AMS Short Course: Zdr Calibration


Date: 27 August 2017

Location: Swissôtel, 323 E Upper Wacker Dr, Chicago, IL 60601, USA

Description: Even though the quantity Zdr was first introduced to the radar meteorology community more than 40 years ago by Seliga and Bringi, the calibration of Zdr continues to be a topic of research, an issue for most radars, and a quantity whose temporal stability is poorly documented and inadequately understood. Gathering data in light rain is perhaps the most accepted technique for Zdr calibration. However, such precipitation events can be uncommon for a radar site and most operational radars have a mission to document the weather and not execute calibration scans thus making detailed calibration studies difficult.

Estimates of Zdr bias can be made by several techniques: 1) vertical pointing data, 2) engineering calibration, 3) crosspolar power technique, and 4) using external targets such precipitation and Bragg scatter. This short course describes the details of these methods and applies them to data from the National Center for Atmospheric Research (NCAR) S-Pol radar to illustrate the concepts. S-Pol data is used to document the drift of the Zdr bias from fine time resolution measurements (less than 10 minute intervals) over extended periods of time (hours and days). The gathered data allows for an identification of the radar components that cause the Zdr bias to drift. An important aspect covered is the Zdr bias drift cause by temperature change of the antenna.

Calibration and data quality experts give presentation about their experiences with NEXRAD and the DWD (German Weather Service) radars. Techniques that are used for Zdr calibration are described, illustrated with data and discussed.   

The goal of the course is to educate the student as to the methods, principles, issues, and signal processing techniques required for accurately estimating Zdr bias and its uncertainty. The course is aimed at students, engineers and scientists who desire to know the details of Zdr calibration and how to apply the techniques to their radars and data.

The course consists of presentations by four radar calibration experts. Power points will be made available to the students. Solar calibration scans are discussed in detail and the signal processing program (in C++) will be given to the students. A remote live demonstration of S-Pol Zdr calibration will be shown.

A luncheon will be provided during the short course.

For more information please contact John Hubbert,  email:, tel: 303 319 6228.