Statistical properties of radar signal scattered from forest components

The statistics of radar signals returned from forest components are investigated through a simulation study based on a first-order scattering theory. A forest canopy is modeled as a volume of needle-shaped or disc-shaped leaves and finite-length, cylindrical branches. It is expected that at radar frequencies above X band, scattering away from normal incidence is largely dominated by leaves while a mixture of leaves and branches is important to model a forest canopy at C band. Thus, simulations of both a volume of leaves and a mixture of leaves and branches are of interest. It is assumed that all leaves and branches are randomly oriented. It is found that for leaves that are small compared with the incident wavelength, signal amplitude is Rayleigh distributed. Generally, this means the length of a needle-shaped leaf can be as long as kL (wavenumber × length) equal to 2, because its volume is small. However, for a disc-shaped leaf ka (wavenumber × radius) should be no more than 0.5 because its volume is much larger. When the leaves are comparable in size to the incident wavelength, signal amplitude assumes a Gamma distribution. The signal amplitude distribution for a mixture of branches and leaves is also Gamma distributed because here the scatterer volume is also large in dimension relative to the incident wavelength