A Preliminary Study of Comparative Measurements of Rainfall Rate Using the Differential Reflectivity Radar Technique and a Raingage Network

Abstract

Radar measurements of average rainfall rate over two separate 550 km2 areas am compared with raingage measurements in the same areas over time intervals of ?1 h. The measurements were performed to test the differential reflectivity (ZDR) technique of Soliga and Bringi (1976) which provides a means of estimating rainfall rate (R)by combining measurements of radar reflectivity factors at horizontal (ZH) and vertical (ZV) polarizations; ZDR(dB) is defined as the ratio of these reflectivities, i.e., ZDR = 10 log(ZH/ZV). Results from an experiment performed near Chicago, Illinois, on 9 August 1978, using the University of Chicagco-Illinois State Water Survey (CHILL) radar and the Illinois State Water Survey's Chicago Hydrometeorological Area Project (CHAP) raingage network are presented. ZDR estimates of rainfall rate compared very favorably with the raingages measurements and were significantly better than estimates obtained from two Z-R relationships, one of which was obtained by raingage calibration. Over one of the 550 km2 areas the ZDR method measured 86% of the rainfall recorded on 26 raingages during an observational period of 80 min, and over the other, 117% of the rainfall recorded on 27 raingages was obtained during a 40 min period.