Attenuation of Light in the Lower Atmosphere*

Researches on the attenuation of light in the lower atmosphere permit the conclusions:(a) From 3500 to 5400A in distances up to 6 km the attenuation of pure air and water vapor is due to molecular scattering with negligible true absorption; (b) from 3000 to 2000A pure air possesses an absorption in addition to molecular scattering, probably due to oxygen, which increases rapidly with decreasing wavelength; (c) the degradation of visible light in normally clear air at sea, probably due to prevalent haze, is such as to reduce light to 1/10 in 10 nautical miles; (d) natural fog degrades visible light either equally across the spectrum or slightly less for red than for blue light but not enough to redden appreciably white or yellow lights.Infrared photographs to distances of 8 nautical miles through haze and fog showed objects at 0.5, 1.2, 4 and 8 miles when the haze and fog were such that objects could just be seen at 0.5, 1, 3 and 6 miles.