Shortwave Direction and Spreading Measured with HF Radar

Abstract

he accuracy of wave direction and spreading at the Bragg-matched wavelength measured with HF radar over a wide range of HF operating frequencies is demonstrated by comparison with buoy data. The agreement for shortwave direction is better than that obtained for wind direction, which has been the more common application of this measurement, because these waves are not always aligned with the wind direction, particularly in short fetch and low wind speed situations. The method assumes a model of shortwave directionality and the validity of this is explored by using the buoy Fourier coefficients, with inconclusive results. The radar measurements do not use the linear dispersion relationship, but the comparison with buoy data does, and the implications of this are discussed.