changes in the local climate can not be excluded. Therefore the perturbation caused by the rectenna is comparable with the one caused by a large city. We recommend to conduct or review studies of existing cases were the perturbation induced are the same as for a 120 km2 rectenna. For higher frequencies the power density will be increased compared to 2.45 GHz and can therefore reach the same order as the natural net flux of radiation. In this case changes in the local climate are highly probable but will affect a smaller area as the rectenna size decreases with frequency. For laser transmission the power will be concentrated on a much smaller area than for microwave transmission. The heating of the receptor site can reach the same order as for a conventional large thermal power plant. The effects caused by the heating shall be compared with the ones of already existing power plants. Recommendations and Conclusions The studies conducted so far show no major environmental impacts in the case of the beaming of 5 GW from geostationary Earth orbit (GEO) to the Earth's surface at a frequency of 2.45 GHz, we can therefore recommend this frequency for general application in the field of power-beaming. For frequencies higher than 3 GHz the presence of water in the atmosphere causes a significant increase in the absorption and scattering of the radiation, therefore we recommend the use of 35 GHz only in very arid areas like deserts. The discussion for wavelength in the NIR-range is more complicated as the absorption-versus-frequency relation is more complex than in the microwave-range. There exist several narrow windows, but their application for power beaming depends on the availability of a suited laser-system. So far few studies on the effect of laser-beaming on the environment have been conducted. For further research we recommend the following steps: • Continue the theoretical work on the impact of microwave-beaming on the ionospheric plasma. • Build up a radio-wave heater for the ionosphere in the power range of a few GW, and investigate the impacts by backscatter radars . • Conduct detailed studies on the meteorological and climatic impacts of microwave and laser-beaming in the lower atmosphere region. 6.1.2 Electromagnetic Effects on Biota The only practical way for space solar power stations to get the energy they collect to Earth is via power beaming. The two primary means of power beaming under consideration today are lasers and microwaves. Both methods can potentially cause damage to the animals and plants around the receiving station. This section addresses a few of the potential problems. Designers of future power receiving stations will have to look carefully at these problems and find ways to mitigate any negative effects. Considerations for Laser Beam Usage The Effect of Laser Beam on Animal Retina and Iris The animal organ that is most sensitive to a laser beam is the retina. A laser beam which is coherent and parallel easily makes a small heat injury called a “Black Spot” on the retina. If a laser beam is weak enough so that it makes no injury on the retina, the beam will never be harmful to any kind of living organism. The location of the beaming satellite can be considered as an infinite distance in comparison with the size of an animal eye ball and the laser beam can be regarded as a parallel ray. Therefore in the worst case, when an animal eye focuses on an infinite distance and is illuminated with the beam, a light spot whose diameter is around its wave length will be made on the retina. Here we show the absorbency of a retina according to the wave length of the laser beam [Inaba et al. Laser handbook, Asakura Shoten, Tokyo, Japan],
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