Comparison of GRACE and GNSS Seasonal Load Displacements Considering Regional Averages and Discrete Points

Abstract

AbstractThe global navigation satellite system (GNSS) and gravity recovery and climate experiment (GRACE) are two independent geodetic technologies that can detect geometric and gravity deformations, respectively. The signals observed by the two technologies mainly include the internal tectonic movement and surface mass loading effects. The former generally exhibits a long‐term stable linear trend, whereas the latter exhibits strong seasonality. Many studies have compared seasonal deformations between GRACE and GNSS or combined them to study the water cycle or tectonic signals. However, whether GRACE and GNSS are comparable and what the magnitude of their differences still remain unclear. In this study, we present simulations and a case study of the Amazon basin to address this ambiguity. The loading deformations were simulated in response to load masses with varying resolutions and distributions. We found that the discrepancy is about 30% in the spatial average between the accurate loading displacement and the truncated‐result at degree‐60 after applying a G300 or DDK4 filter due to a single load mass. The simulated horizontal deformation may have larger discrepancies at a single point in response to the chessboard mass distributions. The case study in the Amazon basin basically verifies our simulation results, which indicate that there is an ∼40%–50% discrepancy between the GNSS‐observed and GRACE‐modeled displacements spatial average, and it may reach several times that at a single point. We demonstrate that the difference between the GRACE and GNSS is significant for both regional average and single‐point analyses.