SCATTERING OF ELECTROMAGNETIC-WAVES BY AT MOSPHERIC HYDROMETEORS AND ITS INFLUENCE ON MILLIMETER-WAVE RADIOMETRIC IMAGING-SYSTEMS

In this paper, the effects of absorption and scattering phenomenon in the atmosphere are evaluated, particularly the variations of radiometr ic contrasts received by a passive imager in various meteorological co nditions. For that purpose, the analysis has been based on radiative t ransfer theory whose vectorial equation has been solved by the invaria nt imbedding method. Atmospheric absorption only has been studied firs t, then scattering effects have been taken into account. The influence on brightness temperatures has been calculated for an airborne and a spaceborne radiometer flying over uniform surfaces, either specular or lambertian, with various disturbing medium along the path. Numerical simulations have been focused on atmospheric window frequencies (35 GH z, 94 GHz and 140 GHz) is order to assess the imaging capabilities of radiometric instruments. Finally a specific method using the invariant imbedding schema and Fourier expansion along the azimuthal dependance has been developed, in order that the case of an imaging radiometer f lying over non uniform surfaces composed of various parcels types coul d be simulated.