EVALUATION OF THE NASA MICROWAVE RADIATIVE TRANSFER MODEL FOR SOIL MOISTURE ESTIMATION USING AQUARIUS BRIGHTNESS TEMPERATURE OBSERVATIONS OVER THE CONTINENTAL UNITED STATES
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The implications of near-surface soil moisture (~5 cm) variability in land surface processes and land-atmosphere interactions is important in regional and global scale climatology since it controls the partitioning of precipitation and radiation fluxes that play a crucial role in dictating weather and climate. Passive microwave (PMW) remote sensing is an increasingly popular approach to measure soil moisture because of its global coverage of the Earth. This study evaluates the performance of the NASA Goddard Earth Observing System, Version 5 (GEOS-5) radiative transfer model (RTM) using Aquarius brightness temperature (Tb) observations with the eventual goal of integrating the RTM into a data assimilation (DA) framework for the purpose of improved soil moisture estimation. Statistics were calculated from two plus years of observations across different climate regions of the United States. Seasonal variations of soil moisture were also investigated. Results suggest the RTM reasonably reproduces Aquarius Tbs, but that systematic biases exist, which must be mitigated prior to inclusion into the DA framework.