Showing papers by "Norman S. Kopeika published in 1981"

Wavelength variation of visible and near-infrared resolution through the atmosphere: dependence on aerosol and meteorological conditions.

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.

General wavelength dependence of imaging through the atmosphere

Abstract: Atmospheric MTF formulations are restated to include contrast reduction by thermal backgrounds received by the imaging system. These backgrounds should be of significance for infrared imaging through the atmosphere. Absorption windows such as 2.0–2.4 and 3.1–4.1-μm wavelengths, which contain minimum atmospheric background, are suggested as usually permitting the best resolution for long range atmospheric imaging of apparently bright objects despite the fact that received object beam radiation may even peak in the 8–13-μm window. The 8–13-μm window is generally better for thermal imaging of objects whose temperatures are close to those of the atmosphere.

Characteristics of holographic scanners utilizing a concave auxiliary reflector

Abstract: The characteristics of 2-D holographic scanners utilizing a concave auxiliary reflector are analyzed. The total resolution capability of the scanner is discussed in detail for the scanner operated at both finite and infinite conjugations, and the factors limiting resolution are indicated. The resolution considerations lead to a near-optimal design procedure which is used in design examples for typical applications in the visible, millimeter, and ultrasonic wavelength regions.