday, December 01. 2017 12:12:21 UTC 
Dear Andrew Klikunov,
Thank you for using our Calculation Service and your message. In the calculation of height_anomaly functional (on the Earth’s surface), we use a topography grid, namely ETOPO1. The resolution of the grid used here is 1min X 1min and this may cause to get different results than the real heights. Therefore, we believe it is normal to get some meters of differences in "h_over_geoid" with respect to real values. You would have a smaller difference when the calculation is performed with a higher resolution topography grid.
Hope it helps.
Best regards,
Sinem 
249 
Andrew Klikunov

Friday, December 01. 2017 08:53:51 UTC 
Hello! After calculating the height anomaly for a particular point on the surface of the Earth, I received a file with a "h_over geoid" 238,29 m and "height_anomaly" 6.297623494132 m. But the normal height (in Baltic system) of this point is 259 m. Why such a big difference? Is it somehow related to the resolution of the EGM2008 geoid model or I'm not doing the correct calculation? 
248 
Sinem

Tuesday, November 28. 2017 07:59:05 UTC 
Dear Zhang Panpan,
Please refer to FAQs, Question #8.
Best regards,
Sinem 
247 
ZHANG PANPAN

Monday, November 27. 2017 09:48:08 UTC 
Dear sir.
I want to download Static Models,but don not.do you have any ideas? thank you. 
246 
Sinem

Monday, November 20. 2017 09:24:15 UTC 
Dear Komal Pasricha,
Internal or external assessment of global gravity field models is not part of ICGEM. We however provide GNSS/levelling comparisons since these datasets are independent from the model content and help us evaluate the models regionally (or globally). At the moment, such independent external gravity anomalies (gravity anomalies that are not used in the development of the models) are not clearly known since most of the gravity anomalies (globally) are included in the determination of the global models.
EIGEN6C4 is developed based on gridded surface gravity data that are provided by DTU (over oceans) and EGM2008 (over continents) (see also the presentation by Foerste et al., 2014, 5th GOCE User Workshop, Paris which can be accessed through ICGEM, list of Static Models). Therefore, the accuracy over land may not be better than the accuracy level of EGM2008. For this reason, you may also want to refer to the JGR paper describing the development and evaluation of EGM2008.
Hope it helps.
Best regards.
Sinem 
245 
Komal Pasricha

Monday, November 20. 2017 08:32:38 UTC 
Dear Sir,
I want to know the accuracy of EIGEN6C4 gravity_anomaly_bg land data. 
244 
Franz Barthelmes

Tuesday, October 17. 2017 10:13:26 UTC 
Dear Ojima,
we are not the authors of DTM2006. It is a set of spherical harmonic coefficients.
As we wrote in entry 218 of our discussion forum the link to this data set is:
http://earthinfo.nga.mil/GandG/wgs84/gravitymod/egm2008/Coeff_Height_and_Depth_to2190_DTM2006.0.gz
In our service we use the topography of the model ETOPO1 (doi:10.7289/V5C8276M).
On the calculation service site:
http://icgem.gfzpotsdam.de/calc
you can use this topography model to compute grids  see the functionals:
topography_grd and topography_shm
and the description there.
Best regards
Franz 
243 
Ojima Apeh

Monday, October 16. 2017 23:59:12 UTC 
Dear Franz
Please, how can I access the 30″×30″ data of the DTM2006.0 database or DTM2006 database for RTM calculation?
Thanks 
242 
Vassilios D. Andritsanos

Wednesday, October 04. 2017 06:43:22 UTC 
Dear Franz.
There is a problem related to the calculation service: For any functional and any model I get
404 Not Found
File not found.
There is something wrong with the system, or is a wrong procedure from my part?
Thanks in advance
Vassilios 
241 
Rogers

Friday, September 29. 2017 18:45:59 UTC 
Dear,
Is the calculation service offline? Always I download the grid I get 404 error. Could you help me?
It is important mention Today I can not identify my server rules.
Thanks 
240 
Franz Barthelmes

Friday, September 08. 2017 11:40:15 UTC 
Dear Yan, dear Prahladh,
thank you for using our service. We try our best to answer questions.
However, let me ask you:
did you read our answers to frequently asked questions (FAQ) (see buttons on the left)?
The article about global models could also be helpful (link at the main ICGEMsite):
http://icgem.gfzpotsdam.de/GlobalModelsEncyclopedia.pdf
Best regards
Franz 
239 
prahladh kindangi

Friday, September 08. 2017 09:50:11 UTC 
Hi ICGEM
how can i calculate the grid space interval and i want to download gravity bouguer anomaly with half kilometer interval, please help me in this regarding and also i want to known which model is suitable for regional studies. 
238 
Yan

Thursday, September 07. 2017 02:52:39 UTC 
Hi ICGEM：
What is the formula for calculating the force of gravity?
Best regards
Yan 
237 
Qi

Thursday, September 07. 2017 01:31:37 UTC 
Dear Franz，
Sorry, I misunderstand the file. Thank you for the reply.
Regards
Qi 
236 
Franz Barthelmes

Wednesday, September 06. 2017 10:10:59 UTC 
Dear Qi,
sorry, I do not understand your question  maybe I'm too old (I use computers for more than 40 years) :( .
The *.gdf files are pure ascii text files. To open it you can use any plain text editor you like.
What do you mean with "projection of the file" ?
Best regards
Franz 
235 
Qi

Tuesday, September 05. 2017 12:12:58 UTC 
Hi ICGEM,
I used the calculation service to obtain the EIGEN6C4 Geoid. After the calculation, I downloaded a .gdf file. Could you tell me how can I open/load this file, particularly with matlab. In addition, what's the projection of the generated gdf file.
Thanks.
Qi 
234 
Franz Barthelmes

Monday, September 04. 2017 10:07:22 UTC 
Dear Yan Zhixue,
on our website (calculation service) the functionals "height_anomaly" and "height_anomaly_ell" are described as:
height_anomaly:
The so called "height anomaly" is an approximation of the geoid according to Molodensky's theory. It is equal to the geoid over sea.
Here it will be calculated, as defined, on the Earth's surface approximated by Bruns’ formula on the ellipsoid plus a first order correction (eqs. 81 and 119 of STR09/02).
height_anomaly_ell:
The height anomaly can be generalised to a 3d function, (sometimes called "generalised pseudoheightanomaly"). Here it can be calculated on (h=0) or above (h>0) the ellipsoid, approximated by Bruns’ formula (eqs. 78 and 118 of STR09/02).
Please let us know, what is unclear.
As well as any gravity field model the normal potential can be represented as a spherical harmonic model plus the centrifugal potential. The spherical harmonic coefficients of the normal potential WGS84 are (in icgemformat):
gfc 0 0 1.000000000000000E+00
gfc 2 0 4.841667749599428E04
gfc 4 0 7.903037334041510E07
gfc 6 0 1.687249611016718E09
gfc 8 0 3.460524681471410E12
gfc 10 0 2.650022244590134E15
These coefficients (plus the centrifugal acceleration) are used to compute the normal gravity for points lying above the ellipsoid (h>0).
Best regards
Franz 
233 
Yan Zhixue

Thursday, August 31. 2017 01:47:55 UTC 
Dear ICGEM：
What's the difference between height anomaly and height anomaly_ell?
Best regards,
Yan Zhixue 
232 
Yan Zhixue

Thursday, August 31. 2017 01:28:45 UTC 
Dear ICGEM team:
What is the normal gravity calculation formula for GNSS points in the equation of elevation anomaly?
Kind regards, 
231 
João Motta

Saturday, August 12. 2017 23:53:39 UTC 
Thanks for letting us now.
Best regards,
João 
230 
Elmas Sinem INCE

Tuesday, August 08. 2017 09:08:26 UTC 
Dear all,
Thank you very much for your messages.
Currently, we are experiencing some technical issues with our server due to a power outage occurred on August 1 on the entire campus. We are expecting to fix this issue by August 15th.
We are sorry for any inconvenience this situation may create and we would be more than happy to help if further assistance is needed.
Best regards,
ICGEM team 
229 
Joao Motta

Monday, August 07. 2017 22:11:10 UTC 
Hi ICGEM maintainers.
I am experience a shortage in the system since August 5. After inserting the parameters (e.g. defining area, degree/order, ...) an click to calculate the system goes 'waiting' with no response. Everytime I go to the calculation service for retrieving information I got stuck, even changing the model, parameters and functional.
I tried from different computers and connections so I imagine it has something to do with the system itself.
Is anyone reporting this as well?
Cheers. 
228 
Cahyo Nugroho

Monday, August 07. 2017 04:12:57 UTC 
Dear ICGEM,
I would like to use the calculation services. Unfortunately it doesn't work. It only says 'waiting' without giving any progress. What could go wrong?
Thank you.
Best regards,
Cahyo Nugroho 
227 
Agustina Pesce

Saturday, August 05. 2017 17:54:55 UTC 
Dear ICGEM team.
The Calculation Service is not working. Isthis possible? When will it be fixed?
Regards,
Agustina PEsce 
226 
Franz Barthelmes

Tuesday, July 04. 2017 11:15:51 UTC 
Dear Judith,
a sharp cut of the model will affect the computed geoid undulations. If the resulting oscillations are strong depends on what is "strong" :) .
The best way is probably (and this is my advise) to try it out. Compute the geoid undulations with sharp cut (Nmax = 89) and with different values for gentlecut. E.g. from 89 to 100, from 89 to 110, from 89 to 120 ...
However, in doing so, not all wavelengths shorter than related to degree 89 are filtered.
This is always the compromise of lowpass filtering:
(1) sharp cut in the frequency domain but oscillations in the spatial domain
(2) smooth cut (smooth transfer function in the frequency domain) with (unwanted) damping of wavelengths of the signal and (unwanted) "let through" of noise.
Sorry for my late response.
Kind regards
Franz 
225 
Judith Flamme

Monday, June 26. 2017 08:21:13 UTC 
Dear Dr. Franz Barthelmes,
i was wondering about the parameters (gentle cut, max value) I can choose if i want to have a geoid (EGM2008) calculated only up to degree 89 (complete, the cut must be after this value) and without oscillations... Do you have any advice on that subject ? In case of a sharp cut, will the oscillations strongly affect the geoid, or not ?
Thanks for helping me,
Kind regards
Judith Flamme 
224 
Franz Barthelmes

Wednesday, June 14. 2017 08:33:23 UTC 
Dear Vassilios,
please type the value for the grid step first with as many digits as necessary for you. Then it will be possible to write the values of the grid selection with the same number of digits.
Best regards
Franz 
223 
Vassilios D. Andritsanos

Wednesday, June 14. 2017 07:02:06 UTC 
Dear Dr. Barthelmes.
I noticed that the coordinates in the grid selection in the calculation service can be written with rounding up to the second digit after the decimal point while the grid spacing can be written without rounding (e.g. 0.083333333333). Is it possible to provide to the calculation service a grid with more than 2digits rounding?
Thank you in advance for you help.
V.D. Andritsanos 
222 
Franz Barthelmes

Monday, June 12. 2017 08:19:53 UTC 
Dear Ngole Moses,
the format of the models is very simple (I think it is selfexplanatory).
You can read it with any text editor which can read plain text.
Are you really not able to write a little software to read (or extract) the coefficients?
A description of the format is here:
http://icgem.gfzpotsdam.de/ICGEMFormat2011.pdf
Best regards
Franz 
221 
Ngole Moses

Friday, June 09. 2017 17:04:53 UTC 
How extracts records m n C s and sigma C of GOCO05c.gfc using matlab code or otherwise 
220 
Franz Barthelmes

Thursday, June 01. 2017 13:27:32 UTC 
Dear Ojima Apeh,
some (but not all) functionals can be calculated for different heights.
Please see the description of the functionals on the calculation service.
Unfortunately the input for the height over ellipsoid is active in any case.
For the functionals which can not be computed at different heights the value will be ignored.
Concerning the zero degree term please read the FAQs.
Best regards
Franz 
219 
Apeh O.I.

Wednesday, May 31. 2017 17:37:29 UTC 
Dear Barthelmes,
Thanks for your kind response.
In calculating geoid heights using ETOPO12250(topography_shm) on WGS84 reference ellipsoid;
(1) Is it necessary to input value for the 'height over the ellipsoid' and what is(are) the implications?
(2) Should the Zero Degree Term checkbox remain 'checked' or should be 'unchecked' and what is(are) the implications?
Simply put, how was ETOPO12250 used to calculate geoid heights used for calculating gravity_Anomally_Bg taking cognisance of 'height over the ellipsoid' and Zero Degree Term?
Best regards 
218 
Franz Barthelmes

Monday, May 29. 2017 11:28:28 UTC 
Here is the link to the Spherical Harmonic Coefficients for Earth's Elevation (Coeff_Height_and_Depth_to2190_DTM2006.0.gz  49 MB)
On the page:
http://earthinfo.nga.mil/GandG/wgs84/gravitymod/egm2008/first_release.html
you find:
http://earthinfo.nga.mil/GandG/wgs84/gravitymod/egm2008/Coeff_Height_and_Depth_to2190_DTM2006.0.gz 
217 
Apeh O.I.

