A TECHNIQUE FOR ACTIVE MEASUREMENT OF ATMOSPHERIC TRANSMITTANCE USINGAN IMAGING-SYSTEM - IMPLEMENTATION AT 10.6 MU-M WAVELENGTH

An active method is presented for measuring atmospheric transmittance with an imaging system. In comparison to other measurement methods, th is method has the advantage of immunity to background noise, independe nce of atmospheric conditions such as solar radiation, and an improved capability to evaluate effects of turbulence on the measurements. Oth er significant advantages are integration over all particulate size di stribution effects including very small and very large particulates wh ose concentration is hard to measure, and the fact that this method is a path-integrated measurement. Attenuation deriving from molecular ab sorption and from small and large particulate scatter and absorption a nd their weather dependences are separated out. Preliminary results in dicate high correlation with direct transmittance calculations via par ticle size distribution measurement, and that even at 10.6 mu m wavele ngth atmospheric transmission depends noticeably on aerosol size distr ibution and concentration.