A dielectric model of the vegetation effects on the microwave emission from soils

A layer of vegetation over the soil surface absorbs some of the radiation emitted from the soil and emits at its own temperature. This results in a reduction of the information in the microwave radiation about the soil surface. To study this problem further the authors use the model of F.T. Ulaby and M.A. El-Rayes (1987) for the dielectric constant of vegetation to estimate the absorption loss and optical depth, τ, of plant canopies for frequencies between 1 and 40 GHz. The authors treated τ as the product of a vegetation parameter b and vegetation water content, VW. They compared both the linear and square root (refractive) mixing models with the observed data in terms of the b parameter. These data were obtained from published reports on the values of τ and VW for crops ranging from prairie grass to corn and soybeans. The data fit the curve for the refractive model quite well. For the refractive model the value of b was independent of VW, while for the linear model there was some dependence on VW. For both models b is roughly proportional to the frequency