c. Bird Exposure There is evidence that birds can be affected at levels of the order of 25-40 mW/cm2 at least at X-band, with pulsed radiation. The evidence suggests an avoidance reaction by birds. Such effects could possibly be exploited to inhibit birds from flying into the receiving antenna area. On the other hand, birds may be attracted by a possible pleasant warming sensation of microwave radiation at least in some climates. More research would have to be conducted to more clearly determine effects of microwaves on birds before deciding the best choice of system parameters for minimum interference of and by birds. d. Aircraft Passenger Exposure The possible effects of microwave exposure on aircraft flying through the beam must be considered. Excessive body exposure to aircraft occupants is unlikely because of the shielding effect of the metal fuselage. Nevertheless, studies would be required to confirm the absence of peculiar focusing effects within the aircraft. The limited duration of flight through such a beam would support the likelihood of no serious problem with regard to human safety from radiation effects. e. Atmospheric Attenuation An investigation of the atmospheric attenuation of power from the main power beam was conducted to determine the attenuation in the four SSPS ground locations under investigation, to compare them with each other, and to recommend a frequency for SSPS power transmission and ground reception for a satellite orbital location at the stable node near 123° West in synchronous equatorial orbit. The three major inputs for the investigation were as follows: (1) The atmospheric attenuation of microwave power equations and the computations for specific conditions were taken from Reference 39* and additional data were obtained from the files of Dr. Vince Falcone, AFCRL, as well as from References 40 and 41. (2) Rainfall' rates, as reported in Reference 42, based upon the procedures of Reference 43, using as basic data Reference 44 with comparative and general information from References 43, 45, 46 and 47 and the files of Mr. Norman Sissewin and associates at AFCRL. ‘An extension of the work in the above reference as applied to analysis of microwave attenuation is based on analytical procedures developed by Dr. Falcone of the AFCRL, Microwave Physics Branch, Bedford, Massachusetts.
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