2002 Annual

Tuesday, 15 January 2002: 3:59 PM
Overview of Range and Velocity Ambiguity Mitigation using the SZ(8/64) Phase Code
Scott Ellis, NCAR, Boulder, CO; and G. Meymaris and C. Frush
Recently, much progress has been made towards the mitigation of the range and velocity ambiguities of weather surveillance radars. The problem is the fact that the unambiguous range increases with increasing pulse repetition time (PRT), while the unambiguous, or Nyquist, velocity decreases with increasing PRT. Therefore, adjusting the PRT to obtain a desirable unambiguous range results in a small Nyquist interval and severe velocity folding. Conversely, a PRT that provides an adequate Nyquist interval delivers unacceptably short unambiguous ranges, resulting in inadequate area coverage and increased multiple trip contamination.

One proposed solution is to phase-code the transmitted signal, enabling the recovery of multiple trip data by re-cohering for the desired trip while suppressing the other trip echoes. Recovering data in both the first and second trips will double the range at a particular PRT, allowing use of short PRT values that provide large enough Nyquist intervals for useful velocity measurements while attaining the desired area coverage. In general, it possible to recover numerous trips. Taking full advantage of this technique requires spectral domain processing, which is not currently available on the WSR-88D radars. Phase-coded time series data has been collected from the KOUN testbed radar in Norman Oklahoma and the recovery technique has been evaluated off-line. This paper will present an overview of the phase coding techniques with emphasis on the processing filter notch width, the spectral reconstruction techniques and censoring of data not meeting some data quality criterion.

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