closely spaced sites were chosen and attempts were made to distribute the sites throughout the contiguous United States. Because the layout of the EHV grid is strongly correlated with existing load-demand centers, the number of sites selected was not evenly proportioned by geographical region. Difficulties in obtaining the necessary statistical meteorological data also precluded selection of the “best” sites for certain geographical regions. However, the number of sites selected [22] is statistically significant enough so that patterns of expected performance for the different regions can be gleaned, especially considering the climatic similarity of many sites within the same region. POWER AVAILABILITY Sources of Statistical Climatic Data Calculation of the power availability at any given site requires statistical climatic data in much greater detail than is routinely accumulated by the U.S. Weather Service for any of their stations. For instance, an extensive model will require information not only concerning sky cover but regarding cloud type, thickness, and frequency of occurrence, which is not available for civilian stations (3). Some work has been performed in this regard using various environmental satellites (e.g., 4-7); however, a statistical data base which incorporates these variables into an analyzed format and which could be referenced to particular U.S. receptor locations does not exist. The most useful climatic data for present purposes are the frequencies of total sky cover (0-10 tenths), which are observational data gathered at almost all military air bases. Total sky cover is a visual gauge of the fractional cloud covering of the entire sky taken by trained observers at designated intervals. The power availability model developed here considers laser transmission under two conditions, i.e., when a cloud-free line-of-sight (cflos) exists between the satellite transmitter and the receptor site and when clouds obscure the beam. The probability of a cflos is a function of the observed frequencies of total sky cover and the propagation zenith angle. The transmission efficiency through cloud cover is calculated using three schemes. The first cloud-cover transmission model gives the worst-case behavior and is believed to establish a lower bound on the calculated power availability by assuming zero transmission through all cloud types except for thin cirriform, middle, and stratiform types. The second model is our best estimate which, admittedly, represents a large amount of subjective judgment. The third and most optimistic model assumes considerable transmission through certain cloud types by virtue of substantial hole boring. These models are believed to accurately bound the expected performance of space-to-Earth laser energy transmission. Power Availability Model The average transmission efficiency for each total sky cover j is where Cj is the probability of a cflos as a function of total sky cover j and zenith angle 3, and t} is the weighted cloud transmissivity if a cloud obscures the beam for
RkJQdWJsaXNoZXIy MTU5NjU0Mg==