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CoverNewton's Bulletin


Issue n. 5, June 2015 - Assessment of GOCE Geopotential Models    [pp. 25-36]



Evaluation of GOCE-based Global Geoid Models in Finnish Territory


T.Saari, M. Bilker Koivula

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Abstract

The gravity satellite mission GOCE made its final observations in the fall of 2013. By then it had exceeded its expected lifespan of 20 months with 35 additional months and observed the Earth's gravitational field from a lower orbit as originally planned during the last 6 months of its mission lifetime. Thus, the mission collected more data from the Earth’s gravitational field than expected, and more comprehensive global geoid models have been derived ever since. The GOCE High-level Processing Facility (HPF) by ESA has published GOCE global gravity field models annually. We compared all of the 13 HPF-models as well as 3 additional GOCE, 12 GRACE and 6 combined GOCE+GRACE models with GPS-levelling data and gravity observations in Finland. The most accurate models were also compared against high resolution global geoid models EGM96 and EGM2008.
The models were evaluated up to four different degrees and order: 150 (the common maximum for the GRACE models), 200, 240 (the common maximum for the GOCE models) and maximum. When coefficients up to degree and order 150 are used, the results from the GOCE models are better than EGM96 (with height anomalies) and are comparable with the latest GRACE models and EGM2008. Similar results are achieved with the coefficients up to 200, as the GOCE models perform clearly better than EGM96 when comparing with the GPS-levelling datasets. When coefficients up to 240 or maximum are used the results of the GOCE-based models are comparable with the high resolution models. The best performance of the satellite-only models is not usually achieved with the maximum coefficients, since the highest coefficients (above 240) are less accurately determined.