Friday, May 26. 2017 11:47:11 UTC 
Really, you are rendering a great service. Please, can you send me a link on how to download DTM2006(for a given area of study) that you used for calculating the topography model for the GGMs. I want to carry out a terrain correction on some points to see if there will be significant improvement in the Bouguer anomaly.
Best regards 
216 
Sven Reißland

Monday, May 22. 2017 15:02:26 UTC 
Dear Aslınur,
the G3Browser will be renewed also. It should happen in the next two to three months.
Best regards,
Sven Reißland 
215 
Aslınur

Friday, May 19. 2017 21:38:58 UTC 
Dear ICGEM researchers,
I see that the website has been renewed but I could not find the G3 Browser. Is it temporary, where or when can I reach the G3 Browser?
Best regards
Aslınur 
214 
Daniel Arana

Tuesday, May 16. 2017 22:49:25 UTC 
Dear ICGEM team.
The link "http://icgem.gfzpotsdam.de/vis3d/gravityfieldtutorial.pdf" is not working.
Regards,
Daniel Arana 
213 
AbdelRahim

Sunday, April 02. 2017 15:13:23 UTC 
Dear, Dr.Franz Barthelmes
Thanks again for helping me
What does it mean: The main Contributions of static solutions for the satelliteonly model have been described the: unconstrained static solution or Kaula regularized (for example: from degree 121 to 200)?
The satelliteonly gravity field model: ITSGGrace2014 (MayerGürr et. al. 2014), derived from GRACE data and consists of two parts:
1. Unconstrained Static Solution ITSGGrace2014s
ITSGGrace2014s: unconstrained static gravity field, complete up to degree and order 200.
2. Regularized Static Solution ITSGGrace2014k
ITSGGrace2014k: complete up to degree and order 200, Kaula regularized from degree 121 to 200.
Regards
Abdel Rahim 
212 
Franz Barthelmes

Wednesday, March 29. 2017 08:46:25 UTC 
Dear Abdel,
usually the global models with a higher maximum degree fits GNSS/leveling
points better. You can compare the table on ICGEM (here are the first models
sorted according to their fit to all points):

Root mean square (rms) about mean of
GPS/levelling minus gravity field model derived geoid heights [m]

Model Nmax USA Canada Europe Australia Japan Brazil All
6196 2691 1047 201 816 1112 12036

EIGEN6C4 2190 0.247 m 0.126 m 0.121 m 0.212 m 0.079 m 0.446 m 0.2359 m
EIGEN6C3STAT 1949 0.247 m 0.129 m 0.121 m 0.213 m 0.078 m 0.447 m 0.2364 m
GECO 2190 0.246 m 0.131 m 0.123 m 0.216 m 0.080 m 0.451 m 0.2370 m
EIGEN6C2 1949 0.249 m 0.129 m 0.123 m 0.214 m 0.080 m 0.445 m 0.2373 m
EIGEN6C 1420 0.247 m 0.136 m 0.128 m 0.219 m 0.082 m 0.448 m 0.2380 m
EGM2008 2190 0.248 m 0.128 m 0.125 m 0.217 m 0.083 m 0.460 m 0.2395 m
GOCO05C 720 0.262 m 0.154 m 0.138 m 0.221 m 0.217 m 0.445 m 0.2539 m
GIF48 360 0.319 m 0.209 m 0.229 m 0.236 m 0.275 m 0.474 m 0.3055 m
GGM05C 360 0.321 m 0.213 m 0.225 m 0.239 m 0.282 m 0.461 m 0.3055 m
EIGEN51C 359 0.335 m 0.234 m 0.248 m 0.234 m 0.312 m 0.476 m 0.3218 m
EIGEN5C 360 0.341 m 0.278 m 0.266 m 0.244 m 0.339 m 0.524 m 0.3423 m
EIGENGL04C 360 0.339 m 0.282 m 0.309 m 0.244 m 0.321 m 0.541 m 0.3464 m
GGM03C 360 0.347 m 0.337 m 0.301 m 0.259 m 0.316 m 0.513 m 0.3566 m
EIGENCG01C 360 0.351 m 0.335 m 0.349 m 0.263 m 0.351 m 0.543 m 0.3682 m
EIGENCG03C 360 0.346 m 0.373 m 0.337 m 0.260 m 0.326 m 0.534 m 0.3702 m
GO_CONS_GCF_2_TIM_R5 280 0.398 m 0.310 m 0.343 m 0.336 m 0.450 m 0.505 m 0.3900 m
ITU_GGC16 280 0.398 m 0.310 m 0.343 m 0.335 m 0.450 m 0.505 m 0.3900 m
GOCO05S 280 0.399 m 0.308 m 0.344 m 0.335 m 0.450 m 0.505 m 0.3902 m
.
.

Nevertheless, meanwhile the satelliteonly models are rather good due to the
GOCE mission. Remember, the model EGM2008 do not contain GOCE data (because it
has been computed earlier).
Compared to the other regions, your rms differences of 0.870 m (EGM2008) and
0.894 m (GOCO05s) for Egypt implies that there are probably some errors in the
GNSS/leveling data.
Best regards
Franz 
211 
AbdelRahim

Friday, March 24. 2017 16:25:14 UTC 
Dear, Franz Barthelmes
Are the maximum degree and order of spherical harmonic model are the best from the lower?
I used the combined model EGM2008 [Pavlis et al. 2012], with the maximum degree and order 2190, and the satelliteonly model which called GOCO05s [Gürr et al. 2015], with the maximum degree and order 280, in Geoid modeling in Egypt.
The resolution of EGM2008 about 5 Arcminutes (≈ 9 km) globally, but I know that the Egyptian gravity data which have been used to establish the EGM2008 about 15 Arcminutes (≈ 27 km) Corresponding to 720 degrees.
The computation of the satelliteonly model GOCO05s, no terrestrial gravity data used, because it’s the satelliteonly model.
Comparisons in Egypt, using the EGM2008 and GOCO05s model, have been carried out in terms of geoid undulations, where the geoid heights were computed from the both models and compared against the geoid heights with respect to the GPS/leveling stations.
The results were as follows:
The average and the RMS difference are 0.225 m and 0.870 m, respectively in case of EGM2008
The average and the RMS difference are 0.136 m and 0.894 m, respectively in case of GOCO05s
What does mean that the average in case of the satelliteonly model GOCO05s better than the high degree model EGM2008, although the EGM2008 contains terrestrial gravity data for Egypt?
Regards
Abdel Rahim 
210 
Franz Barthelmes

Thursday, March 23. 2017 14:43:30 UTC 
Recollection
Imagine the 3 gravity fields:
(1) gravity field of the Earth, described in the rotating Earth fixed coordinate
system, under the assumption that Moon and Sun do not exist
==> tide free gravity field model
(2) gravity field of the Earth, described in the rotating Earth fixed coordinate
system, plus the gravity fields of the Moon and the Sun averaged over a long
time (which is called the permanent tidal effect), plus the effect of
Earth's deformation, caused by Moon and Sun, on the gravity field (also
averaged over time)
==> mean tide gravity field model
(3) gravity field of the Earth, described in the rotating Earth fixed coordinate
system, without the gravity fields of the Moon and the Sun, but, with the
indirect effect of Earth's deformation
==> zero tide gravity field model
The differences of these three gravity fields can be described (as the gravity
field itself) in terms of spherical harmonics. Strictly, these spherical
harmonic series go up to infinity. But, because the permanent (i.e. averaged
over time) tidal effects change the gravity field only very globally, it turned
out that it is sufficient to change only the coefficient C20, which describes
the flattening of the equipotential surfaces of the gravity field. 
209 
AbdelRahim

Monday, March 20. 2017 10:38:58 UTC 
Why use the coefficient C2,0 to Conversion between different permanent tide systems in any spherical harmonics model? 
208 
AbdelRahim

Thursday, February 02. 2017 11:23:38 UTC 
Dear, Franz
Thanks you very much for helping me, and I hope very much that in the following
I want to get more information about applications and use of global gravity field models in Geodesy or in general .
Regards
Abdel Rahim 
207 
Franz Barthelmes

Wednesday, February 01. 2017 18:36:59 UTC 
There are three tide systems that are considered in the computation of a geoid
model (see, e.g., https://cddis.nasa.gov/926/egm96/doc/S11.HTML).
The geoid in the three systems can be summarized as follows:
• Tidefree (or nontidal): This geoid is considered for a tidefree Earth with all
(direct and indirect) effects of the Sun and Moon removed.
• Meantide: This geoid is considered in the presence of the Sun and the Moon
(or, equivalently, if no permanent tidal effects are removed).
• Zerotide: This geoid is considered if the permanent direct effects of the Sun
and Moon are removed, but the indirect effect component related to the elastic
deformation of the Earth is retained.
The transformation between the different tide systems in our Calculation Service
only changes the coefficient C 20 
206 
AbdelRahim

Sunday, January 29. 2017 19:02:03 UTC 
What is meant of:
the spherical harmonic model of the Earth's gravitational field have been described as different tide systems such as Tide free, zero tide and mean tide?
More clarification is needed.... how it's done 
205 
Clauri

Saturday, December 10. 2016 04:25:47 UTC 
i would like to ask about how many way, WGS2008 is generated, i mean may be by directly measured terestrially or by sattelite or as combination.THx 
204 
Franz Barthelmes

Monday, September 19. 2016 16:36:45 UTC 
Dear Yawen She,
why do you think that the differences between gravity_anomaly_sa and
gravity_anomaly calculated with our service are to big? How big are they in
your computation?
The formulas for the computation are described in our STR 098/02, available at:
http://icgem.gfzpotsdam.de/ICGEM/theory/str0902revised.pdf
The formulas for the gravity anomaly according to Molodensky (functional
"gravity_anomaly") are (31),(32),(101) and (121) to (124).
The formulas for the gravity anomaly in spherical approximation (functional
"gravity_anomaly_sa") are (100) and (126).
The differences between both for the model EIGEN6C2 are shown in figure (14).
They range from min = 189 mgal to max = 302 mgal.
Kind regards
Franz 
203 
yawen she

Sunday, September 18. 2016 08:40:14 UTC 
Dear researchers:
I calculated the gravity_anomaly, gravity_anomaly_sa and geoid with EIGEN6C4
model by using your calculating service in WGS84 reference frame. The
difference between the gravity_anomaly_sa and gravity_anomaly should be due
to the geoid as your description. However, the large difference between these
two anomalies cannot be explained by the geoid. Thus, I wondered that is the
calculation of the gravity_anomaly is right?

202 
Franz Barthelmes

Monday, September 12. 2016 10:18:41 UTC 
Dear AbdelRahim,
I will contact you by email.
Best regards
Franz Barthelmes 
201 
AbdelRahim

Friday, September 09. 2016 05:54:08 UTC 
What is meant by Anomaly degree variances of Global Geopotential Models?
Anomaly degree variances and error degree variances used to Evaluation of the Global Geopotential Models
to choose the best for geoid determination or others applications

200 
Franz Barthelmes

Tuesday, April 19. 2016 07:57:39 UTC 
Dear Eugenia,
the monthly Equivalent Water Heights (EWH) at the G^{3} Browser are computed from the spherical harmonic
coefficients of the monthly models minus the coefficients of a mean model
(EIGEN6). These differencecoefficients can be used after filtering or without
filtering. The formulas for computing EWH from spherical harmonic coefficients
of a gravity field model are described in:
Wahr, J., M. Molenaar, and F. Bryan (1998),
Time variability of the Earth's gravity field: Hydrological and oceanic
effects and their possible detection using GRACE,
J. Geophys. Res., 103(B12), 3020530229, doi:10.1029/98JB02844.
and
John M. Wahr
TimeVariable Gravity From Satellites
http://igpphome.ucsd.edu/~mrsiegfr/wahr2007.pdf
Why do you want to transform EWH into height anomalies? The G^{3} Browser offers
both: EWH and height anomalies.
Best regards
Franz

199 
Maria Eugenia Gomez

Monday, April 18. 2016 17:33:38 UTC 
Dear ICGEM team,
I was looking into your G3 Browser and I wonder how you estimate the equivalent water hight from you monthly grace models. Which formualtion do you use.
And if you can suggest some reading about how to transform equivalent water height into height anomalies.
Kind regards,
Eugenia

198 
Franz Barthelmes

Wednesday, April 13. 2016 12:10:35 UTC 
This is an answer to frequently asked questions concerning the computation of
the geoid from a gravity field model and the so called "zero degree term".
Unfortunately the meaning of "zero degree term" is not unique.
Let's recapitulate what the geoid is and how it will be calculated from the
spherical harmonic coefficients of a gravity field model.
A spherical harmonic model of the Earth's gravitational field consists of the
coefficients C_{lm} and S_{lm}, a value for the geocentric gravitational constant GM,
and a value for R. For the model, R is nothing more than a mathematical reference
parameter. GM is an essential part of the model, multiplied by the coefficient
C_{00} (which usually is near 1) it is the mass of the Earth as it has been estimated
for this model. Additionally the tide system must be known. These values represent
the 3dimensional function of the geopotential W(x,y,z) (outside the masses).
The Geoid is one particular equipotential surface of the gravity potential of
the Earth. (Remember: the gravity potential is the gravitational potential plus the
centrifugal potential). Among all equipotential surfaces, the geoid is the one which
coincides with the undisturbed sea surface and its fictitious continuation below
the continents. If we know the gravity potential W we know all equipotential
surfaces, but we don't know which one is the geoid. To calculate the geoid from
a selected model we must know which potential value W = constant = W_{0} the real
geoid has.
Therefore, usually the geoid is given as geoid undulations or geoid heights with respect to
a reference system which consists of a geometrical rotational ellipsoid (normal ellipsoid)
and an associated ellipsoidal normal potential U = U(x,y,z). The geometrical ellipsoid
should approximate the real geoid as good as possible (in the least squares sense).
The normal potential is defined in such a way that its value on the normal ellipsoid
is U = constant = U_{0} and approximates the real value W_{0} as good as it is known
(at the time when this reference system is defined).
Hence, the reference system also defines the value W_{0} = U_{0}.
A reference system is defined by 4 defining parameters, which are usually the
following ones:
 equatorial radius of the Earth: R
 flattening: f
 geocentric gravitational constant: GM (mass of the Earth * Newton's gravitational constant)
 angular velocity of the Earth: omega
In this case U_{0} is a derived parameter.
Sometimes U_{0} is used as defining parameter instead of GM.
⇒ Consequently, it makes no sense to say:
"geoid heights of the model xy (e.g. EGM2008)"
⇒ We must say:
"geoid heights of the model xy with respect to the reference system abc (e.g. WGS84)"
Of course, our philosophy is not to change ("improve") any coefficients of the
models including the value of GM of the model and not to change ("improve")
the defining parameters of the reference system with respect to which the geoid
should be calculated.
⇒ our "zerodegreeterm" is only caused by different values of GM*C_{00} of the
model, and GM of the normal potential, i.e. the reference system.
Sometimes additionally the effect of a new (better) value for W_{0} (which differs
from the reference system's value U_{0}) is included into the "zerodegreeterm".
But we do not do that because in this case it is not possible to say:
"geoid heights of the model xy with respect to the reference system abc.
To use an improved value of W_{0} ( ≠ U_{0}) we think it is better to change the
reference system (such that U_{0} = W_{0}) instead of adding a correction term afterwards.
If you want to do so you can use your own reference system (user_defined) in the calculation
service of ICGEM.

