Abstract
The high frequency radars in the Super Dual Auroral Radar Network (SuperDARN) estimate the elevation angles of returned backscatter using interferometric techniques. These elevation angles allow the ground range to the scattering point to be estimated, which is crucial for the accurate geolocation of ionospheric measurements. For elevation angles to be accurately estimated, it is important to calibrate the interferometer measurements by determining the difference in the signal time delays caused by the difference in the electrical path lengths from the main array and the interferometer array to the point at which the signals are correlated. This time delay is known as tdiff. Several methods have been proposed to estimate tdiff using historical observations; these methods are summarised in this paper. Comparisons of the tdiff estimates from the different calibration methods are presented and sources of uncertainty discussed. The effect of errors in the estimated tdiff value on the accuracy of geolocation is evaluated and discussed. The paper concludes with a series of recommendations for both scientific SuperDARN data users and SuperDARN radar operators.
Highlights
The Super Dual Auroral Radar Network (SuperDARN) is a major tool for studying ionospheric and magnetospheric dynamics in both the polar regions (Chisham et al, 2007) and at mid-latitudes (Nishitani et al, 2019)
The SuperDARN radars are equipped with interferometers that make it possible to determine the elevation angle of arrival of returning radio signals, and to estimate the most likely propagation path to the scattering volume (Milan et al, 1997; André et al, 1998; McDonald et al, 2013; Burrell et al, 2015; Shepherd, 2017; Chisham, 2018)
The radars chosen for the initial study were Inuvik SuperDARN radar (INV) and Rankin Inlet (RKN) from the polar radars in northern Canada, Hankasalmi SuperDARN radar (HAN) from the auroral zone in Finland, and Christmas Valley East (CVE) from midlatitudes in the USA
Summary
The Super Dual Auroral Radar Network (SuperDARN) is a major tool for studying ionospheric and magnetospheric dynamics in both the polar regions (Chisham et al, 2007) and at mid-latitudes (Nishitani et al, 2019). One of the most important measurements that the high frequency (HF) radars make is the line-of-sight Doppler velocity of ionospheric F-region plasma that moves as a result of E×B drift. Combining this velocity data from the extensive fields-of-view (FOVs) of multiple SuperDARN radars allows the production of polar maps of ionospheric convection (Ruohoniemi and Baker, 1998). Combining velocity measurements from multiple radars requires a high level of accuracy in the geolocation of the radar backscatter targets To achieve this accuracy, the propagation paths of the HF radio signals to and from the scattering locations need to be well estimated (Greenwald et al, 2017). These VHMs have limited accuracy, and at far ranges their use can result in errors in the estimation of the ground range to the backscatter location of 100s of km (Yeoman et al, 2008)
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