Application of SuperDARN interferometry for improved estimates of Doppler velocity and echo geolocation

Abstract

It has been previously established that the Doppler velocities of F-region ionospheric echoes observed by the Super Dual Auroral Radar Network (SuperDARN) at high frequencies (HF, 8–20 MHz) are persistently lower than those measured by other instruments at the same locations. This was attributed to the ionospheric refractive index for HF radio waves being noticeably smaller than one. The refractive index values can be obtained in two ways: based on electron density estimates from a co-located instrument or a model, or by deriving them from SuperDARN elevation angle data. To compare these methods, we considered line-of-sight Doppler velocity observations by the Rankin Inlet (RKN) SuperDARN radar and the Resolute Bay Incoherent Scatter Radars (RISR). The velocity data were supplemented by electron density measurements from RISR. The elevation angle data were also used for accurate determination of SuperDARN echo geolocation because the actual ground range to the echo location may significantly differ from that obtained with the conventional SuperDARN models. The RISR Doppler velocity values were used as a reference to the RKN observations via 0.5-hop and 1.5-hop propagation paths. Correction by the index of refraction based on both maximum electron density from the RISR and elevation angle data from RKN brought 0.5-hop data close to the RISR velocity values, with the latter representing a self-contained approach. However, for 1.5-hop echoes from the polar cap, the uncorrected SuperDARN velocities exceeded those from RISR. We discuss potential causes of this apparent anomaly.