Umov Effect for large nonspherical particles for remote sensing of cirrus clouds

Abstract

The Umov effect is the inverse correlation between the maximum of the linear polarization of the light scattered on an object and the geometrically albedo of this object. The importance of studying this effect should be considered in the context of one of the complex and important tasks of remote sensing: determining the concentration of particles in optically thin clouds. Since the intensity of the scattered light depends on two unknown quantities: the concentration of particles in the cloud and the phase function of the particles of the cloud. Then to retrieve the concentration from the measured signal, it is necessary to know the phase function in advance. In real observations, the phase function is, usually, not known. The Umov effect will make it possible to estimate some necessary unknown characteristics of particles in a cloud, which determine the phase function. This paper is devoted to the study of this effect for particles with sizes much larger than the wavelength of the incident light. The report presents a solution to the problem of light scattering by randomly oriented particles of irregular shape for particles with sizes of 100 and 200 microns, for a wavelength of 0.532 microns. The solution was obtained within the both frameworks: the physical optics method and the geometric optics approximation. It was found that if the imaginary part of the refractive index less than 0.001, the Umov effect is observed with good accuracy for particles of size from 100 to 200 microns. However, the Umov effect is violated when the imaginary part of the refractive index is greater than 0.001.