In a recent survey of WSR-88D sites, operational staff indicated a desire for faster volume coverage patterns (VCPs) that also mitigate range aliasing. In 2004, the Radar Operations Center (ROC) fielded a new technique called the Multiple Pulse Repetition Frequency (PRF) Dealiasing Algorithm (MPDA) that combines three sequential Doppler scans with PRFs of about 1300, 1100, and 850 Hz, respectively, to mitigate range aliasing. Another technique to mitigate range aliasing, the Sachidananda-Zrnic phase coding algorithm (SZ-2), is being fielded in the summer of 2007. SZ-2 uses advanced signal processing to separate strong trip from weak trip signal. The two algorithms, when combined, recover an average of 98 percent of velocity area data out to 230 km. One major drawback with the combined technique is that a volume scan takes about five minutes and forty-five seconds to complete.

The ROC has investigated using two instead of three Doppler scans at each of the two lowest elevation angles. This is possible because the SZ-2 algorithm provides the bulk of the velocity recovery. Using two scans reduces the volume scan time about thirty seconds. Five data cases collected from the ROC's test bed WSR-88D were analyzed. Four cases with widespread precipitation were collected during the fall and winter 2006. The fifth case, a mesoscale convective system (MCS), was collected in June 2007. Using two instead of three Doppler scans yields an average velocity area recovery of 96.87 percent for the four widespread precipitation cases and 96.65 percent for the MCS case. Velocity dealiasing errors were also scored. Starting with a score of 100, points were deducted for different sized errors in the velocity field. For the widespread precipitation cases, using two instead of three Doppler scans decreased the number of errors slightly (0.045 percent decrease in errors); for the MCS there was a 1.70 percent increase in errors. These initial results support operationally fielding the combined algorithms with the middle (1100 Hz PRF) scan removed thus helping to meet the needs of radar sites.