Use of Data-Based Calibration to Harmonize the Swedish Weather Radar Network

The radar has become a critical tool for weather surveillance, and the weather radar network plays a key role for a national weather service. Any inconsistent radar data among a network would negatively affect the accuracy of weather observation and forecast. Consequently, the calibration process becomes essential to obtaining consistently accurate radar data. There are some considerations for calibrating and harmonizing the network. Ideally, the calibration would be performed online, could be easily repeated, and/or could be done in real-time. As a result, the data-based calibration becomes a practical option for this purpose.

Swedish national weather radar network (SWERAD) consists of 12 C-band polarimetric weather radars. In order to calibrate and harmonize the network, the Swedish Meteorological and Hydrological Institute (SMHI) and Enterprise Electronics Corporation (EEC) have agreed to, and recently began, a radar calibration campaign since July 2019. The major purpose is to calibrate the reflectivity (Z_H) and differential reflectivity (Z_DR) among the network so that the accuracy of precipitation estimation and forecast can be improved for the entire country. The physical consistency-based reflectivity calibration method (Cao et al. 2016) and the automated differential reflectivity calibration method (Cao and Knight, 2019) are used for the data processing and analysis. These two methods rely on the polarimetric data of weather echoes and will have little effect on the major operational tasks. Since late July, the corresponding radar scan strategy has been added into the 12 radars to collect the useful datasets for the calibration. The current study presents the data analysis results for this campaign.