Improving the Quality of Dual Polarization Estimates with Multiscan Data Hybridization

Altering the temporal separation between radar samples exercises the ambiguity tradeoff known as the Doppler dilemma. Relatively long pulse repetition times (PRTs) reduce the occurrence of range ambiguities, while short PRTs extend the Nyquist interval and reduce velocity ambiguities. The WSR-88D volume coverage patterns employ scans at lower (less than 7 degrees) elevation angles that make use of long and short PRTs. Split cut scans collect two, 360 degree scans with the first using the long PRT and the second using the short PRT. Batch mode scans collect both long and short PRT data within each radial for a single 360 degree scan. The purpose of employing both long and short PRTs is to obtain measurements that maximize the physical extent of the data collection and reduce the occurrence of velocity aliasing, respectively.

The recently added dual-polarization capabilities for WSR-88D radars produce estimates that are calculated using samples collected with both the long and short PRT scans in the split cut mode. While dual-polarization estimates do not benefit from the short PRT in the same way radial velocity does, a general improvement in the statistical accuracy and ground clutter filter performance is observed due to the increase in the number of samples. It is therefore advantageous to combine the measurements obtained over the range extent of the long PRT with the more accurate short PRT data. Given the range ambiguities associated with the short PRT, it is necessary to account for the possibility of overlaid echoes and the statistical deterioration that can occur in such cases. In this work, criteria for determining the appropriate power thresholds for use of the short PRT for combined split cut PPIs in the event of overlaid echoes are explored through the use of simulations. Results for a variety of meteorological scenarios are used to identify and evaluate appropriate thresholds. Recommendations stemming from and analysis of the simulation output will be presented, and it is anticipated that the use of the hybridization technique will improve the statistical properties of base moment data, and therefore improve WSR-88D dual-polarization data quality.