The angles of elevation (a) above the horizon of the line of sight to the orbiting powertransmitting antenna are as follows: Elevation Angle Nadir Location Name Latitude Longitude to Satellite a Angle = 90-a Southwest SSPSS.W. 33° N 113°30'W 50° 40° Northwest SSPS N.W. 46° N 119°30'W 37° 53° Midwest SSPS M.W. 36°30'N 87°40'W 31° 59° Northeast SSPS N.W. 41°30'N 78°30'W 20° 70° Figure 90 presents the data at each of the four ground base locations derived from input (1). Specific percentage attenuation is shown at each station for 3.3 GHz for comparative purposes. There is a significant imprecision evidenced by the data points at the 2- and 3-GHz frequencies not fitting the nominal curve. This is believed to be associated primarily with the computer program's utilization of interpolated data from Table I of Reference 41, which is particularly imprecise in the 2- and 3-GHz region. The programs are currently being updated utilizing data from Reference 42. The cloud models used in the program assumed the maximum intensities associated with the 2-km diameter core to be applied over the entire field of the microwave power beam which would, of course, result in conservative estimates of the total power attenuation. Based on the information obtained, the following preliminary conclusions were reached: 1. There is significantly higher attenuation in the Northeast and Midwest than in the Southwest and Northwest for both high and low probability of rainfall. This is due largely to the East being generally more humid and the longer beam paths through the atmosphere. 2. The Northwest has the lowest attenuation for the low probability events. This is due primarily to the minimum precipitable water content achieved bv the cooling of the air mass as it moves from West to East over the Olympic Mountains and the Cascade range and the precipitation of most of the precipitable water content on the western side of the mountains. 3. The Southwest has the lowest attenuation at the higher probabilities of occurrence due to a low average precipitation and also the shortest distance for transmission of power through the atmosphere. The two Western locations would be favored from the atmospheric attenuation point of view. Except for the Northwest, frequencies above 4 GHz are significantly attenuated. Attenuation grows progressively worse as frequency increases. As long as the frequency is in the region of 3.3 GHz, the penalties for any ground location compared to the “optimum,” although significant, are not overwhelming.
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