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Dynamic Calibration of Tipping-Bucket Rain Gauges Investigators
Introduction Tipping-bucket rain gauges (TBRs) are widely used within the United States and abroad because they are simple and durable. Before being used, the TBRs should be calibrated. There are two methods of TBR calibration commonly used: static and dynamic. Static calibration methods assume that the volume of water needed to cause the bucket to tip is independent of the rainfall rate. However, this will result in "undercatchment" (underestimation) of rainfall rate and total amounts (see reference). By contrast dynamic calibration methods account for the undercatchment by calibrating when the buckets are in motion. In dynamic calibration, true rainfall rates are compared to the rainfall rates that are computed from applied flow rates and the rain gauge diameter and bucket volume (measured rates). Thus the dynamic calibration accurately reflect the relationship between the true and measured rates of rainfall. Dynamic calibration is time-consuming hence an automated TBR calibration is desirable. Method The calibration system consists of a personal computer, a programmable pump, a digital scale, a water tank and some wires and elastic pipes (see equipment). The computer environment is DOS 6.2. Two computer programs: PUMPCAL and TIPCAL control the calibration process. The input parameters for calibration are stored in an ASCII file named pump.seq. The dynamic calibration is performed in two steps.
The ASCII files pump01.cal and gauge01.cal are used as the inputs of post-data analysis. The post-data analysis is done in Microsoft Excel® with Programmed Macro Code. The data and graphs can be used for further analysis. Sample Results
M. D. Humphery and J. D. Istok et al, "A New Method for Automated Dynamic Calibration of Tipping-Bucket Rain Gauge", Journal of Atmospheric and Oceanic Technology, Volume 14, Dec, 1997, pp. 1513-1519. |
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