Space-wise approach to satellite gravity field determination in the presence of coloured noise

Abstract

For many years the gravity field of the Earth was only seen by satellite geodesy as the main factor affecting the orbit and consequently it was retrieved together with a number of other perturbations. It is since the advent of a new generation of accelerometers that non gravitational perturbations could be separated from the gravity effects and a new era of gravity field estimates from space was born. In the preparatory work of data analysis for the new missions, performed by the geodetic community, three approaches have been proposed and numerically tested: the brute force method (direct approach), the semi analytical (time-wise) method and the space-wise method. In particular, the time-wise method takes advantage of the incoming time flow of data and, after performing a Fourier transform of the observation equations, exploits the prevailing block diagonal structure of the normal equations to estimate the harmonic coefficients of the gravity field. Complementary to it, the spacewise approach has been developed, which goes back to the traditional computation of the harmonic coefficients by some integration technique or by collocation. Some advantages and disadvantages are peculiar of both methods; particularly the space-wise approach has for long ignored the marked signature of the noise spectrum due to the specific measuring conditions of space-born accelerometers. The application of a proper Wiener filter, exploiting the correlation along the orbit, embedded into an iterative scheme seems to be the right answer. In the paper the solution of this major problem of the space-wise approach is illustrated and simulation results are discussed

Frequency-dependent data weighting in global gravity field modeling from satellite data contaminated by non-stationary noise

“…frequency dependent) noise in satellite gravimetry data. Migliaccio et al (2004) proposed to apply a Wiener filter to the data. Since such a filter influences both noise and signal, a number of iterations are needed until the computed gravity field model matches the observations.…”

GOCE: Gravitational Gradiometry in a Satellite

“…There exist various competing strategies for the actual determination of the field coefficients t nm , depending on whether the gradients are regarded in situ measurements on a geographical grid, along the orbit tracks, as a time series along the orbit or as Fourier-coefficients derived from the latter (compare, e.g., Migliaccio et al, 2004;Pail and Plank, 2004;Brockmann et al, 2009;Stubenvoll et al, 2009). These methods take into account the noise characteristics of the components and their orientation in space.…”

GOCE gravitational gradients along the orbit

“…3, whereas the GOCE gravity field analyses are covered in (Pail et al 2011). See also Förste et al 2007;Migliaccio et al 2004;Pail and Plank 2004). The different steps of the GG preprocessing method are summarized in Sect.…”