Threshold Calculation for Coherent Detection in Dual-Polarization Weather Radars

2012 ◽  
Vol 48 (3) ◽  
pp. 2198-2215 ◽  
Author(s):  
Igor R. Ivic ◽  
Dusan S. Zrnic ◽  
Tian-You Yu
Keyword(s):  
Coherent Detection ◽  
Dual Polarization ◽  
Weather Radars

Calibration Issues of Dual-Polarization Radar Measurements

2005 ◽  
Vol 22 (8) ◽  
pp. 1138-1155 ◽  
Author(s):  
Alexander V. Ryzhkov ◽  
Scott E. Giangrande ◽  
Valery M. Melnikov ◽  
Terry J. Schuur
Keyword(s):  
High Elevation ◽  
Absolute Calibration ◽  
Dual Polarization ◽  
Light Rain ◽  
Weather Radars ◽  
Mechanical Constraints ◽  
Wide Range ◽  
Temporal Averaging ◽  
The Impact ◽  
Self Consistency

Abstract Techniques for the absolute calibration of radar reflectivity Z and differential reflectivity ZDR measured with dual-polarization weather radars are examined herein. Calibration of Z is based on the idea of self-consistency among Z, ZDR, and the specific differential phase KDP in rain. Extensive spatial and temporal averaging is used to derive the average values of ZDR and KDP for each 1 dB step in Z. Such averaging substantially reduces the standard error of the KDP estimate so the technique can be used for a wide range of rain intensities, including light rain. In this paper, the performance of different consistency relations is analyzed and a new self-consistency methodology is suggested. The proposed scheme substantially reduces the impact of variability in the drop size distribution and raindrop shape on the quality of the Z calibration. The new calibration technique was tested on a large polarimetric dataset obtained during the Joint Polarization Experiment in Oklahoma and yielded an accuracy of Z calibration within 1 dB. Absolute calibration of ZDR is performed using solar measurements at orthogonal polarizations and polarimetric properties of natural targets like light rain and dry aggregated snow that are probed at high elevation angles. Because vertical sounding is prohibited for operational Weather Surveillance Radar-1988 Doppler (WSR-88D) radars because of mechanical constraints, the existing methodology for ZDR calibration is modified for nonzenith elevation angles. It is shown that the required 0.1–0.2-dB accuracy of the ZDR calibration is potentially achievable.

Detection and Estimation of Radar Reflectivity from Weak Echo of Precipitation in Dual-Polarized Weather Radars

2014 ◽  
Vol 31 (8) ◽  
pp. 1677-1693 ◽  
Author(s):  
Reino Keränen ◽  
V. Chandrasekar
Keyword(s):  
Cross Correlation ◽  
Noise Suppression ◽  
Geometric Mean ◽  
Intrinsic Noise ◽  
Diagonal Element ◽  
Radar Reflectivity ◽  
Consistent Estimate ◽  
Dual Polarization ◽  
Weather Radars ◽  
Finite Sums

Abstract In operational weather radar, precipitation echoes are often weak when compared to the underlying noise. Coherence properties of dual polarization can be used for enhancing the detection and for the improved estimation of weak echoes of precipitation. The enhanced detectability results from utilizing coherent averages of precipitation signals, while the uncorrelated noise vanishes asymptotically, explicit in the off-diagonal element Rhv of the echo covariance matrix. In finite sums, the noise terms as well as the uncertainties associated with them are suppressed. A signal can be detected in weaker echo by an analytically derived censoring policy. The coherent sums are readily available as the cross-correlation function of the antenna voltages H and V, which estimates Rhv in the mode of simultaneous transmission and reception. The magnitude of Rhv is a consistent estimate of the copolar echo power, leading to the copolar radar reflectivity of precipitation, which refers to the geometric mean of the reflectivities in H and V polarizations. Because of the intrinsic noise suppression, estimates of the copolar reflectivity are, in relative terms, more precise and more accurate than the corresponding estimates of reflectivity in specific channels, for weak signals of precipitation. These aspects are discussed quantitatively with validation of the key features in real conditions. The advances suggest for dedicated dual-polarization surveillance scans of weak echo of precipitation.

