An Improved Model for the Earth’s Gravity Field

Abstract

Precision orbit determination methods, along with a new technique to compute relative data weights, have been applied to the determination of the Earth’s gravity field and other geophysical parameters from the combination of satellite ground based tracking data, satellite altimetry data, and the surface gravimetry data. The University of Texas Earth’s gravity field models, PTGF-4 and PTGF-4A, were determined from data sets collected for fifteen satellites, spanning the inclination ranges from 15° to 115°, and surface gravity data. The satellite measurements include laser ranging data, doppler range-rate data, and satellite-to-ocean radar altimeter data, which include the direct height measurement and the differenced measurements at ground track crossings (crossover measurements). The surface gravity data were used in terms of geopotential normal equations (complete to degree and order 50) derived from the Ohio State University 1°×1° gravity anomaly data. PTGF-4 was computed using satellite tracking data and altimeter crossover data, whereas PTGF-4A was determined using these data sets as well as direct altimeter data and surface gravity data. The estimated parameters for PTGF-4A included geopotential coefficients for a model complete to degree and order 50, tidal coefficients, tracking station coordinates and models for the quasi-stationary sea surface topography. Error analysis and calibration of the formal covariance indicate that GEOSAT orbits can be computed radially at the 15–21 cm level.