Active microwave soil moisture sensing under vegetation cover

Our understanding of the derivation of soil moisture content from observing the interaction between electromagnetic waves and bare soil on the one hand, and vegetated terrain on the other has developed at different rates. The retrieval of soil moisture from radar measurements for bare surfaces is possible by means of inversion algorithms based on theoretical surface scattering models (e.g. Su et al. , 1996). The interaction between electromagnetic waves and vegetated terrain involves both surface and volume scattering. The development of theoretical models for vegetated terrain is therefore extremely difficult. One such attempt was initiated by Lang (1981) and resulted in the development of a backscattering model following the wave approach (Lin et al., 1994). We use this model to investigate the effect of different crop parameters on the radar signal. This results in the definition of the conditions under which retrieval of soil moisture is still possible. These conditions are expressed both in terms of vegetation parameters (height, density, water content) and antenna configuration (frequency, polarization, incidence angle).