Rainfall estimation and rain gauge comparison for x-band polarimetric CASA radars

The Center for Collaborative and Adaptive Sensing of the Atmosphere (CASA) developed and deployed four polarimetric and Doppler-capable distributed, collaborative and adaptive X-band radars in Oklahoma with the capability to detect and track tornadoes and storms in the lower troposphere with high spatial and temporal resolution. This paper presents an analysis of the performance of X-band rainfall estimation composite algorithms and the conventional reflectivity-rainfall relationship. The polarimetric estimators are developed by different combinations of radar products including horizontal equivalent reflectivity (Z_h), differential reflectivity (Z_dr) and specific differential phase (K_dp)- The Micronet Little Washita rain gauge network is used for validating rainfall estimates of the KCYR CASA radar. In addition, NEXRAD WSR-88D KFDR radar data are analyzed and compared with the rain gauge network and the CASA radar estimates. Fourteen hours of data collected during August 2006 from three different storms are analyzed. Both convective and stratiform events are represented in the radar data analysis. An accuracy of point radar measurement is assessed for different rain intensities. Results demonstrate an improvement in hourly rainfall accumulation estimation for average rainfall intensities beyond 5 mm/hr with the use of polarimetric estimators. An increase in absolute difference standard error with distance by the use of absolute difference in radar and rain gauges estimates is also evaluated.