Calibration of L-MEB for soil moisture retrieval over forests

Soil moisture retrieval from passive microwave remote sensing over densely vegetated areas, such as forests, has become a pertinent subject in the light of ESA's upcoming soil moisture and ocean salinity (SMOS) mission. Even though it is probably not possible to retrieve soil moisture over forested areas with the accuracy required by SMOS, understanding forest radiative transfer properties at L-band (1.1-1.7 GHz) is still important for soil moisture retrieval in partly forested pixels. The forward model to be used by the SMOS level 2 soil moisture algorithm is 'L-MEB', from 'L-band microwave emission of the biosphere'. This paper shows the results of L-MEB model calibration over two forest types in terms of various soil and vegetation parameters, together with an assessment of model performance in both forward and inverse mode. While, as expected, the retrieval of soil moisture over forest areas does not give results up to the standard required by SMOS, the forward model does result in an acceptable root mean square error in terms of 'reconstructed' brightness temperatures.