Laserfiche WebLink
<br />SECTION 11. - PHOTOCELL GRAPH <br /> <br />A photocell placed at the end inside a yard-long b"lack PVC pipe looked at two <br />120 watt floodlamps mounted in a spruce tree north of the GMO. The system <br />usua lly funct i oned as a transmi ssometer, but some dayl i ght usually increased the <br />signal. The photocell output was recorded by a Rustrak strip chart on a <br />pressure sensitive paper. The photocell system was operated from the roof of <br />the GMO. <br /> <br />The graphs from this photocell identify daytime cloud types by the te>ttures, <br />shapes, and intensity levels. Clouds of some type were present most days. <br />Middle and upper level clouds produce slowly varying graphs. ScatterE!d and bro- <br />ken stratocumulus result in a graph rapidly varyin91 between very bright and <br />darker blue sky values. At night a constant signal is cr~ated by the <br />floodlamps. Periods of obscurration (fog-cloud, precipitation) lessened the <br />signal. Sometimes blowing snow clogged the PVC tube and created a low signal <br />until the snow was removed by hand or by melting. Toward the end of the season <br />the photocell began malfunction'ing like last winter, possibly from microcracks <br />from thermal stress. Analysis of the data will therefore require great care. <br />No summary of useful dates is provided because it is not yet clear which por- <br />tions of the data are without fault. Part of the photocell and time-lapse <br />camera vi ews overlap. <br /> <br />11-1 <br /> <br />__L__ ~__~ <br />