Universität zu Köln

Myagkov, Alexander, Kneifel, Stefan ORCID: 0000-0003-2220-2968 and Rose, Thomas (2020). Evaluation of the reflectivity calibration of W-band radars based on observations in rain. Atmos. Meas. Tech., 13 (11). S. 5799 - 5826. GOTTINGEN: COPERNICUS GESELLSCHAFT MBH. ISSN 1867-8548

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Abstract

This study presents two methods for evaluating 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 nonRayleigh scattering effects and attenuation have a nonnegligible 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 one to estimate the absolute radar calibration using a minimization technique. The main advantage of the self-consistency method is its lower 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 on the conventional disdrometerbased 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 4mm h(-1) 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.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Myagkov, Alexander UNSPECIFIED UNSPECIFIED UNSPECIFIED Kneifel, Stefan UNSPECIFIED orcid.org/0000-0003-2220-2968 UNSPECIFIED Rose, Thomas UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-312274
DOI:	10.5194/amt-13-5799-2020
Journal or Publication Title:	Atmos. Meas. Tech.
Volume:	13
Number:	11
Page Range:	S. 5799 - 5826
Date:	2020
Publisher:	COPERNICUS GESELLSCHAFT MBH
Place of Publication:	GOTTINGEN
ISSN:	1867-8548
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language CLOUD RADAR; DIFFERENTIAL EVOLUTION; ABSOLUTE CALIBRATION; OPTICAL DISDROMETER; SIZE DISTRIBUTIONS; ICE CRYSTALS; DOPPLER; RETRIEVAL; PHASE; PRECIPITATION Multiple languages Meteorology & Atmospheric Sciences Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/31227