Continental hydrology retrieval from GPS time series and GRACE gravity solutions

Abstract

Monitoring of continental hydrology by measuring gravity variations is one of the primary aims of the Gravity Recovery and Climate Experiment (GRACE) mission. We proposed to combine the GRACE measurements with GPS time series provided by the IGS to strengthen the long wavelengths of the hydrology solution. This strategy is necessary because GRACE monthly gravity solutions not yet match the targeted baseline accuracies at the lower spherical harmonic degrees. The method of GPS inversion has been proposed by Blewitt et al (2001), and sensitivity studies have shown that GPS could contribute up to 60% to degrees 2-4, and up to 30% for selected higher degrees in a combination. New in our approach is a) the introduction of a physically motivated regularization method that guarantees stable GPS-inversions up to higher degrees, while minimizing spatial aliasing, and b) the combination with GRACE in a weighted least-squares sense. We find geocenter estimates which are consistent with previous studies. We estimate a variation in the Earth's flattening term which closely resembles independent estimates from SLR. Finally, we provide some lowdegree combined GPS+GRACE mass redistribution grids. © Springer-Verlag Berlin Heidelberg 2007.