Calibrating SuperDARN interferometers using meteor backscatter

Accurate geolocation of ionospheric backscatter measured by the Super Dual Auroral Radar Network (SuperDARN) high-frequency radars is critical for the integrity of polar ionospheric convection maps, which involve combining SuperDARN line-of-sight velocity measurements originating from multiple locations. Geolocation requires estimation of the propagation paths of the high-frequency radio signal to and from the scattering volume. The SuperDARN radars comprise both a main and interferometer antenna array to allow the estimation of the elevation angle of arrival of the returning signal, and hence its most likely propagation path. However, over the history of operation of SuperDARN (>20 years) elevation angle data have not been routinely used owing to problems with the calibration of phase difference measurements. Instead, virtual height models have been used to estimate the most likely propagation paths, and these are often of limited accuracy. Here we present a method for calibrating SuperDARN interferometer measurements using backscatter from meteor trails measured in the near field-of-view of the SuperDARN radars. We present estimates of calibration factors for the SuperDARN radar in Saskatoon, Canada, at different temporal resolutions: 3 months, 10 days, and 1 day. The calibration factor varies over the 9-year interval studied, such that employing a single value for the whole interval would lead to significant errors in elevation angle measurements at times. The higher-resolution results show the ability of the technique to determine the calibration factor routinely at a high time resolution.