An operational triple-PRT Doppler scheme for the French radar network

Abstract

This paper presents the design and the test of an operational (staggered) triple-PRT (pulse repetition time) scheme that was implemented in July 2004 on the French operational C-band Trappes radar. The three interleaved pulse repetition frequencies (PRFs: PRF1, PRF2, and PRF3) that are used have the particularity to be very low and very close to each other (379, 325, and 303 Hz). The associated individual Nyquist velocities, VN1, VN2, and VN3, range between 4 and 5 m s-1 and the corresponding unambiguous distances are between 495 and 395 km. The ratios VN2/VN1 and VN3/VN1 are, respectively, equal to 6/7 and 4/5. The resulting extended Nyquist velocity is equal to 60 m s-1. One month of data (August 2004) representing more than 10 000 plan position indicators (PPIs) of clear-air, convective, and stratiform rain has been analyzed and histograms of errors have been computed. All histograms are symmetrical and show a well-defined peak centered on zero. The error distributions of the dual-PRT (V12, V13, and V23) and triple-PRT (V123) velocities present secondary peak that correspond to dealiasing failures. Overall, the dealiasing success rate for V123 is beyond 92%. A simulation "à la Zrnić" of I and Q time series is then used to reproduce the observed error histograms and exhaustively compare dual versus triple PRT for various extended Nyquist velocities. This last step shows that (i) for the same Nyquist velocity, triple PRT systematically overperforms the dual PRT in terms of the dealiasing success rate and (ii) among the couples that yield a Nyquist velocity equal to 60 m s-1, the (4/5; 6/7) couple that is in place on Trappes is optimal. © 2006 American Meteorological Society.