Multipulse and double-pulse velocities of Scandinavian Twin Auroral Radar Experiment (STARE) echoes



[1] The Scandinavian Twin Auroral Radar Experiment (STARE) coherent radars are a powerful instrument for studying auroral zone plasma convection. In recent years the STARE radars have been collecting both double-pulse (DP) and multipulse (MP) data to measure the Doppler velocity of auroral echoes. We assess here DP-MP measurements for eight events covering 28 hours of operation. More often, there is a reasonable agreement between the DP and MP velocities. Exceptions are afternoon-evening observations for which the Finland radar DP velocity is nearly half the MP velocity obtained through fitting of the autocorrelation function of a received signal (ACF-FIT), although the DP and MP1 (first lag) velocities are in reasonable agreement. We demonstrate that for periods with strong differences between the DP and MP ACF-FIT velocities the spectra are strongly asymmetric, and the phase angle–lag number dependence is nonlinear with a slower rate of angle increase at small-number lags (<3) and a faster rate of angle increase at larger-number lags. Contrary to the DP velocity, the MP ACF-FIT velocity (obtained in some cases without one or two first-lag data) is fairly close to the spectral power peak and power-weighted (over spectrum) velocity. In an attempt to understand the DP-MP velocity differences, we consider the role of the asymmetry of observed spectra and show that it can explain the discrepancies but only partially. As another potentially important effect, we consider the possibility of weak, but not negligible, cross-range correlation between the signals coming from the target and aliasing volumes that are closely spaced for the current STARE mode of operation.