Using the STARE double pulse system to obtain the mean velocity and velocity of long-lived irregularities

The STARE and SABRE auroral radars use double pulses to measure one value of the autocorrelation function (ACF) to obtain the Doppler velocity of the irregularities in the E-region auroral zone. If the pulse separation of each double pulse is τ, then the measured velocity tends towards the mean velocity V_DP as τ → 0, and towards the velocity of the long-lived irregularities V_LL as τ → ∞. A practical implementation using these results is presented, which allows measurement of these two physically important velocities from just four pulse spacings, rather than the 11 or 15 currently used to obtain the full velocity spectrum in the STARE and SABRE radars, and thus gains greater precision or better time resolution. The two line-of-sight velocities, V_DP and V_LL, are in general not equal, with V_LL greater in magnitude than V_DP (sometimes much greater). Comparison of V_DP and V_LL for the two STARE stations and one of the SABRE stations shows interesting differences, and a number of statistically significant features. V_LL probably measures the velocity of primary irregularities whenever these exist with the appropriate k vector. Both velocities ought to be measured routinely, and also for comparison with other techniques.