Infrared Transmission through the Atmosphere

An analytic expression for transmission in terms of optical path and pressure is combined with an analytical expression for equivalent atmospheric path length in terms of height and slant angle to yield a single expression for transmission in terms of height and slant angle. Separate equations are developed for carbon dioxide absorption, and for water vapor absorption. The latter may be used with almost any water vapor distribution in the atmosphere. A function due to Chapman is used instead of the usual secant factor for slant paths in order to extend the use of the equations to angles of incidence up to 90°. Wavelength dependent parameters are presented based upon Zachor’s analytic fits to laboratory data.