Simulation colorimetry of the earth-atmosphere system

Luminance, dominant wavelength, and spectral purity of the sky radiation as a function of the zenith angle, and of the radiation reflected by different types of Lambert surfaces along the nadir direction, but received by observers at ground level as well as at the top, are presented for several plane-parallel models of the terrestrial atmosphere. These colorimetric parameters of the diffuse radiation are determined from the computed radiances at 23 unequally spaced wavelengths in the spectral region 0.365–0.784 μ. The diffuse radiation is evaluated after taking into account all orders of scattering. The atmospheric models used are for average cloudfree midlatitude summer situations, and vary from an aerosol-free absorption-free model at one end to a model with a large amount of aerosol and absorption by ozone and water vapor at the other. This study illustrates the manner in which the aforementioned colorimetric parameters are affected by the atmospheric conditions, solar position, direction of observation, position of observer, and the wavelength dependence of the reflectivity of the surface underlying the atmospheric model.