Abstract:
A first-order (tau-omega) microwave radiative transfer model (RTM) is coupled to the Goddard Earth Observing System, Version-5 (GEOS-5) Catchment Land Surface Model in preparation for the assimilation of global brightness temperatures (Tb) from the L-band (1.4 GHz) Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions. Simulations using literature values for the RTM parameters result in Tb biases of 10-50 K against SMOS observations. Multi-angular SMOS observations from the year 2010 are used to calibrate parameters related to the microwave roughness h, vegetation opacity tau and/or scattering albedo omega separately for each observed 36 km land grid cell. A particle swarm optimization is used to minimize differences in the long-term (climatological) mean and temporal standard deviations between SMOS observations and simulations, without attempting to reduce the shorter-term (seasonal to daily) errors. After calibration, global Tb simulations for the validation year 2011 are largely unbiased for multiple incidence angles and both H- and V-polarization (e.g. global average absolute difference of 3.1 K for Tb_H(42.5 deg)). This calibrated system is then used to assimilate multi-angular SMOS Tb observations to improve soil moisture and temperature estimates. We will present the results of SMOS Tb assimilation and discuss the problems and advantages compared to the assimilation of SMOS soil moisture retrievals.