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Application of the SZ Phase Code to Mitigate Range–Velocity Ambiguities in Weather Radars

C. FrushNational Center for Atmospheric Research, Boulder, Colorado

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R. J. DoviakNational Severe Storms Laboratory, Norman, Oklahoma

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M. SachidanandaIndian Institute of Technology, Kanpur, India

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D. S. ZrnićNational Severe Storms Laboratory, Norman, Oklahoma

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Abstract

It has been demonstrated through simulations that the SZ phase code method of mitigating range ambiguities has a performance that exceeds any other known phase-coding scheme. This paper describes an implementation of this code on a weather radar and compares its performance with that derived from simulations. Spectral data obtained from NCAR's S-Pol radar, which had its transmitted phases coded with the SZ(8/64) switching code, are presented to illustrate the steps in this method. It is shown that fully coherent transmitters, such as that used in the U.S.'s WSR-88D weather radars of the National Weather Service, have a system phase stability that takes full advantage of the unique properties of the SZ-coding method. The performance of this coding technique is evaluated by implementing it on a research WSR-88D weather radar. Results verify the dramatic increase in the area of reliable velocities compared to that provided by techniques presently employed in the operations. The performance of the SZ algorithm to retrieve weak signals overlaid by stronger signals is evaluated in the spectral domain by comparing a subjective analysis of the data field where the two overlaid echo spectra can be visually separated and mean Doppler velocities calculated.

Corresponding author address: Dr. Richard J. Doviak, National Severe Storms Laboratory, 1313 Halley Circle, Norman, OK 73069. Email: dick.doviak@noaa.gov

Abstract

It has been demonstrated through simulations that the SZ phase code method of mitigating range ambiguities has a performance that exceeds any other known phase-coding scheme. This paper describes an implementation of this code on a weather radar and compares its performance with that derived from simulations. Spectral data obtained from NCAR's S-Pol radar, which had its transmitted phases coded with the SZ(8/64) switching code, are presented to illustrate the steps in this method. It is shown that fully coherent transmitters, such as that used in the U.S.'s WSR-88D weather radars of the National Weather Service, have a system phase stability that takes full advantage of the unique properties of the SZ-coding method. The performance of this coding technique is evaluated by implementing it on a research WSR-88D weather radar. Results verify the dramatic increase in the area of reliable velocities compared to that provided by techniques presently employed in the operations. The performance of the SZ algorithm to retrieve weak signals overlaid by stronger signals is evaluated in the spectral domain by comparing a subjective analysis of the data field where the two overlaid echo spectra can be visually separated and mean Doppler velocities calculated.

Corresponding author address: Dr. Richard J. Doviak, National Severe Storms Laboratory, 1313 Halley Circle, Norman, OK 73069. Email: dick.doviak@noaa.gov

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