Dependence of attenuation in a vegetation canopy on frequency and plant water content

Numerical results are presented supporting observations that the attenuation through a layer of vegetation is proportional to the water content of the vegetation. The calculations are based on a discrete scatter model for the vegetation in which the canopy is modelled as a sparse layer of randomly oriented particles (leaves, stalks, etc.) over a homogeneous ground plane (soil). An expression for attenuation is obtained from the solution for the mean wave and the Ulaby-El-Rayes formula is used to relate the dielectric constant of the vegetation to its water content. In the low frequency extreme, the attenuation varies almost linearly with water content and frequency. In contrast, in the high frequency extreme, the attenuation is relatively independent of both water content and frequency.