NEXRAD Range and Velocity Ambiguity Mitigation

Significant strides have been made in development of techniques to mitigate range and velocity ambiguities which plague Doppler weather radars. Two complementary techniques, staggered PRT and SZ-2 phase coding, have been suggested and are undergoing tests. SZ-2 phase coding is proposed for the lowest two elevation scans and staggered PRT for the rest of volume coverage pattern.

Analysis and simulations indicate that phase coding cannot eliminate the long PRT scan for reflectivity estimation if the estimates must be unambiguous to 460 km. Phase coding is effective on uniform PRT sequences which are conducive to spectral analysis and good ground clutter filtering. Increase in clear range is at least twice the unambiguous range of the inherent uniform PRT, but not all overlaid echoes can be separated. Further, multiple overlaid signals might also cause total loss of information.

Staggered PRT can provide clear range and relatively large unambiguous velocity. But for large unambiguous range, the errors in spectral moments might be prohibitive. Tests are in progress to determine if a compromise between errors and dwell time exists such that a staggered PRT could be applied at the lowest elevations. The main disadvantage of staggered PRT is that ground clutter filtering is more complex (although as effective as filters based on uniform PRTs) and that spectral analysis, although possible, is severely impaired by the non uniform spacing of samples.

Herein we present images of reflectivity, Doppler velocity, and spectrum width fields obtained by processing time series data from the KOUN (research WSR-88D) radar. This radar can generate and process staggered PRT sequences. It can also produce phase coded sequences and decode signals from the first trip.

         Staggered PRT Technique

         SZ(8/64) Phase Coding Technique

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Last modified on 01/17/2012

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