The Ultraviolet Transmission Coefficient of the Earth’s Atmosphere

Abstract

Thermocouple measurements have been made at four different altitudes in the neighborhood of Albuquerque, New Mexico, of the intensity of solar radiation transmitted by a silver filter. These have been used to determine values of the transmission coefficient defined by I=Iam where I and I0 are respectively the observed and incident energies, a the transmission coefficient and m the air mass traversed in units of the vertical air path directly overhead at sea level and normal pressure. The results, corrected by the use of Hann’s empirical equation for the effect of water in the path, gave for a at 3140 m, 0.47; at 2059 m, 0.47; at 1769 m, 0.46; and at 1556 m, 0.43. The last result, from observations on the New Mexico campus is low probably because of dust scattering; the others are in agreement within the errors. The theoretical value calculated from Rayleigh’s law of molecular scattering, and using a new value (λ3240) for the wave length of maximum solar energy transmitted by a silver film, is 0.479. The conclusion is, that at least above 1700 m altitude, and for clean dry air, the Rayleigh law for pure molecular scattering is adequate to account for the atmospheric depletion of solar radiation in the silver transmission band. The somewhat discordant results of earlier investigators are discussed.