4. The Distribution and Number of Satellites - The Briefing Document speaks only to a 60-satellite system. Upwards of 120 satellites have been considered and the possibility of other nations building such systems cannot be excluded. We have identified five weak areas in the atmospheric characterization: 1. Wavelength Dependence of Diffuse Sky Brightness - The Briefing o Document calculation is good for approximately 5000A chosen as a compromise between the high scattering in the blue and somewhat lower values in the red. As an illustration of how much worse the situation may be in the blue, it should be recalled that the opacity -1 3 due to aerosols goes as A * , while Rayleigh scattering goes as X-4. 2. Variable Conditions - The estimate of the increase in night sky brightness due to the SPS found in the Briefing Document is based on an empirical study of the image profile of astronomical objects. Figure 1 shows how much the wings of the radiance profile of the sun can vary as a function of location and conditions. It is the wings of the profile that are of primary interest in computing the increased sky brightness. While the King profile in the Briefing Document may represent the conditions of a particular local sky, conditions such as subvisual cirrus or high turbidity could raise the wings of the profile considerably. 3. Polarization Effects - The added SPS sky brightness should be polarized just as scattered moonlight and the day sky are. The Briefing Document does not address this issue. 4. The Effects of the Specular Beam - As noted in the Briefing Document, we have had no estimates of the effects of the specular beam yet. Atmospheric scattering of the beam radiation as it passes near an observatory may be an even greater problem than the brief periods when the same site is actually in the beam.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==