Weather radar signal processing techniques

Mitigation of Range and Velocity Ambiguities for the NEXRAD Network

Range-velocity ambiguities on the legacy WSR-88D (top) and using the SZ-2 algorithm (bottom) (data collected with the KOUN radar on 10/08/02 1511 GMT)

In pulsed Doppler weather radars, the range and Doppler velocity ambiguity problems are coupled such that trying to alleviate one of them worsens the other. Thus, special techniques are necessary to resolve both ambiguities to the levels required for the efficient observation of severe weather. Efforts in this area are expected to culminate in significantly improved data quality. The increased data quality will result in an improved ability to detect severe weather, flash floods, winter storms, and provide aviation forecasts.

Over the last decade, two techniques have emerged as viable candidates to address the mitigation of range and velocity ambiguities in the WSR-88D thus reducing the amount of purple haze obscuration currently encountered during the observation of severe phenomena. These are: systematic phase coding (SZ-2) and staggered pulse repetition time (SPRT). The two techniques are complementary since they offer advantages at specific elevation angles; hence, they can be simultaneously incorporated into the same volume coverage pattern (VCP).

One of the major accomplishments on this project has been the NEXRAD Software Recommendation and Evaluation Committee’s (SREC) official approval of the SZ-2 and SPRT algorithms for inclusion in the ORDA. This was the result of successful technology transfer to the National Weather Service (NWS) Radar Operations Center (ROC) . The first stage of NEXRAD upgrades dealing with range and velocity ambiguities involved the operational implementation of the SZ-2 algorithm in 2007. The second stage deals with the operational implementation of SPRT, which is targeted for 2014.

As part of this project, we designed operational Volume Coverage Patterns (VCP) using SPRT and completed the analysis of a spectral clutter mitigation algorithm that can meet NEXRAD operational system specifications. Additionally, we introduced a range-overlaid recovery algorithm that allows increased range coverage of the Doppler moments in SPRT. Both, the clutter filter and the range-overlaid algorithms were merged into the algorithm as a complete SPRT solution capable of meeting NEXRAD operational needs.

In addition, we designed and tested a polarimetric SPRT algorithm, which will allow operational implementation of this technique after the entire fleet of WSR-88D radars is upgraded to dual-polarization. With the recommended changes, we have provided the NWS Radar Operations Center with a complete SPRT solution capable of meeting NEXRAD operational needs in the dual-polarization era.

For more information, please go to the R/V Ambiguity Mitigation webpage.

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