Atmospheric Aerosol Backscatter Models in the Infrared

A review is given of the problems encountered in modeling atmospheric aerosol backscattering at infrared wavelengths,βIR. The region of the atmosphere discussed is the lowest 20 kilometers; the main emphasis of the review is on the scattering properties at CO2 laser wavelengths (9.1 to 11.1 μm) but scattering at the Nd-YAG laser wavelength (1.06 μm) will also be discussed together with the results of calculations carried out for intermediate wavelengths. The review contains a summary of the relevant aerosol characteristics and the different methods of calculating the aerosol backscattering function, both from measured aerosol characteristics and from optical measurements made at other wavelengths, are described and their accuracy assessed. Effects of changing atmospheric humidity and temperature on the backscatter are presented and related to the real atmosphere. Modeled values for aerosol backscatter for different geographical regions and at different heights above the earth's surface are given.