HOW DOES THE RADAR COLLECT DATA?

To adequately sample the atmosphere the WSR-88D employees several scanning strategies or volume coverage patterns. A Volume Coverage Pattern (VCP)is a series of 360 degree sweeps of the antenna at selected elevation angles completed in a specified period of time. Four separate scan strategies are used now with the possibility of others being implemented in the future.

Volume Coverage Pattern 31 (VCP 31) is a clear air mode strategy and is used to detect early formation of convective precipitation, air mass discontinuities and to obtain wind profiles. It uses a long pulse and sweeps 5 elevation angles in 10 minutes. There are separate surveillance and doppler scans on the lowest three elevation angles.

Volume Coverage Pattern 32 (VCP 32) is the same as VCP 31 but uses a short pulse wave.

Volume Coverage Pattern 11 (VCP 11, Severe Weather) is a precipitation mode strategy. VCP 11 uses a short pulse wave and sweeps 14 elevation angles in 5 minutes. The radar uses separate surveillance and doppler scans at the 2 lowest angles (i.e. the two lowest elevation angles are scanned once for reflectivity and a second time for velocity. A combined waveform is used at higher elevation angles). The lowest seven angles are contiguous. The resulting data are used in algorithms to determine storm tracks, shear and mesocyclones. Other algorithms compute precipitation amounts and wind profiles.

Volume Coverage Pattern 21 (VCP 21), a second precipitation mode strategy, is used to observe more distant storms; it uses a short pulse and sweeps 9 elevation angles in 6 minutes. There are separate surveillance and doppler scans at the two lowest elevation angles with the lowest five angles being contiguous.