MICROWAVE EMISSION OF VEGETATION - SENSITIVITY TO LEAF CHARACTERISTICS

This paper presents an analysis of leaf-characteristics effects on the microwave emission of land surfaces. In order to simulate these effects, a radiative transfer model is presented. The medium consists of a vegetated layer containing randomly oriented leaves, modeled as elliptic-shaped scatterers, over the ground surface. Radiative transfer equations are solved with a discrete ordinate-eigenanalysis method. The calculation of the phase matrix of the elliptic scatterers is based on the generalized Rayleigh-Gans approximation which increases the frequency range of the modeling. The sensitivity of brightness temperature and polarization ratio to leaf characteristics, volume fraction, gravimetric moisture, size, shape, and inclination distribution is investigated at L-, C-, and X-bands. The behavior of the simulated emission of a soybean canopy versus frequency and incidence angle is studied for different soil moisture levels. These computations are consistent with measurements performed with a multifrequency radiometer. Up to 10 GHz the microwave emission appears to contain significant information on underlying soil moisture.