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On the Performance of a Low-Cost K-Band Doppler Radar for Quantitative Rain Measurements

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  • 1 Institut für Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe/Universität Karlsruhe, Karlsruhe, Germany
  • | 2 Institute for Atmospheric Science, Swiss Federal Institute of Technology, Zurich, Switzerland
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Abstract

This paper deals with the ability of a vertically pointing, FM–CW Doppler radar to measure quantitatively raindrop size distributions and rainfall intensity. The wavelength of the radar is 12.5 mm (K band). To improve estimates of the rainfall intensity, radar-received noise, Mie scatter, and radar calibration corrections are applied to the radar data. The electronic noise correction rendered the radar particle size retrievals below 0.7-mm drop diameters invalid; exponential extrapolation of the spectrum below drop diameters of 0.7 mm decreased the rain intensity up to 20%. Proper Mie corrections to the particle backscatter cross sections decreased the rain intensity between 5% and 30%. Calibration of the radar against a Joss–Waldvogel disdrometer led to a decrease in rain intensity of 49%. The electronic noise, Mie scatter, and calibration corrections yielded a correlation coefficient of 0.94 in a comparison of the radar and disdrometer data for a case study. The daily rain sums over half a year derived from radar measurements at a height of 100 m above ground were on average 12% higher than measurements with a conventional Hellmann rain gauge.

Corresponding author address: Dr. Martin Löffler-Mang, Institut für Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe GmbH, Postfach 3640, D-76021 Karlsruhe, Germany.

Email: loeffler-mang@imk.fzk.de

Abstract

This paper deals with the ability of a vertically pointing, FM–CW Doppler radar to measure quantitatively raindrop size distributions and rainfall intensity. The wavelength of the radar is 12.5 mm (K band). To improve estimates of the rainfall intensity, radar-received noise, Mie scatter, and radar calibration corrections are applied to the radar data. The electronic noise correction rendered the radar particle size retrievals below 0.7-mm drop diameters invalid; exponential extrapolation of the spectrum below drop diameters of 0.7 mm decreased the rain intensity up to 20%. Proper Mie corrections to the particle backscatter cross sections decreased the rain intensity between 5% and 30%. Calibration of the radar against a Joss–Waldvogel disdrometer led to a decrease in rain intensity of 49%. The electronic noise, Mie scatter, and calibration corrections yielded a correlation coefficient of 0.94 in a comparison of the radar and disdrometer data for a case study. The daily rain sums over half a year derived from radar measurements at a height of 100 m above ground were on average 12% higher than measurements with a conventional Hellmann rain gauge.

Corresponding author address: Dr. Martin Löffler-Mang, Institut für Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe GmbH, Postfach 3640, D-76021 Karlsruhe, Germany.

Email: loeffler-mang@imk.fzk.de

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