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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/amt-2020-133
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-133
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  21 Apr 2020

21 Apr 2020

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A revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Evaluation of the reflectivity calibration of W-band radars based on observations in rain

Alexander Myagkov1, Stefan Kneifel2, and Thomas Rose1 Alexander Myagkov et al.
  • 1Radiometer Physics GmbH, Meckenheim, Germany
  • 2Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany

Abstract. This study presents two methods to evaluate the reflectivity calibration of W-band cloud radars. Both methods use natural rain as a reference target. The first approach is based on a self-consistency method of polarimetric radar variables, which is widely used in the precipitation radar community. As previous studies pointed out, the method cannot be directly applied to higher frequencies, where non-Rayleigh scattering effects and attenuation have a non-negligible influence on radar variables. The method presented here solves this problem by using polarimetric Doppler spectra to separate backscattering and propagational effects. New fits between the separated radar variables allow to estimate the absolute radar calibration using a minimization technique. The main advantage of the self-consistency method is its less dependence on the spatial variability in radar drop-size-distribution (DSD). The estimated uncertainty of the method is 0.7 dB. The method was applied to three intense precipitation events and the retrieved reflectivity offsets were within the estimated uncertainty range. The second method is an improvement of the conventional disdrometer-based approach, where reflectivity from the lowest range gate is compared to simulated reflectivity using surface disdrometer observations. The improved method corrects first for the time-lag between surface DSD observations and the radar measurements at a certain range. In addition, the effect of evaporation of raindrops on their way towards the surface is mitigated. The disdrometer-based method was applied to 12 rain events observed by vertically-pointed W-band radar and showed repeatable estimates of the reflectivity offsets at rain rates below 4 mm/h within 0.9 dB. The proposed approaches can analogously be extended to Ka-band radars. Although very different in terms of complexity, both methods extend existing radar calibration evaluation approaches, which are inevitably needed for the growing cloud radar networks in order to provide high-quality radar observation to the atmospheric community.

Alexander Myagkov et al.

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Alexander Myagkov et al.

Alexander Myagkov et al.

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Latest update: 21 Sep 2020
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Short summary
This study shows two methods to evaluate the reflectivity calibration of W-band cloud radars. Both methods use natural rain as a reference target. The first method is based on spectral polarimetric observations and requires a polarimetric cloud radar with a scanner. The second method utilizes disdrometer observations and can be applied to scanning and vertically pointed radars. Both methods show consistent results and can be applied for the operational monitoring of the measurement quality.
This study shows two methods to evaluate the reflectivity calibration of W-band cloud radars....
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