Study of Alternatives for Combining Satellite and Terrestrial Gravity Data in Regions with Poor Gravity Information

Abstract

The satellite missions CHAMP, GRACE and GOCE are substantially contributing for the improvement of the Earth gravity field knowledge. However, the respective satellite gravity information remains still limited to around 80 km of spatial resolution. In this condition, it is necessary to use local surface data in shorter wavelengths to obtain more accurate resolutions. This paper deals with strategies to model the Earth gravity field in medium and high frequencies, based on merging Global Geopotential Models (GGMs) and Digital Elevation Models (DEMs). A test area was established in southern Brazil, between the parallels 22ºS and 27ºS and meridians 48ºW and 55°W. The presented methodology uses GOCE_DIR2, already available in the degree and order of 240; GOCE_TIM2, in the degree and order of 250; GOCO02S, in the degree and order of 250; and the combined model EIGEN-06C, in the degree and order of 1420. In order to generate the proposed model, a Residual Terrain Model (RTM) technique was applied, based on the GMRT v2.0 (Global Multi-Resolution Topography 2.0 version) model data. When applying RTM technique, the proposed model achieved better resolutions than the original contained in GGMs. In the absolute analysis, the RMS in GNSS/leveling stations has been reduced by around 17 %, 18 %, 20 % and 20.5 %, respectively for GOCE_DIR2, GOCE_TIM2, GOCO02S, and EIGEN-06C models. The absolute discrepancies were reduced by around 18 % for the satellite-only models and by 28.6 % for the EIGEN-06C. Considering baselines in the range from 55 to 550 km, the contribution of the RTM for the improvement of the original resolution in ppm was around 38 %, 54 %, 57 % and 6.5 %, respectively for GOCE_DIR2, GOCE_TIM2, GOCO02S, and EIGEN-06C models.