A SIMPLE ALGORITHM TO RETRIEVE SOIL-MOISTURE AND VEGETATION BIOMASS USING PASSIVE MICROWAVE MEASUREMENTS OVER CROP FIELDS

A simple algorithm to retrieve soil moisture and vegetation water content from passive microwave measurements is analyzed in this study. The approach is based on a zeroth-order solution of the radiative transfer equations in a vegetation layer. In this study, the single scattering albedo accounts for scattering effects and two parameters account for the dependence of the optical thickness on polarization, incidence angle, and frequency. The algorithm requires only ancillary information about crop type and surface temperature. Retrievals of the surface parameters from two radiometric data sets acquired over a soybean and a wheat crop have been attempted. The model parameters have been fitted in order to achieve best match between measured and retrieved surface data. The results of the inversion are analyzed for different configurations of the radiometric observations: one or several look angles, L-band, C-band or (L-band and C-band). Sensitivity of the retrievals to the best fit values of the model parameters has also been investigated The best configurations, requiring simultaneous measurements at L- and C-band, produce retrievals of soil moisture and biomass with a 15% estimated precision (about 0.06 m(3)/m(3) for soil moisture and 0.3 kg/m(2) for biomass) and exhibit a limited sensitivity to the best fit parameters.