conducted at lower frequencies than 2.45 GHz in order to achieve the same ionospheric heating with lower power densities according to the law mentioned above. However, the results are not final and we recommend the construction of a radio wave heater at the desired transmission frequency that will exceed the heating of a 5 GW radio wave power beam. The laser-plasma interactions in the ionosphere at a wavelength range of 5 -10 pm were investigated by Beverly (1979). He found the effects to be negligible. However no experiments were conducted. Effects on the Lower Atmosphere The dominant effects upon transmission of electromagnetic radiation through the lower atmosphere are molecular absorption and scattering. Molecular absorption for frequencies below 3 GHz is nearly constant (about 0.7%) and independent of the atmospheric water content. The losses due to scattering below 3 GHz are tolerable and do not exceed 4% in the worst case (heavy thunder storm). For frequencies above 3 GHz the absorption increases and depends strongly on the water content in the atmosphere due to the pressure broadened absorption line of water near 22 GHz and a Oxygen absorption line near 60 GHz. For medium humidity the power loss at 35 GHz is about 5% (Manson, 1976). Rain (5 mm/h, 10 km path length) can increase the loss considerably (see also Figure 6.2). [Manson, 1976] Figure 6.2 Transmission Efficiency - Molecular Absorption and Rain Therefore we recommend not to use frequencies higher than 3 GHz in areas with high probability of rain, snow, hail or thunderstorm. However, frequencies above 3 GHz (especially 35 GHz) can still be used in very dry areas as deserts. For laser-transmission the analysis is more difficult because there is a complex absorption structure in the atmosphere for the Near infrared (NIR)-wavelength. range with many transmission- ‘windows'. A detailed study was conducted for line-selected CO-laser by Beverly (1979). We shortly summarize the results of this study here. It was found that for the selected wavelength (5.078 pm and 5.068 pm) the atmospheric loss is strongly dependent upon weather-conditions and season. For 50° latitude the transmission varies between 70% and 95%. The study concludes that global climate changes are highly improbable, however local climate changes can occur and turbulences may be produced which could be hazardous to intruding aircraft. The perturbations of the plasma chemistry in the mesosphere and thermosphere is believed to be not significant. However this is not confirmed and further research is necessary. Serious environmental modifications (e.g. depletion of the ozone-concentration) is proclaimed not to be possible. Power Leakage at Rectenna Site For a 5 GW beam, 2.45 GHz space power satellite at GEO, the heat release at the rectenna site over an area of 120 km2 (40° latitude) will be in the between of 6.5 W/m2 and 9.5 W/m2 (estimated efficiency, Lee, 1978). This has to be compared with the net flux of all radiation at the surface of 75 W/m2. Thus, the perturbation of the average surface heat exchange is of the order of 10%. The estimated man-made heat dissipation in the city of Cincinnati in 1971 was 25 W/m2. This means that
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