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<br />3. DATA SOURCES <br /> <br />3.1 WSSI Photographic Replicator <br /> <br />, <br /> <br />The photographic ice-crystal replicator designed and built by WSSI to <br /> <br />obtain the ice-crystal data necessary for this investigation is shown in <br /> <br />Figure 1. It consists of a modified 35-mm radar camera mounted over a <br /> <br />moving black velvet belt. The belt carries the ice crystals from an <br /> <br />adjustable settling area to the camera where they are photographed auto- <br /> <br />matically. The belt is continually cleaned with a rotating brush on the <br /> <br />underside of the instrument. The belt moves at a rate of slightly less <br /> <br />than 8 centimeters per minute, and the slit width at the settling area <br /> <br />can be varied from 2.5 to 7.5 centimeters. The camera can be set to <br /> <br />photograph one frame per minute, three frames per minute, or six frames <br /> <br />per minute. At six frames per minute, the frames overlap so that about <br /> <br />half of anyone frame has already appeared in the previous photograph. <br /> <br />In addition to the crystals, a frame number, a clock, and an information <br /> <br />slate appear on one side of each photograph. A typical frame from the <br /> <br />photographic replicator is shown in Figure 2. The optics of the camera <br /> <br />are adjusted so that the ice crystals appear 0.52 times actual size on <br /> <br />the film and particles down to 50 microns can be identified. The camera <br /> <br /> <br />holds 100-foot rolls of 35-mm high resolving microfilm, allowing data to <br /> <br /> <br />be taken continuously for over 24 hours when set to photograph one frame <br /> <br /> <br />per minute. <br /> <br />-6- <br />