Range and Velocity Ambiguity Mitigation on the Wsr - 88 D : Performance of the Sz - 2 Phase Coding Algorithm

It is well known that for Doppler radars transmitting uniformly spaced pulses there is a coupling between the unambiguous range (ra) and unambiguous velocity (va) given by rava = cλ/8, where c is the speed of light and λ is the radar wavelength. As shown by this relation, ra or va can only be increased at the expense of a proportional decrease of the other. Because range and velocity ambiguity problems are coupled, this is a fundamental limitation: trying to overcome one tends to worsen the other. The Radar Operations Center of the National Weather Service has sponsored the National Severe Storms Laboratory (NSSL) and the National Center for Atmospheric Research (NCAR) to develop methods for mitigating the effects of velocity and range ambiguities on the WSR-88D. In a joint effort, NSSL and NCAR have recently recommended an algorithm for the initial deployment of range and velocity ambiguity mitigation techniques on the Open Radar Data Acquisition (ORDA) subsystem. The algorithm, referred to as SZ-2, is based on systematic phase coding that uses the SZ(8/64) code and will replace the Doppler half of split cuts at the lowest elevation angles of the antenna beam. This paper shows the performance of the SZ-2 algorithm on weather data collected with NSSL’s KOUN radar in Norman, OK. Comparisons with existing “legacy” algorithms demonstrate the ability of the SZ-2 algorithm to effectively mitigate range and velocity ambiguities in future enhancements of the NEXRAD radar network.