THEORETICAL SCATTER AND EMISSION MODELS FOR MICROWAVE REMOTE SENSING

Theoretical backscatter and emission angular behaviors of the Kirchhoff rough surface scatter model are studied. It is shown that the Kirchhoff surface under the stationary phase approximation can conserve energy to within 0.5% if the energy in the range of (pi)/2 < (scattered polar angle) < (pi) is included. It is demonstrated that the Kirchhoff surface scatter model under the scalar approximation with the composite correlation function can be of practical value in interpreting the passive and active data from sea and land.;Using the doubling method and the Kirchhoff surface scatter model, an emission model for the Rayleigh layer with irregular interfaces is developed. It is shown that an increase in top-boundary roughness slows down the angular variation relative to the plane case, and an increase in bottom-boundary roughness causes an increase in nadir-brightness temperature. Comparisons between the emission model and emission measurements from the snow layer around X-band indicate its potential use in passive data interpretation.;Using the doubling method, a scatter model for the Rayleigh layer with the top Kirchhoff rough surface interface is developed. It is shown that in near-nadir backscattering surface scattering is generally dominant over the interaction between the surface and volume scattering, while the reverse is true for the incident angle beyond 40(DEGREES). An increase in surface roughness causes an increase near-nadir diffuse scattering particularly for the cross-polarization component. Comparisons with angular measurements from snow and sea ice at frequencies lower than 17 GHz indicate that useful estimate can be obtained from the scatter model in conjuction with the Polder and Van Santen permittivity model.