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 peaks 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.

Quantitative precipitation estimation based on high-resolution numerical weather prediction and data assimilation with WRF – a performance test

“…Radar reflectivities as well as radial velocities from the Doppler precipitation radar systems of the French ARAMIS network (Tabary et al, 2006) were assimilated. In total, data from 24 radars were included.…”

Using Gap-Filling Radars in Mountainous Regions to Complement a National Radar Network: Improvements in Multiple-Doppler Wind Syntheses

“…A triple-PRT scheme is used (Tabary et al 2006) allowing for an unambiguous Nyquist velocity of 60 m s…”

“…With the implementation of a triple-pulse repetition time (PRT) scheme (Tabary et al 2006) for the French ARAMIS radar network, Bousquet et al (2007Bousquet et al ( , 2008b showed that mitigation of the ''Doppler dilemma'' allowed for long-range data collection, with a high Nyquist velocity, dramatically reducing contamination of data with velocity aliasing. Given this potent addition to the French radar network, real-time wind-field syntheses were possible over a large region of northern France (Bousquet el al.…”

“…Application of median filters to remove erroneous radial velocity data from radars using dual-PRF and triple-PRT schemes has been successfully implemented in the past (Tabary et al 2006;Bousquet el al. 2008b;Montmerle and Faccani 2009).…”

Observation opérationnelle du vent 3D dans les nuages à partir des radars du réseau Aramis

“…La capacité de détection en air clair est potentiellement très intéressante car elle augmente considérablement le taux de disponibilité des mesures de vent, en particulier les profils VAD. Tabary et al, (2006) ont estimé à 80 % le taux de disponibilité de profils de vent en très basses couches lors des mois d'été. Cela ouvre des perspectives intéressantes pour le suivi météorologique des situations, l'assimilation dans les modèles de prévi-sion et la surveillance de la qualité de l'air, où les modèles utilisés ont un besoin crucial d'informations précises sur la structure de la couche limite.…”