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Last modified
1/25/2010 6:27:28 PM
Creation date
10/4/2006 11:48:58 PM
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Floodplain Documents
County
Statewide
Basin
Statewide
Title
Sensitivity of WSR-88D Rainfall Estimates to the Rain Rate Threshold and Rain Gauge Adjustment: A Flash Flood Case Study
Date
6/8/1998
Prepared By
NOAA
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />procedure is working. It is the ratio of the number of second-tilt reflectivity bins used in the <br /> <br />hybrid scan relative to the total possible number of bins. Since bi'scan maximization was <br /> <br />disabled in these PPS runs, the CBR remains at 0.0 throughout almost the entire event indicating <br /> <br />that first tilt reflectivity bins were used, A CBR of 1,0 means that only second-tilt reflectivity <br /> <br />bins are used in constructing the hybrid scan which was the case for the first few volume scans <br /> <br />when the percent echo area reduction (Fig. 5b) exceeded the threshold value of75%. Recall <br /> <br />however that over the Buffalo Creek basin, the second tilt reflectivity bins were used exclusively. <br /> <br />Hourly time series of a) computed gauge-radar multiplicative bias estimate (GIR), b) <br /> <br />mean square error of the bias estimate, c) total number of available gauge-radar pairs, and d) the <br /> <br />number of pairs used in the Adjustment algorithm's Kalman filter procedure after automated <br /> <br />quality control are illustrated in Fig. 6. Even though as many as 31 gauge-radar pairs (out of a <br /> <br /> <br />maximum possible 50) were available for any hour during the period, only at most 17 pairs <br /> <br /> <br />passed the two quality control steps of the PPS for any given hour (Figs. 6c and 6d). In order for <br /> <br /> <br />a gauge-radar pair for a given hour to pass quality control, the hourly gauge and radar rainfall <br /> <br />must both exceed 0.6 mm (i.e., it must have rained), and the difference between the gauge and <br /> <br />radar amounts must not exceed 2.0 standard deviations of the mean difference for all gauge-radar <br /> <br />pairs for that hour (Fulton et al. 1998). A minimum of six pairs must pass the quality control <br /> <br />steps in order for a bias to be estimated for that hour, <br /> <br />Due to an insufficient number of pairs, a bias estimate was not computed until hour 2550 <br /> <br />(0150 UTC 13 July) valid for the hourly period 2400-2500 UTC. Before this time, the bias <br /> <br /> <br />estimate is simply the default value of 1.0 implying no bias. However, after that, bias estimates <br /> <br /> <br />are computed for each of the next six consecutive hours until hour 3150 UTC when the number <br /> <br />9 <br />
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