Methods for the extraction of long‐period ocean wave parameters from narrow beam HF radar sea echo

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Abstract
This paper describes inversion methods for HF radar sea echo Doppler spectra, giving parameters of the ocean wave spectrum in the important long‐wavelength region. Radar spectra exhibiting very narrow spikes in the higher‐order structure adjacent to the first‐order lines are indicative of ocean wave components with a single dominant wavelength. In the simplest method of interpretation these components are assumed to be unidirectional; in this case we show how to extract wave period, direction, and rms wave height. If this simple model does not provide a good fit to the data or if the radar side bands have the form of broad peaks, we use a model for the wave spectrum with a cardioid distribution in direction and a Gaussian distribution in wave frequency. Parameters identifiable from this model include the rms wave height, dominant direction and period, and the angular spread in the direction and frequency distributions. In normal surface wave experiments the major source of error or noise is the random surface height of the sea; we describe the resulting statistics of the radar spectrum and trace the propagation of uncertainty to the derived ocean parameters.