A physical model is presented describing the backscatter from coniferous bo
real forests in the lower VHF-band in terms of Stem volume. By using measur
ements of mean amplitude in high-resolution SAR images (rather than intensi
ty), a linear dependence on stem volume can be obtained. The model fits wel
l with the measurements made using the coherent all radio band sensing (CAR
ABAS) SAR in the southern boreal forest, indicating the possibility of retr
ieving stem volume, and hence biomass, with an accuracy similar to that rea
ched by standard ground-based measurements. No saturation of the scattering
is seen up to biomasses of 550 m(3)/ha.