Polarimetric X-band weather radar measurements in the tropics: radome and rain attenuation correction

Abstract

Abstract.A polarimetric X-band radar has been deployed during one month (April 2011) for a field campaign in Fortaleza, Brazil, together with three additional laser disdrometers. The disdrometers are capable of measuring the raindrop size distributions (DSDs), hence making it possible to forward-model theoretical polarimetric X-band radar observables at the point where the instruments are located. This setup allows to thoroughly test the accuracy of the X-band radar measurements as well as the algorithms that are used to correct the radar data for radome and rain attenuation. For the campaign in Fortaleza it was found that radome attenuation dominantly affects the measurements. With an algorithm that is based on the self-consistency of the polarimetric observables, the radome induced reflectivity offset was estimated. Offset corrected measurements were then further corrected for rain attenuation with two different schemes. The performance of the post-processing steps was analyzed by comparing the data with disdrometer-inferred polarimetric variables that were measured at a distance of 20 km from the radar. Radome attenuation reached values up to 14 dB which was found to be consistent with an empirical radome attenuation vs. rain intensity relation that was previously developed for the same radar type. In contrast to previous work, our results suggest that radome attenuation should be estimated individually for every view direction of the radar in order to obtain homogenous reflectivity fields.

Overview: Precipitation characteristics and sensitivities to environmental conditions during GoAmazon2014/5 and ACRIDICON-CHUVA

“…The Doppler radar X-band dual-polarization dataset was obtained by the mobile Meteor 50DX Selex radar during the CHUVA project (Schneebeli et al, 2012). The radar data underwent three main processing steps, including differential phase shift (PhiDP) filtering and specific differential phase (KDP) derivation, differential reflectivity (ZDR) offset correction, and horizontal reflectivity (Zh) and ZDR attenu- ation correction.…”

“…X-band radars are more prone to signal attenuation due to rain than C-and S-band radars. It is therefore mandatory to correct the signal for attenuation prior to any analysis using reflectivity data if such a correction is possible (Schneebeli et al, 2012). With a dual-polarization system, one can use the differential phase shift to calculate the attenuation due to rain.…”

Evaluation of GPROF-SSMI/S rainfall estimates over land during the Brazilian CHUVA-VALE campaign

“…To reduce these limitations, the specific differential propagation phase (Kdp) was used instead of the Z-R relation in order to attain more accurate retrievals (Gorgucci et al, 2006). Moreover, the reflectivity is heavily affected by attenuation of the radome and the rain medium itself (Schneebeli et al, 2012). In order to eliminate cases with wet radome attenuation, data from the radar were only considered when no precipitation was detected by the UNIVAP rain gauge (close toradar location) within about 3 minutes from the radar scan.…”

Improved Estimation of the Specific Differential Phase Shift Using a Compilation of Kalman Filter Ensembles

“…These algorithms need to be separated into two groups: the first group containing algorithms whose K dp estimates are purely based on Ψ dp measurements [12]- [15] and the second group using auxiliary data like the reflectivity Z and(or) the differential reflectivity Z dr together with consistency relations between polarimetric observables in order to obtain an improved fine-scale structure of K dp or a more accurate estimate of δ hv [16], [17]. As shown in [17] and [18], K dp can be estimated very accurately with an algorithm from the second group but only in rain conditions and if the radar is well calibrated. As soon as the consistency relations between the polarimetric variables are violated (by beam blockage, partial beam filling, nonliquid precipitation, or radar miscalibration), 0196-2892 © 2013 IEEE.…”