RECTENNA-RELATED ATMOSPHERIC EFFECTS J. Lee, Energy and Environmental Systems Division Argonne National Laboratory, Argonne, IL 60439 1. INTRODUCTION The primary interest in the assessment of possible environmental effects arising from the existence and operations of the satellite power system (SPS) rectifying antennas (rectennas) is meteorological in nature. The presence of a rectenna covering an area of approximately 100 km2 would be expected to alter the aerodynamic characteristics of the surface in its immediate vicinity. A change in surface roughness affects the vertical fluxes of momentum and thermal energy, and a change in radiative properties (albedo and emissivity) affects the surface energy budget. The operation of a rectenna would add an additional heat source at the surface. The consequences of these changes would be expected to alter the wind velocity profile and stability of the planetary boundary layer and hence to alter the local cloud population. The possible influence of microwave transmission through the troposphere would be due to the absorption, especially in clouds, of microwave energy along the beam path, causing local heating. On the other hand, the presence of convective or turbulent air motions and the existence of hydrometers cause refraction, scattering, and absorption of microwave and can lead to beam wandering and spreading. The scope of this discussion is limited to the effect of SPS on tropospheric atmosphere. Many issues of concern regarding the effects of atmospheric conditions on SPS beam propagation can be found in the proceedings of a workshop held in August, 1978, and will not be discussed here. 2. PREVIOUS STUDIES A preliminary assessment based upon the maximum microwave-beam power density of 230 W/m2 and an average waste heat release rate of 7.5 W/m2 from a rectenna covering approximately 100 km2 was conducted in 1977 by the Johnson Space Center.2 The findings were that the effects of an SPS rectenna on weather and climate would be small compared to the direct environmental consequences of construction, and that the rectenna's influence would be similar to that of an average suburban development. Microwave heating of the lower atmosphere through gaseous absorption would be negligible. Any actual effects of microwave heating inside a cloud would not be detected in the presence of the natural variance of cloud and storm phenomena. Scattering by particles, even in heavily-polluted atmosphere, would also be negligible. 3. CONSENSUS OF AUGUST 1978 WORKSHOP1 The above study was reviewed at the August 1978 workshop and the conclusions were updated. Three main topics were discussed: the effects of waste-heat release on the atmosphere at the rectenna site; microwave interactions with the atmosphere; and the possible effects of the microwave beam on atmospheric electrification processes. The following brief summary highlights the most important issues. Rectenna Waste Heat and Structure. Construction of a rectenna would modify the thermal and radiative properties of the ground on which it is built; operations would introduce a heat source at the surface. Although the magnitude of the perturbation of the average surface heat budget would be on the order of
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