EXPERIMENTAL INVESTIGATION OF THE INFLUENCE OF THE RELATIVE POSITION OF THE SCATTERING LAYER ON IMAGE QUALITY - THE SHOWER CURTAIN EFFECT

The imaging quality of optical systems in a turbid environment is infl uenced not only by the content of the turbid layer between the object and the optical receiver but also by the inhomogeneity of that medium. This is important, particularly when imaging is performed through clo uds, nonhomogeneous layers of dust, or over vertical or slant paths th rough the atmosphere. Forward small-angle scattering influences image quality and blur more severely when the scattering layer is closer to the receiver. in this study it is the influence of the relative positi on of the scattering layer on the image quality and modulation transfe r function (MTF) that is investigated. The scattering layer in control led laboratory experiments consists of calibrated polystyrene particle s of known size and quantity in a small cuvette. A point source was im aged by a computerized imaging system through a layer containing polys tyrene particles, and the point-spread function (PSF) was recorded. Th e aerosol MTF was calculated using the measured SF. The MTF was measur ed as a function of changing relative distance of the scattering layer from the receiver, whereas the object-plane-to-receiver distance was constant. The experimental results were compared to theoretical shower curtain effect models based on the solution from radiative transfer t heory under the small-angle approximation. Although the general trend of the experimental results certainly agrees with the theoretical mode ls, it could be that the small-angle approximation method might be of Limited validity at such low spatial frequencies. Aggregation also cau ses some disagreement with predictions from theory. (C) 1998 Optical S ociety of America.