Auroral backscatter observed at HF from Ottawa

Bistatic HF radar recordings of auroral scattering sources north of Ottawa, Canada were made during 1980–1981 using the sampled aperture receiving array of the Communications Research Centre, Ottawa and swept‐frequency CW transmissions from the Rome Air Development Center facilities, Rome, New York. Doppler frequency spreads in excess of ±100 Hz (corresponding to scatter motions of 2200 m/s) were obtained at least 35% of the time. The peak of the Doppler frequency distribution was sometimes shifted from zero by as much as 50 Hz, and significant contributions often occurred at Doppler frequencies greater than 150 Hz. Signals simultaneously received on both arms of a two‐arm direction‐finding array were used to identify the specific elevations and bearings of the backscatter signals. A detailed study of a particular hour‐long period is reported. On the basis of elevations and bearings obtained from data recorded at different times (minutes apart), for different Doppler frequencies and different delay times, a large number of “apparent” auroral backscatter sources are identified. All of these sources were probably located in the F layer. The source regions were elongated mainly in the north‐south direction and extended over at least 3° of latitude. Between such sources, north‐south corridors were found in which echo returns were either absent or very weak.