An experimental investigation of skywave sea-state radar techniques at a latitude near the Auroral Zone

In 1980 the Communications Research Centre (CRC) undertook a limited experimental program to investigate the feasibility of measuring sea-state characteristics off the east coast of Canada by means of high-frequency skywave radar. The propagation path, from the radar receiver at Ottawa, Ontario, to the observation area east of Newfoundland and Labrador, was tangent to the auroral zone, at times within and at best only a few degrees of latitude south of the auroral absorption zone. The experiment was conducted on a number of occasions between October 1980 and April 1982, for a period of about 6 h at midday on each occasion. Several agencies were involved: CRC personnel designed and conducted the experiment, using the Sampled Aperture Receiving Array (SARA) facility, and carried out the bulk of the analysis; transmissions were provided from Ava, New York, by the Rome Air Development Center (RADC); the Centre for Cold Ocean Resources Engineering (C-CORE) at Memorial University of Newfoundland, St. John´s, assembled ground-truth maps, operated a transponder, and developed an algorithm for automatic derivation of wave direction. CRC analysis techniques relied heavily upon computer-aided manual selection and interpretation of the Doppler spectra. Early attempts to construct automatic algorithms for the extraction of wave-height statistics encountered intractable problems, although the C-CORE wave-direction algorithm did meet with some success. Under quiet ionospheric conditions it was found that wave heights sometimes could be measured with acceptable accuracy, although accurate measurement was difficult when wave heights were low (2 m). Wave direction was more easily derived; it was usually observable even when wave heights could not be measured. The project demonstrated that a skywave radar could function at northern latitudes, but the limitations of the experimental facilities left practicability still in question. Considerable improvement would be expected, however, if unlimited freedom of choice of operating frequency were permitted, if the transmitter signal were focused to increase the power density in the target area, and if the receiving array were more comprehensive, i.e., designed specifically for the task.