Transfer of visible radiation in the atmosphere

• Published in: Atmospheric environment 1981, Vol.15 (10), p.1805-1820
• Main Author: Dave, J.V.
• Format: Article
• Language: English
• ISSN: 0004-6981
• DOI: 10.1016/0004-6981(81)90216-X

The problem of the transfer of visible radiation in the terrestrial atmosphere is addressed from the visual-air-quality point-of-view. Attention is therefore focused on computations of the luminance, dominant wavelength, and spectral purity of the sky radiation requiring radiance values for a number of wavelengths in the 0.38–0.78 μm interval of the electromagnetic spectrum. These colorimetric parameters are determined, for five different plane-parallel atmospheric models, from values of the radiances at 23 unequally spaced wavelengths. The diffuse radiation is evaluated after taking into account all orders of scattering, but after neglecting the polarization aspects of the scattered radiation. The atmospheric models studied are for average, cloudfree, mid-latitude summer conditions, and vary from an aerosol-free, absorption-free model at one end to a model with a very large amount of aerosols and absorption by ozone, water vapor and oxygen at the other. These models are assumed to rest on a ground obeying Lambert's law of reflection. Discussion of results is confined to variations of the aforementioned colorimetric parameters as a function of the zenith angle of observation in a vertical plane passing through the sun and the observer, but for several positions of the sun, and for several atmospheric conditions. For a few selected cases, results obtained after including all orders of scattering are compared with those obtained after consideration of the first scattering of the incoming solar, and outgoing ground-reflected radiation. The main features of the sunlit sky for various cloud free atmospheric conditions and for various sun's positions are, qualitatively speaking, well-reproduced by the model calculations. Attention is drawn to the need for a detailed comparison of the colorimetric measurements taken simultaneously with the observations of various atmospheric parameters of crucial importance, and computations carried out with the input parameters representative of the experimental conditions; and also to the need for including absorption by other gases and sphericity of the earth-atmosphere system in future modeling studies.