The Effects of Atmospheric Turbulence

Abstract

As discussed in Chapters 1 and 2, the absorption and reemission of radiation in the atmosphere affect the signal level at the detector and also limit the sensitivity, in terms of the background power. In addition, aerosol and molecular scattering are particularly important background sources in the visible region of the spectrum, because of the sun’s radiation. Detailed data on absorption and scattering may be found in Wolfe (1965) and in the RCA Electro-Optics Handbook, hereinafter referred to as EOH (1974). We shall treat some of these effects in Chapter 11, but here shall consider another atmospheric property, turbulence, which has a profound effect upon heterodyne as well as incoherent-detection efficiency. The literature on turbulence is voluminous, and has recently been reviewed by Fante (1975). We shall here give a simple one-dimensional treatment based upon the work of Fried (1967a). In the first section, we find the limitation on effective aperture area in a heterodyne system and in the second, the minimum field of view allowed for an incoherent detector.