Consistent Estimate of Ultra-High Resolution Earth Surface Gravity Data (UHR-GravDat)
Final Report Abstract
The objective of the UHR-GravDat project was to create a global set of consistent surface gravity data with a spatial resolution of 2.5’ or roughly 5 km spacing at the Earth’s surface. Because the granted funding was 50 % of the requested funding, we had to reduce the ambitions of the project. This was mainly achieved by two measures: 1) We focused on a proof-of-concept for the marine gravity field, but did not compute a global patchwork. Nevertheless, a global dataset has been produced of consistently processed satellite altimeter data and is ready for further use; 2) We focused on the global evaluation of topographic models, but did not attempt to combine this with available terrestrial gravity anomalies as this cumbersome task would not have been possible within the time constraints. The main achievements of project are threefold: 1. We have shown that a consistent reprocessing of satellite altimeter orbits is a prerequisite to obtain the highest quality gravity field information over the oceans. For example, the inclusion of temporal gravity field variations within precise orbit determination leads to spatial coherent improvements, which are confirmed by the multi-mission crossover (MMXO) analysis. 2. The MMXO ensures the consistency between the different satellite altimeter missions. We have shown that deriving regional gravity fields from this dataset alone may give large errors in coastal or data void areas. A methodological interesting concept was investigated where we introduced a priori information in a relative sense. Specifically, we derived deflections of the vertical from a topographic potential model, which were used as pseudo-observations. Although these observations cannot replace true observations, they help to stabilize the satellite altimetry solution close to the coast, and are thought to aid in a seamless land-ocean transition when terrestrial gravity and satellite altimetry are combined. 3. We produced a 1’ high-resolution model of topographic potential in terms of ellipsoidal and spherical harmonics. As mentioned under point 2) this model can be used as a priori information to stabilize the marine gravity field solution, but it also contributes to the consistency between land and ocean areas. In addition, our results indicate that it might be inappropriate to use spherical harmonics for the evaluation of the high-resolution gravity field at the Earth’s ellipsoid. It is probably better to use ellipsoidal harmonics instead, especially for high latitudes.
Publications
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(2014): High resolution spherical and ellipsoidal harmonic expansions by Fast Fourier Transform. Stud. Geophys. Geod. 58, No. 4, pp. 595–608
Gruber, C., Abrykosov, O.
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(2014): Influence of time variable geopotential models on precise orbits of altimetry satellites, global and regional mean sea level trends. Advances in Space Research 54(1): 92-118
Rudenko, S., Dettmering, D., Esselborn, S., Schöne, T., Förste, C., Lemoine, J.-M., Ablain, M., Alexandre, D., Neumayer, K.-H.
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(2014): Multi-mission cross-calibration of satellite altimeters: constructing a long-term data record for global and regional sea level change studies. Remote Sensing 6(3): 2255-2281
Bosch, W., Dettmering, D., Schwatke, C.
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(2015): Impact of time variable gravity on annual sea level variability from altimetry, In: International Association of Geodesy Symposia, Springer Berlin Heidelberg
Esselborn, S., Schöne, T., Rudenko S.
