APPLICATION OF THE METHOD OF ANGULAR GREENS-FUNCTIONS AND THE INVARIANCE-PRINCIPLE IN THE LINEAR-THEORY OF REFLECTION OF OPTICAL RADIATION

This paper considers the problem of reflection of stationary scalar op tical radiation from plane media with disordered scattering centers. W e propose a new approach to the calculation of spectra of backscattere d radiation combining the Ambartsumyan invariance principle and the me thod of separated fluxes. The total reflection function (RF) is repres ented as a series over partial RFs. Each of the partial RFs describes the component of reflected radiation consisting of photons that emerge from a medium changing the sign of their velocity projection in the d irection of the interior normal to the surface of the medium a definit e number of times. Using the nonlinear Ambartsumyan equation, we deriv ed linear integral equations for partial RFs of any order, which permi tted us to use the method of angular Green's functions to sequentially calculate all the partial RFs. We derive an integral equation for the angular Green's function in albedo problems of the theory of transfer of optical radiation. Using the derived equations, we calculate the t otal and partial reflection coefficients for model media with bidirect ional scattering phase functions, which allowed us to verify the ident ity of the results obtained by different methods. A simple approximate method of ''backward collisions'' is proposed for the calculation of Green's functions in real 3D media with sharply anisotropic scattering centers. Using this method, we have calculated the first partial RF, which provides the main information concerning the angular spectrum of reflected radiation in strongly absorbing media. The results obtained in this study are compared with the results of calculations performed by other authors.