Maximum-Likelihood Estimation of the Directional Distribution of 0.53-Hz Ocean Waves

L. R. Wyatt Sheffield Centre for Earth Observation Science, School of Mathematics and Statistics, University of Sheffield, Sheffield, United Kingdom

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L. J. Ledgard Sheffield Centre for Earth Observation Science, School of Mathematics and Statistics, University of Sheffield, Sheffield, United Kingdom

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C. W. Anderson Sheffield Centre for Earth Observation Science, School of Mathematics and Statistics, University of Sheffield, Sheffield, United Kingdom

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Abstract

The maximum-likelihood method is used to extract parameters of two-parameter models of the directional spreading of short wind waves from the power spectrum of high-frequency (HF) radar backscatter. The wind waves have a wavelength of half the radio wavelength that, for the data presented here, is at a frequency of 0.53 Hz. The parameters are short-wave direction, which at this frequency can be identified with wind direction, and the directional spread angle, the parameterization of which is model dependent. For the data presented here, the results suggest that the Donelan directional spreading model provides a better description of directional spreading than the coss model. The HF radar and wave buoy measurements are compared and show good agreement. Measurements are presented that show the temporal and spatial structure of the short-wave field responding to the passage of a frontal system.

Corresponding author address: Dr. L. R. Wyatt, University of Sheffield, School of Mathematics and Statistics, Applied Mathematics Section, P.O. Box 597, Sheffield S10 2UN, United Kingdom.

Email: L.Wyatt@sheffield.ac.uk

Abstract

The maximum-likelihood method is used to extract parameters of two-parameter models of the directional spreading of short wind waves from the power spectrum of high-frequency (HF) radar backscatter. The wind waves have a wavelength of half the radio wavelength that, for the data presented here, is at a frequency of 0.53 Hz. The parameters are short-wave direction, which at this frequency can be identified with wind direction, and the directional spread angle, the parameterization of which is model dependent. For the data presented here, the results suggest that the Donelan directional spreading model provides a better description of directional spreading than the coss model. The HF radar and wave buoy measurements are compared and show good agreement. Measurements are presented that show the temporal and spatial structure of the short-wave field responding to the passage of a frontal system.

Corresponding author address: Dr. L. R. Wyatt, University of Sheffield, School of Mathematics and Statistics, Applied Mathematics Section, P.O. Box 597, Sheffield S10 2UN, United Kingdom.

Email: L.Wyatt@sheffield.ac.uk

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