Studies of GRACE Gravity Field Inversion Techniques

The geophysical inverse problem using satellite observations, such as GRACE, to estimate gravity change and mass variations at the Earth's surface is a well-known ill-posed problem. Different methods using different basis function (representing the gravity field) for different purposes (global or regional inversion) have been employed to obtain a stable solution, such as Bayesian estimation with prior information, the repro-BIQUUE of variance components and iterative least-squares estimation with simultaneous updating of a prior covariance, and to achieve enhanced spatial resolutions. The gravity field representation methods include spherical harmonics, regional gridded data (including mascons), and various wavelet representations (Poisson wavelets, Blackman band-limited regional wavelets with global representation). Finally, the use of data types (KBR range, range-rate, range-rate-rate) and data-generation methods (e.g., nonlinear orbit determination and geophysical inverse approach, energy conservation principle, etc) could also reflect relative inversion accuracy and the content of signal spectra in the resulting solution. In this contribution, we present results of a simulation experiment, which used various solution techniques and data types to attempt to quantify the relative advantage and disadvantage of each of the techniques.