Ocean Wave Directional Spectra Estimation from an HF Ocean Radar with a Single Antenna Array: Methodology

Abstract

A method to estimate ocean wave directional spectra using a high-frequency (HF) ocean radar was developed. The governing equations of wave spectra are integral equations of first-and second-order radar cross sections, the wave energy balance equation, and the continuity equation of surface winds. The parameterization of the source function is the same as that in WAM. Furthermore, the method uses the constraints that wave spectral values are smooth in both wave frequency and direction and that the propagation terms are small. The unknowns to be estimated are surface wind vectors at radial grids whose centers are the radar position, and wave spectral values at radial and wave frequency-direction grids. The governing equations are discretized in the radial and wave frequency-direction grids and are converted into a nonlinear minimization problem. Identical twin experiments showed that the present method can estimate wave spectra and dynamically extrapolate wave spectra, even in an inhomogeneous wave field.

A study on motion responses of classic spar platforms subjected to short crested waves

“…Fernandes [10] studied the measured directional spectrum by the phase-time-path-difference (PTPD) method. Another method to estimate the directional spectra using high frequency ocean radar was studied by Hisaki [11]. Hogben and Cobb [12] established a method for parametric modeling of directional spectra that could account for wind generated sea and swell waves.…”

Southward recirculation of the East China Sea Kuroshio west of Okinawa Island

“…We analyzed ocean surface currents observed by HF ocean radars. HF ocean radar is used to measure ocean surface currents [e.g., Barrick et al, 1977;Prandle and Ryder, 1985;Takeoka et al, 1995;Hisaki et al, 2001;Hisaki and Naruke, 2003] and surface waves [e.g., Hisaki, 1996Hisaki, , 2002Hisaki, , 2004Hisaki, , 2005Hisaki, , 2006 over broad spatial areas. The method is to radiate high-frequency radio waves and analyze the backscattered signals from the ocean.…”

Ocean wave directional spectra estimation from an HF ocean radar with a single antenna array: Observation

“…It is important to be able to estimate ocean surface wave spectra for a wide variety of marine applications including uses in physical oceanography, wave forecasting, ship routines and coastal engineering. One promising technology for wave measurement is high‐frequency (HF) ocean radar, which radiates HF radio waves to the sea surface and measures ocean surface currents [ Barrick et al , 1977; Prandle and Ryder , 1985; Takeoka et al , 1995; Hisaki et al , 2001; Hisaki and Naruke , 2003] and surface waves [ Hisaki , 1996, 2002, 2004, 2005] by analyzing the Doppler spectra of backscattered signals.…”

“…In addition, a large area is required to deploy the antenna system. To ameliorate these problems, Hisaki [2005] developed a method of estimating ocean wave spectra with a single radar. To the best of our knowledge, this is the first method that incorporates the wave model into the inversion method to estimate wave spectra from HF ocean radar.…”

“…Ocean wave directional spectra can be estimated even at positions where only first‐order Doppler spectra are available by incorporating the wave energy balance equation. Nevertheless, this new method was not applied to actual ocean data by Hisaki [2005]. The purpose of the present study was to apply the method developed by Hisaki [2005] to actual Doppler spectra obtained from HF radar observation, and to compare wave parameters with in situ observations.…”