The seasonal cycle in global mass transport: Combining geodetic observations to get the picture

Xiaoping Wu⁽¹⁾, Danan Dong⁽¹⁾, Richard Gross⁽¹⁾, Mike Heflin⁽¹⁾, Angie Moore⁽²⁾, Fabiano Oyafuso⁽³⁾ and Susan Owen⁽¹⁾

⁽¹⁾ Jet Propulsion Laboratory, CALTECH, 4800 Oak Grove Drive, MS 238-600, Pasadena, CA 91109, United States
⁽²⁾ Jet Propulsion Laboratory, CALTECH, 4800 Oak Grove Drive, MS 238-540, Pasadena, CA 91109, United States
⁽³⁾ Jet Propulsion Laboratory, CALTECH, 4800 Oak Grove Drive, MS 169-315, Pasadena, CA 91109, United States

Abstract

Climate driven surface mass variations including non-steric sea-level change, Greenland and Antarctica ice mass fluctuations, and land hydrological cycles have significant impact on the world community. These variations also result in several distinct geodetic signatures of time-variable gravity, topography, load induced surface deformation, and geocenter motion to place the geodetic discipline at the forefront of global mass transport research. Despite significant recent advancements in geodetic technologies, currently, no single technique or system can provide a complete spatiotemporal spectrum of the change process. On the other hand, multi-satellite data using different techniques contain complementary as well as overlapping information. Comparing and combining them not only facilitate data calibration and validation but also provide the best chance of resolving ambiguities and increasing accuracy and resolution.

We study seasonal and interannual surface mass variations using GRACE gravity, GPS-measured load-induced surface deformation, and a TOPEX/Poseidon/Jason-1 altimetry-assimilated relative ocean bottom pressure model. Complete spherical harmonic spectra of incremental surface mass up to degree and order 50 are successfully inverted monthly from various data combinations with reduced aid of a priori information. Comparisons of the results have enabled us to identify and remove systematic errors in certain data types. Combination of GRACE/GPS/OBP effectively fills data coverage gaps and dramatically improves resolution and accuracy of the estimates, including much more robust degree-1 surface mass coefficients and all 3 equivalent geocenter motion components with < 0.4 mm precision in annual amplitudes. When used with optimal point and regional averaging techniques employing full covariance matrices, the combination results also achieve superior global patterns and regional averages. Further improvement can be expected from incorporating direct SLR geocenter motion measurements and a long record of SLR/VLBI deformation measurements.