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Real-Time Radar Reflectivity Calibration from Differential Phase Measurements

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  • 1 J. S. Marshall Radar Observatory, Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada
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Abstract

An algorithm based on the self-consistency between the horizontal reflectivity ZH and the specific differential phase KDP has been devised for the calibration of the reflectivity measurements of the McGill S-band dual-polarization radar and implemented in real time in the fall of 2012. By combining pairs of measured and theoretical differential propagation phases (ΦDP) along rain paths from several azimuths, elevation angles, and radar cycles, a robust calibration estimate is obtained even in relatively light precipitation, provided the number of pairs is of the order of at least 103. It confirmed the stability of the radar system as further corroborated by disdrometer and ground echo comparisons. However, the two-parameter ZH–KDP technique proved to be inadequate in convective situations because it overestimates ΦDP differences of paths with heavy precipitation. An ex post facto analysis has revealed that a three-parameter (ZH–KDP–ZDR) relationship provides a much better agreement with the measured ΦDP differences regardless of the intensity of the precipitation along the rain paths. The main usefulness of the technique remains its ability to derive a reliable calibration correction factor even in light precipitation; thus, it is readily applicable in climate regimes and/or at times of the year characterized by the absence of strong convection capable of providing the large ΦDP differences previously thought necessary for such a technique to be successful.

Corresponding author address: Dr. Aldo Bellon, J. S. Marshall Radar Observatory, P.O. Box 193, Macdonald Campus, Ste-Anne-de-Bellevue QC H9X 3V9, Canada. E-mail: aldo.bellon@mcgill.ca

Abstract

An algorithm based on the self-consistency between the horizontal reflectivity ZH and the specific differential phase KDP has been devised for the calibration of the reflectivity measurements of the McGill S-band dual-polarization radar and implemented in real time in the fall of 2012. By combining pairs of measured and theoretical differential propagation phases (ΦDP) along rain paths from several azimuths, elevation angles, and radar cycles, a robust calibration estimate is obtained even in relatively light precipitation, provided the number of pairs is of the order of at least 103. It confirmed the stability of the radar system as further corroborated by disdrometer and ground echo comparisons. However, the two-parameter ZH–KDP technique proved to be inadequate in convective situations because it overestimates ΦDP differences of paths with heavy precipitation. An ex post facto analysis has revealed that a three-parameter (ZH–KDP–ZDR) relationship provides a much better agreement with the measured ΦDP differences regardless of the intensity of the precipitation along the rain paths. The main usefulness of the technique remains its ability to derive a reliable calibration correction factor even in light precipitation; thus, it is readily applicable in climate regimes and/or at times of the year characterized by the absence of strong convection capable of providing the large ΦDP differences previously thought necessary for such a technique to be successful.

Corresponding author address: Dr. Aldo Bellon, J. S. Marshall Radar Observatory, P.O. Box 193, Macdonald Campus, Ste-Anne-de-Bellevue QC H9X 3V9, Canada. E-mail: aldo.bellon@mcgill.ca
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