FLOOD03496 - Laserfiche WebLink

Home Browse Search

of pairs falls again below the minimum required number of six. The computed bias estimates from the Adjustment algorithm range between 1.00 and 0.96 during this period (Fig. 6a) based on 7-17 input gauge-radar pairs (Fig. 6d) and indicate that the radar estimates are in very good agreement with. the gauge measurements. Hourly scatter plots of gauge-radar accumulations are shown in Fig. 7. Filled (open) circles represent gauge-radar pairs that passed (did not pass) the quality control steps. Ifless than six pairs were available for any given hour, all of those pairs will be indicated as open circles for that hour implying that a bias could not be computed. The time of bias estimation (in decimal hours UTC) is indicated at th'e top of each panel and is nonnally at or shortly after H+50 minutes. For example, the first panel shows a time of 19,912 UTC (=1955 UTC) and represents the gauge., radar pairs valid for the hourly time period from 1800-1900 UTe. For the six-hour period from 25.886 to 30,85 UTe when gauge-radar bias estimates were computed by the algorithm, the gauge-radar pairs fall along or very close to the diagonal line. The multiplicative bias estimates deviate, at most from 1.0 at hour 28.902 with a bias estimate of 0.96, indicating slight radar overestimation relative to the gauges for that hour. Thus the PPS seems to be yielding accurate estimates of the accumulation compared to the available hourly rain gauges. 5. Impact of the method of forming gauge-radar pairs Because the neat alignment of points in Fig. 7 seemed unusually good, the method for fonning the gauge-radar pairs within the algorithm was examined in greater detail for this case. The first step in the PPS Adjustment algorithm is the pairing together of hourly gauge and radar rainfall estimates. The algorithm examines the radar estimates for the nine (3x3) polar grid bins 10