The Attenuation and Backscattering of Infrared Radiation by Ice Fog and Water Fog

摘要

Ice-fog crystals consisting of many spherical particles, and some hexagonal plates and columns, were observed at ambient temperatures of about -40C in the Fairbanks, Alaska, area during mid-winter. The concentrations and the size distributions of the ice-fog crystals were measured. The attenuation and backscattering of infrared radiation by ice-fog crystals were computed for optical wavelengths of 2.2 microns, 2.7 microns, 4.5 microns, 5.75 microns, 9.7 microns and 10.9 microns using the Mie theory. The minimum attenuation coefficients and backscattering functions of ice fog were found to be at 9.7 microns wavelength in the observed wavelengths. Optical attenuation coefficients and volume backscattering functions of water fogs were also computed using the Mie theory. The minimum attenuation coefficients and backscattering functions of water fog were found to be at 10.9 microns wavelength in the region of 2.2 microns, 2.7 microns, 4.5 microns, 5.75 microns, 9.7 microns and 10.9 microns. Both the attenuation coefficients and backscattering functions of ice fog are within the same order of magnitude as water fog for equivalent fog concentrations and wavelengths. (Author)