Observing Earth's mass transport processes with the Swarm satellites

The Swarm satellites provide highly accurate GPS data, from which we are able to derive monthly gravity fields, which quantify the Earth mass transport processes at the spatial scales longer than roughly 1500km (SH degree 13). To improve the signal content of these models, we combine individual solutions produced from four different gravity field inversion strategies, namely the Celestial Mechanics Approach (Beutler et al. 2010), the Decorrelated Acceleration Approach (Bezdek et al. 2014), the Short-Arcs Approach (Mayer-Gurr 2006) and the Improved Energy Balance Approach (Shang et al. 2015). We combine the individual solutions at the level of Normal Equations in order to best exploit the sensitivity of the different approaches and produce the highest quality of gravity field solutions possible. We illustrate the major geophysical signals that Swarm is able to observe at the surface of the Earth, in the form of trends and periodic variations. We also compare these estimates with the corresponding GRACE-based estimates, considering the periods when the two data sets overlap, and assess the impact of the Swarm-based Earth mass transport studies during the absence of GRACE and GRACE-FO operations.