197 
Franz Barthelmes

Tuesday, March 15. 2016 10:18:11 UTC 
Dear Peter,
this model (GOCO05S) is not a static model. It depends not only on the spatial
coordinates (x,y,z) or (radius, longitude, latitude) but also on time.
A static model consists of the spherical harmonic coefficients C(l,m) and S(l,m)
where l is called degree, and m order. The potential W (of such a static model)
at a given position, i.e. W(r,long,lat), is calculated by summing up over
degree and order of a spherical harmonic expansion (see, e.g. equation 108 of
the report:
http://icgem.gfzpotsdam.de/ICGEM/theory/str0902revised.pdf )
In the model GOCO05S each coefficient (up to degree and order 100) has a static
part, a linear trend with time and a sinusoidal time change with an annual
period.
If G(t) is a coefficient Clm(t) or Slm(t) its value for the time t is:
G(t)=gfct(t0)+trnd*(tt0)+asin*sin(2pi/T*(tt0))+acos*cos(2pi/T*(tt0))
where
gfct(t0) is the static part at time t0
trnd is the linear trend
asin is the amplitude of the sinepart
acos is the amplitude of the cosinepart
T is the annual period
(Remember that the amplitude and phase of a sinusoidal wave with fixed period
can be transformed mathematically into a sineamplitude and a cosineamplitude
together with the same period)
(see also posting 111)
"V(t)" in the description of GOCO05S is (in my opinion) misleading.
The formula delivers the value of each coefficient for the time t and not the
potential which is is denotated by "V".
For more details concerning the model GOCO05S contact the authors.
I hope this will be helpful (?).
Best regards
Franz

196 
Peter Ntimoah

Friday, March 11. 2016 15:40:33 UTC 
Hi There,
I would like to thank you so much for the service you provide through ICGEM website.
I am doing my research on geoid and gravity field. I am using my own software (in Matlab).
I am wondering about GOCO25S geopotential model, how can I solve the following information that are mentioned in the gfc file
"To compute a gravity field functional at an arbitrary time t, the expression
V(t) = gfct + trnd * (tt0)/T + acos*cos( 2pi * (tt0)/T ) + asin*sin( 2pi * (tt0)/T )
with t0 as the reference epoch and T as the annual period (365.25 d), has to be used.
The reference epoch is 20080101 (MJD 54466)"
I can not understand it well
Your help is much appreciated,
Thank you,
Peter 
195 
Jesse Jones

Tuesday, February 23. 2016 21:29:04 UTC 
Impressed, a lot of effort and research involved. Keep up the Great work. 
194 
Ologun Fermi

Friday, January 22. 2016 05:43:56 UTC 
It is quiet a good job done here. weldone

193 
Wolfgang Köhler

Monday, November 23. 2015 09:18:24 UTC 
Dear Duanlin, Mohsen and other ICGEMusers with similar problems,
downloading the model gfcfiles to your PC with a usual web browser is very easy:
 Click the link "Table of Models" on the left navigation tab of our ICGEMhomepage.
This opens a table with all global gravity field models.
 Then goto the line with the model of your interest and click on
the blue link labelled "gfc" in the column "download" with the left mouse button.
This opens a new tab on your browser displaying the model gfcfile as text.
(Please consider, that downloading models with high maximal degree can take some time, since they are quite large files.
So it is preferable to download them as compressed files using the blue "zip" link.)
 Then use the button "Save page As" in your browser and write
it to the directory, where you want it to be placed on your PC.
That's all.
kind regardsW. Köhler (administrator) 
192 
Duanlin Lin

Saturday, November 21. 2015 09:32:11 UTC 
I am intrested in some model in this place,but sometimes I do not know how to donwlode the
data in this place.I will be very appreciated if you can sent the Guest Book Formular to me.
Thank you.

191 
mohsen

Saturday, September 19. 2015 18:02:08 UTC 
Hi,
How can I open gfc files ?? 
190 
gambhir Singh

Monday, September 07. 2015 09:20:15 UTC 
Very good site,It gives us all the information required 
189 
Franz Barthelmes

Tuesday, June 16. 2015 07:06:43 UTC 
Dear Wei You,
yes, of course, it is allowed to download all models.
It depends on your browser how you manage it.
For Firefox the addon "DownThemAll" will do it.
Best regards
Franz 
188 
Wei You

Wednesday, June 10. 2015 10:15:19 UTC 
Dear experts in ICGEM,
Recently, I want to dowoload all the monthly gravity field models from the ICGEM website.
But I can only download one file at one time. So how can I download all the files together at one time? Is it not allowed?
Thanks.
Best regards
Wei You
10/6/2015 
187 
Carol G. Bently

Friday, May 29. 2015 08:28:04 UTC 
I enjoy whyour website is uр too. Thіs is some kind of hard and clever wоrk but results into an exposure! Keep up the good work.

186 
Carol Bently

Thursday, May 14. 2015 07:38:59 UTC 
I'll say this website must be read by others. For instance, students that make a research on something like this. It's a big help for them. Thanks.

185 
Michael Raftery

Monday, May 11. 2015 12:29:11 UTC 
Excellent site. Thank you for all the hard work you do on this important topic. 
184 
Abdelrahim

Saturday, May 09. 2015 15:25:21 UTC 
Hi all,
I am a new user of ICGEM.
Are all coefficients of all model are fully
normalized and unitless
Connect
Abdel Rahim Ruby Abdel hamid Hassanain
Demonstrator
Department of Surveying Engineering
Faculty of Engineering Shoubra  Benha University
Univ. email: abdelrahim.ruby@feng.bu.edu.eg
Email: abd_roby87@yahoo.com
Website: http://www.bu.edu.eg/staff/abdelreheemroby3
108 Shoubra St.  Cairo Egypt
Postal Code: 11629
Tel: 01114812396 
183 
Abdelrahim

Saturday, May 09. 2015 15:18:47 UTC 
I have local Gravity Data.....the question here,
How to use this data to improve or update Global Gravity Field Models (GGMs)?
Like EGM96 or how to combining an EGM with terrestrial
data
Connect
Abdel Rahim Ruby Abdel hamid Hassanain
Demonstrator
Department of Surveying Engineering
Faculty of Engineering Shoubra  Benha University
Univ. email: abdelrahim.ruby@feng.bu.edu.eg
Email: abd_roby87@yahoo.com
Website: http://www.bu.edu.eg/staff/abdelreheemroby3
108 Shoubra St.  Cairo Egypt
Postal Code: 11629 
182 
Franz Barthelmes

Tuesday, May 05. 2015 09:08:25 UTC 
Dear Craig,
it is always the same problem with "reduced" gravity data.
They are reduced somehow and nobody knows exactly how :) .
If you know the reductions, than you can use the table with the descriptions
of the functionals (at the site "calculation service") to find out which is the
best functional.
Or reverse all reductions. The result should be the full measured gravity value
at the defined coordinates at the Earth surface (ellipsoidal lat, long, height).
The according functional is "gravity_earth".
Or reverse all reductions and subtract the normal gravity for the same
coordinates (including ellipsoidal height!).
The result should be the gravity disturbance at the Earth's surface.
The according functional is "gravity_disturbance".
Or reverse all reductions and subtract the normal gravity for the same lat. and
long. but at the telluroid (Earth's surface minus height anomaly).
The result should be the gravity anomaly according to Molodensky's theory.
The according functional is "gravity_anomaly".
Or reverse all reductions and apply the free air reduction down to the geoid
and subtract the normal gravity computed at the ellipsoid (same lat. and long).
The result should be the classical gravity anomaly. (Maybe your terrestrial
data are reduced in this way?)
The according functional is "gravity_anomaly_cl".
The exact free air reduction should be the exact downward continuation.
Usually it will be approximated by dg/dh * H and, hence, it will be not exact.
The classical gravity anomaly can be approximated by the spherical approximation
(the differences of some approximations are shown in
STR 09/02 available on the ICGEM site).
The usual definition of the simple Bouguer anomaly is: classical gravity
anomaly minus the attraction of the Bouguer plate.
Because the difference of the classical gravity anomaly and the spherical
approximation of the gravity anomaly is much smaller than the uncertainty
(the error) of the influence of the Bouguer plate, we use the spherical
approximation to compute the "gravity_anomaly_bg".
So, you see, there are different possibilities to compare measured and
reduced "gravity data" with computed ones :) .
Kind regards
Franz 
181 
Craig Miller

Monday, May 04. 2015 18:10:19 UTC 
Hi
Many thanks for providing this service! I have a couple of questions about the EIGEN6C4 model functionals.
I would like to use these functionals to provide "regional"
data for a terrestrial data set I have.
My terrestrial data is reduced using modern ellipsoid based formulas and heights. Which of the model functionals would be the closest approximation
of terrestrial freeair data reduced using ellipsoid heights? Secondly in your description of the
gravity_anomaly_bg functional you say that " ... it will be calculated by the spherical approximation of the classical
gravity anomaly minus 2πGρH".
I'm confused by the "spherical approximation of the classical anomaly" bit.
In the description of the spherical approximation (gravity_anomaly_sa functional)
it states that it is reduced to the ellipsoid, however the classical anomaly description says it is reduced using the geoid.
Is this a contradiction or have I missed something?
Finally, I don't expect the terrestrial data and model functionals to be exactly the same, but over a small area (say 50 x 50 km) would
you expect the difference to be a simple DC offset or a more complicated shape.
ie would it be possible to merge the terrestrial and EIGEN6C4 data sets or should they be treated individually?
Regards
Craig

180 
Michael E. Chapman

Thursday, April 30. 2015 03:08:42 UTC 
This is an absolutely marvelous service. Keep up the good work!! 
179 
Franz Barthelmes

Wednesday, April 15. 2015 10:52:46 UTC 
Dear Abdelrahim,
I will contact you per email.
Kind regards
Franz 
178 
Abdelrahim

Wednesday, April 15. 2015 08:54:19 UTC 
How development Global Gravity Field Models like EGM96?
I have some questions about Global Gravity Field Models (ICGFM).
Where How to Calculate Coefficients of this model?
I.e. I need the program to compute spherical harmonic analysis of EGM model. 
177 
Guy Bouyrie

Tuesday, April 07. 2015 09:39:29 UTC 
A wonderful job that allows no longer make use of Java JRE !
Thank you !
Guy Bouyrie
UdPPC  Bordeaux (France) 
176 
Li Yongsheng

Monday, March 16. 2015 04:57:53 UTC 
thanks 
175 
Tadesse Tujuba

Wednesday, March 11. 2015 07:52:57 UTC 
Dear Sir,
You are offering a very nice service freely. That is great.
I want to use the Java Applet free service. How can I use it?
Thank you 
174 
Franz Barthelmes

Monday, March 02. 2015 10:59:46 UTC 
Dear John Ryan,
I use the GMTroutine xyz2grd to convert the ICGEMgrids into GMTgrids.
There are many examples and tutorials about GMT on the net.
Kind regards
Franz 
173 
John Ryan

Tuesday, February 24. 2015 22:52:59 UTC 
Thank you very much for providing this resource to the research community! As
you do for the ImageFile option in the model calculation utility, I would like
to use GMT and be able to use different map projections. For this purpose it
would be very helpful to learn about (1) converting the gdf file into something
GMT can read, and (2) example GMT script(s). Is this information available
somewhere on the web site? 
172 
Franz Barthelmes

Friday, January 16. 2015 13:24:58 UTC 
Dear Hakim SAIBI,
I will contact you per email.
Kind regards
Franz Barthelmes

171 
Hakim SAIBI

Thursday, January 15. 2015 00:38:32 UTC 
Hi all,
I am a new user of ICGEM.
I want to generate monthly Bouger anomaly maps.
Please help me with one example.
Thanks 
170 
Jessica

Wednesday, November 26. 2014 22:22:36 UTC 
error: connection to ICGEM: server at port 1891 could not be established. 
169 
Wolfgang Köhler

Tuesday, November 11. 2014 11:01:23 UTC 
Dear Dawit,
in principle, this should be no problem.
Do you have any suggestions?
kind regards
W. Köhler (administrator)

168 
Dawit

Tuesday, November 11. 2014 10:08:40 UTC 
Hi Sir/Madam,
I have just visited your webpage and was impressed with contents and practical
applications in water resources management.
Do yo mind expanding the list of basins in Australia?
Thanks
Dawit 
167 
Wolfgang Köhler

Friday, November 07. 2014 07:49:47 UTC 
Dear ICGEM users,
Oracle's
new security policy since Java version 8 by default inhibits the TCP connection to our server socket,
which is the basis of our service. Without this connection no data transmission between server and client works.
If possible, avoid upgrading to Java 1.8!
Please note, that our ICGEM service never requests a Java update  such requests are always originated by your
internet browser.
If you have to upgrade anyway, we can offer an intermediate solution, to circumvent this problem.
However, that requires some administrative action on your client computer.
You have to modify the central 'java.policy' file on your PC
(see also
java.net.SocketPermission in Applets).
It is not very simple to find and edit this file under Windows, but this modification solves the problem.
The actual location of this file depends on your operating system and Java version, it is something like
"C:\Program Files\Java\jre7\lib\security\java.policy"
(or similiar, eg. C:\Program Files (x86)\Java\jre1.8.0_25\lib\security)
and you have to add an entry:
permission java.net.SocketPermission "139.17.6.102:*", "connect, accept ,resolve";
to allow your PC the TCPconnection to our ICGEMserver (IP=139.17.6.102).
Here you can download a tested java.policy file.
This should work for all Java versions.
Wolfgang Köhler (administrator)

166 
Ernest Berkman

Thursday, November 06. 2014 15:39:01 UTC 
It appears as if you are using Java Plugin 10.65.2.20
and I am Using JRE version 1.7.0_65b20 Java HotSpot(TM) Client VM
so the appelet does not run. Any suggestions. Windows 7 64 bit 
165 
Deepika

Monday, November 03. 2014 04:52:02 UTC 
This is great
new security policy simply great.

