Global soil moisture retrieval from a synthetic L‐band brightness temperature data set

A technique to retrieve surface soil moisture was assessed at the global scale using a synthetic data set of L‐band (1.4 GHz) brightness temperatures T B for 2 years, 1987 and 1988. The global T B database consists of half‐degree continental pixels and accounts for within‐pixel heterogeneity, on the basis of 1 km resolution land cover maps. The retrievals were performed using a three‐parameter inversion method applied to the L‐band Microwave Emission of Biosphere model (L‐MEB). Three land surface variables were retrieved simultaneously from the multiangular and dual‐polarization T B data: surface soil moisture wg , vegetation optical depth τ, and surface temperature T S . The retrievals were obtained in two T S configurations: T S was either unknown or known with an uncertainty of 2 K. Applying these two assumptions, global maps of the estimated accuracy of the wg retrievals were produced, and the capability of the T B to monitor wg was evaluated. A sensitivity study was carried out in order to analyze the effect of the main parameters that may affect the retrieval accuracy: the fraction cover of open water and forests, frozen soil conditions, and the radiometric noise on T B . These results contribute to the better definition of the potential of the observations from future spaceborne missions such as the Soil Moisture and Ocean Salinity (SMOS) project.