COMPARISON BETWEEN THE MICROWAVE EMISSIVITY AND BACKSCATTER COEFFICIENT OF CROPS

After recalling the definitions of some basic quantities measured by active and passive microwave sensors, the interrelations between emission and scattering are discussed. The particular case of a half-space of isotropic scatterers, for which a simple relation between emissivity and backscatter coefficient holds, is considered as a reference to examine the response of active and passive systems to real agricultural fields. Both theoretical and experimental results at X-band are reported. Theoretical results are obtained by modeling the vegetation as an ensemble of small disks overlaying the ground; the emissivity and backscatter coefficient for different stages of growth are computed and compared. Experimental data collected by ground-based and airborne active and passive systems confirm the general trends predicted by the model, although with some quantitative discrepancies.