E.M. Ivanova, V.E. Karasik, V.M. Orlov

The present paper is devoted to the peculiarities of process of vision in biological highly scattering media with low specific coefficient of absorption and highly anisotropic scattering. One of the most important characteristics to be concerned when speaking of vision through turbid media is a modulation transfer function (MTF) which describes the change in contrast of the object depending on the spatial frequency due to the process of scattering and absorption in medium. With the help of image transfer theory the scattering layer MTFs are investigated within three approaches used for radiative transfer equation solution: small angle approximation, diffuse approximation and hybrid method. Small angle approach is used in «close region», in turbid media with low absorption this method is valid for optical thicknesses  ≤ 6-8. Diffuse approximation can be used in «far range», for optically thick scattering layers ( > 15) with low absorption P1-method returns reliable results. And for solution of radiative transfer function for optical thicknesses of  > 5 hybrid method has been offered. It is based on two-staged procedure which takes into consideration the light field from photons, scattered in small angles, and diffusely scattered photons - photons being scattered multiply in large angles. The present paper provides MTFs for all three approaches and the applicability range of each depending on the value of optical thickness of scattering media with low ab-sorption.