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10 47. At the opposite end of the scale of complexity from snoHboards are satel- lite ob8ervations of :mowpack. Although studies of the utility of satellite photo- graphs as a means of snow' surveying have been carried Ollt, present re:301utions are most useful for qualitative asseSDments of snow storago. A quite comprehensive report on the operational applications of satellite snowcover observations has been published (Rango, 1975). Although most of the \-lork reported. concerns use of photo- graphic observations made from LAITDSAT and NOAA sa telli tes, efforts to infer sno\-lpack density from shortHave radiation data are also discussed (HcHillan and. Smith, 1975). Satellit~ telemetry can play a useful role in acquiring precipitation data from remote areas (Kahan, 1976). 48. A related remote sensing approach using airbo:rne detection of natural terrestrial gamma radiation which is subject to attenuation by snOWCO'ier has been investigated in the Soviet Union (Kogan, et a1., 1965) and in the United States (PeCk, et al., 1971). 49. Snow gauges \-[hich operate on the princ:iple of detecting the transmitted radiation from a radj,oactive SOUTce in the 'snol'Tpack have been developed (Sm:Lth and Willen, 1966) and are proving useful in practical 8.1)plica tions, If combined with on-site data processing equipment and telemetry, they make possible remote monitor- ing of changes in the makeup of the snol'1pack. 50. The accuracy of the various sensors available for measuring snow has been studied by the California Cooperative SnO"\'1 Surveys Program since 1965 at the Alpha Instrument Evaluation Site (Peterson and Bro'wn, 1975). A comprehensive diseussion of the evaluations has been ,given by Bro,'ln, et a1. (1976). VII ANCHURY HYDROLOGICAL CONSIDERATIOli'S 51. There are hydrological aspects of precipitation enhancement that need to be considered .rhether or not streamflow data are to provide the basis for evaluation. There are impacts on the environment due to heavy precipi ta tion .rhich are aecepted as the natural course of events until the time that someone uBdertakes to increase the precipitation artificially. }'rom that moment on, any inconvenient "\'leather is apt to be associated l'Tith the cloud-seeding effort in the minds of the inconvenienced. If the impact goes beyond inconvenience, to the point of hazard or damage, it is quite possible that legal proceedings I'rill be initiated. If redress of the perceived I...rong is not achieved through legal means, sabotage of field equipment used in the cloud- seeding project becomes an attractive alternative. It really does not matter "\'lhether the weather event being objected to \,;as actually associated with cloud-seeding or not, the attitude of some persons affected is apt to be the same unless there has been, in advance, an aggressive programrne to ensure both safe operation and effective communication about the safety of the cloud-seeding operation. 52. To this end, planners of precipitation enhancement programmes are well advised to Ul""1dertake assessments of the nature of impacts that heavy precipitation may have, both inside and outside the target area. These impacts include avalanch- ing, mudslides, elevated soil moisture values, excessive sediment t:cansport, and damaging flooding. Suspension of cloud-seeding activities "\ihenever heavy prec,ipi ta- tion can be expected to produce hydrological impacts requires the prior establishment of monitoring systema and identification of criteria for making the decision to suspend. The more a,fare the affected public is of the existence of these criteria and the more involvement respected local people have in the decision-making process to invoke suspension, the greater the pl'obabili ty of trouble-free operation of the precipitation enhancement programme.