2002 Annual

Tuesday, 15 January 2002: 3:59 PM
Censoring for Overlaid Echo Leakages in Phase-Coded WSR-88D Data
Shel Gerding, NCAR, Boulder, CO; and G. Meymaris, S. Ellis, and C. Frush
Weather radars, such as the WSR-88D, can use Doppler returns to measure received power, velocity and turbulence of the atmosphere. Long pulse repetition time (PRT) signals can effectively measure power to several hundred kilometers, but are restricted by velocity folding in accurately measuring velocities. Short PRT signals can more accurately measure velocities, but have a shorter unambiguous range. Short PRT return signals can also be plagued by second, and sometimes third, trip echos interfering with the signals of interest. In current NEXRAD radars, the long PRT power is used for censoring for overlaid echos in short PRT data. Censored regions are indicated by "purple haze" in WSR-88D products. Phase-coding the radar's transmitted waveforms enables returns from different trips to be decoded and reconstructed in the frequency domain. Phased-coded signals have the advantage of having a larger effective range and larger unambiguous velocity range. One of the advantages of using phase-coded radar signals is that data quality is improved and purple haze is reduced. Ideally, phase-coded short PRT signals can provide all the information that the long PRT signals can, plus improved velocity estimates, since less velocity folding occurs when the unambiguous velocity range in increased. Unfortunately, leakages from overlaid echos can occur due to imperfections in the reconstruction methods and the interactions between radar returns. For phase-coded radars to be used effectively, these leakages need to be objectively identified and the corresponding power and velocity estimates need to be censored.

In this paper, censoring methods for overlaid echo leakages in phase-coded radar velocity and power estimates are explored. Two potential indicators of leakages are spectrum width and local standard deviation of the velocity field. The studies presented here use data from the National Severe Storm Lab's (NSSL) KOUN NEXRAD radar in Norman, OK, USA. The long PRT data corresponds to the first two trips in the phase-coded short PRT data. To evaluate the censoring techniques, objective measures of quality, such as the difference in velocity estimates between the phase-coded short PRT data and the long PRT data, are used. The final goal is a recommendation for a censoring technique for phase-coded.

Supplementary URL: