Surface mass redistribution from joint inversion of GPS site displacements, ocean bottom pressure (OBP) models, and GRACE global gravity models (JIGOG)

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In a collaborative effort between TUD-DEOS, AWI and GFZ, we aim at developing a strategy for the joint inversion of time series of GPS site displacements, ocean bottom pressure (OBP) data, and standard and non-standard, short-time GRACE gravity models, into mass transfers. Whereas geoid changes are linked to mass redistributions both directly and indirectly, GPS site displacements respond to mass flux indirectly through loading of the Earth.Previous research has indicated that, when combining monthly GRACE solutions with GPS, GPS could significantly contribute to spherical harmonics of global mass redistribution of up to degree 5, including degree 1. GPS sites are sparse for ocean areas and heterogeneous for continental areas. A joint inversion, accounting for error variance-covariance, site distribution and the individual sensitivities of GPS and GRACE in combination with OBP information, will provide more reliable results on all spatial scales than just combining degree-1 from GPS and higher degrees from GRACE. We plan to optimize the inverse methodology developed by Kusche and Schrama (2005a,b), to develop a complementary regional methodology, to incorporate bottom pressure from numerical ocean models, investigate consistency aspects, and validate results. Because relevant mass variations take place at sub-monthly scales GFZ will additionally contribute with nonstandard short-time (7-10 days) GRACE and GRACE/SLR combined gravity field solutions. A major application will be the determination of variations of the total ocean mass. In conjunction with measured oceanic volume variations we will be able to determine thermal expansion and thus global ocean warming with a much higher accuracy than conventional estimates can provide.