Abstract
Measurements of square wave response over a 4.1-km near-field horizontal path are presented for different wavelength regions. Relatively high winds generate increased concentrations of soil-derived aerosols that noticeably dampen low-spatial-frequency IR response. At diurnal Cn minimums, when turbulence is not severe, even more severe dampening of higher-spatial-frequency IR response by these aerosols is observed also, thus confirming the existence and wavelength dependence of the aerosol modulation transfer function predicted by R. F. Lutomirski [ Appl. Opt. 17, 3915 ( 1978)]. However, when such aerosols are of reduced concentration, best-quality imaging through the atmosphere is observed in the IR rather than in the visible. This model of the wavelength dependence of imaging through the atmosphere is thought to be independent of geographical location. Since the size distributions of soil-derived aerosols remain relatively constant up to altitudes of approximately 5 km, their effects should be quite relevant for vertical and diagonal imaging as well.
© 1981 Optical Society of America
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