Satellite radar altimeter measurements have shown spn tial and tempora
l variations in the backscattered signal from desert surfaces. In orde
r to understand these variations we have carried out extensive in situ
measurements for the validation of a compilation of existing backscat
ter models. The model predictions are in excellent agreement with grou
nd- and satellite-based measurements of the radar backscatter coeffici
ent, and show that the altimeter backscatter measurements are strongly
affected by variations in soil moisture following rainfall and by the
presence of dew On the surface. Regional, but time-invariant, differe
nces in backscatter are attributed to variations in surface topography
.