not strictly true for the reflected light from SPS. For the specular component of the reflection, only a narrow cone in the atmosphere is illuminated, leaving most of the sky essentially unaffected to the extent that multiple scattering can be neglected. However, as is shown in Figure 20, the angular distribution of the diffuse component of the reflection is fairly flat. Any point in the line of sight of the observer is therefore illuminated by about the same intensity. This is then nearly equivalent to a source such as the sun which illuminates the entire atmosphere with parallel light of the same intensity. Multiple scattering is treated by the same adjustments as were made for the sun. For the general case where the observer's line of sight does not intersect the specular component of the reflection, the sky brightness can be obtained from Table 4. To obtain the sky brightness of Satellite Power System vehicles, the ground irradiance H is scaled to the direct solar irradiance by the formula As an example of the procedure, consider the diffuse reflection intensity -7 2 of 8 x 10 W/m from the SPS solar panels in GEO (02). At an apparent point in the sky of £ = 30°, = 60°, and Z = 45°, Table 4 gives B = B + B = 2 _q ? * P 111 + 16 = 127 lumens/ft . Thus I = 7.3 x 10 W/m , and the sky irradiance is 0.9% of the direct irradiance from SPS.
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