National Weather Service forecasters have been requesting radar scanning strategies, or volume coverage patterns (VCPs), for the WSR-88D that are faster and that have denser far-range coverage at lower elevation angles. In response to these requests, the Radar Operations Center and the National Severe Storms Laboratory are developing new VCPs to replace the four existing VCPs 11, 21, 31, and 32. The proposed new scanning strategies are tentatively called VCPs Alpha, Beta, Gamma, Delta, Epsilon, and Zeta. After successful testing, VCPs Alpha, Beta, and Gamma were recommended for implementation into the WSR-88D by the WSR-88D Technical Advisory Committee in August 2000. The other three VCPs currently are being tested.

VCP Alpha (9 unique elevation angles from 0.5-4.9 deg in 10 min), using a long-pulse mode, is intended for clear air measurements. VCP Beta (12 unique elevation angles from 0.5-8.1 deg in 5 min) is designed to sample shallow convection. VCP Gamma (14 unique elevation angles from 0.5-19.5 deg in 4.1 min) is a faster and denser (at lower elevation angles) version of VCP 11 designed to sample deep convection. VCP Delta (tentatively completing 6 unique elevation scans from 0.5-6.5 deg in 2.3 min) permits scanning of fast-evolving damaging events such as tornadoes and microbursts. The lower elevation angles in VCPs Alpha-Delta are separated by about 0.5 deg, as compared to the conventional 1.0 deg.

VCPs Epsilon and Zeta, modified versions of VCPs Gamma and Delta, are designed to be used in situations having Doppler velocity aliasing problems. VCP Epsilon tentatively completes 12 unique elevation angles (0.5-19.5 deg) in 5 min, while VCP Zeta tentatively completes 5 unique elevation angles (0.5-6.5 deg) in 3.3 min. For both of these VCPs, the elevation increment between the three lowest elevation angles is about 0.8 deg. At each of the lowest three elevation angles, reflectivity along with three Doppler velocity scans are measured; each Doppler velocity scan has a different pulse repetition frequency (PRF). At each of the remaining elevation angles, the customary reflectivity and Doppler velocity at a single PRF are measured. An algorithm uses the multiple PRF measurements at the lowest three elevation angles to deduce the most likely Doppler velocity values. VCPs Epsilon and Zeta provide an interim solution until a multiple PRF capability is incorporated into the WSR-88D.