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As a prerequisite to the adaptive cancellation of the deleterious effects that the atmosphere can have on image propagation, one needs a propagation model that incorporates as many of the major atmospheric mechanisms as possible that can exist to simultaneously perturb the attendant electro-magnetic wave field. The two principal mechanisms are: 1) scattering due to turbulent fluctuations of the temperature and humidity fields of the atmosphere and 2) scattering and extinction due to atmospheric aerosols and hydrometeors. Collectively, these are taken here to define the turbid atmosphere. Studies have recently been made on wihoc theoretical I and empirical 2, 3 bases where these effects are taken to occur simultaneously on a propagation path but what one ultimately needs is a unified treatment of such situations. There are also other important aspects of the problem that have been hitherto neglected in atmospheric image propagation modelling, viz., the fact that aerosol concentrations along the propagation path are not usually uniformly dispersed along the path and, more importantly, because of prevailing turbulent mixing and motion due to the ever present wind, the concentrations are random functions in the transverse position across the path. This latter aspect can give rise to fluctuating components of the image and spectral contrasts of a target and therefore necessitates a statistical description of these well known imaging parameters as well as the associated optical transfer function. Such statistical fluctuations in the propagating radiation field can, for example, degrade the overall signal-to-noise ratio of an optical device because, in addition to the shot noise which is determined by the average signal level at the imaging device, there is a component that results from the random aerosol scattering mechanism that can, in most cases, dominate over that of turbulence. In the case of the sensitive sensors in use at this time, this noise component may exceed that due to turbulence. What is more important, however, is that if these effects are to be compensated for by a passive adaptive imaging technique (i.e., adaptive image correction without the use of a reference source which is usually a necessity in actual situations) a complete description is needed to use as a priori control information. However, as always, it is desired to strive to keep such a model amenable to analytic solution.
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