Vertical backscatter profile of forests predicted by a macroecological plant model

Abstract

This study describes a new application of a macroecological model to describe the vertical profile of radar backscatter through forest canopy. Given layers of equally sized cylindrical scatterers, the model predicts that one layer within the forest canopy dominates the backscatter profile. This prediction is based on first-order theoretical approximations, in addition to results from a radiative transfer model parameterized by the macroecological model. This model is used to pre-empt specific backscatter trends with results predicting that Rayleigh and Optical backscatter follow negative and positive exponential trends respectively when plotted with respect to backscattering coefficient and branching level through the canopy. A maximum value is predicted by the model associated with the branching level located at the transitional zone between Rayleigh and Optical scattering. This finding follows directly from the size density distribution within a forest combined with dramatic reductions in cross-sectional trends exhibited through the transition. It is a result unrelated to resonant scattering or the effects of penetration depth. The feasibility of describing radar interactions using geometric optics is explored when limits are imposed on the physical optics scattering solution. The findings offer a significantly new way of understanding the distribution of scattering from differently sized elements in a canopy, and challenge the widely held assumption that backscatter–biomass relationships saturate due to increased opacity of the canopy.