Recovery of Terrestrial Water Storage Change from Low-low Satellite-to-satellite Tracking

Book excerpt: Abstract: Gravity Recovery and Climate Experiment (GRACE) spaceborne gravimetry provides a unique opportunity for quantifying geophysical signals including terrestrial water storage change for a wide variety of climate change and geophysical studies. The contemporary methodology to process GRACE data for temporal gravity field solutions is based on monthly estimates of the mean geopotential field with a spatial resolution longer than 600 km (the Level-2 or L2 data products), after appropriate Gaussian smoothing to remove high-frequency and geographically-correlated errors. Alternative methods include the direct processing of the GRACE low-low satellite-to-satellite tracking data over a region of interest, leading to improved or finer spatial and temporal resolutions of the resulting local gravity signals. The GRACE Level 1B data have been analyzed and processed to recover continental water storage in a regional solution, by first estimating in situ Line-Of-Sight (LOS) gravity differences simultaneously with the relative position and velocity vectors of the twin GRACE satellites. This new approach has been validated using a simulation study over the Amazon basin (with three different regularization methods to stabilize the downward continuation solutions), and it is demonstrated that the method achieves an improved spatial resolution as compared to some of the other GRACE processing techniques, including global spherical harmonic solutions, and regional solutions using in situ geopotential differences.