Properties and Applications of EOF-Based Filtering of GRACE Solutions

Abstract

Several filter strategies have been proposed in the past to deal with noise in the GRACE gravity field solutions, particularly with the North-South stripes. These strategies have led to several families of filters, roughly characterized by the properties stochastic vs. deterministic and isotropic vs. anisotropic. One type of filter that has been shown to be very effective is based on Empirical Orthogonal Functions (EOF) analysis in combination with white-noise testing of the resulting time series in the spectral domain (Wouters and Schrama: Geophys. Res. Lett. 34, 2007 doi: 10.1029/2007GL032098). In this paper, we recast the EOF procedure into a filter equation, i.e. the filter transfer is described explicitly. This allows us to emphasize the characteristics of the EOF-based filter. Moreover, our formulation provides an easy means to propagate the GRACE fields into degree variances and spatial covariance functions.