<title>Blurring effect of aerosols on imaging systems</title>

Abstract

The main aerosol effect on imaging performance is brightness reduction through scattering losses. This is fairly well understood and modeled. However, one phenomenon that is almost always overlooked is the blurring of images that can result from forward-scattered radiation, i. e. the radiation reaching the image plane after being scattered by airborne particles. The paper describes a simple experiment to measure the visible point spread function, or the image of a point source, through fog and rain. The images were recorded with a CCD camera. Frame addition was used to reduce the statistical noise. Series of images were made with different neutral density filters and later recombined to increase the dynamic range beyond the 8-bit gray level range of the frame grabber. The results show the effects of range, particle density and particle size. The measurements are generally in good agreement with model predictions. As it turns out, the aerosol blurring effects are important only for rain and for some advection fogs with a sufficient number of particles in the size range of 100 jim.