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16 Figure 19.-Bigg-Warner Nuclei Counter. Lodge, figure 19. This equipment belongs to Col- orado State University and is operated by a CSU observer. Readings have been made at 0900 and 1800 each day for almost 2 years as a control on CSU operations at Climax, Colo. Additional read- ings were made when special conditions warranted. Precipitation Measurement Equipment Before outfitting the network with snow sensors, we conducted a I-month evaluation test of all sensor types at the laboratory. The test area contains: 3 unshielded 3 ft? snow-boards at 2, 6, 12 foot heights, I shielded 3 ft? snow-board at 6 foot height, 1 compressed-scale weighing gage, 1 snow-pillow with electronic readout, 1 heated tipping-bucket snow-rate gage, 1 tipping-bucket rain-rate gage. and 2 optical snow-rate gages. As a result of this evaluation, we chose the optical snow-rate gage for the measurement network; our PARK RANGE ATMOSPHERIC WATER RESOURCES PROGRAM conclusions regarding all types can be summarized as follows: In our laboratory location-which experiences little wind-the height of the snow-boards made little differ- ence, but the shielded snow-board always had the highest recovery when any wind was present. The shielded snow-board always recovered more water than any other sensor, except the optical gage which was calibrated against the snow-board. The difference be- tween snow-board and sensor water recovery was often of the order of 30 percent. The compressed scale weighing gage-l inch H20 full scale with a 1 inch antifreeze charge-proved highly re- liable and relatively accurate for total precipitation measurements. It has almost no value for determining precipitation-rate. The snow-pillow-with pressure transducer and electronic readout-performed reliably, but inaccurately due to bridging. Full scale output of the readout recorder is 0.5 inch. H20-the output wave form approximates the actual rate only when rates are very high. So long as no bridging was present, the output reading was about as accurate as the compressed-scale weighing gage. The heated tipping-bucket gage performs accurately and reliably for snow rates greater than about 0.02 inch H20/hr. and less than about 0.15 inch H20/hr. and for ambient temperatures greater than about 100 F. The tipping bucket rain-rate gage operates well under rates of up to 10 inches H20 (hr.; this has been confirmed by data taken during Oregon coast storms. The optical snow-rate' gage is reliable, has an instantane- ous threshoTd of 0.01 inch H20/hr. and a full scaTe range of 0,3' inch H20/hr.-as calibrated against the shielded snow-board and short-time samples taken with poly- ethylene sheets. Full scale range can be increased to 1 inch H20fhr. by an internal adjustment. J Shielded and unshielded snow-boards are ply- wood, painted white. Shielding of one snow-board is provided by 4-foot snow fencing mounted 2 feet from the board and projecting 3 feet above it, figure 20. The compress~d-scale weighing gage, figure 21, is a standard 12 inch H20, dual traverse, Belfort gage with drum readout, but modified to have an aperture about six times that of the original. Each traverse of the pen is 1.2 inch H20 giving-with a 1 inch anti-freeze charge-a weighing potential of about 1 inch of water. The gage has worked per- fectly since installed. Figure 22 is an example of the data readout. The snow-pillow, figure 23, is 12 feet in diameter and filled with 65 percent methanol and 35 percent water. Readout is by means of a 0-2 psi (55 inches H20), infinite resolution pressure gage whose out- ~