where Bp is the intensity due to single scattering of the light from the major source, such as the sun, and Bm is the brightness due to other less intense sources such as earth reflections and multiple scattering, typically about 1/4 that of Bp. By assuming that the sky is composed mostly of molecular scatterers, the following expression for B was obtained: r where 3' is the absorption coefficient of the effective ozone region, 6 is the visual attenuation coefficient, 6 is the ratio of the weak to the strong polarized component, I ’ is the irradiance at the top of the atmosphere, and 0, x-|, and are geometric relationships defined in Figure 31. This expression with the assumptions made which simplify the expression to this form were found to be accurate to within about 4% for £ and £ = 75°, except for the molecular sky assumption. To account for particulate scatter it was necessary to increase the scattering coefficient from a theoretical value of .0126/km to .017/km. An expression for B^ was similarly derived, resulting in the following expression: where a-| and b^ are the downward flux and the upward flux, respectively, of light from the secondary sources, evaluated at x-j , and bQ is the upward flux evaluated at the surface of the earth. The other variables are as defined previously. The fluxes are obtained by the following expression:
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