RADIATION-FIELD IN A MULTILAYERED GEOPHYSICAL MEDIUM - ICE-WATER-AEROSOL-VEGETATION-SOIL (IWAVES) MODEL

Multiangular data which will be available with the upcoming satellite platforms (EOS, ENVISAT, ADEOS) offer a great potential for monitoring land surfaces on the global scale to the extent that physically based models describing the transfer of radiation can be developed. The pre sent study constitutes an additional step toward modeling this radiati ve transfer with in particular the physical processes involved at the boundary between land vegetated surfaces and the atmospheric layer abo ve. Our primary objectives are to address issues related to the pertur bation by an atmospheric layer of the solar radiance field incident on the top of the vegetation canopy and the interpretation of the radian ce field emerging from the atmospheric layer when isotropic scattering from the surface is a priori assumed. Indeed, the application of an i nappropriate model for the interpretation of remotely sensed data can produce inaccurate retrievals of both the surface and atmosphere chara cteristics. In the present study the radiation transport problem in th is coupled system is solved analytically for uncollided and first coll ided radiation and uses a discrete ordinates method for multiple-scatt ered radiation. A sensitivity analysis of the multilayered ice-water-a erosol-vegetation-soil model is conducted in order to quantify the eff ects of atmospheric and surface perturbations within the whole system. The results are essentially reported in terms of bidirectional reflec tance factors at visible and near-infrared wavelengths, which allows t he use of very different radiative properties of the vegetation layer. The consequences of assumptions made on one or the other of these med ia are investigated;through an inversion experiment.