A timewise kinematic method for satellite gradiometry: GOCE simulations

Abstract

Abstract. We have defined new algorithms for the data processing of a satellite geodesy mission with gradiometer (such as the next European mission GOCE) to extract the information on the gravity field coefficients with a realistic estimate of their accuracy. The large scale data processing can be managed by a multistage decomposition. First the spacecraft position is determined, i.e., a kinematic method is normally used. Second we use a new method to perform the necessary digital calibration of the gradiometer. Third we use a multiarc approach to separately solve for the global gravity field parameters. Fourth we use an approximate resonant decomposition, that is we partition in a new way the harmonic coefficients of the gravity field. Thus the normal system is reduced to blocks of manageable size without neglecting significant correlations. Still the normal system is badly conditioned because of the polar gaps in the spatial distribution of the data. We have shown that the principal components of the uncertainty correspond to harmonic anomalies with very small signal in the region where GOCE is flying; these uncertainties cannot be removed by any data processing method. This allows a complete simulation of the GOCE mission with affordable computer resources. We show that it is possible to solve for the harmonic coefficients up to degree 200 ÷ 220 with error to signal ratio ≥ 1, taking into account systematic measurement errors. Errors in the spacecraft orbit, as expected from state of the art satellite navigation, do not degrade the solution. Gradiometer calibration is the main problem. By including a systematic error model, we have shown that the results are sensitive to spurious gradiometer signals at frequencies close to the lower limit of the measurement band. If these spurious effects grow as the inverse of the frequency, then the actual error is larger than the formal error only by a factor 2, that is the results are not compromised.

Accurate Establishment of Error Models for the Satellite Gravity Gradiometry Recovery and Requirements Analysis for the Future GOCE Follow-On Mission

“…At present, the recovery methods for the satellite gravity gradiometry mainly include the space-wise method (Reguzzoni and Tselfes 2009Pertusini et al 2010, Sanso et al 2011, Liu et al 2012, the time-wise method (Milani et al 2005, Pail et al 2010Eshagh 2011, the space-timewise method (Zheng et al 2011b), and the direct method (Bruinsma et al 2010, Pail et al 2011b, and so on. On 10 November 2013, the GOCE satellite has ended its extended mission to map the Earth's gravitational field.…”