164 
Hakim

Thursday, October 30. 2014 00:10:39 UTC 
Hello everyone, my name is Hakim Saibi from Kyushu Univ. I am here to use and
learn more about GRACE models. Thanks 
163 
Wolfgang Köhler

Monday, October 20. 2014 06:25:10 UTC 
Dear Afri,
the same advice as in the last posting given to Arinda (just below in posting 161).
Please read the listed references.
W. Köhler

162 
Afri Yudhawan

Monday, October 20. 2014 02:59:55 UTC 
Dear administrator,
I have some problems about showing the visualization of geoid. The plugins showed me only a blue sphere.
I've installed the newest java version but the site still only shows the blue sphere.
Could you help showing the visualization for me, please? Or do you have some advices for me?
Thanks for your kindly attention.
Afri Yudhawan
+6281315126209
Geodesy and Geomatics Engineering
Bandung Institute of Technology
Indonesia 
161 
Wolfgang Köhler

Friday, October 17. 2014 09:59:46 UTC 
Dear Arinda,
please read the information given at the bottom of the visualization page
under the topic 'Troubleshouting' and the posting 147 in
this guestbook below.
If nothing of the hints works for you, please send me an Email.
kind regards
Wolfgang Köhler 
160 
Arinda

Friday, October 17. 2014 05:31:59 UTC 
Hello, I tried to access this site for my lecture assignment.
I need to see geoid model in visualization part. But, I just saw blue sphere although I've tried it over 10 times.
Could you please tell me, is it something wrong with my laptop or my connection.
I've tried some connection, but it didn't help.
Thank you, I hope for your kind response.
Sincerely,
Arinda 
159 
Tang Kieh Ming

Thursday, October 16. 2014 23:28:04 UTC 
Dear,
After finish computing and unable to get gridfile from calculation services. Any solution?
Thks & Rgds.
kiehming 
158 
Franz Barthelmes

Monday, August 11. 2014 08:07:52 UTC 
Dear Petros,
our service offers the possibility to compute the topography from a spherical
harmonic model or from the etopo1 grid (as described in the table on the
calculation service site). It doesn't offer the calculation of the gravitational
attraction of these topography.
Kind regards
Franz

157 
Petros Manousakis

Friday, August 08. 2014 04:53:04 UTC 
Dear administrators,
It is the second time I contact you.
The first time was by email about a problem I had and your answer had been very helpful!
This time, I would like to ask if your applet could calculate the topographic correction (TC)
in grid fore some region,(e.g. using a topography model), so to use it in RemoveRestore method.
If not, is there an internet site that does it so?
Thank you in advance,
Petrow Manousakis 
156 
Franz Barthelmes

Monday, July 21. 2014 06:36:01 UTC 
Dear Victorino Garcia,
please see postings No. 142 and 143.
Kind regards
Franz Barthelmes 
155 
Ramon Garcia

Friday, July 18. 2014 13:37:48 UTC 
This website is great. One can evaluate practically any GGM produced so far.
Would be very helpful if you allow to evaluate the GGMs for not gridded points,
so one can only put the coordinates file to get the geoid or other functions
of the geopotential. Or, Could you tell me where can I get a program to do
this type of geoid evaluations.
Thanks
Victorino Garcia 
154 
Franz Barthelmes

Friday, July 18. 2014 08:03:06 UTC 
Dear Sai,
it is a little difficult for me to understand what you mean.
The details of the computation of the monthly solutions are documented in the
Report:
http://ebooks.gfzpotsdam.de/pubman/item/escidoc:108022:2/component/escidoc:108023/1202_rev_ed.pdf?mode=download
(also available on the ICGEMSite "Models from Dedicated Time Periods").
Yes, the monthly solutions also contain the change in gravity
(or geoid heights, or equivalent water heights) before and after big
earthquakes. A good idea to get an overview if such effects are visible is the
use of one of the tools:
http://www.thegraceplotter.com/
or
http://icgem.gfzpotsdam.de/GooglePlotter/Grace_Plotter.html
If you put the marker, e.g., at the position near the big earthquakes in the
Sumatra region (end of 2004) or near Japan (first part of 2011) you will see
the jumps in the graph.
Kind regards
Franz

153 
sai

Thursday, July 17. 2014 08:25:30 UTC 
I have a doubt regarding GSM2 data, it contains dynamic field alone or both
static n dynamic(variation due to ocean, atmosphere and geodynamic processes
like earthquakes).I want to use this data for calculating gravity variations
before and after the earthquake.Please kindly help me in this regard.Thank you
very much in advance. 
152 
Wolfgang Köhler

Monday, June 30. 2014 06:30:48 UTC 
Answer to Ajeet Kumar:
Please read my posting #147 in this Guest Book below.
It should help you solving your problem with Java.
Kind regards
Wolfgang Köhler 
151 
Ajeet Kumar

Saturday, June 28. 2014 11:42:53 UTC 
My browser does not support Java Applets. To use this applet, How can i Enable Java for my browse
I am using Windows 8 , Ram 4 GB, System Type 64 bit, Processer Intel (R) Core TMI i7 37770 CPU @3.4 GHz

150 
Franz Barthelmes

Wednesday, May 07. 2014 07:07:53 UTC 
Dear Tongong Ayuba Badung,
we are a service for global gravity field models and not for gravity
measurements.
The service for gravity measurements is the
Bureau Gravimétrique International / International Gravimetric Bureau
(see: http://bgi.omp.obsmip.fr/ ).
Our service ICGEM offers the possibility to compute different functionals
(e.g.: gravity, gravity anomalies, gravity disturbances or geoid undulations)
from one of the global models on a grid of your choice (see the calculation
service of ICGEM).
I would recommend to use the most recent combination model EIGEN6C3stat
(which contains satellite data, terrestrial gravity measurements and data from
satellite altimetry).
If you have questions please contact me.
Kind regards
Franz Barthelmes 
149 
Tongong Ayuba Badung

Wednesday, May 07. 2014 04:46:30 UTC 
I wish to know more on how to obtain terrestrial gravity data in large
quantities covering a large area 
148 
Joe Olliver

Tuesday, April 01. 2014 10:58:20 UTC 
I was very pleased to be able to access the GOCE results on your website after
all efforts to cut throught the bureaucratic jungle of the ESA download
procedure had failed. Please keep up the good work.
Regards
Joe Olliver
Earth Sciences
Oxford University 
147 
Wolfgang Köhler

Monday, March 10. 2014 09:25:34 UTC 
Dear Alberto Benavidez,
the problems you mention are due to a
new security policy, that
Oracle has introduced with the new Java version (7u51) by January 2014.
From this version the browser refuses to execute Java applets, which are the basis of our service, by default.
The easiest way to fix this problem is to stick (or go back) to older versions of Java (1.6).
Another way is to use the Java Control Panel and add our site to the
Exception Site List:
You may either add all HTMLpages which you want to use
(eg. icgem.gfzpotsdam.de/ICGEM/potato/Service.html),
or yet better add the Jarfile (which includes all applets of our service)
as http://icgem.gfzpotsdam.de/ICGEM/potato/Potato.jar.
The third possiblity is to reduce the Java security level to the lowest value.
And, last but not least, there are open source alternatives to Oracle's Java, namely "IcedTea".
Kind regards
Wolfgang Köhler 
146 
Alberto Benavidez

Sunday, March 09. 2014 23:30:38 UTC 
Dear Dr. Frank Barthelmes,
I have been working using the ICGEM's resources for some years, as I let
you know on May 2012 (Postings 121 and 122). I used Windows XP and Java 6 in my
computer. However recently I upgraded them to Windows 8.1 and Java 7. As a result
I am able to get a connection with the Calculation Service and the literature and
figures of the "Calculation of Gravity Field Functionals on Ellipsoidal Grids" but
the location of the form to input request data and obtain the outputs remains blank,
and the following error warning appeared:
ClassNotFoundException
ServiceApplet.class
I tested several forms of the command: java cp, but I coudn't get the correct
answer.
Do the Calculation Service already have a solution to fix this problem?
Sincerely.
Alberto Benavidez

145 
Franz Barthelmes

Wednesday, February 05. 2014 10:42:57 UTC 
Dear Alexander,
do you mean GOCEdata in the sense of "measurements" or gravity field models
derived from GOCE data? Our service only offers the models and do not offer
measurements.
Kind regards
Franz 
144 
Alexander Marchenko

Wednesday, February 05. 2014 09:45:46 UTC 
Dear Colleagues,
More than 10 yr ago
I was working into
GFZ Potsdam. Today I
decided to came back
to the LEO
satellites, in
particular, to the
GOCE
data processing.
Could you help me
with GOCE data,
since ESA data
format require
especial
transformation or
corresponding
software.
Best regards,
Alexander Marchenko 
143 
Franz Barthelmes

Monday, January 27. 2014 09:26:25 UTC 
Dear Ruth,
I understand your question. But in our calculation service we only offer the
possibility to calculate values on a lat.long.grid. Values on a regular grid
can be calculated from spherical harmonics much more efficiently than for
irregularly distributed points. The software of the calculation service can only
produce regular grids. Unfortunately, up to now, we don't have the time to offer
the additional possibility to calculate values for irregularly distributed points.
Best regards
Franz

142 
RUTH DA MAIA MOREIRA

Friday, January 24. 2014 15:39:55 UTC 
Hi,
I would like to to make a suggestion about the way we have obtain the values of the functionals on
calculation service. I have to obtain the values for specific points, not for a grid. There is no a
way to do this quickly, like put an archive *.txt or similar with the coordinates I need and obtain
the values. I have to do this point by point, and there are many points, what takes me a lot of
time. Could you consider the possibility of doing a function to solve this dificulty?
Thank you so much.
Yours sincerely,
Ruth

141 
Grzb

Thursday, November 28. 2013 11:30:52 UTC 
Hello from Jarmul's Cave 
140 
xiaole

Thursday, November 14. 2013 08:17:03 UTC 
Thank you very much for the work you have done!
And I think the guest book will be usefull. 
139 
Franz Barthelmes

Monday, May 13. 2013 05:54:22 UTC 
Dear Nabila,
on the page "Models from Dedicated Time Periods" of our service below the headline
"Nonisotropic smoothing and subtracting of a mean model" are the coresponding references.
Why do you use release 04? The releases 05 are available and are better!
Kind regards
Franz 
138 
Nabila

Sunday, May 12. 2013 11:27:40 UTC 
Hi,
I'm using GRACE data
GFZ release04 DDK2
for my thesis. But
what is DDK2 filter?
My supervisor told
me to use DDK2
filter, but I can't
find clear
description about
it.
Thank you.
Nabila 
137 
Lei Qiu

Friday, December 14. 2012 06:44:05 UTC 
service is very good,but it is a little bit slow to open the website 
136 
Dr. Ioannis Haranas

Wednesday, October 24. 2012 16:34:53 UTC 
Very useful site! 
135 
Franz Barthelmes

Thursday, September 20. 2012 05:38:55 UTC 
Dear Stanid Song,
the models consist of coefficients of spherical harmonics
(search for "spherical harmonics" at google :) ).
L is degree
M is Order
C stands for even coefficient
S stands for odd coefficient
sigma stands for standard deviation
Kind regrards
Franz 
134 
Stanid Song

Wednesday, September 12. 2012 12:37:42 UTC 
what does ¡°L,M,C,S,sigma C,sigma S¡± stand for ? 
133 
Franz Barthelmes

Monday, September 10. 2012 11:01:30 UTC 
Dear Prof. Lopes,
thank you for using our service.
I am afraid that I did not understand your question correctly.
What do you mean with "routine for data manipulation"?
You write that you use the harmonic coefficients. For that you need a routine
to compute the geoid from the coefficients, thus I guess you have such a
routine.
Then you write: " however I'm not getting a routine that calculates the model
derived from geoid as EINGEN6C".
What do you mean? The gravity field model is the set of coefficients.
From this model (i.e. from these coefficients) you can calculate different
functionals of the (model of the) gravity field. One functional is the geoid
with respect to a defined reference system (there is no "EIGEN6Cgeoid without
defining a reference system).
You can use our "calculation service" to calculate geoid heights from one of
the models (plus a reference system) on a grid of your choice. If you need help
in using the calculation service, please let me know.
(I will also answer per email.)
Kind regards
Franz

132 
Alexandre B. lopes

Friday, September 07. 2012 16:50:39 UTC 
Dear,
First I would like to commend the work of ICGEM. It is very good and useful.
I'm a user of the geoid models. I use them in determining geostrophic currents in the South Atlantic
Generally work with the harmonic coefficients, however I'm not getting a routine that calculates the model derived from geoidas EINGEN6C. How do I proceed in this case?
I leave it as a suggestion to place a routine in FORTRAN for data manipulation.
Cordial greetings.
Thank you.
Alexandre B. Lopes 
131 
Franz Barthelmes

