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  • Author or Editor: Andrew L. Pazmany x
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James B. Mead
and
Andrew L. Pazmany

Abstract

Quadratically varying phase codes applied from pulse to pulse can be used to impart a range-dependent frequency shift in the decoded signal of a pulsed radar. Radars employing such codes can operate at extremely high pulse repetition frequencies (PRFs) with overlaid signals from multiple echo trips separated in the spectral domain. When operating at high PRFs, the radar duty cycle can approach 50% in a single-antenna system. High duty cycle operation results in a substantial increase in average transmit power with a proportional increase in signal processing gain as compared to a conventional pulsed radar. The shortest quadratic phase code, or base code, has a length equal to the number of echo trips M that can be unambiguously resolved in the spectral domain. The decoded waveform is essentially free from range sidelobes under ideal conditions. However, amplitude and phase errors associated with nonideal phase coding result in range sidelobes that appear at all echo trips in the decoded signal. These sidelobes can be suppressed by using a composite phase code composed of a periodically repeating base phase code added to a much longer quadratic code with a proportionally slower phase variation. Meteorological data gathered with a Ka-band radar operating at 3.0-MHz PRF at 45% duty cycle are presented. A comparison of these data with data gathered in short-pulse mode at a duty cycle of 0.3% exhibited a 21-dB improvement in the Doppler spectrum signal-to-noise ratio, equal to the ratio of the respective duty cycles.

Open access
Andrew L. Pazmany
and
Samuel J. Haimov

Abstract

Coherent power is an alternative to the conventional noise-subtracted power technique for measuring weather radar signal power. The inherent noise-canceling feature of coherent power eliminates the need for estimating and subtracting the noise component, which is required when performing conventional signal power estimation at low signal-to-noise ratio. The coherent power technique is particularly useful when averaging a high number of samples to improve sensitivity to weak signals. In such cases, the signal power is small compared to the noise power and the required accuracy of the estimated noise power may be difficult to achieve. This paper compares conventional signal power estimation with the coherent power measurement technique by investigating bias, standard deviation, and probability of false alarm and detection rates as a function of signal-to-noise ratio and threshold level. This comparison is performed using analytical expressions, numerical simulations, and analysis of cloud and precipitation data collected with the airborne solid-state Ka-band precipitation radar (KPR) operated by the University of Wyoming.

Full access
Andrew L. Pazmany
,
James B. Mead
,
Howard B. Bluestein
,
Jeffrey C. Snyder
, and
Jana B. Houser

Abstract

A novel, rapid-scanning, X-band (3-cm wavelength), polarimetric (RaXPol), mobile radar was developed for severe-weather research. The radar employs a 2.4-m-diameter dual-polarized parabolic dish antenna on a high-speed pedestal capable of rotating the antenna at 180° s−1. The radar can complete a 10-elevation-step volume scan in about 20 s, while maintaining a 180-record-per-second data rate. The transmitter employs a 20-kW peak-power traveling wave tube amplifier that can generate pulse compression and frequency-hopping waveforms. Frequency hopping permits the acquisition of many more independent samples possible than without frequency hopping, making it possible to scan much more rapidly than conventional radars. Standard data products include vertically and horizontally polarized equivalent radar reflectivity factor, Doppler velocity mean and standard deviation, copolar cross-correlation coefficient, and differential phase. This paper describes the radar system and illustrates the capabilities of the radar through selected analyses of data collected in the U.S. central plains during the 2011 spring tornado season. Also noted are opportunities for experimenting with different signal-processing techniques to reduce beam smearing, increase sensitivity, and improve range resolution.

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Andrew L. Pazmany
,
John C. Galloway
,
James B. Mead
,
Ivan Popstefanija
,
Robert E. McIntosh
, and
Howard W. Bluestein

Abstract

The Polarization Diversity Pulse-Pair (PDPP) technique can extend simultaneously the maximum unambiguous range and the maximum unambiguous velocity of a Doppler weather radar. This technique has been applied using a high-resolution 95-GHz radar to study the reflectivity and velocity structure in severe thunderstorms. This paper documents the technique, presents an analysis of the first two moments of the estimated mean velocity, and provides a comparison of the results with experimental data, including PDPP images of high-vorticity regions in supercell storms.

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