Spectral Approaches to Solving the Polar Gap Problem

Abstract

Due to its sun-synchronous orbit, GOCE (Gravity field recovery and steady-state Ocean Circulation Explorer) observations do not cover the polar areas of the Earth. The impact of the limited spatial observation geometry on gravity field recovery is referred to as the polar gap problem. This chapter gives an overview on both spatial and spectral approaches to overcome the polar gap problem. Furthermore we confront strategies based on GOCE data only with methods augmenting additional external gravity field information. Concerning the latter, we present the combination of the GOCE normal equations system with spectral a priori information in terms of tailored regularization. With regard to a GOCE-only solution, we adopt band-limited base functions, commonly referred to as Slepian functions that are optimally concentrated within the spherical belt of GOCE data availability. In terms of regional gravity field determination this approach definitively solves the polar gap problem.