Friday, July 06. 2012 06:33:07 UTC 
Dear Kelly,
it is nice to hear that our site is useful for you.
Basically our service consists of 3 parts:
 collecting of global gravity field models (sets of spherical harmonic
coefficients)
 visualisation service
 calculation service
The visualisation service calculates the grid on our computer and transfers it
(together with the java program) to your computer. Thus, the visualisation
depends on the possibilities of java and the resources of your computer.
The calculation service calculates grids on our computer and provides them for
downloading. The format of the grids should be (hopefully) selfexplanatory.
Additionally we offer (tick at PSFile at the bottom of the input mask) a plot
of these grids. You can use these grids as input to rendering programs on your
computer.
All things we offer are based on the global models. The computation,
estimation, determination of the global models is not a task of our service.
If new data (containing gravity field information) become available (regional
terrestrial or global satellite measurements) it could (and will) be used to
compute a new improved global model by the groups responsible for that. Then we
will include this new model into our service :) .
Thanks again for using our service. If you have further questions, please
contact us.
Kind regards
Franz Barthelmes 
130 
Wolfgang Köhler

Thursday, July 05. 2012 10:43:46 UTC 
Dear Kelly,
many thanks for your positive feedback to our service!
The problem with the visualization that you mentioned is clearly
a memory overflow.
Grids of 0.2° or 0.1° require huge amounts of PCmemory (8GB or more)
and also a Javaimplementation, which is able to use it.
I am not quite sure, if I understand your first question correctly,
but one option is, to use our "Calculation Service".
It allows you, to compute a highresolution grid (up to 0.1°) of
plenty of models and then download it to your computer.
Then you can use any rendering program to display it as 3Dsurface.
Please tell us, if this is what you wanted.
The second question, regarding the acceptance of outside gravity
data will be answered soon by another collegue of our service.
kind regards
W. Köhler 
129 
Kelly Bellis

Thursday, July 05. 2012 07:39:31 UTC 
Love this site!
THANK YOU!!! THANK
YOU!!!
If this is the wrong
forum for posting
these questions,
please forgive me,
but I'm hoping that
others might benefit
from this
discussion /
questions / answers.
Aside from getting
the PotatoApplet to
utterly crash when
attempting to render
at .2, or it simply
freezes (see console
transcript
below) what I'm
searching for is the
highest resolution
3D surface available
of the most current
(static) geoid model
so that it might
be rendered in
another program.
Deciding upon the
"boost" or level of
height exaggeration
ahead of that
creation like what
the PotatoApplet
allows would be
fantastic.
Separately, the
second thing I'm
curious about is if
the ICGEM might
accept outside
gravity data to
model, in
particular; gravity
data produced
through the GRAVD
program.
generating sphere
with 900x1800 points
nt = 1800
Exception in thread
"Thread12"
java.lang.OutOfMemoryError:
Java heap space
at
Sphere3D.build_triangles(Sphere3D.java:90)
at
Sphere3D.(Sphere3D.java:35)
at
Potato3D.(Potato3D.java:11)
at
Scene3D.make_potato(Scene3D.java:189)
at
Scene3D$3.run(Scene3D.java:179) 
128 
Franz Barthelmes

Friday, June 15. 2012 13:11:03 UTC 
Dear Andrew Richardson,
I will answer by email.
Regards
Franz Barthelmes 
127 
Andrew Richardson

Friday, June 15. 2012 00:38:58 UTC 
Hi,
My name is Andrew Richardson.
I run a Hydrographic survey company in Perth Australia.
I have been looking through your Calculation of Gravity Field Functionals on Ellipsoidal Grids
online applet.
What do I need to do, if possible, to replicate N values for Australia.
Do the models you provide figures for match in any way the AUSGeoid09.
I have been testing values for onshore and offshore and comparing to AUSGeoid09 values and cannot get them to match in any way.
Can you explain how the online service can provide figure that will be relevant for me.
I am just trying to find the Geoid separation between the ellipsoid.
Hope you can help
Regards
Andrew Richardson
Director Surrich Hydrographics 
126 
Franz Barthelmes

Thursday, May 31. 2012 10:54:42 UTC 
Answer to the question from Dr.Sanjit Kumar Pal
(which could be of general interest)
================================================
Frequently asked questions are:
(1) "Which series of monthly models shall be suitable?
(for some particular problem)"
and
(2) "How should I filter these models?"
Answer to (1):
The software packages of the 3 analysis centres CSR, GFZ and JPL are
independent. But they use the same processing standards to generate the
GRACE Level2 products.
From point of view of ICGEM it is not possible to say that the models from
one centre are better (for some particular problem) than the others.
Best idea is to use all 3 and compare them :) .
Answer to (2):
The monthly solutions of the 3 centres are produced (basically) unconstrained
and are provided without any filtering. The reason is that it depends on the
specific application how and how strong filtering is necessary.
Only the user can decide how to filter.

125 
Franz Barthelmes

Wednesday, May 30. 2012 08:59:52 UTC 
Dear Sheda,
the transformation between the different tide systems in our software only
changes the coefficient C20.
The formulas which we use are:
c20zt = c20tf + rk*x (zero tide <= tide free)
and
c20mt = c20tf + (1d0+rk)*x (mean tide <= tide free)
with
x = 1.39d8
rk = 0.3d0
Kind regards
Franz 
124 
Dr S K Pal

Saturday, May 26. 2012 11:44:47 UTC 
Good afternoon...!
This site is scientifically very resourceful
I am interested in Satellite Gravity data for possible correlation
with earthquake Occurrence/ ground base GPS data of stain
accumulation over land
I want to fetch one data set of 5 Degree x 5 Degree Gravity data of July,2008
and another set of data of December,2008 over Himalayn Region.
1. Which monthly model(Monthly/JPLRLl05/JPLRLl04/CSRRL05/GFZRL04)shall be suitable?
2. Which MODELFILE (filtered models begin with "kfilter_DDK" / "GSM2")shall be suitable?
Thanks to you all.
sanjit 
123 
she.daa

Friday, May 25. 2012 15:11:51 UTC 
Hello, thank you for ICGEM help me about result of the calculation. I had a new
problem, can I know what description about tide system in calculation services.
Tide free, zero tide and mean time. I guest mean tide setting is when the value
of the tide halfway between mean high water and mean low water. 
122 
Franz Barthelmes

Monday, May 21. 2012 07:14:38 UTC 
Dear Alberto,
on our calculation service site (scroll down on the site) is a short description
which formulas we use for the Gaussian Filtering. Gaussian filtering of the
gravity field values on the sphere is equivalent (for small filterlength) to
multiplying the spherical harmonic coefficients with an appropriate Gaussian
function depending on the spherical harmonic degree. That is what we do.
More details can be found in:
Jekeli, C. (1981), Alternative methods to smooth the Earths gravity field,
Tech. Rep. 327, Dep. of Geod. Sci. and Surv., Ohio State Univ., Columbus.
Kind regards
Franz

121 
Alberto Benavidez

Thursday, May 17. 2012 22:59:26 UTC 
I have been applying your resources in order to calculate the gravity parameters for
Uruguay. For such task I mainly use the EIGEN6C geopotential model (need to say
that in the past I did the same job with the GOCE's results). Recently I have
been quite interested to filter that data and utilize it in geophysical investigations.
Therefore I employed the related gaussian option you offered and obtained several
outputs. However I am not completely able to grasp the mathematical procedure and
tools (convolution or FFT2D) applied there. For that reason I'd truly appreciate
your help to get some information about the topic.

120 
Franz Barthelmes

Wednesday, April 25. 2012 10:45:10 UTC 
Dear Jaydragon,
can you please explain what kind of research do you want to do and which software
do you need?
Kind regards
Franz Barthelmes 
119 
Leo

Thursday, April 19. 2012 13:25:47 UTC 
I want to do some research about the GRACE, where I can get the code of program? 
118 
Wolfgang Köhler

Wednesday, April 18. 2012 06:58:34 UTC 
Dear Sheda,
I have checked your last usage of the
"Calculation Service" and can find no error on our site.
It was the
calculation "gif48174500.inp" with input parameters:
...
gridstep
0.0166667
longlimit_west 98
longlimit_east 105
latlimit_south
0
latlimit_north 9
....
The calculated grid
"gif48174500.gdf" was exactly the requested one.
It spans the rectangle
long=[98.000  104.9833] * lat=[9.000  0.000].
Also the
corresponding PSfile "gif48174500.ps" seems correct to me.
Could
you please give us some more information, which calculation actually went
wrong?
And please (this applies to all requesters) give as
reference the name
of the calculated file!
(The name of the file, which you see after calculation
in the yellow
status line).
This would allow us an easier check.
kind regards
Wolfgang Köhler 
117 
she.daa

Tuesday, April 17. 2012 15:53:05 UTC 
hello, i had using calculation service for gravity anomaly, my grid is between 1
to 10 for longitude, 1 to 7 for latitude. But the data only calculate the last
grid. (10 , 7). I very appreciated if this problem can solve it. Thank you. 
116 
Franz Barthelmes

Tuesday, April 10. 2012 06:19:54 UTC 
Dear Sreejith Kattumadam,
thank you for using our service.
The "gentlecut"possibility in our calculation service is described in the
document: "Low Pass Filtering of Gravity Field Models by Gently Cutting the
Spherical Harmonic Coefficients of Higher Degrees" and can be downloaded at:
http://icgem.gfzpotsdam.de/ICGEM/potato/gentlecut_engl.pdf
You can cite it by citing the service ICGEM.
Kind regards
Franz 
115 
sreejith

Monday, April 09. 2012 10:04:39 UTC 
Hi,
Can anybody suggest hoew to how to cite the gentlecut_engl.pdf doccument
with regards
sreejith 
114 
Igor Protsenko

Monday, December 26. 2011 18:48:35 UTC 
Thanks a lot!
Gaint job and frendly interface. 
113 
Wolfgang Köhler

Friday, December 09. 2011 13:13:05 UTC 
Dear Sheda,
please have a look at our main page ('ICGEM Home').
There you will see under the topic
Some ICGEM related documents
a link
Description of the ICGEMformat
There you will find what you need.
kind regards
W. Köhler

112 
she.daa

Thursday, December 08. 2011 13:31:58 UTC 
my name is sheda from Malaysia and
I'm a degree student at Faculty of planning and surveyingUiTM
I'm currently testing global geopotential model(gravity data) with
local gravity data.
I had download data GGM but I not very understand the format.
Is there any format that I should refer it? can I know what is the link?
Kind regard,
sheda

111 
Franz Barthelmes

Friday, November 18. 2011 10:22:19 UTC 
Dear Marko,
I understand your question and we are aware of the (minor (?)) problem.
I think, this is of general interest and I'll try to explain it briefly:
Our knowledge about the global gravity field (i.e. the accuracy of the global
models) became better and better and now it is possible to calculate not only
mean models over a long period of measurements but also time variations of
the gravity field. One result is that also models from short time periods
(one month or shorter) are calculated and provided to the public. These models
have, naturally, lower spatial resolution. On the other hand, the FrenchGerman
group (GRGS and GFZ), which calculates the EIGENmodels, found that it is
possible to use all the available measurements of a long time span to estimate
some additional parameters describing time variations without losing the
accuracy of the usual (static) coefficients (i.e. without losing the high
spatial resolution). As a result the models EIGEN6S and EIGEN6C contain,
additionally to the (traditional) spherical harmonic coefficients, also some
parameters which describe some basic time variations of these spherical
harmonic coefficients. These additional parameters are the amplitudes of sine
and cosine shaped time variations with annual and semiannual periods as well
as values for the linear trends of all coefficients up to degree and order 50.
(Remember that the amplitude and phase of a sinusoidal wave with fixed period
can be transformed mathematically into a sineamplitude and a cosineamplitude
together with the same period). These new parameters are important e.g. for
exact orbit calculations or special investigations of time variations of the
gravity field.
To calculate functionals from such a model, strictly speaking, you have to know
for which time you want to have it. Then, in a first step, use the formulas
given in the header of the model to calculate the coefficients for the epoch
of interest and, in the second step, use the coefficients of this epoch in the
same way as for the static models.
Up to now the calculation service of ICGEM do not offer this possibility.
The main reason (apart from finding time to change the software :) ) is that I
think people who need it have their own software so that only few users will
really need it at ICGEM and I'm afraid that all the others could be confused.
Simply ignoring these additional parameters will not result in the mean model
over the time span of the measurements. It will also not result in the model
for the reference epoch (t=t0) because the sinusoidal oscillations (of the two
periods) are (in general) not zero at t=t0 (the cosine terms in the formula
are 1 for t=t0).
It will result in a model from which the annual and semiannual periods are
subtracted (and without trend). This is probably better than a mean model
over a time span which is not an integer multiple of the periods.
Best regards
Franz

110 
Marko Pavasovic

Thursday, November 17. 2011 10:18:37 UTC 
Dear ICGEM Team,
My name is Marko Pavasovic and I'm a PhD student at Faculty of Geodesy  University of Zagreb, Croatia.
I'm currently testing global geopotential models by comparing height anomalies obtained from global geopotential modelas (combined solutions)
with GNSS/levelling undulations at the territory of our country and having trouble with understanding EIGEN6C time depended coefficients.
For height anomalies computation at exact point with known coordinates from certain global geopotential model I'm using "f477s_B.for" Fortran program written by Professor R.H. Rapp.
I don't quite understand which coefficients to use regarding to time depended ones in EIGEN6C model so can You please help me with that and give me short explanation how to use this model to calculate height anomalies?.
Thank You.
Winh Kind Regards,
Marko Pavasovic

109 
Jisun Lee

Thursday, November 10. 2011 12:23:26 UTC 
I've sent a email to ask sth about the models.
Please check the email having a title of "Question for the result (EGM2008 and EIGEN6C)"

108 
Wolfgang K�hler

Sunday, November 06. 2011 08:30:25 UTC 
Dear Leejs,
I do not understand exactly, what is the problem.
You should open the link 'Table of Models' on the left side.
Then you click on the 'Download' button X inside the table,
in the model of your choice
and you have it on your computer.
kind regards
wolfk

107 
leejs

Sunday, November 06. 2011 07:15:26 UTC 
I would like to check the new geopotential model to calculate the local geoid in Korea.
Please let me download the latest model "eigen6c" 
106 
Franz Barthelmes

