Uncertainties of the Gravity Recovery and Climate Experiment time-variable gravity-field solutions based on three-cornered hat method

Vagner G Ferreira,Bernhard Heck,Henry D C Montecino,Caleb I Yakubu

doi:10.1117/1.jrs.10.015015

Abstract

Currently, various satellite processing centers produce extensive data, with different solutions of the same field being available. For instance, the Gravity Recovery and Climate Experiment (GRACE) has been monitoring terrestrial water storage (TWS) since April 2002, while the Center for Space Research (CSR), the Jet Propulsion Laboratory (JPL), the GeoForschungsZentrum (GFZ), and the Groupe de Recherche de Geodesie Spatiale (GRGS) provide individual monthly solutions in the form of Stokes coefficients. The inverted TWS maps (or the regionally averaged values) from these coefficients are being used in many applications; however, as no ground truth data exist, the uncertainties are unknown. Consequently, the purpose of this work is to assess the quality of each processing center by estimating their uncertainties using a generalized formulation of the three-cornered hat (TCH) method. Overall, the TCH results for the study period of August 2002 to June 2014 indicate that at a global scale, the CSR, GFZ, GRGS, and JPL presented uncertainties of 9.4, 13.7, 14.8, and 13.2 mm, respectively. At a basin scale, the overall good performance of the CSR was observed at 91 river basins. The TCH-based results were confirmed by a comparison with an ensemble solution from the four GRACE processing centers.

Highlights

The twin satellite mission Gravity Recovery and Climate Experiment (GRACE) was launched on March 17, 2002
The intercomparison of the Stokes coefficients (Sec. 3.1) from the four GRACE processing centers (CSR, GFZ, Groupe de Recherche de Géodésie Spatiale (GRGS), and Jet Propulsion Laboratory (JPL)) showed an overall good agreement in terms of correlation coefficient between each pair of solutions up to degree 50 and order 40, with the GRGS being less correlated with the Science Data System (SDS) processing centers (Fig. 1)
The overall comparisons of three-cornered hat (TCH)-based uncertainties pertaining to the period from August 2002 to June 2014 showed that the four solutions (CSR, GFZ, GRGS, and JPL) lie within 5 to 15 mm in terms of global grids, as well as basin-averaged values of terrestrial water storage anomalies (TWSA)

Summary

Introduction

The twin satellite mission Gravity Recovery and Climate Experiment (GRACE) was launched on March 17, 2002. Additional studies from GRACE are related to monitoring the groundwater withdrawal in India[7] and China,[8] contributions of glaciers and ice caps to sea-level rise,[9] and evaluation of naturally and anthropogenically induced variations in water availability in Africa.[10] In this work, the aim is to assess the quality of the GRACE-derived TWSA fields inverted from the level-2 products that were calculated by four different centers Three of these centers are identified in the mission proposal as the GRACE Science Data System (SDS), while the other is the solution provided by the Groupe de Recherche de Géodésie Spatiale (GRGS) at the Centre National d’Études Spatiales (CNES).[11,12] The three SDS centers are the University of Texas Center for Space Research (CSR),[13] the NASA Jet Propulsion Laboratory (JPL),[14] and the Deutsches GeoForschungsZentrum (GFZ).[15]

Objectives

Methods

Results

Conclusion