Calibration procedures for global precipitation-measurement ground-validation radars

The calibration of weather radars has a direct impact on the accuracy of measurements and is therefore critical for most applications. For this reason, calibration has been an active topic of study since the early days of radar meteorology, involving both the research and operational communities. More recently, the discussion on radar calibration has been enriched by new challenges. First, the operational use of dual-polarization radars has created a new set of demands for differential measurements. Second, the use of radars in a network has highlighted the importance of best practices and standards to assure that all the radars of the network provide meaningful and comparable measurements. Moreover, modern technology has provided many avenues for automating the calibration process, thereby minimizing errors. This paper was developed from the 2013 Weather Radar Calibration Laboratory Workshop, held at the Colorado State University (CSU) CHILL radar facility, Colorado, and from guidelines for calibrating ground-validation radars of the NASA/ JAXA Global Precipitation Measurement (GPM) mission. This paper takes a fundamental look at the weather-radar calibration process. It aims to illustrate to a broad audience how a collection of consolidated techniques and modern technologies can be used for the purpose of calibrating radar, with special attention to dual-polarization systems. Examples referred to real measurements at several radar facilities are shown.