Wednesday, November 02. 2011 09:11:49 UTC 
Dear Sreejith,
yes, it is a good idea to use the gentlecut option to avoid oscillations due to
sharp truncation. But, the lower limit for "start_gentlecut" is 8. The (internal)
reason for that is the subtraction of the normal potential in terms of spherical
harmonics up to degree 8. In my opinion it make no sense to start with
"gentlecut" lower than 8. If you really want to damp also the very low degrees
you can use the option of the Gaussian filtering, e.g. with
flength_definition = halfresponse" and filterlength_degree = 10.
Kind regards
Franz 
105 
sreejith

Wednesday, November 02. 2011 05:48:15 UTC 
Hi,
I am trying to use
ICGEM calculation
service to generate
EGM2008 filed
tuncated at n=12. To
avoid oscillations
due to sharp
truncation
at n=12, I want to
roll of coeficients
between n=2 and 25.
When I use
truncation option
with start gentlecut
= 2 and
max_usd_degree=25,
i get the out put
showing trucation
starting at n=8. Can
anybody help to
solve this issue.
with best regards
sreejith 
104 
Franz Barthelmes

Monday, September 19. 2011 06:39:53 UTC 
Dear Lester,
thank you for using our service and thank you for the suggestion.
Although I understand your wish to have the GOCE gradient data on our service
too, I must disappoint you.
We are the centre for global Earth MODELS, thus we offer gravity field
MODELS (up to now only in form of spherical harmonic coefficients) and
not the DATA which were used to derive the models.
We have the models (spherical harmonic coefficients) which have been derived on
the basis of the new GOCE measurements and you can use our calculation service
to calculate different gravity field functionals from these models. But
regrettably the calculation of all second derivatives of the potential (the
full tensor) are not included in our software. We continuously improve our
software but the tensor of the second derivatives are not on the "to do list"
for the next future. The reason is that we think this is something very
specific and only few users would need our service for it.
Kind regards
Franz Barthelmes 
103 
Lester Anderson

Thursday, September 15. 2011 06:54:50 UTC 
Hello,
I have a suggestion that would be useful to many. Would it be possible to include
in the table of models and calculation service, the GOCE gradient data for all the
tensors?
So we could then get Gzz, Gxx, Gyy, Gxz, Gyz, Gxy with the results in Eotvos. I
know that the raw data is available through ESA but it is not convenient or user
friendly.
ICGEM already has the gravity data for GOCE so it seems logical to include the gradients
too. The calculation service does allow the computation of Gzz as the second
derivative of the potential (I believe that is the correct function).
I would be interested in your response.
Regards
Lester Anderson B.Sc M.Sc DIC 
102 
Wolfgang Köhler

Tuesday, March 15. 2011 09:26:09 UTC 
Dear Mr. Ashraf,
I will answer you per email. But since this is a common
cause of problems, here also again.
I cite from the bottom of our HTMLpage "Calculation Service":
If all applets on this service are not working at all, the problem might be
your local firewall.
Some newer, very restrictive, firewalls block
also outgoing connections.
The applets need to contact the server
icgem.gfzpotsdam.de, on port 1891 to query data.
Please contact your
network administrator to allow this connection for you.
As described there, I assume, that your local firewall blocks
the connection to our server.
You have to open that port, to enable it.
Kind regards
W. Köhler, administrator

101 
ashrafrateb

Tuesday, March 15. 2011 08:26:15 UTC 
Dear dr Wolfgang
My Greetings
iam Ashraf rateb from NARSS,Cairo , Egypt
My research is to study the africanarabian plate boundaris based on Gravitational model (EGM2008)
I want to inquery about the funcationals of the gravitational model but there are some errors.
it take me this masseage
no connection to ICGEM  server at port 1891
what this meaning?
and how to solve it
all regards
ashraf

100 
Franz Barthelmes

Monday, February 14. 2011 16:30:26 UTC 
Dear FALAYI OLUSEYE SEINDE,
thank you for using our Service.
Unfortunately I do not understand your request.
I will contact you by email.
Kind regards
Franz Barthelmes 
99 
FALAYI SEYE

Thursday, February 03. 2011 18:25:51 UTC 
My names are FALAYI OLUSEYE SEINDE, I live in Nigeria
Africa and im 24, Im a fresh graduate of Physics with option in
Geophysics and presently Im serving in one of the state in Nigeria
and I will be through with the National Youth Services in October
2011.
Sir I did my project on the Recovery of Earth Gravity Field
using Grace. Grace is a cycle satellite mission where the
intersatellite range, rangerate and range acceleration are derivable
from a Kband microwave device , but the monthly data collected was
not explanatory to me and I wish to acquire more knowledge on the work
especially in the variation in availability of underground water in
Africa. I am anticipating for positive response. Thank you sir God bless you 
98 
Franz Barthelmes

Tuesday, January 25. 2011 11:08:42 UTC 
Dear Maria,
the default values in the input mask of the calculation service are
longlimit_west = 0 and longlimit_east = 360. Do you see something else?
the positive direction of the longitudes is eastwards.
The keywords "longlimit_west" and "longlimit_east" of the input mask of the
calculation service means the following:
The value for "longlimit_west" must be smaller than (or equal to) the value
for "longlimit_east". The longitudes can range from 0° to 360° (0 to 2*pi) or
from 180° to +180° (pi to+pi), i.e. negative values are also allowed.
If both values are negative, 360° will be added for internal reasons.
Here are some examples:
longlimit_west = 180°
longlimit_east = +180°
produce a global grid as well as
longlimit_west = 0°
longlimit_east = 360°
but in both cases the longitudes 0° = 360° or 180° = +180° are twice in the
calculated grid (which is not necessary for plotting but it doesn't matter).
For gridstep = 2° a global grid can be calculated with:
longlimit_west = 2°
longlimit_east = 360°
For regional grids all combinations are possible as long as
longlimit_west < longlimit_east:
e.g.
longlimit_west = 13.123°
longlimit_east = 27.456°
longlimit_west = 80°
longlimit_east = 60°
will internally be changed to 280° to 300° in the grid file.
Is this the answer to your question?
Kind regards
Franz 
97 
Maria Alejandra Saume

Sunday, January 23. 2011 21:40:18 UTC 
Good afternoon, I am wondering about the coordinate system. I really dont
understand how longitude is changing, because the page said that the eastern
longitude is 0 and the western is 360, and I see this in the other way.
I need to answer this question because I need to explain the input data
for my thesis.
I appreciate your help
Maria Saume
Caracas, Venezuela

96 
Franz Barthelmes

Tuesday, September 28. 2010 08:01:51 UTC 
Dear Leyla,
I will answer per email.
Kind regards
Franz 
95 
Leyla Sugaipova

Tuesday, September 28. 2010 06:03:16 UTC 
Hello!
Many thanks for your useful service, indeed.
I have a question:
In section "Evaluation of the models:
Spectral Comparison with the Model EIGEN51C" you give
figures showing "... the signal amplitudes per degree of
the model and of EIGEN51C, the amplitudes of the difference to EIGEN51C per
degree and as a function of maximum degree". Could you, please, explain the last
part "... as a function of maximum degree". What maximum degree is meant here?
Thank you very much 
94 
Victor Zlotnicki

Sunday, August 29. 2010 22:30:29 UTC 
You provide an extremely useful service. 
93 
Franz Barthelmes

Wednesday, July 21. 2010 14:01:33 UTC 
Answer to all questions concerning the GOCEmodels:
===================================================
Yes, we will include all published GOCEmodels into our service.
We have the first 3 GOCE models presented at the ESA Living Planet Symposium 2010,
Bergen, June 27  July 2, 2010, Bergen, Norway. Our ICGEMpages are prepared.
But up to now ESA didn't officially released these models, so we have to wait.
Kind regards
Franz Barthelmes 
92 
Nils

Wednesday, July 21. 2010 12:11:53 UTC 
Moin!
Vielen Dank für den Service, der mich bisher fast jeden Tag zuverlässig
mit Daten und auch Fragen versorgt. :)
Eine simple Frage habe ich noch:
Werden in nächster Zeit auch die GOCE Schweremodelle eingebunden?
viele Grüße aus Kiel
Nils 
91 
Franz Barthelmes

Wednesday, July 14. 2010 11:39:30 UTC 
Dear Moamen Awed Habib,
you can use our calculation service (button "Calculation Service") to calculate
different functionals from global Earth gravity field models. A short description
of the available functionals are on the calculation service site. A more detailed
description is under "Theory".
The model with the highest spatial resolution is EGM2008 but we don't know which
terrestrial gravity measurements from the area of your interest (Egypt) are in
the model.
Kind regards
Franz Barthelmes 
90 
Moamen awed habib

Wednesday, July 14. 2010 10:51:53 UTC 
I would like to introduce my salf
My names :moamen awed habib
Country: Egypt
Mob :0020115404736
Add: 1st gala rezek elmaleka faysal giza Egypt
I am post guarded and I prepare research about evaluation of three newly
geopotential model for my country Egypt and if you can i need gravity anomaly
based on terrestrial observation and undulation based on ellipsoidal height
and orthometric height data
With my best regard

89 
Bhupendra Thakor

Tuesday, July 06. 2010 03:29:13 UTC 
Hi, Good Knowledge provider for the people who really dedicated thinking for gravity ,
& As i think this would be only the solution for the next generation for clean energy and innovation. 
88 
W. Koehler

Monday, May 24. 2010 16:33:32 UTC 
Dear Mr. Clauser,
I prefer to answer your question in English,
because it might be of interest for other readers.
At first, thank you very much for your commendation of our website!
Your remark that some links on our table of models are dead, has
two aspects: these links are usually given by the producers of the models
and thus not under our control. When they are changed, we are in general not
informed.
On the other hand, the special models "eigenxx" you mentioned
are models of GFZ, and we are responsable for them ourselves ;(
We will update them asap.
Kind regards
W. Koehler

87 
Christoph Clauser

Monday, May 24. 2010 13:15:52 UTC 
Vielen Dank für die außerordentlich nützliche Seite!
Eine Fehlfunktion trat auf: Wenn ich im "Table of Models" auf die Namen klickte
(z. B. eigen5c) gab es eine Fehlermedlung vom GFZServer, der die verlinkte Seite
nicht fand.
Freundliche Pfingstgrüße!
C. Clauser 
86 
Hajo

Saturday, May 08. 2010 14:01:49 UTC 
Hallo Kollegen,
... das ist einfach eine tolle Seite mit so vielen guten didaktischen Hinweisen
und numerischen Möglichkeiten! Der "Besuch" gehört zum regelmäßigen Programm meiner
Übungen und ist für viele BSc/MSc/Dipl.Arbeiten unersetzlich!
Vielen Dank  wie früher schon einmal mitgeteilt,
Hajo Götze

85 
Franz Barthelmes

Thursday, April 29. 2010 13:20:29 UTC 
Dear Varuna,
sorry, I fear I can't really answer your 4 questions.
Question (1): There are similar questions (with answers) in the guest book.
The model EGM2008 is (up to now) the only model with a resolution of degree and
order 2190 and with terrestrial data which are not available for others.
The real resolution of the model in an area of interest (e.g. India) depends on
the data which have been used from this region to establish the model. We are
not the authors of EGM2008. I good idea to get an impression of the resolution
of a model in an area of interest is to generate a plot of this area using our
calculation service.
Question (2): Please ask an expert in this field :) .
Question (3): Use the internet for searching and study the literatur (sorry :))
Question (4): The improvement is very easy ;) If you want to improve a global
gravity field model for a specific area you must have gravity field data
relevant for this area which are not yet in the model. Then use one of the
wellknown mathematical methods (techniques, algorithms) to calculate an
improved model.
Kind regards
Franz 
84 
G VARUNA KUMAR

Tuesday, April 27. 2010 07:04:03 UTC 
Dear Sir,
For Indian region, which model is best suitable?
Regarding gravity measurements, using relative gravimeter CG3 , is it necessary to close the loop every day for computation of drift?
References / Software for development of a regional Geopotential model or Global Geopotential model?
How to improve the accuracy of EGM96 or EGM2008 for the Indian region?
With regards,
Varun 
83 
W. Koehler

Monday, March 22. 2010 08:54:20 UTC 
Dear Rajesh,
please use the button "Calculation Service" on the left side.
Kind regards. 
82 
Rajesh Kumar

Monday, March 22. 2010 06:26:33 UTC 
I wanted to use "Service for Computing Data from Models" under software but unfortunatitly
i am unable to find that option . how can i use this service?
Appreciated if you reply soon.Thanking you. 
81 
Bill Oberg

Thursday, February 18. 2010 16:46:31 UTC 
I am working on a project with other scientists that hopefully
will predict earthquakes using Iasobergs.
I will try to integrate these images with my study.
Thank you.
Bill Oberg

80 
Victor Glaznev

Saturday, February 13. 2010 07:24:47 UTC 
Fine!
I often use yours Calculation and Visualization Service for education and science purposes.
Million thanks for authors!

