Gravity Observation Combination (GOCO) 
The main objective of the GOCO initiative is to compute highaccuracy and highresolution global gravity field models from complementary gravity data sources:
satellite gravity missions GOCE, GRACE and CHAMP, and SLR data (satelliteonly models of the GOCOS series)
plus terrestrial gravity field and satellite altimetry data (combined models GOCOC)
The combination is done by superposition of full normal equations and applying optimized relative weighting strategies.
GOCO has been initiated in the frame of ESA's GOCE Data AO (project no. 4248), with the project partners responsible for the GOCEonly timewise (TIM) models as the nucleus.
The GOCO consortium is composed of the following institutions, coordinated by the IAPG:
TU München, Institute of Astronomical and Physical Geodesy Roland Pail (PI) Thomas Gruber (CoPI), Thomas Fecher, Moritz Rexer 

University of Bonn, Institute of Geodesy and Geoinformation WolfDieter Schuh (CoPI), Jürgen Kusche (CoPI) JanMartin Brockmann, Ina Krasbutter, Silvia Becker, Annette Eicker, Judith Schall 

Graz University of Technology, Institute of Theoretical Geodesy and Satellite Geodesy
Torsten MayerGürr (CoPI) Daniel Rieser, Norbert Zehentner 

Austrian Academy of Sciences, Space Research Institute Oliver Baur (CoPI) Eduard Höck, Walter Hausleitner, Andrea Maier, Sandro Krauss 

University of Bern, Astronomical Institute Adrian Jäggi (CoPI) Ulrich Meyer, Lars Prange 
Model 
Data 
Reference 

GOCE, GRACE 
Pail R., et al. (2010): Combined satellite gravity field model GOCO01S derived from GOCE and GRACE, Geophys. Res. Lett., 37, L20314, doi:10.1029/2010GL044906 Link. 

GOCE, GRACE, CHAMP, SLR 
Goiginger H., et al. (2011): The combined satelliteonly global gravity field model GOCO02S. European Geosciences Union General Assembly 2011, Wien, 04.04.2011 PDF. 

GOCE, GRACE, CHAMP, SLR 
MayerGürr T. et al. (2012): The new combined satellite only model GOCO03s. Abstract submitted to GGHS2012, Venice (Poster). 

GOCO04S  A GOCO04S model was not processed.  
GOCE, GRACE, Kinematic orbits (8 satellites), SLR (6 satellites) 
MayerGürr T., et al. (2015): The combined satellite gravity field model GOCO05s. Presentation at EGU 2015, Vienna, April 2015. 
Optimum combination based on the following data sets:
Model 
GOCO01S 
GOCO02S 
GOCO03S 
GOCO05S 

GOCE gradiometry 
2 months 
8 months 
18 months 
Complete mission (Nov. 2009 – Oct. 2013) 
GRACE 
ITGGrace2010s 
ITGGrace2010s 
ITGGrace2010s 
ITSGGrace2014s 
Kinematic orbits 
– 
CHAMP, GOCE 
CHAMP, GOCE 
Swarm A+B+C, TerraSarX, TandemX, CHAMP, GRACE A+B, GOCE 
SLR 
– 
5 years, 5 sat. 
5 years, 5 sat. 
LAGEOS, LAGEOS 2, Starlette, Stella, Ajisai, Larets 
Constraints 
Kaula, deg > 170 
Kaula, deg > 180 
Kaula, deg > 180 
Kaula, deg > 150 
For GOCE gradiometry the same processing strategy as for the timewise (TIM) GOCEonly models (Pail et al., 2011) has been used.
The data periods of GOCE gradiometry contained in GOCO01S to GOCO03S and GOCO05S correspond to those of the pure GOCE models GOCE_TIM_R1 to GOCE_TIM_R3 and GOCE_TIM_R5.
In addition to static coefficients up to degree/order 280, GOCE05S contains also temporal variation parameters for trend and annual signals up to degree/order 100. The reference epoch is 20080101 (MJD 54466).
Degree error medians of the GOCOS solutions, the GOCEonly model GOCETIMR5 and the GRACEonly model ITSGGRACE2014s.
Geoid differences of GOCO models at 675 GPS/levelling data points in Germany, complete to degree/order 200:
GOCOC: Currently diverse numerical studies on combination models based on satellite, terrestrial gravity and satellite altimetry data are performed. Target date: 2015
Your feedback is very important for us! Therefore, please send your questions, experience with the GOCO models and validation results to info@goco.eu.
Fecher T., Pail R., Gruber T. (2011):Global gravity field determination by combining GOCE and complementary data; in: Ouwehand, L. (eds.) Proceedings of the 4th International GOCE User Workshop, ESA Publication SP696, ESA/ESTEC, ISBN (Online) 9789290922605, ISSN 1609042X, 2011; PDF.
Goiginger H., Rieser D., MayerGuerr T., Pail R., Schuh W.D., Jäggi A., Maier A., GOCO Consortium (2011): The combined satelliteonly global gravity field model GOCO02S. European Geosciences Union General Assembly 2011, Wien, 04.04.2011; PDF.
Maier A., Baur, O., Hausleitner W., Höck E., Krauss S., Goiginger H., Pail R., Jäggi A.; Schuh W.D. (2011): Lowdegree gravity field coefficients from SLR data for the new combined gravity field model GOCO02S. European Geosciences Union General Assembly 2011, Wien, 04.04.2011.
MayerGürr T., Rieser D., Höck E., Brockmann J..M., Schuh W.D., Krasbutter I., Kusche J., Maier A., Krauss S., Hausleitner W., Baur O., Jäggi A., Meyer U., Prange L., Pail R., Fecher T., Gruber T. (2012): The new combined satellite only model GOCO03s. Abstract submitted to GGHS2012, Venice (Poster).
MayerGürr T., Pail R., Gruber T., Fecher T., Rexer M., Schuh W.D., Kusche J., Brockmann J.M., Rieser D., Zehentner N., Kvas A., Klinger B., Baur O., Höck E., Krauss S., Jäggi A. (2015): The combined satellite gravity field model GOCO05s. Presentation at EGU 2015, Vienna, April 2015.
Pail R., Bruinsma S., Migliaccio F., Förste C., Goiginger H., Schuh W.D., Höck E., Reguzzoni M., Brockmann J.M., Abrikosov O., Veicherts M., Fecher T., Mayrhofer R., Krasbutter I., Sansò F., Tscherning C.C. (2011): First GOCE gravity field models derived by three different approaches; Journal of Geodesy, Vol. 85, Nr. 11, pp 819843, Springer, ISSN 09497714, DOI: 10.1007/s001900110467x; Link.
Pail R., Goiginger H., Schuh W.D., Höck E., Brockmann J.M., Fecher T., MayerGürr T., Kusche J., Jäggi A., Rieser D., Gruber T. (2011). Combination of GOCE data with complementary gravity field information (GOCO). Proceedings of 4th International GOCE User Workshop, München, 31.03.2011; PDF.
Pail R., Goiginger H., Schuh W.D., Höck E., Brockmann J.M., Fecher T., Gruber T., MayerGürr T., Kusche J., Jäggi A., Rieser D. (2010): Combined satellite gravity field model GOCO01S derived from GOCE and GRACE. Geophysical Research Letters, Vol. 37, EID L20314, American Geophysical Union, ISSN 00948276, DOI: 10.1029/2010GL044906; Link.