Local geoid determination with in situ geopotential data obtained from satellite-to-satellite tracking

Abstract

A new satellite mission to map the Earth's gravitational field (GRACE) is based on inter-satellite tracking using micro-wave ranging which can be used to solve for parameters of a global spherical harmonic model of the gravitational field using traditional satellite orbital perturbation analysis. An alternative algorithm has been developed to use the inter-satellite range-rate, supplemented by GPS baseline vector velocities and accelerometer data, to estimate in situ geopotential differences. The collection of these data, treated as a set of boundary values in potential theory, should yield higher geopotential resolution in the polar latitudes than provided by a truncated spherical harmonic model because of the high concentration of data in these areas. On the other hand, in situ data must be downward continued for local geoid determination, whereas this is already incorporated in the spherical harmonic models. Simulations confirm that although spherical harmonic estimations also yield relatively higher accuracy near the poles, local geoid estimation from in situ geopotential difference measurements is even more accurate at the poles, by a factor of two or higher for the case of nineteen days' worth of GRACE data.