scholarly journals Dual-polarization OFDM-OQAM for communications over optical fibers with coherent detection

2013 ◽  
Vol 21 (5) ◽  
pp. 6409 ◽  
Author(s):  
François Horlin ◽  
Jessica Fickers ◽  
Philippe Emplit ◽  
André Bourdoux ◽  
Jérome Louveaux
Keyword(s):  
Optical Fibers ◽  
Coherent Detection ◽  
Dual Polarization

Recent advances in classification of observations from dual polarization weather radars

2013 ◽  
Vol 119 ◽  
pp. 97-111 ◽  
Author(s):  
V. Chandrasekar ◽  
R. Keränen ◽  
S. Lim ◽  
D. Moisseev
Keyword(s):  
Dual Polarization ◽  
Weather Radars ◽  
Recent Advances

Orthogonal Channel Coding for Simultaneous Co- and Cross-Polarization Measurements

2009 ◽  
Vol 26 (1) ◽  
pp. 45-56 ◽  
Author(s):  
V. Chandrasekar ◽  
Nitin Bharadwaj
Keyword(s):  
Channel Coding ◽  
Electromagnetic Waves ◽  
Polarization State ◽  
Dual Polarization ◽  
Colorado State University ◽  
Weather Radars ◽  
Current Implementation ◽  
Polarization States ◽  
Linear Depolarization Ratio ◽  
Orthogonal Phase

Abstract Dual-polarization weather radars typically measure the radar reflectivity at more than one polarization state for transmission and reception. Historically, dual-polarization radars have been operated at copolar and cross-polar states defined with respect to the transmit polarization states. Recently, based on the improved understanding of the propagation properties of electromagnetic waves in precipitation media, the simultaneous transmit and receive (STAR) mode has become common to simplify the hardware. In the STAR mode of operation, horizontal and vertical polarization states are transmitted simultaneously and samples of both horizontal and vertical copolar returns are obtained. A drawback of the current implementation of STAR mode is its inability to measure parameters obtained from cross-polar signals such as linear depolarization ratio (LDR). In this paper, a technique to obtain cross-polar signals with STAR mode waveform is presented. In this technique, the horizontally and vertically polarized transmit waveforms are coded with orthogonal phase sequences. The performance of the phase-coded waveform is determined by the properties of the phase codes. This orthogonal phase coding technique is implemented in the Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) radar. This paper outlines the methodology and presents the performance of the cross-polar and copolar parameter estimation based on the simulation as well as data collected from the CSU–CHILL radar.

scholarly journals The Use of Coherency to Improve Signal Detection in Dual-Polarization Weather Radars

2009 ◽  
Vol 26 (11) ◽  
pp. 2474-2487 ◽  
Author(s):  
Igor R. Ivić ◽  
Dušan S. Zrnić ◽  
Tian-You Yu
Keyword(s):  
Signal Detection ◽  
Electric Fields ◽  
Cross Correlation ◽  
Time Series Data ◽  
Signal To Noise Ratio ◽  
Hybrid Approach ◽  
Series Data ◽  
Dual Polarization ◽  
Weather Radars ◽  
Detection Schemes

Abstract Currently, signal detection and censoring in operational weather radars is performed by using thresholds of the estimated signal-to-noise ratio (SNR) and/or the magnitude of the autocorrelation coefficient at the first temporal lag. The growing popularity of polarimetric radars prompts the quest for improved detection schemes that take advantage of the signals from the two orthogonally polarized electric fields. A hybrid approach is developed based on the sum of the cross-correlation estimates as well as the powers and autocorrelations from each of the dual-polarization returns. The hypothesis that “signal is present” is accepted if the sum exceeds a predetermined threshold; otherwise, the data are considered to represent noise and are censored. The threshold is determined by the acceptable rate of false detections that is less than or equal to a preset value. The scheme is evaluated both in simulations and through implementation on time series data collected by the research weather surveillance radar (KOUN) in Norman, Oklahoma.

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