A dual-pulse repetition frequency scheme for mitigating velocity ambiguities of the NOAA P-3 airborne Doppler radar

Abstract

To mitigate some of the deleterious effects of the relatively small unambiguous Doppler velocity range (Nyquist interval) of airborne X-band Doppler radars, a technique has been developed to extend this interval. This technique, termed the batch-mode dual-PRF (pulse repetition frequency) technique, utilizes two batches of pulses that are each averaged to produce two velocity estimates at each range bin, with each batch at a different sampling rate. Comparison of the two velocity estimates produces a difference velocity that is used to dealias the second estimate within an extended velocity range that is larger than the Nyquist velocities of either of the two original samples. In this implementation, the choices of the two PRFs are restricted to ratios of 3/2 or 4/3 of the lowest PRF. Due to the spread of the input Doppler spectrum and spatial displacement from one radial to the next, however, this batch-mode technique can produce processor velocity dealiasing mistakes, particularly in high wind shear environments. For PRFs less than about 2000 s-1, processor mistakes can easily exceed 10% of all data points. With higher PRFs using the 3/2 ratio, the number of processor mistakes decreases to a few percent of the total number of samples even when observing strong convective storms and mesoscale convective systems. Test results from convective storm environments are shown from the airborne Doppler radar operated on the National Oceanic and Atmospheric Administration's P-3 instrumented aircraft for a variety of base PRFs and ratios to show the utility of this technique.