GRACE-derived surface water mass anomalies by energy integral approach: application to continental hydrology

We propose an unconstrained approach to recover regional time-variations of surface mass anomalies using Level-1 Gravity Recovery and Climate Experiment (GRACE) orbit observations, for reaching spatial resolutions of a few hundreds of kilometers. Potential differences between the twin GRACE vehicles are determined along short satellite tracks using the energy integral method (i.e., integration of orbit parameters vs. time) in a quasi-inertial terrestrial reference frame. Potential differences residuals corresponding mainly to changes in continental hydrology are then obtained after removing the gravitational effects of the known geophysical phenomena that are mainly the static part of the Earth’s gravity field and time-varying contributions to gravity (Sun, Moon, planets, atmosphere, ocean, tides, variations of Earth’s rotation axis) through ad hoc models. Regional surface mass anomalies are restored from potential difference anomalies of 10 to 30-day orbits onto 1◦ continental grids by regularization techniques based on singular value decomposition. Error budget analysis has been made by considering the important effects of spectrum truncation, the time length of observation (or spatial coverage of the data to invert) and for different levels of noise.