79 
Hunja Waithaka

Thursday, February 11. 2010 04:06:20 UTC 
This is quite a resourceful site. Keep up the good work. 
78 
Franz Barthelmes

Tuesday, January 26. 2010 14:41:33 UTC 
Please address questions about the accuracy of the models to the authors of
the models.
Kind regards
Franz 
77 
Ghadi Younis

Monday, January 18. 2010 07:29:59 UTC 
Dear Franz,
thanks for clearing the confusion, I think a description of the height system (ellipsoidal or Orthometric) can solve the confusion in the future.
other question: what is the accuracy of gravity data from EIGEN04c EIGEN05c and EGM2008?
best regards,
Ghadi Younis 
76 
Franz Barthelmes

Friday, January 15. 2010 13:21:42 UTC 
*** The height coordinate ***
Hello Everyone,
the question of Ghadi Younis showed me that my item from 15. August 2009 in
"Latest Changes" was not correct. For the functionals:
 gravity_disturbance
 gravity_anomaly
 gravity_earth
 height_anomaly
a column with the height coordinate of the point where the functional are
calculated were added. This height coordinate is not the ellipsoidal height as
stated. It is the bilinear interpolation of the digital terrain model which is
the height above sea level (i.e. above the geoid).
The calculations are (and were) correct.
During the calculation from spherical harmonic models the positions have to be
transformed into ellipsoidal height coordinates (and then into spherical
coordinates) and for that the geoidal heights are added. But the output is
(and was) the unchanged bilinear interpolation of the digital terrain model
(and I think it is the more useful information).
==> So the mistake was only the description.
*** Sorry for the confusion. ***
Kind regards
Franz

75 
abdullah susanto

Thursday, January 14. 2010 04:31:16 UTC 
my name abdullah susanto
I'm student S1 in GeodesyITS Surabaya, Indonesia

74 
Franz Barthelmes

Friday, January 08. 2010 11:07:04 UTC 
Dear Ghadi Younis,
I was a little incorrect in my last answer.
I said: "The grid coordinates are always ellipsoidal coordinates." and
"The topography of the Earth's surface is calculated by bilinear interpolation
of the etopo2v2grid." > This is correct.
But: The heights of etopo2v2 refer to sea level and not to the ellipsoid
(as far as I know ;) ).
Therefore, in the program geoid heights are added to the interpolated
etopo2heights to get the height coordinates of the Earth's surface with
respect to the ellipsoid.
Kind regards
Franz 
73 
Franz Barthelmes

Wednesday, January 06. 2010 16:53:53 UTC 
Dear Ghadi Younis,
the grid coordinates are always ellipsoidal coordinates. The topography of the
Earth's surface is calculated by bilinear interpolation of the etopo2v2grid.
The heights there are ellipsoidal heights (as far as I know).
Kind regards
Franz 
72 
Zakarneh

Wednesday, January 06. 2010 11:42:51 UTC 
Dear Franz.
I need to have deflections of Vertical
sincerely yours,
Zakarneh 
71 
Ghadi Younis

Wednesday, January 06. 2010 11:40:09 UTC 
Dear Franz,
thanks for your answer.
when I calculate gravity_earth .. is the given height in the output file Orhomrtic or ellipsoidal height?
because differeces ib BadenWürttemberg are +50 meter.
I am working in local Gravity and Geoid modelling .. in TUDarmstadt and HSKarlsruhe.
I get additional observations to direct observations from.
DFHBF(www.dfhbf.de),EGG97 , egm2008 and Eigen05c models.
all provide deflections of vertical. except eigenmodel using Calculation service.
Regards,
Ghadi Younis 
70 
Franz Barthelmes

Tuesday, January 05. 2010 13:58:32 UTC 
Dear Ghadi Younis,
yes, you are right, the calculation of grids of deflections of the vertical
would be useful. We are working on that  it is a question of priorities :).
Is there anybody else who need it? ;)
Kind regards
Franz 
69 
Slim Pickens

Monday, January 04. 2010 18:41:54 UTC 
Thanks for this site! 
68 
Ghadi Younis

Monday, January 04. 2010 17:38:43 UTC 
Hallo ,
it would be nice if the caculation service can also
calculate deflections of vertical in the given grid..
added to geoid or heights anomalies grid or seperstely in a seperate grid computation 
67 
Franz Barthelmes

Friday, November 20. 2009 09:41:29 UTC 
Dear Henry Codallo,
there are functionals of the Geopotential which are defined in space
(as e.g. the potential itself or the second rderivative) and there are
functionals which are defined only as 2d functions depending on longitude and
latitude (as e.g. the geoid or the classical gravity anomaly). For the latter it
makes no sense to ask to which surface it refers. Look at the table on the
calculation site or the report available under "Theory of the Calculation
Service" to see how the functionals are defined. Take it as an exercise course
to find out what kind of functional the Bouguer anomaly is :) .
Kind regards
Franz 
66 
henry codallo

Thursday, November 19. 2009 11:29:27 UTC 
Ok I Know, but if i want a grid of anomaly bouger , this grid will be referenced to the ellipsoid and not to the geoid?? or it doesnt matter?? (height ellipsoid value 0)
thanks
henry codallo

65 
Franz Barthelmes

Wednesday, November 18. 2009 10:10:52 UTC 
Dear Henry Codallo,
"height over ellipsoid" means: height over the ellipsoid of the used reference
system (e.g. wgs84), measured along the direction of the normal gravity vector
(along the ellipsoidal normal). If you use h=0 (which is not possible for all
functionals) the functional is calculated on the ellipsoid. You can find more
about that in the report:
http://icgem.gfzpotsdam.de/ICGEM/theory/str0902.pdf
Kind regards
Franz 
64 
henry codallo

Tuesday, November 17. 2009 21:51:32 UTC 
hello friends,
what the height over ellip means???
what happen if i let the default value 0 when i'm computing a grid for example for all venezuela???
thanks
best regards
henry codallo 
63 
David Philip

Sunday, October 25. 2009 12:01:05 UTC 
Superb is my first impression. The graphics and the explanations are excellent.
I hope to learn a lot.
Best regards
David Philip 
62 
Franz Barthelmes

Friday, October 02. 2009 10:57:05 UTC 
Dear Johnny,
the short answer is: The grids are calculated without any interpolation.
Why do you think there could be interpolation? With the coefficients of the model,
together with the spherical harmonic functions, we can calculate the functionals
at any arbitrary point in space. The functionals are calculated exactly at the
gridpoints of your choice without any interpolation. The calculation
(estimation, approximation) of the coefficients is another problem.
Kind regards
Franz 
61 
Johnny Merchan

Thursday, October 01. 2009 15:49:12 UTC 
Greetings,
I'm Johnny Merchan  Venezuela
Another question, taking into account the issue of spherical harmonics.
In the Calculation Service exist interpolation?.
What is that interpolation?.
For example Krigging, bilinear, minimum curvature, Natural neighbor, etc.
Again, thank you

60 
Franz Barthelmes

Monday, September 28. 2009 14:31:42 UTC 
Dear Johnny Merchan,
the generation of a global gravity field model in spherical harmonic
coefficients is much more complicated than simply converting an equidistant
grid into spherical harmonics. Usually the computation of the spherical
harmonic coefficients of a socalled combined model
(there are also "satelliteonly models") is a sophisticated combination of
gravity field information from satellites, from altimetry over the oceans,
from irregularly distributed terrestrial measurements and a lot of additional
information about the atmosphere, the ocean etc.
The maximum degree and order of the mathematical representation of EGM2008 in
spherical harmonics is 2190. That means formally (mathematically) the
resolution can not be better then about 10km halfwavelength (hills or dales).
The real resolution of the model in an area of interest (e.g. Venezuela :))
depends on the data which have been used from this region to establish the
model. We are not the authors of EGM2008. I good idea to get an impression of
the resolution of a model in an area of interest is to generate a plot of this
area using our calculation service.
Kind regards
Franz Barthelmes 
59 
Johnny Merchan

Thursday, September 24. 2009 17:14:45 UTC 
Greetings,
I'm Johnny Merchan
It's great Calculation Services of ICGEM.
I am currently using the Earth Gravity Model 2008 to a gridstep of 0.5 degrees for Venezuela.
I ask. What is the Earth Gravity Model 2008 gridstep without interpolation?.
Originally, what is the spacing of the data Earth Gravity Model 2008 without interpolation?
ó know what the sampling rate model of the data Earth Gravity Model 2008?.
Thank you very much
Caracas  Venezuela

58 
Nadezhda Konanova

Wednesday, July 22. 2009 09:06:48 UTC 
your posting 
57 
W. Koehler

Monday, June 22. 2009 08:01:30 UTC 
Dear Rogers,
you are right, this possibilty was broken due to an implementation mistake.
Now it is possible again, to compute one point and one line of points.
kind regards
wolfk 
56 
rogers

Friday, June 19. 2009 13:49:08 UTC 
Isn't it more possible to calculate information about only one point?
Before it was possible utilizing the same point in the grid...
Thanks.
Rogers 
55 
Wolfgang Köhler

Friday, June 12. 2009 19:10:00 UTC 
Dear Paolo,
sorry, I have checked my logfiles and see that you are right.
The problem is, that I had to install a safetycheck today, that prevents the server from massive parallel usage by some users.
This check obviously failed in your case.
I have to see what exactly is going wrong there, but this will have to wait until
Monday.
Sorry for the trouble.
wolfk 
54 
Fernando Paolo

Friday, June 12. 2009 16:00:54 UTC 
Please, what is going on???
I have waited for the calculation service, and now all the
time I try to perform some calculation I receive the message:
* sorry, you have already 3 processes running at the moment...*
I DO NOT HAVE ANY PROCESS RUNNING! 3 process? I could not started even one.
Fernando Paolo
University of Sao Paulo. 
53 
Liang Fang

Friday, June 05. 2009 14:52:53 UTC 
I want to use this model to do some test. 
52 
Liang Fang

Friday, June 05. 2009 14:50:02 UTC 
your posting 
51 
Franz Barthelmes

Thursday, May 28. 2009 10:08:42 UTC 
Dear Carolina,
the topography in spherical harmonics (model DTM2006) is used to calculate the
geoid undulations from pseudo height anomalies considering the topographical
effect (spherical shell approximation) for the functionals:
geoid
gravity_anomaly_cl
and additionally
a digital terrain model is used (bilinear interpolation of the ETOPO2v2grid)
to calculate the exact height on the Earth's surface (geoid + topography)
for the functionals:
height_anomaly
gravity_disturbance
gravity_anomaly
gravity
The zero degree term is a constant offset due to a possible difference
between the GMvalues of the model and the reference system (normal potential).
Kind regards
Franz Barthelmes 
50 
Carolina

Wednesday, May 27. 2009 21:25:31 UTC 
your posting
I want to know to calculate disturbance whether the calculation includes a digital terrain model
and what is the diferncia of calular or not the term of order zero
thank you very much 
49 
Victor Zlotnicki

Thursday, May 14. 2009 05:52:43 UTC 
Extremely useful. Although I have the spherical harmonic reconstruction code,
and I use it routinely to convert GRACE to water equivalent,
the evaluation of various functionals, with various Tide systems and with
various smoothing radii, done so quickly, is extremely valuable and saves
me a lot of time. Thank you very much!
Victor 
48 
Franz Barthelmes

Monday, May 11. 2009 12:12:38 UTC 
Dear Rogers,
can you formulate your question more precisely, please?
In our Calculation Service we offer the calculation of Molodenskygravity
anomalies, classical gravity anomalies and the spherical approximation.
For more information please look at the short description on the site
"Calculation Service" or at "Theory of the Calculation Service".
Kind regards
Franz Barthelmes 
47 
rogers

Friday, May 08. 2009 17:53:36 UTC 
How to reduce gravity anomalies from ellipsoid to surface of earth? 
46 
Franz Barthelmes

Monday, April 20. 2009 10:17:43 UTC 
Dear Alexandre B. Lopes,
it is nice to hear that our service is useful. If you have any questions
don't hesitate to contact me (email: bar@gfzpotsdam.de).
We are always interested to know how the service could be improved.
So if you have critics or suggestions for improvement  let us know.
Kind regards
Franz Barthelmes 
45 
Alexandre B. Lopes

Monday, April 13. 2009 22:23:18 UTC 
The service is very good. I use to calculate and to compare geoid models. I work
with ocean dynamics topography (MSSN) and geostrophic circulation.
I use follows geoidal models:
1  EIGEN5C;
2  EGM2008.
thanks

44 
Franz Barthelmes

Tuesday, April 07. 2009 11:34:25 UTC 
Dear Francisco Palominos,
on the web pages of our service you can also find the model references
(button "model references") and a link to the original site of the model
(if available).
I will send you information about the eigen1 model per email.
Kind regards
Franz Barthelmes 
43 
Francisco Palominos

Tuesday, April 07. 2009 00:26:54 UTC 
Hello my name is Francisco Palominos , I am a student of Engineer GeomÃ¡tic of the University of ConcepciÃ³n Chile, and I need information about geoidal models in especial EGM96, EGM2008, and eigen 1.
can you answer me in Spanish please?
If you do not can , no matter
thank you... 
42 
Alpay ABBAK

Sunday, March 01. 2009 14:20:07 UTC 
Dear colleage,
'E' symbol is not written in degree 2 order 0 of GGM03s coefficients.
Best regards...

