Modelling radar backscatter from crops during the growth cycle

A radiative transfer model that represents vegetation as a collection of randomly oriented disks and almost vertical cylinders on a rough surface was implemented and used for interpreting radar backscattering from wheat and sunflowers fields. The model was used to simulate the growth cycle of wheat and sunflowers by using as inputs bio-physical data collected on the agricultural test site of the RESEDA project. A comparison with experimental data from the ERS/SAR and the French ERASME scatterometer collected at two frequencies, two polarisations and two incidence angles was carried out. The comparison shows that model simulations reproduce temporal trends and average values of experimental results fairly well, but in some cases some significant discrepancy exists between the absolute values. Moreover, the backscattering coefficient was found to be sensitive to the geometrical characteristics of wheat and sunflowers. Indeed, as the leaf area index increases, backscattering increases in the case of sunflowers, and decreases in the case of wheat.