Continental Water Storage Changes from GRACE Line-of-Sight Range Acceleration Measurements

Spaceborne gravimetry such as GRACE provides a unique opportunity to observe basin-scale surface and subsurface global water storage changes with unprecedented accuracy and temporal and spatial coverages. The contemporary methodology to process GRACE data for hydrologic studies is in terms of monthly spherical harmonic geopotential solutions with a spatial resolution longer than 600–800,km (half-wavelength), after proper smoothing. Alternative methods include the direct processing of satellite-to-satellite K-Band Range (KBR) rate data and to estimate the localized gravity field, and the so-called mascon methods. In this study we estimate monthly continental water thickness changes over the Amazon Basin for one year (2003) by calculating in-situ Line-Of-Sight (LOS) gravity differences inferred by the GRACE KBR range acceleration. A regional inversion method based on Bayesian statistics is used to estimate water thickness changes from the LOS gravity difference observations. Power Spectral Density (PSD) comparison with the spherical harmonic monthly solutions at both 600 and 800 km resolutions indicates that the LOS gravity solution has more power at degree 13 or higher, implying that it is a viable technique for potentially enhancing spatial resolutions of GRACE solutions at these frequencies.