Direction of arrival measurement of HF signals propagated over high latitude paths

The errors measured by HF direction finders on signals received over high latitude propagation paths are usually much greater than those of signals received via the mid and low latitude ionosphere. These errors have generally been attributed to the propagation path reflection points being in or near the auroral oval where large gradients in electron density are known to occur. These gradients form tilted reflection surfaces which allow off great circle propagation paths between the transmitter and the DF site. In November 1990 a controlled series of experiments were undertaken, in the high Arctic, at Alert, North West Territories, Canada, (82.5 degrees N, 62.4 degrees W) with a goniometer based and an interferometer based DF system. An interesting feature of the data collected during the tests was that on some days very large bearing swings (>+or-50 degrees ) were measured by both instruments and on two propagation paths. Furthermore, the interferometer also indicated changes in the elevation angle of arrival although these were not, in general, well correlated with the bearing changes. A possible cause of these errors is identified and the geophysical parameters responsible for the disturbance discussed.<
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