The Earth’s atmosphere has significant effects on the propagation of electromagnetic (EM) radiation and accordingly degrades the performance of electro-optical systems. These effects are attributed to atmospheric turbulence and to absorption and scattering of EM waves by atmospheric molecules and aerosols. In this paper we develop a detailed model of the effects of absorption and scattering on the optical radiation propagating from the object plane to an imaging system based on the classical theory of EM scattering. Scattering has the effect of de-correlating the light leaving the target from the unscattered light reaching the imaging system, and scattering has the effect of broadening the angle at which the scattered light arrives at the receiver compared to the unscattered light. Absorption has the effect of reducing the amount of power available for the image. Both of these effects depend upon the atmospheric species present, their EM properties, and wavelength. We use this detailed model to compute the average point spread function (PSF) of an imaging system that properly accounts for the effects of the diffraction and scattering, and the appropriate optical power level of both the unscattered and the scattered radiation arriving at the pupil of the imaging system. Since the scattered radiation is temporally and spatially de-correlated from the unscattered radiation, we model the effects of the unscattered radiation and the radiation scattered from the various species as additive in the image plane. The key result of this study is the significant effect of atmospheric scattering on the contrast and spatial resolution of images acquired by imaging systems, due to the increased level of the scattered radiation PSF and the reduced level of the direct radiation PSF, upon increasing the atmospheric optical depth.
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