Laboratory studies of a vibrating wire precipitation gage

A series of laboratory and field experiments were made in an effort to identify calibration issues associated with the use of vibrating wire (VW) transducers for measurement of precipitation. To determine the magnitude of hysteresis, two Geonor T-200 weighing-bucket precipitation gauges, each with three vibrating wires, were placed in a temperature-controlled chamber. Measurements of VW frequency and equivalent "precipitation" were made for various combinations of temperature cycle times (minutes to hours), temperature range (as large as + 30 C to – 30 C), and bucket amount (empty to nearly full). In general, the tests show that the precipitation error is sensitive to all three parameters as well as the particular VW transducer. To make a useful evaluation, it is important to keep the test conditions in line with natural variations in temperature. Thus, field tests under dry atmospheric conditions were performed at a site south of Boulder, CO. In addition, comparisons of precipitation rate and accumulated precipitation in actual rain and snow events were made using a variety precipitation gauges and wind shields. The results of these experiments will show current and future users of vibrating wire methodology for measurement of precipitation some of its strengths and limitations based on our investigation of the Geonor T-200. The results also will be used to help determine the optimal precipitation gauge and wind shield for NOAA’s new Climate Reference Network.