A.N. Sviridov

State Unitary Enterprise "RD&P Centre "Orion", Moscow, Russia

   The calculation (for two spectral ranges used in thermal imaging: 3...5 mm and 8...14 mm) of thermal contrasts and potentials of the infrared images of objects of observation (OO) are carried out, both at the availability of counterradiation of the environment and without it. (Thus, as well as in [1], the counterradiation is termed radiation, hitting on OO, from the sky, from the Earth surface and from subjects around it. It was supposed, that OO temperature does not differ essentially from the temperature of the Earth surface.)
   It is shown, that in the infrared image in viewed spectral ranges (unlike the images of these OO in a visual spectral range) (both at counterradiation and without it) disappearence of some local areas (LA) - OO areas which temperatures or (and) reflectivities differ from average ones always takes place.
   It is offered to characterize each LA of OO by a numerical coefficient gi, which value is determined by its temperature, reflectivity and averange for OO values of these quantities. The calculation of numerical values of coefficient of disappearing LA depending on the enviroment temperature are carried out.
   It is shown, that the availability of counterradiation, alomgside with diminution of the image contrast, can (under certain conditions) bring to inversion, i.e. LA with smaller coefficient of radiation becomes more bright than LA with larger coefficient of radiation.
   Potential of a steady component of OO optical image is shown to be ~10 times more in spectral range of
8...14 mm), than in 3...5 mm spectral range.

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