The measurement of the ocean wave directional spectrum from HF radar Doppler spectra


  • Lucy Wyatt


A model-fitting technique to extract the ocean long wave directional spectrum from the Doppler spectrum of HF backscatter from the sea surface is described here. This technique is an extension of one developed by Lipa and Barrick [1982] and extends the ocean wave frequency range that can be measured using radar frequencies in the lower HF range (6-18 MHz). Results of the application of this technique to a wide variety of simulated radar spectra are presented which demonstrate some of the weaknesses of the method as well as its strengths. The method predicts accurate estimates of the longwave amplitude spectrum as long as all wave components are propagating at an angle which is not perpendicular to the radar beam. When there are wave components perpendicular to the beam, this direction is estimated with very good accuracy, but there is an associated overprediction in amplitude. The solutions indicate that substantial improvements in accuracy are possible if two radars are used to survey the same patch of sea from two different directions.