On the postprocessing removal of correlated errors in GRACE temporal gravity field solutions

We revisit the empirical moving window filtering method of Swenson andWahr (GeophysResLett 33:L08402, 2006) and its variants, Chambers (Geophys Res Lett 33:L17603, 2006) and Chen et al. (Geophys Res Lett 34: L13302, 2007), for reducing the correlated errors in the Stokes coefficients (SCs) of the spherical harmonic expansion of the GRACE determined monthly geopotential solutions. Based on a comparison of the three published approaches mentioned, we propose a refined approach for choosing parameters of the decorrelation filter. Our approach is basedon the error pattern of theSCs in themonthlyGRACE geopotential solutions.Wekeep aportionof the lower degreeorder SCs with the smallest errors unchanged, and high-pass filter the rest using a moving window technique, with winX. J. Duan (B) Department of Mathematics and Systems Science, National University of Defense Technology, 410073 Changsha, China e-mail: [email protected] J. Y. Guo · C. K. Shum Division of Geodetic Science, School of Earth Sciences, Ohio State University, 275 Mendenhall Lab, 125 S. Oval Mall, Columbus, OH, 43210, USA e-mail: [email protected] C. K. Shum e-mail: [email protected] W. van der Wal Department of Geomatics Engineering, University of Calgary, 2500 University Drive N.W., Calgary, AB, Canada T2N 1N4 W. van der Wal Delft Institute of Earth Observation and Space Systems, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands e-mail: [email protected] dow width decreasing as the error of the SCs increases. Both the unchanged portion of SCs and thewindowwidth conform with the error pattern, and are adjustable with a parameter. Compared to the three published approaches mentioned, our unchanged portion of SCs and windowwidth depend on both degree and order in a more complex way. We have used the trend of mass change to test various parameters toward a preferred choice for a global compromise between the removal of the correlated errors and the minimization of signal distortion.