| Transport theory is the mathematical description of non-equilibrium statistical mechanics in the level of kinematic theory. In photon transport theory, three types of problems are usually considered:1. Evaluation of the photon number density, starting from the knowledge of the various cross-sections, of the ingoing flux and of the shape of the surface.2. Identification of the spatial behaviour of the cross-sections, starting from the knowledge of the exiting photon flux.3. Identification of the surface starting from the photon far-field, and assuming that the relevant physical quantities of the medium are known.It was discussed in [1] how one can obtain the approximate solution of the total cross-section from the knowledge of the exiting photon flux , In [5], it was discussed how one can obtain the dimension of the cloud and its total cross-section from exiting photon flux under the assumptions of slab geometry.In this article we will discuss the following three problems: 1. For general transport equation, we obtain the approximate solution of the scattering cross section from exitig photon flux. 2. For general transport equation, by the method of least sequares we give another approximate solution of total cross section through n times observations. 3. Under the assumptions of spherical symmetry we evaluate the dimension of the cloud from exiting photon flux. Our conclusion is : For general transport equation and some special transport equations (slab geometry, spherical symmetry, pillar symmetry) we can evaluate some relevant physical quantities and geometrical properties from the exiting photon flux. The method we will use is to transform the transport equation into integral equation by integrating it along its characteristics, then we prove the nonlinear operator K is monotone and continuous with respect to its arguments and obtain the existence of K~-1. Consequently, we can evaluate some relevant physical quantities and geometrical property of the medium.
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