Abstract
Surface mass variations inferred from the Global Positioning System (GPS), and observed by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) complement each other in terms of spatial and temporal coverage. This paper presents an analysis of regional surface mass variations inverted from GPS vertical displacements under different density distributions of GPS stations, and compares the GPS-derived mass variations with GRACE/GFO inversion results in spatial and temporal domains. To this end, GPS vertical displacement data from a total of 85 permanent GPS stations of the Crustal Movement Observation Network of China (CMONOC), the latest GRACE/GFO RL06 spherical harmonic (SH) solutions and GRACE RL06 mascon solutions are used to investigate surface mass variations in four regions or basins, including the Yunnan Province (YNP), Min River Basin (MRB), Jialing River Basin (JLRB), and Wu River Basin (WRB) in Southwest China. Our results showed that the spatial distributions and seasonal characteristics of GPS-derived mass change time series agree well with those from GRACE/GFO observations, especially in regions with relatively dense distributions of GPS stations (e.g., in the YNP and MRB), but there are still obvious discrepancies between the GPS and GRACE/GFO results. Scale factor methods (both basin-scaled and pixel-scaled) were employed to reduce the amplitude discrepancies between GPS and GRACE/GFO results. The results also showed that the one-year gap between the GRACE and GFO missions can be bridged by scaled GPS-derived mass change time series in the four studied regions, especially in the YNP and MRB regions (with relatively dense distributions of GPS stations).
Highlights
Surface mass variations mainly include terrestrial water storage (TWS) change, melting of polar ice sheets and mountain glaciers, atmospheric pressure change, ocean mass change, and mass changes associated with solid Earth geophysical phenomena
This study aims to further analyze the performance of regional mass variations inverted by Global Positioning System (GPS) vertical displacement data under different density distributions of GPS stations, and examine the consistency of mass changes inferred from GPS vertical displacements, Gravity Recovery and Climate Experiment (GRACE), and the latest GRACE Follow-On (GFO) observations in the spatial and temporal domains, and demonstrate the feasibility of GPS-derived mass variations to fill in the gap between GRACE and GFO missions
In order to analyze the influence of a single GPS station (i.e., GZGY and KMIN) on the inversion of mass variations over Southwest China, a closed-loop simulation was conducted based on the simulated GPS vertical displacements
Summary
Surface mass variations mainly include terrestrial water storage (TWS) change, melting of polar ice sheets and mountain glaciers, atmospheric pressure change, ocean mass change, and mass changes associated with solid Earth geophysical phenomena. Compared with GRACE/GFO, GPS has its own advantages: (1) The GPS network is widely distributed globally, and the observation data can be obtained in near real time at millimeter-level accuracy with higher spatio–temporal resolution; (2) the GPS surface deformation, especially the vertical displacement, is more sensitive to changes of local (~10 km) and regional mass loading, and the spatial resolution of mass changes inverted from a dense GPS network can reach ~50 km [16,17]; (3) due to the continuous and real-time monitoring of the surface deformation by GPS networks, GPS-derived mass variations can help bridge the gap between the GRACE and GFO missions [15,16]
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