General wavelength dependence of imaging through the atmosphere

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-microm 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-microm window. The 8-13-microm window is generally better for thermal imaging of objects whose temperatures are close to those of the atmosphere.