Local geoid computation by the spectral combination method

Abstract

The spectral combination method is investigated for the determination of a local geoid in Lower Saxony (Germany) using a global geopotential model, radial gravity gradients from the upcoming GOCE satellite mission, and gravity anomalies. The main goal of this study is to test the method v/ith regard to the validation of GOCE data products. In order to prove the effectiveness and numerical accuracy of the method, the computations are done in a closed-loop simulation based on the EGM96 geopotential model. The gravity field signal is decomposed into long, medium and short wavelength components using corresponding spectral weight functions. The long wavelength information up to about degree n = 30 is computed from a global geopotential model, the medium wavelength part (n = 30-130) is taken from radial gravity gradients at GOCE altitude (250 km), and the high frequency part (n= 130-360) is derived from terrestrial gravity anomalies. The modified spherical Butterworth filter and a cosine filter are tested as spectral weighting functions. The results from the closed-loop simulation are discussed, and an error analysis is done considering the commission and omission errors of the input data sets.