convective or turbulent air motions a spectrum of atmospheric refractivity develops. These variations can lead to beam wandering and spreading. The scattering and absorption by hydrometeors depends on their size, shape, number concentration, and composition. If these properties are specified, calculations can be made of atmospheric attenuation and of the spreading of the beam. Contributions to beam wandering and spreading from the planetary boundary layer, cloud systems, jet stream turbulence and stratified atmospheric layers must all be considered. These atmospheric effects impact on the power beam and pilot beam stability problem. Slowly varying and drifting anomalies, large-area events, or numerous smaller-area anomalies in the power beam and the pilot beam cause spatial and temporal modulations that vary the illumination of the ground- based rectenna, and because of adverse geometry, cause large variations in pilot signal parameters. The latter have a strong potential for causing serious ambiguities in the control decisions and system stability considerations . These considerations impact on the waste heat releases assumed in the feasibility studies mentioned above. The most useful studies will vary the heat releases and affected areas by an order of magnitude to account for loss of control in worst-case situations. Studies should also include anomaly events appropriate to higher frequencies; in the 10 to 30 GHz range. Since the rectenna for these frequencies may be smaller than that of the 2.45 GHz system, the smaller anomalies become more directly important to fluctuation components. The higher frequencies would lead to increased atmospheric interactions, greater attenuation losses and refractive and scatter sensitivities. Direct interactions with the atmospheric electricity fields are not thought to be crucial at the 2.45 GHz frequency. However, the mere physical presence of the rectenna may have some modifying influence on the occurrence and electrical behavior of thunderstorms over and around the rectenna. The specific recommendations of the panel regarding research in the immediate future are to: 1. Conduct literature surveys and analytical calculations of the radiative and roughness characteristics of the
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