Applications of transport theory in optical remote sensing of land surfaces

A particle/radiative transport theory widely used in nuclear engineering was applied to investigate photon transport in layers of land surfaces which consist of vegetation and soil for application to optical remote sensing. A numerical simulation code has been developed for three dimensional vegetation canopies to compute reflected radiation by the canopy-soil systems. The code solves a discretized form of the linear Boltzmann transport equation using an Adaptive Weighted Diamond-Differencing and source iteration method. Sample problems demonstrate variations of reflectance spectra of vegetation canopies as a function of soil brightness and leaf area index, and also indicate a pattern of spectral variations induced by the soil brightness changes.;Special attention has been paid to the variation patterns of canopy reflectances, known as vegetation isolines. Mathematical expressions of vegetation isolines, called vegetation isoline equations, are derived in terms of canopy optical properties and two parameters that characterize soil optical properties called soil line parameters. Behavior of vegetation isolines is analyzed using the derived equations as a function of leaf area index and fractional area covered by green-vegetation. The analyses show certain trends of the behavior of vegetation isolines. The vegetation isoline equations are then applied to investigate the performance of two-band vegetation indices and to estimate the effects of the soil line parameters. It is concluded that the vegetation isoline equations are useful for investigating patterns of canopy reflectance variations and the effects of these patterns on vegetation indices.