On the Inversion of GRACE Observables for Local Geoid Determination

Abstract

An analysis is made on the feasibility of using in-situ GRACE measurements for geoid determination. The method investigated consists of local downward continuation using integral inversion. The observables considered are potential differences (DT) and gravity disturbance differences (DGD). The regularization of this ill-posed problem is studied using the Tikhonov, damped singular value decomposition, and conjugate gradient methods. In the search for the best regularization parameter (alpha), the L-curve method is found to succeed when only random errors in the measurements corrupt the solution. However, with model errors, the method does not produce satisfactory results. An empirical method is formulated to find a near optimum alpha. Simulations show that the Tikhonov regularization yields best results. Combined with B-spline smoothing and applied to simulated data for 30 days of gravity mapping, the method produces local geoid (20-degree harmonic model removed) errors of about 12 cm and I I cm for 1.2 degree resolution using DT and DGD, respectively. All simulations are made using the geopotential model EGM96.