Proceedings Article | 5 November 2020
KEYWORDS: Modulation transfer functions, Atmospheric particles, Molecules, Aerosols, Turbulence, Spatial frequencies, Absorption, Scattering, Atmospheric optics
The most important part of visible-infrared image characteristic simulation, is the degradation simulation of the image in the actual turbid atmosphere. Aerosols, molecules, turbulence, and imaging devices in the atmosphere are the dominant factors in the image degradation process. These effects occur simultaneously in the real-world atmosphere. According to the equivalence principle, the MTF of molecule can be calculated, whose results show that the absorption and scattering effect of molecule cannot be treated easily as a dampen on image contrast but is as important as that of aerosol. At and near some absorption bands, molecule MTF at high spatial frequency is smaller than aerosol MTF at high spatial frequency; at weak-absorption and strong scattering bands, molecule MTF is comparable to, even bigger than, aerosol MTF at high spatial frequency. In turbulence free atmosphere, the dominant factor that affects the image quality is determined on the dependence of weather and wavelength. At molecular absorption lines, the effect of molecule is dominant, whereas, at visible bands, the effect of aerosol is comparable to, even more important than, that of molecule. When the turbulence is considered, the result is a little complex. If turbulence blurs the image seriously and the cut-off spatial frequency is much smaller than that of overall turbid atmosphere MTF, the image degradation is dominant by the turbulence. In addition, the cut-off spatial frequency of aerosol MTF or molecule MTF is generally smaller than 2 cycles/mrad even 1 cycles/mrad, which means that aerosol MTF or molecule MTF will be dominant factors for imaging degradation when the turbulence is weak enough in atmosphere.
