Phase calibration of interferometer arrays at high-frequency radars

Elevation angles of backscattered signals are calculated at the Super Dual Auroral Radar Network (SuperDARN) high-frequency radars using interferometric techniques. These elevation angles make it possible to estimate the geographic location of the scattering point, an essential piece of information for many ionospheric studies. One of the most difficult parameters to measure is the effective time delay caused by the difference in the electrical path length that connects the main array and the interferometer arrays to the correlator (δtc). This time delay causes a bias in the measured difference in the signal phase, also known as a phase bias. Phase calibration is difficult due to unknown physical attributes of the hardware and the remote location of many radars. This leads to the possibility of sudden external changes, slow temporal drift, and a dependence on transmission frequency. However, it is possible to estimate δtc using the radar observations themselves. This article presents a method for estimating δtc using backscatter with a known location, such as backscatter from artificially generated irregularities, meteor echoes, or distinct groundscatter, which incorporates the uncertainty in the observations and may be used autonomously. Applying the estimated δtc is shown to improve elevation angle uncertainties at one of the SuperDARN radars from their current potential tens of degrees to less than a degree.