Modeling and estimation of a low degree geopotential model from terrestrial gravity data
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Date
1988-03
Journal Title
Journal ISSN
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Publisher
Ohio State University. Division of Geodetic Science
Abstract
The development of appropriate modeling and adjustment procedures for the estimation of harmonic coefficients of the geopotential, from surface gravity data was studied, in order to provide an optimum way of utilizing the terrestrial gravity information in combination solutions currently developed at NASA/Goddard Space Flight Center, for use in the TOPEX/POSEIDON mission. The mathematical modeling was based on the fundamental boundary condition of the linearized Molodensky boundary value problem. Atmospheric and ellipsoidal corrections were applied to the surface anomalies. The 1° x 1° mean free-air anomalies of the Ohio State University's June 1986 global anomaly field were used. Low degree ( <50) potential coefficient sets were estimated through a rigorous least squares adjustment. The high frequency content of the anomalies was removed prior to the adjustment using the OSU86F high degree expansion. Terrestrial gravity solutions were found to be in good agreement with the satellite ones over areas which are well surveyed (gravimetrically), such as North America or Australia. However, systematic differences between the terrestrial only models and GEMT1, over extended regions in Africa, the Soviet Union and China, were found. In Africa, gravity anomaly differences on the order of 20 mgals and undulation differences on the order of 15 meters, over regions extending 2000 km in diameter, occur. Comparison of the GEMT1 implied undulations with 32 well distributed Doppler derived undulations gave an RMS difference of 2.6 m, while corresponding comparison with undulations implied by the terrestrial solution gave RMS difference on the order of 15 m, which implies that the terrestrial data in that region are substantially in error.