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. I. INTRODUCT~ON ANY parameters influence the microwave emission M of land surfaces, the most important being soil and vegetation water content, vegetation structure and biomass, surface temperature, and soil roughness. Theoretical models can be most useful to understand the effect of these different parameters on the microwave remotely sensed data. The microwave thermal emission of vegetation-covered soil can be divided into three main components: the upward canopy emission, downward and soil reflected canopy emission, upward soil emission (11-. The vegetation canopy attenuates and scatters these radiations. Therefore, theoretical models which have been developed to simulate the thermal emission of vegetation canopies have taken into account volume absorption and scattering by the discrete scatterers of the vegetation: leaves, branches and stalks. Volume scattering can be modeled through two types of approaches: the wave approach and the radiative transfer approach. Even though the radiative transfer approach does not take into account diffraction effects in the computation Manuscript received April 17, 1992; revised August 24, 1992; rerevised J.-P. Wigneron is with INRA, Bioclimatologie, BP91, 84143 Montfavet J.-C. Calvet is with Meteo-FranceiCNRM, Toulouse, France. Y. Kerr is with LERTS, CNES-CNRS, 31055 Toulouse cedex, France. A. Chanzy is with INRA, Science du sol, BP91, 84143 Montfavet cedex, A. Lopes is with CESR, UMR-CNRS BP4346, 31029 Toulouse cedex, IEEE Log Number 9207390. November 25, 1992.