SPECTRAL-ANALYSIS OF BLOCK AVERAGED DATA IN GEOPOTENTIAL GLOBAL-MODELDETERMINATION

The recovery of the harmonic coefficients of the anomalous potential f rom a geodetic quantity sampled over a regular grid is affected by the non-exact discrete orthogonality of spherical harmonics; larger error s occur for block-average quantities owing to the non-simple behaviour of the block-average operator when applied to spherical harmonics. Fo urier coefficients, on the contrary, can be recovered by exact formula s both from point data and block-averaged data; furthermore, Fourier a nalysis enables to give a rigorous description of aliasing from high-d egree harmonic components for the sphere. The harmonic coefficients of a truncated model can then be obtained by solving linear systems. Num erical simulations confirm the advantages of the method.