An integrated approach to monitoring the calibration stability of operational dual-polarization radars

Abstract

Abstract. The stability of weather radar calibration is a mandatory aspect for quantitative applications, such as rainfall estimation, short-term weather prediction and initialization of numerical atmospheric and hydrological models. Over the years, calibration monitoring techniques based on external sources have been developed, specifically calibration using the Sun and calibration based on ground clutter returns. In this paper, these two techniques are integrated and complemented with a self-consistency procedure and an intercalibration technique. The aim of the integrated approach is to implement a robust method for online monitoring, able to detect significant changes in the radar calibration. The physical consistency of polarimetric radar observables is exploited using the self-consistency approach, based on the expected correspondence between dual-polarization power and phase measurements in rain. This technique allows a reference absolute value to be provided for the radar calibration, from which eventual deviations may be detected using the other procedures. In particular, the ground clutter calibration is implemented on both polarization channels (horizontal and vertical) for each radar scan, allowing the polarimetric variables to be monitored and hardware failures to promptly be recognized. The Sun calibration allows monitoring the calibration and sensitivity of the radar receiver, in addition to the antenna pointing accuracy. It is applied using observations collected during the standard operational scans but requires long integration times (several days) in order to accumulate a sufficient amount of useful data. Finally, an intercalibration technique is developed and performed to compare colocated measurements collected in rain by two radars in overlapping regions. The integrated approach is performed on the C-band weather radar network in northwestern Italy, during July-October 2014. The set of methods considered appears suitable to establish an online tool to monitor the stability of the radar calibration with an accuracy of about 2 dB. This is considered adequate to automatically detect any unexpected change in the radar system requiring further data analysis or on-site measurements.

Polarimetric X‐band weather radars for quantitative precipitation estimation in mountainous regions

“…Vaccarono et al . () have conducted a similar analysis in Italy using C‐band radars and shown that the biases measured between radars situated at different altitudes varied with the melting layer height.…”

“…This theory provides a good explanation of the observed biases, but also reveals that the dual-pol attenuation correction currently used at Météo-France to account for the attenuation of the melting snow is biased. Vaccarono et al (2016) have conducted a similar analysis in Italy using C-band radars and shown that the biases measured between radars situated at different altitudes varied with the melting layer height.…”

Evaluation of Doppler Radar Data for Assessing Depth-Area Reduction Factors for the Arid Region of San Bernardino County

“…The availability of reflected power and phase details along two directions enables calculating additional parameters (eg, differential reflectivity, differential phase and correlation coefficient) which can then be used to arrive at improved precipitation estimates, and can better differentiate between heavy rain, hail, snow and sleet. The works of Zrnicand Ryzhkov [14], Doviak et al [15], Bringi and Chandrasekar [16], Vaccarono et al [17] provide more resources including precipitation equations relating to Dual Polarization or polarimetric radar.…”

An Integrated Approach to Weather Radar Calibration and Monitoring Using Ground Clutter and Satellite Comparisons

“…Radar calibration techniques are often evaluated separately. Yet, as proposed by Vaccarono et al (2016), it is possible to retrieve additional information about calibration changes by combining different calibration techniques (the so-called integrated approaches).…”