An assessment of multiparameter radar rain rate algorithms using an optimal area approach

An optimal area method is described which is used as a basis for comparing Kdp, (Kdp,Zdr) and Zh based estimates of rain rates with gauge measured rain rates. This method differs from conventional methods which typically use a square L×L area centered on the gauge. The spatial structure of the rms error field, which is the difference between Kdp-based rain rate and gauge-measured rain rate is used in an objective manner to define the optimal area over which the radar data is averaged; additionally, an optimum time delay is calculated. Three convective rain events (with pea-to-marble sized hail) are analyzed using the data from the CSU-CHILL Radar and gauge data. In two cases, a young capacitance rain gauge installed in a chase van was used to record rainfall. The chase van was directed by radar for storm cell intercepts. Another radar algorithm using the principle of the optimal area was also developed relying on radar data only. In this algorithm radar data from different elevation angles are used to arrive at an optimal area and time delay. These rainfall estimates are then compared with gauge reports to provide an independent measure of accuracy and assessment of the various rain rate algorithms