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<br />- 60 - <br /> <br />these requirements well and which is therefore used at the distrometer site in PEP, is <br />the tipping bucket raingauge described by Joss and Tognini (1967). The instrument is shown <br />schematically in Fig. 14. The tipping bucket has a volume of 2 cm3 and the collecting sur- <br />face is 200 cm2 resulting in a resolution of 0.1 mm of precipitation. The sy~tem's collector <br />ring and funnel are heated independently so that the power necessary to hold; the funnel at <br />a temperature above zero allows to distinguish between liquid and solid precipitation. Each <br />tipping of the bucket is recorded by a reed contact and printed out together: with time. The <br />time between failure for 20 instruments installed at different altitudes in Switzerland has <br />been determined to be over one year. <br /> <br />An example of the cross-check between the data obtained from this tipping bucket in- <br />strument and the raindrop spectrometer will be demonstrated at the workshop~' <br /> <br />Snow measurements are inherently difficult because the wind and icing problems are even <br />more acute than with rain measurements. Site selection and installation of the snow meas- <br />uring instruments must be done with utmost care. The most common instruments are a pole or <br />a snow ruler from which the daily (or seasonal) depth of accumulated snow can be read di- <br />rectly. For many purposes the water equivalent of new snow (in mm H20) must be known. A <br />common method, apart from a raingauge which is heat~d or provided with another melting a- <br />gent such as CaC12' is used in the snow sampler. A snow sampling tube (~ 500' cm3) is bored <br />through the snowpack and a depth measurement is obtained. Then the tube is extracted and the <br />snow contained in the tube weighed or melted to yield the water equivalent. Normally many <br />samples are taken at different predetermined points separated by distances of the order of <br />30 m in a representative area. In recent years, new methods based on the pre~sure exerted <br />by the snowpack on a pillow or on the absorption of gamma radiation from a cobalt probe on <br />theground, have been developed for the time-resolved measurement of snow. To assess the <br />accuracy and comparability of snow measurements is ~omplex and the reader is referred to <br />the literature (Struzer, 1969; Larson and Peck, 1974; Goodison, 1978, and references there- <br />in). <br /> <br /> <br />Fig. 14: Tipping bucket raingauge RG 200.2 <br />(Joss and Tognini, 1967). HI and H2 are <br />heating coils, Fl' F2 tsmperatwre sensors, <br />W is the tipping bucket of 20m3 and E the <br />electronics cabinet. <br /> <br />~ <br />