Some of these concerns appear to be groundless. However, it should be borne in mind that a recent review of the literature on biological effects of microwave exposure reached the following conclusion: "Only intensive experimental study can reveal whether the SPS concept safely can be implemented." On the basis of present information, and taking into account the fact that many of the studies of biological effects were done with pulsed radiation and therefore do not necessarily apply to the continuous wave emissions projected for the SPS, it is known that safety standards will have to be established. The same general prescription is, of course, applicable to all other objects likely to be impacted by SPS microwaves. However, it is probable that aircraft with passengers and cargo passing quickly through such a beam and birds in quick transit would not be adversely affected. No adverse effect on the ozone layer of the atmosphere is anticipated. Further research will be necessary to determine safety margins insofar as there is a possibility of harm to airspace and ecosystems. Measuring skills and equipment may have to be perfected since until the 1970s precise tools were lacking. Two areas of scientific measurement are critical to exposure standards. Densitometry is used to measure incident microwave D. R. Justesen, H. A. Ragan, L. E. Rogers, A. W. Guy, D. J. Hjeresen, W. T. Hinds, and R. D. Philips, "Final Report, Compilation and Assessment of Microwave Bioeffects: A Selective Review of the Literature on Biological Effects of Microwaves in Relation to the Satellite Power System," Department of Energy, Pacific Northwest Laboratory for Division of Solar Energy, PNL-2634, UC-41, p. xiii, May 1978. Stanislaw Baranski and Przemyslaw Czerski, Biological Effects of Microwaves, p. 183, 1976. Interim Guidelines, op. cit., pp. D-l, D-2, Figure D-l. See Annex to this Chapter.
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