Testing X-Band ZDR Calibration Using Dry Snow

Differential reflectivity (ZDR) calibration is critical for ensuring high quality microphysical retrievals using dual-polarized radar data. Standard calibration practice utilizes a vertically pointing scan to detect bias in ZDR data. However, since it isn’t always advantageous or even possible to use the vertical scanning approach, we explore the viability of dry snow as an alternative calibration target. Specifically, we compare dry snow ZDR calibration at X-band to vertical ZDR calibration scans, which haven’t been tested conclusively to this date. We used a full year’s worth of volume scans from the X-band Teaching and Research Radar (XTRRA) at Purdue University. ZDR bias computed from vertical calibration scans, included with each volume, were analyzed as a control dataset against ZDR bias from dry snow-classified gates. . A semisupervised hydrometeor classification algorithm (HCA) was used to retrieve dry snow gates, while temperature profiles were retrieved from hourly HRRR BUFKIT data. Preliminary results show that this method is viable, but with considerable limitations due to assumptions in hydrometeor classifications and seasonal variations in the mean vertical ZDR. Application of this technique to mobile radar data collected during the cold season is reported elsewhere at this conference.