Mid-Term Report of SSG 3.185 (1999–2001)



Nico Sneeuw

Institut für Astronomische und Physikalische Geodäsie

Technische Universität München



This report describes the activities and accomplishments of the special study group (SSG) 3.185, Merging data from dedicated satellite missions with other gravimetric data, in the time-frame 1999-2001. The general objectives of SSG 3.185 are to investigate issues related to merging (spatial domain, spec-trally and/or normal matrix combination) and to come up with results and proposals that may support CHAMP/GRACE/GOCE communities in their data processing and merging strategies.


1 Members

The special study group 3.185 consists of the following members:

Sneeuw N (president) IAPG, TU Munich Germany
Albertella A DIIAR, Politecnico Milano Italy
Bettadpur SV  CSR, Univ. Texas USA
Bouman J SRON, Utrecht The Netherlands
Bruton AM AGEM, Univ. Calgary Canada
Gruber T  GFZ Potsdam  Germany
Kenyon S NIMA  USA
Kusche J  DEOS, Delft Univ. Technology The Netherlands
Lemoine JM CNES, GRGS France
Pavlis NK Raytheon ITSS Corp USA
Schuh WD TG, Univ. Bonn  Germany

At the beginning of the study group activities Bouman’s affiliation was the Delft University of Technology, The Netherlands, whereas Kusche was at the University Bonn, Germany. Sneeuw will start at the University of Calgary in the course of 2001.


2 Activities

E-mail discussion:       Interaction between the members of SSG 3.185 has been stimulated by putting forward certain questions through e-mail. There have been two provocative questions so far:

1.        In view of the expected accuracy of the gravity field missions CHAMP, GRACE

and GOCE: why would we need old satellite data? This question was discussed

from several viewpoints:

a)reprocessing of orbits, e.g. for altimetry

b) decorrelation of gravity field parameters

c) a priori information and regularization

d) calibration

e) time-varying gravity field, especially low degrees

2.        When merging satellite data with terrestrial data: how does the inhomogeneity of the terrestrial database affect the satellite results? This discussion hasn’t been closed yet. Partial answers to this question are found in the work by Pavlis and by Kusche, cf. references.


Validation working group Gruber chairs the IGeS working group Preparation of Standard Procedures for Global Gravity Field Validation. Members are­amongst others Albertella, Kenyon, Pavlis and Sneeuw. Objective of the working group is the definition of standard test procedures for global gravity field evaluation. These activities entail the validation of satellite gravity field solutions with terrestrial data and hence cover many aspects of SSG 3.185.


Simulation data set Kusche has strongly been involved in the provision of simulated data sets for CHAMP, GRACE and GOCE. This was a joint activity with Special Com-mission SC7 Satellite Gravity Field Missions, chaired by K.-H. Ilk, and SSG 2.193 Gravity field missions: calibration and validation, chaired by P. Visser. These data are available on CD and on-line through http://www.geod.uni-bonn.de/SC7-data/. They are of tremendous help in validating gravity recovery software, merging schemes and so on.


Ph.D. theses Four members of the SSG finished their Ph.D. theses on areas relevant to the SSG: Bouman, Bruton, Gruber and Sneeuw. See the list of references.


GRACE Bettadpur and Gruber are GRACE project team members. In particular they are involved in the GRACE science data processing system, which touches on many aspects of the SSG’s goals.


GOCE Albertella, Bouman, Gruber, Kusche, Schuh and Sneeuw actively participate in the GOCE project and in studies of the European Space Agency (ESA) on GOCE-related issues, e.g. (Sünkel, 2000). Especially issues like merging SST with SGG, regularization, local data in polar gaps and other SSG-related objectives are addressed.


3 Selected meetings

The members of SSG 3.185 participated at several meetings, giving presentations and contributing to the proceedings. Participation of SSG-members was never high enough, though, to warrant a formal SSG-meeting. Discussion of the relevant SSG-topics was therefore—beside the aforementioned e-mail discussions—restricted to informal contacts. The following list of meetings contains the highlights, although it is certainly not com-plete:

EGS 2000 Nice, France. In particular session G3.01 The Earth gravity field (joint EGS/AGU): Global high-resolution geopotential modelling

GGG 2000 Banff, Canada. Gravity, Geoid and Geodynamics 2000

AGU 2000 Fall Meeting San Francisco, USA

German Geodetic Week 2000 Potsdam, Germany

EGS 2001 Nice, France. In particular session G1 The new gravity missions (CHAMP GRACE, GOCE)


4 Relevant publications by members of the SSG

Albertella A, F Sans`o, N Sneeuw (1999). Band-limited functions on a bounded spherical domain: the Slepian problem on the sphere, J. Geodesy 73:436-447

Albertella A, N Sneeuw (2000). The Analysis of Gradiometric Data with Slepian Functions, Phys. Chem. Earth (A) 25(9–11):667–672

Bouman J (2000). Quality assessment of satellite-based global gravity field models, NCG Publications on Geodesy 48

Bruton AM (2000). Improving the Accuracy and Resolution of SINS/DGPS Airborne Gravimetry,UCGE Report 20145

Glennie CL, KP Schwarz, AM Bruton, R Forsberg, AV Olesen, K Keller (2000). A comparison of stable platform and strapdown airborne gravity, J. Geodesy 74:383–389

Gruber T (1999). Global Gravity Field Modelling, in: National Report of the Federal Republic of Germany on the Geodetic Activities in the Years 1995-1999, compiled by: B Heck, R Rummel, E Groten, H Hornik; DGK Reihe B, Heft Nr 308, München 1999

Gruber T, C Reigber, P Schwintzer (2000). The 1999 GFZ pre-CHAMP high resolution gravity model, in: K.P. Schwarz (Ed.) Proceedings of IAG Symposium 121, Geodesy Beyond 2000 –The Challenges of the First Decade, pp 89–95

Gruber T, A Bode, C Reigber, P Schwintzer, G Balmino, R Biancale, J-M Lemoine (2000). GRIM5-C1: Combination solution of the global gravity field to degree and order 120, Geophys. Res. Letters 27(24):4005-4008

Gruber T (2000). Hochau oesende Schwerefeldbestimmung aus Kombination von terrestrischen Messungen und Satellitendaten ueber Kugelfunktionen, Scientific Technical Report STR00/16, GeoForschungsZentrum Potsdam

Gruber T (2001). High Reslution Gravity Field Modeling with Full Variance-Covariance Matrices, submitted to J. Geodesy , 7-2000

Kusche J, KH Ilk, S Rudolph (2000). Impact of terrestrial data on future satellite gravity field solutions, in: Towards an Integrated Global Geodetic Observing System (IGGOS), R Rummel, H Drewes, W Bosch, H Hornik (eds.), IAG symposium 120, pp. 189–192, Springer

Kusche J, R Klees (2001). Regularization for GOCE, submitted

Kusche J (2001). Implementation of multigrid solvers for satellite gravity anomaly recovery, J. Geodesy 74:773–782

Pavlis NK (2000). On the modeling of long wavelength systematic errors in surface gravimetric data, in: K.P. Schwarz (Ed.) Proceedings of IAG Symposium 121, Geodesy Beyond 2000 –The Challenges of the First Decade, pp 131–136

Sneeuw N (2000). A semi-analytical approach to gravity field analysis from satellite observations, Deutsche Geodätische Kommission, Reihe C, Heft Nr. 527 see also:


Sünkel H (ed.) (2000). From Eötvös to mGal, ESA/ESTEC contract No. 13392/98/NL/GD  



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