Surface mass redistribution inversion from global GPS deformation and Gravity Recovery and Climate Experiment (GRACE) gravity data

Abstract

[1] Monitoring hydrological redistributions through their integrated gravitational effect is the primary aim of the Gravity Recovery and Climate Experiment (GRACE) mission. Time-variable gravity data from GRACE can be uniquely inverted to hydrology, since mass transfers located at or near the Earth's surface are much larger on shorter timescales than those taking place within the deeper Earth and because one can remove the contribution of atmospheric masses from air pressure data. Yet it has been proposed that at larger scales this may be achieved independently by measuring and inverting the elastic loading associated with redistributing masses, e.g., with the global network of the International GPS Service (IGS). This is particularly interesting as long as GRACE monthly gravity solutions do not (yet) match the targeted baseline accuracies at the lower spherical harmonic degrees. In this contribution (1) we describe and investigate an inversion technique which can deal jointly with GPS data and monthly GRACE solutions.(2) Previous studies with GPS data have used least squares estimators and impose solution constraints through low-degree spherical harmonic series truncation. Here we introduce a physically motivated regularization method that guarantees a stable inversion up to higher degrees, while seeking to avoid spatial aliasing. (3) We apply this technique to GPS data provided by the IGS service covering recent years. We can show that after removing the contribution ascribed to atmospheric pressure loading, estimated annual variations of continental-scale mass redistribution exhibit pattern similar to those observed with GRACE and predicted by a global hydrology model, although systematic differences appear to be present. (4) We compute what the relative contribution of GRACE and GPS would be in a joint inversion: Using current error estimates, GPS could contribute with up to 60% to degree 2 till 4 spherical harmonic coefficients and up to 30% for higherdegree coefficients.Citation: Kusche, J., and E. J. O. Schrama (2005), Surface mass redistribution inversion from global GPS deformation and Gravity Recovery and Climate Experiment (GRACE) gravity data,

Detecting seasonal and long-term vertical displacement in the North China Plain using GRACE and GPS

“…The Level-2 gravity products consist of sets of complete spherical harmonic (Stokes) coefficients out to some maximum degree and order (typically l max = 120) averaged over monthly intervals. When considering large-scale mass redistribution in the Earth system on a timescale ranging from weekly to interdecadal, it is reasonable to assume that all relevant processes occur in a thin layer at the Earth's surface (Kusche and Schrama, 2005). In this analysis, we assume that the gravitational and geometrical response of the Earth can be described by the theory of Farrell (1972), where the loads' Love numbers only depend on the spherical harmonic degree.…”

“…In this analysis, we assume that the gravitational and geometrical response of the Earth can be described by the theory of Farrell (1972), where the loads' Love numbers only depend on the spherical harmonic degree. Thus, the elastic displacements due to the surface mass change can easily be represented in terms of spherical harmonic coefficients for the gravity field and load Love numbers, k l , l l , and h l (Wahr et al, 1998;Kusche and Schrama, 2005). Level-2 products are generated at several project-related processing centres, such as the Center for Space Research (CSR) at the University of Texas, GeoForschungsZentrum in Potsdam, Germany, and the Jet Propulsion Laboratory in California.…”

“…The mathematical relationships (Kusche and Schrama, 2005;van Dam et al, 2007) between the radial surface displacement (Up or Height) and the Stokes coefficients of mass is…”

“…The global-scale mass variations closely related to changes in terrestrial water storage (TWS) are observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission, while the surface elastic displacement can be estimated if the load and rheological properties of the Earth were known (Farrell, 1972). The majority of previous loading studies solved the three components of crustal motion by the adopting joint analysis of GRACE time-variable gravity field coefficients and GPS data (Kusche and Schrama, 2005;van Dam et al, 2007;Fu et al, 2013). In principle the loading effects caused by the majority of mass redistributions near the Earth's surface are from water, atmospheric, and ocean transports on daily to interannual timescales (Kusche and Schrama, 2005).…”

“…The majority of previous loading studies solved the three components of crustal motion by the adopting joint analysis of GRACE time-variable gravity field coefficients and GPS data (Kusche and Schrama, 2005;van Dam et al, 2007;Fu et al, 2013). In principle the loading effects caused by the majority of mass redistributions near the Earth's surface are from water, atmospheric, and ocean transports on daily to interannual timescales (Kusche and Schrama, 2005). The contribution to the surface displacement made by the variations of the atmospheric and ocean can be reasonably modelled by using global atmospheric surface pressure data and space geodetic data respectively.…”