Visual Measurements of Atmospheric Transmission of Light at Night

Abstract

Measurements of the visual transmission of the atmosphere were made at night across Chesapeake Bay over a period of two years. A visual telephotometer was used to measure the illumination produced at a distance of 8.77 sea miles by a series of calibrated light sources. With this range it was possible to measure atmospheric transmission values between 0.4 and 0.9 per sea mile corresponding to daylight visual ranges from 4 to 40 sea miles with an accuracy of ± 2 percent. Under stable atmospheric conditions the data obtained at night were in good agreement with direct observations of the daylight visual range made before sunset and after the following dawn.