41 
Franz Barthelmes

Friday, January 09. 2009 08:34:39 UTC 
Dear Alpay ABBAK,
the spectral behaviour of each model is shown on our service (button
"evaluation of models"). How the curves of signal amplitudes per degree look like
depend on how the models have been calculated (inputdata, mathematical method
of approximation, stabilisation method etc.). I don't understand the
question: "What rule checks the signal amplitude of the model, absolutely?"
May be your question is: "What is the rule of thumb of the signal amplitudes
per degree of the REAL gravity field of the Earth?"
Kind regards
Franz Barthelmes
(ICGEMTeam)

40 
Alpay ABBAK

Sunday, December 28. 2008 13:34:56 UTC 
dear colleague,
I wonder what is the rule of thumb in signal amplitudes per degree of any model?
Namely, What rule checks the signal amplitude of the model, absolutely?
thanks for your interest. 
39 
Franz Barthelmes

Tuesday, December 02. 2008 12:55:47 UTC 
Dear Olalekan Isioye,
yes we want to improve our service step by step and we are greateful for all
proposals. Unfortunately I don't understand what you mean with:
"...that users can download specifically what they want from little information
that can be provided by users"
So please be so kind and tell us what you would like to download?
Kind regards
Franz Barthelmes
(ICGEMTeam) 
38 
olalekan ISIOYE

Monday, December 01. 2008 10:37:39 UTC 
Your calculation service should be inprove on. such that users can download
specifically what they want from little information that can be provided by
users 
37 
wolfk

Friday, November 14. 2008 10:24:59 UTC 
This+is+the+first+test+of+the+new+GuestBook+functionality.%0D%0AEnjoy. 
36 
Franz Barthelmes

Thursday, October 30. 2008 09:44:50 UTC 
Dear Robert Onslow,
thank you for using our Service and thank you for calling our attention to the mistake.
Uo to now nobody has noticed it because missing coefficients usually will assumed
to be zero by the software.
After talking to the authors of GGM03s it has been corrected on our service.
Kind regards Franz Barthelmes 
35 
Robert Onslow

Wednesday, October 29. 2008 14:55:56 UTC 
Also, GGM03 l=1 m = 1 is missing
Robert 
34 
Robert Onslow

Wednesday, October 29. 2008 14:48:36 UTC 
Is the ICGEM version of the GGM03 model correct?
Please see l=180, m = 179 and l = 180, m = 180.
Robert 
33 
Franz Barthelmes

Tuesday, October 14. 2008 14:21:50 UTC 
Dear William Rose,
thank you for using our service. The calculated (predicted) gravity relates to the
Earth's surface calculated by the geoid from the gravity field model plus the
topography model. The topography model is necessary for two different purposes:
(a) to calculate the geoid undulations from height anomalies by adding a
topography dependent correction term, and
(b) to calculate the exact coordinates on the Earth's surface (if needed for the
functional  e.g. gravity).
For (a) a spherical harmonic expansion of the topography is used with the same
resolution (maxed_used_degree) as the used gravity field model, and for (b) we
use bilinear interpolation of the original ETOPO2grid to calculate the
elevation of position as accurate as possible.
If you specify the functional "topography" our service calculates the topography
from the spherical harmonics. Unfortunately up to now the grid interpolation of
the topography is not provided as output, we will think about offering it too.
Some hints:
I would use the new high resolution gravity field model EGM2008.
The coordinates should be as accurate as possible.
For Johannesburg I get with EGM2008:
for lat: 26.2 long: 28.08333
=> elevation from shm: 1538.4 m
=> elevation from grid: 1712.5 m
=> gravity: 978545.95868 mgal
for lat: 26 long: 28
=> elevation from shm: 1669.9 m
=> elevation from grid: 1402.99 m
=> gravity: 978586.956722 mgal
If you have better values for the elevation it is a good idea to use the
gravity gradient for correction. A general question is: how accurate do you need
the gravity at the point of interest?
I hope this helps a little, if you have further questions please contact me at
bar@gfzpotsdam.de
Kind regards
Franz Barthelmes 
32 
William Rose

Monday, October 13. 2008 18:03:07 UTC 
I'm not a geologist. I'd like to know the gravity in Phildelphia, USA and
Johannesburg, SA for purposes of calibrating an accelerometer. I have entered
the lat & long of each location in your calculator to get two "grids" with one point
each. I specify "gravity" as the functional to be computed. Is the
gravity which is then computed the predicted gravity for "sea level" at that lat &
long? If so, I will subtract 0.197 mGal/m*actual city elevation, to adjust for
elevation of each city. Or does the software report the gravity at the "predicted
elevation" for that location (the elevation reported when I specify "topography"
as the output)? In that case, the elevation correction will be smaller. For example,
"topography" reports an elevation of 1450 m for Jo'burg's lat & long, so I would
subtract 300m*0.197 mGal/m, since Jo'burg is at 1750 m, 300 m higher than the
"topography" mdoel.
Thank you. 
31 
'Franz Barthelmes

Thursday, September 04. 2008 14:02:21 UTC 
Dear Sekhar,
the formal resolution of a model in spherical harmonics depends on
the highest degree and order of the development. The real resolution in the area
of your interest depends on the data, which are included in (approximated by) the
model. We are not the authors of the model EGM2008. Our "table of available models"
have links to the original sites of the models. For EGM2008 it is:
http://earthinfo.nima.mil/GandG/wgs84/gravitymod/egm2008/index.html
Kind regards,
Franz Barthelmes 
30 
'Sekhar'

Thursday, September 04. 2008 02:20:59 UTC 
Dear sir,
what is the accuracy of EGM2008 model in case of land. If i want to utilise this
data, what could be minimum area, minimum grid interval i can select, if i do it
through your calculation service. My interest was analysis of geoid at different degrees
over extent of 5degreex 5 degree for geodynamic studies related to himalayas.
Can u suggest any literature related to this.
sekhar 
29 
Ahmad

Tuesday, August 05. 2008 17:37:59 UTC 
it will make more sence if you show the COMMENTS in the HTML page not into a
Text Area. 
28 
Ahmad

Tuesday, August 05. 2008 17:36:24 UTC 
Nice guest book :) 
27 
Franz Barthelmes

Monday, June 30. 2008 11:45:41 UTC 
Dear Terepaima Tabare, I tried to write you an email to "terepaimatabare@gmail.com"
but it failed. So please write me an email to "bar@gfzpotsdam.de".
Kind regards
Franz Barthelmes 
26 
Terepaima Tabare

Thursday, June 26. 2008 15:18:44 UTC 
My e mail is terepaimatabare@gmail.com , thak you for helpme and your service is very
good, and the grids is of great utility for gravity maps of my country. 
25 
Terepaima Tabare

Thursday, June 26. 2008 15:09:05 UTC 
Hello I am the engineer Terepaima Tabare, I write to request information about
training courses and training in the use, handling in applications of satellite
data derived from satellites and Grace CHAMP. I write from the agency Bolivarian
for space activities in which Venezuela institution work. As an institution we
are interested in training in this area. Where you can find such courses?; if
there is no possibility that there is a design according to our needs?.
Thank you very much
Caracas Venezuela 
24 
Franz Barthelmes

Tuesday, May 20. 2008 16:41:36 UTC 
Dear Rajasekhar, I guess with "at different harmonics" you mean the bandpass
filtering of the geoid by calculating geoidgrids using only the coefficients of a
"band" of degrees l: lmin < l < lmax.
You can do this by using our calculation service to generate grids with different
values for "max_used_degree" and computing the griddifferences as a second step by
yourself. If you have further questions, do not hesitate to contact me at
"bar@gfzpotsdam.de". Kind regards, Franz Barthelmes 
23 
Rajasekhar

Tuesday, May 20. 2008 14:00:39 UTC 
Dear sir,
i want to analyse the geoid at differnet harmonics from recently available models
EGM2008; EIGENGL04C.
This will helpful to study geoid at different wavelengths. Can u
suggest is there any program or software to do this exercise.
Rajasekhar 
22 
Franz Barthelmes

Friday, May 16. 2008 08:55:09 UTC 
Dear Ariel Silva Hidalgo, thank you for using our service. Unfortunately in our
ICGEMTeam nobody speaks spanish. I guess you ask for a manual in spanish?  No,
all things are in english (as usual in science ;)). Kind regards, Franz Barthelmes.
My email is: bar@gfzpotsdam.de 
21 
Ariel Silva Hidalgo

Thursday, May 15. 2008 20:51:43 UTC 
Gracias por realizar sitios como éste. Felicitaciones por el trabajo realizado,
me ha sido de extrema utilidad. ¿Publicarán algún manual en español? 
20 
Franz Barthelmes

Monday, April 14. 2008 10:57:06 UTC 
Dear Terepaima Tabare, on our site "calculation service" is an explanation,
what the functionals are. For example: "The gravity anomaly (according to
Molodensky's theory) is defined as the magnitude of the gradient of the potential
on the Earth's surface minus the magnitude of the gradient of the normal potential
on the Telluroid (Earth's surface minus height anomaly). Here it will be calculated
as exact as possible." I think this is nonambiguous.
To help you, please tell me what you don'nt understand.
Best regards Franz Barthelmes.
My email is bar@gfzpotsdam.de 
19 
terepaima

Friday, April 11. 2008 20:23:48 UTC 
HI, I an Ing. Terepaima Tabare from Venezuela. I am a bit new to this, I like know
information of gravity product that your seriously.. I would like to clarify that which
anomaly you offer in the calculation service?? air free anomaly or Bouguer anomaly?
and I like to read abaut the kind of corrections applied to the data for example in the
model EIGENGL04C. I want to Modeling gravimetric with this type of satellite data!!
Thank you.. 
18 
Alpay ABBAK

Friday, February 01. 2008 08:42:02 UTC 
Hi, I am PhD student of Turkey. I would like to know if there is any paper about
evaluation of models and methods in your site. Thanks...
my email: aabbak@selcuk.edu.tr 
17 
Franz Barthelmes

Wednesday, November 14. 2007 10:14:35 UTC 
Dear Maria Eugenia,
a short description what the functionals are is on the calculation service site.
A poster with the formulas can be downloaded from:
ftp://ftp.gfzpotsdam.de/pub/home/sf/bar/publications/PosterICGEMFormulas.pdf
A description of the theory behind the calculation service is in preparation.
If you have more detailed questions please contact me on
bar@gfzpotsdam.de (I don't know your email address). 
16 
Maria Eugenia

Wednesday, November 07. 2007 16:33:02 UTC 
Hi, I am a PhD student of Argentina. I would like to know if there is any paper with the
explanation of the formulation involved in your calculator, as exist for EGM96.
Thanks 
15 
rodrigo abarca del rio

Thursday, December 28. 2006 11:29:21 UTC 
HiThe Evaulation service is not working, nor the software download service.regards
rodrigo abarca del rio
dgeo
universidad de concepcion
chile 
14 
Steve Kaye

Wednesday, November 15. 2006 10:35:20 UTC 
This is a firstclass site and data  excellent service. Thank you.A little
feedback. I'm using EIGENGL04C, in combination with Scripps Institute
satellite derived gravity and my own data from some islands, to produce Bouguer
anomaly regional and residual images and maps for the Banda Arc area in
Indonesia. Using your data removes (partially) the subjectivity typically
present in the old 'classical' methods for producing regionals and residuals.
The results are very promising and I look forward to extending the work over
land masses once the 'geoidheight' function is available. You can see soem of
this work at http://www.stevekaye.nadsl.net/regional_and_residual_gravity.htm 
be careful, large images! 
13 
phani

Friday, July 28. 2006 04:49:09 UTC 
I am PhD student at National Geophysical Research institute, India. Iam
interested work with satellite gravity data as a part of my PhD work. Iam
interested in analysis of satellite gravity anomalies and geoid over India and
anomalies. Recently i seen a paper in Gondawana Research by Choi at al.,, they
analysed Grace data over north eastern China and korean peninsula. They used
GRACECHAMP gravity data of 130,317 spherical harmonic coeffiecints to degree
and order 360. Iam also interested in same kind of qualitative work over India,
which is part of my PhD work. for this how can i extract from the site
http://icgem.gfzpotsdam.de/ICGEM/ICGEM.html.Iam confused to provide min_degree
used, max_degree used and orders only_start, orders _only end, start gentle cut.
Can u suggest in this regard to over come this problem. Can u suggest any
literature related to these parameters. 
12 
jenny

Friday, June 23. 2006 04:15:05 UTC 
I enjoyed staying with your site, will surely come back to learn more. 
11 
Franz Barthelmes

Tuesday, June 06. 2006 14:27:23 UTC 
Hi hluzo, tide system transformation is basically a C20 change.For further
details contact me: bar@gfzpotsdam.de 
10 
hluzo

Friday, June 02. 2006 13:39:04 UTC 
Great idea to have ICGEM.I have also questions about tide systems. How can I
transform the global gravity model from one tide system to another? Is it only
C20 transformation? Does it exist a universal formula for tide system
transformation? 
9 
David Sandwell

Friday, May 05. 2006 17:13:08 UTC 
This is a nice service. I'm computing height anomaly and gravity anomaly for
EIGEN04. 
8 
chris

Sunday, April 16. 2006 19:34:12 UTC 
can i get this applet? 
7 
wolfk

Monday, February 13. 2006 23:00:00 UTC 
Of course, you can use this applet, if you keep the copyright notice.
However, please note that it needs data transfer from the server. 
6 
Alex

Monday, February 13. 2006 09:58:02 UTC 
Can i use this applet or does it have copyright etc? 
5 
Franz Barthelmes

Thursday, December 08. 2005 16:32:52 UTC 
Answer to the question by Peter Löwe concerning the computation of geoid undulations:
Up to now we offer the possibility to calculate the height anomaly on the ellipsoid,
which is often called the "pseudo height anomaly". To calculate the geoid from the pseudo height anomaly it is
necessary to know the density distribution of all topographical masses above the geoid.
A simple approximation is to consider the influence of an equivalent Bouguer plate.
This is what we plan to offer soon. Don't overestimate the accuracy of this approximation and note that the
spherical harmonic models up to degree and order 360 (e.g. eigencg03c) do not contain structures (bumps)
smaller then ca. 50km. 
4 
Peter Löwe

Thursday, December 08. 2005 09:41:07 UTC 
when will it be possible to use the "Service for Computing Data from Models" for
computation of geoid undulations referred to EIGENCG03C ? 
3 
Franz Barthelmes

Tuesday, July 26. 2005 14:42:48 UTC 
Answer to M. Sadiq: Thank you for your interest. You can use the software under
the button "Service for Computing Data from Models". There you can calculate
grids for areas of your choice. For further questions please contact me:
bar@gfzpotsdam.de Kind regardsFranz 
2 
M Sadiq

Saturday, July 23. 2005 12:57:11 UTC 
I am Ph.D. Student at QuaidiAzam University Islamabad, Pakistan. My topic of
study is Gravitational geopotential modeling. I need the Gravity field
parameters of EIGEN CG03C gravity model e.g. Height anomaly, Gravity anomaly and
Geoid Undulations etc. Is there any software to calculate these parameters of
the model. Could it be provided to me for research purpose. I need data for the
whole area of Pkistan of above mentioned parameters.Kind regardsM Sadiq 
1 
hans

Tuesday, May 10. 2005 00:42:30 UTC 
It is very nice. 