Simple model of a polarized bidirectional scattering cross section at 10.6 mum: application to SiO(2) sand.

A model is proposed to interpret the polarized scattering behavior for natural soils. The model is based on the vector radiative transfer equation and is developed to the second order. Higher orders are modeled with a simple expression. The particles are assumed to have a large dimension with respect to the wavelength, allowing for the light to be locally specularly reflected. Apart from the complex refractive index, the model has only one extra parameter directly related to the compactness of the medium. Predicted values are compared with carefully calibrated measurements of the polarized bidirectional scattering cross section obtained with coarse SiO(2) sand. The model parameters retrieved from the fit are quite realistic. Good agreement is obtained between model-computed and experimental data for the angular behavior and the amplitude, without further adjustment. Comparison between model-computed total unpolarized bidirectional scattering cross section, Hapke's nonpolarized model, and measurements also shows good agreement.

Scattering of a CO(2) laser beam at 10.6 microm by bare soils: experimental study of the polarized bidirectional scattering coefficient; model and comparison with directional emissivity measurements.

The bistatic polarized scattering by bare soil samples of a CO(2) laser beam at 10.6 microm has been experimentally studied. Large differences between HH and VV curves are usually observed, particularly in the forward plane. A simple phenomenological parameterization is proposed, based on the assumption of totally incoherent scattering by a rough medium. The normalized function F(theta)/F(0) accounting for slope distribution and shadowing is found from angular backscatter to be of the form cos(m)(theta), with m = 5.24 for all samples. This result is generalized to account for the bistatic case. The index of refraction of the medium is obtained from the ratio of HH and VV curves in the forward plane. Good agreement is found between experimental and calculated curves in the case of sand. The directional reflectivity and emissivity are calculated and compare well with experimental data. The calculated emissivity at nadir, for lambda = 10.6 microm, is within 0.5% of the value directly measured from emitted radiation. The backscattered peak has not yet been addressed in detail, therefore preventing relating in a semiquantitative manner the intensity of the backscattered light and the emissivity.

Emissivity signatures in the thermal IR band for remote sensing:calibration procedure and method of measurement.

Problems encountered in thermal infrared spectral emissivity signatures for remote sensing are addressed. Instrument calibration procedure is described, with particular attention to stray light effects. A method, which derives from the box method, for the absolute determination of spectral signatures of bare soils and mineral samples is proposed and illustrated with several materials (sand, loess, SiC powders). Excellent agreement is found between emissivity values obtained in this way, and values deduced from reflectivity measurements at 10.6 microm, as far as the angular behavior of the bidirectional reflectivity is taken into account. Comparison with spectral reflectivity measurements shows good spectral correlation.