TECHNIQUE OF ESTIMATION OF ALL-WEATHER CAPABILITY IN OPTICAL CONTROL CHANNELS
The article herein deals with the all-weather factors estimation techniques in optical control and information transfer channels on the basis of the conditions package which determines atmosphere transparency. The analysis herein considers the surface layer up to the cloud base. The algorithm has been elaborated on the basis of meteorological visibility distribution vs atmosphere humidity deficit. The used meteorological visibility distribution data have been received experimentally by the Atmosphere Optics Laboratory working with the General Geophysical Observatory (St. Petersburg) in 1967 fusing from four meteorological points in the former Soviet Union: Voeykovo (St. Petersburg), Meganom (the Crimea), Chakvi (Batumi, Georgia ), and Pitsunda (Abkhazia). The humidity deficit depends on air temperature and relative humidity to allow using an empirical distribution law - “temperature - relative humidity”- for its determination applied to cold, moderate and hot climate. Contributed by a package of precipitation and fog data it allows obtaining a complete attenuation index for optical signals atmospheric transmission, predicting operational range and estimating the frequency ratio of the channel for a fixed range operation taking into consideration a package of ambient conditions. The range determination technology for area objects is realized on the basis of the linear filtration theory, which compares object-under-observation contrasts passed through scattering and inhomogeneous atmosphere with the contrasts resolved by the hardware. Atmospheric signal attenuation is determined using the Rayleigh equation and the Mie theory. To illustrate the technique herein, the article offers all-weather factors data received using three types of the hardware with a narrow (about 1°) field of view: a TV camera (wave length range Dl=0.5÷0.7 µm), a medium waves thermal imager (Dl=3.7÷4.8 µm) and a long waves thermal imager (Dl=7.7÷10 µm). The task was to detect a 3×3 m object with a visual contrast 0.2 and temperature contrast DТ=2°. The data have been received at two meteorological points with quite different climatic characteristics: humid and cold Dixon and hot and dry Ashkhabad. The modeling shows that under cold and humid climate conditions a thermal imager appears to be much superior to a TV camera, and in a hot dry climate the thermal imager all-weather capability is 10÷15 % higher compared to the one obtained under humid cold conditions.