Eighth Symposium on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, and Land Surface


Field Measurements of temperature sensitivity in Geonor vibrating-wire transducers

Claude E. Duchon, University of Oklahoma, Norman, OK

The primary instrument for measuring precipitation in the United States Climate Reference Network (USCRN) is the Geonor vibrating-wire weighing-bucket gauge. A gauge can have 1 to 3 vibrating-wire transducers, each transducer producing an audio signal in proportion to the accumulated mass (mixture of water, antifreeze, and oil) in the bucket. For a fixed mass in the bucket the audio signal recorded by each transducer changes in response to the temperature of and, perhaps, the temperature gradient in the transducer. The coefficient of accumulation (frequency) with temperature is negative, i.e., an increasing temperature results in a decreasing accumulation (frequency).

When there is no precipitation, daily plots of 1-minute accumulation versus temperature measured inside the gauge typically show an elongated elliptic pattern as a consequence of the frequency associated with the apparent accumulation lagging behind the temperature variation. Analysis of the data shows that the frequency of accumulation is much more sensitive to temperature when the bucket is relatively full compared to when is relatively empty. For example, when there are 500 mm in the bucket the coefficient is about -0.14 mm/10 C (-0.0055 inch/10 C) versus 0.05 mm/10 C (-0.0020 inch/10 C) when the accumulation is 75 mm. While these figures strictly apply to the average of the particular set of 3 wires evaluated and average daily gauge temperatures between 25 and 30 C, it is expected that the coefficients apply to Geonor vibrating wires, in general. The presentation also will include temperature sensitivity comparisons for individual wires and gauge temperatures as low as 0 C.

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Session 4, Atmospheric Observations: Part Two (Room 618)
Tuesday, 13 January 2004, 8:30 AM-2:45 PM, Room 618

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