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A small-aperture receiving array occupying a small area provides convenience for the layout of high-frequency (HF) radars. However, this kind of antennas has a wide beam, which adversely affects the wave measurements. To solve this problem, a method for extracting wave parameters from wide-beam radar echoes, which models current variations across the beam, is proposed in this article. The nondirectional wave spectrum is extracted from the echoes of a small-aperture HF radar, and wave parameters such as the significant wave height, peak, and mean wave period are then calculated from it. Simulation is carried out to assess the performance of the method for different current velocities, radar frequencies, and wind conditions. The proposed method is then applied to a nine-day dataset collected by a multifrequency HF radar with a circular receiving array (MHF-C) radar for further validation via comparisons between the radar-estimated and the buoy-measured wave parameters. Some factors that may affect the performance of wave height measurements are analyzed, such as the signal-to-noise ratio and radial current velocity. The correlation coefficient (CC) between the radar-estimated and the buoy-measured significant wave height is 0.90, and the root mean square difference (RMSD) is 0.51 m. For the mean wave period, the CC is 0.61 and the RMSD is 0.67 s. The results demonstrate that the significant wave height and the mean wave period extracted by the proposed method are consistent with the buoy-measured values, and the proposed method can overcome the broadening influence of the Doppler spectrum caused by ocean currents. [ABSTRACT FROM AUTHOR]

Surface wave spectral properties of centimeter to decameter (cmDm) wavelengths are of great interest to microwave remote sensing of the ocean. They are obviously different from the high-frequency extension of the wind-wave spectrum models developed for ocean science and engineering applications, which focus on the longer waves in the energetic peak region of the wave spectrum. For more than six decades, the cmDm waves are generally considered to be in the equilibrium range, and its spectral function has a constant slope: −5 or −4 in the 1-D frequency spectrum, and −3 or −2.5 in the 1-D wavenumber spectrum. The observed wind-wave spectral slopes, however, are not constant. As a result, the cmDm wave properties are significantly different from those inferred from an equilibrium spectrum model. Surface slope measurements are more suited for studying the cmDm waves. Microwave radar backscattering cross sections have been used to study the shorter range of cmDm waves. L-band lowpass-filtered mean square slope (LPMSS) is contributed by waves longer than about 0.6 m, here referred to as the decimeter to decameter (dmDm) waves. The analysis of LPMSS has improved the modeling of dmDm waves. Ultimately, the spectral slope variation is a critical characteristic of cmDm waves. The wave spectrum model formulated with the variable spectral slope consideration produces very good agreement with L-band scatterometer and reflectometer measurements. [ABSTRACT FROM AUTHOR]

We propose a method based on combining wave tracing and linear wave theory for the estimation of wave period and bathymetry in coastal areas from satellite images. The method depends on several parameters for which we provide ranges of variations adapted to the instrument. Experimental results are conducted on several sites located around the Hawaiian island of Oahu, using 13 Landsat-8 images. Results show that wave period estimations are compatible with the wave buoy measurements in all cases. In addition, bathymetry estimation results show a standard deviation of less than 15% of the observed depth out of the surf zone until 20 m for sites with a direct exposure to the swell and with an absence of clouds. The proposed method, which does not rely on ancillary data, represents a promising tool for bathymetry estimation using satellite images in which waves are present. [ABSTRACT FROM PUBLISHER]

By using ten years of collocated Precipitation Radar and buoy data, the relationships between Ku-band normalized radar cross section (σ°) and integrated wind and wave parameters (e.g., significant wave height, wave period, wave steepness, and wave age) at low incidence angles are analyzed for different sea states using correlation and dependence analysis. The results show that the relationships are significantly different for different sea states. Second, the potential for inverting these parameters directly from a single σ° is investigated. The results reveal that the retrieval of wind speed above 10 m (U10) is most suitable for a nonpure-swell sea and that the performance of significant wave height (Hs) retrieval decreases with the ratio of swell to wind waves. For wave period and wavelength, a feasible inversion can only be performed for a wind-wave-dominated sea. Wave steepness (δa) is strongly correlated with σ° in all sea states and can even be higher than that for U10 in pure-swell seas. It is suggested from the present data set that real wave age (β) may be retrieved from a swell-dominated sea and, therefore, has a low-value cutoff. Furthermore, the extent to which U10 retrieval depends on sea state is examined by calculating the correlation coefficient between σ° residuals and various standard wave parameters and, then, by determining the partial correlation coefficient between σ° and each wave parameter controlled by U10. Both results indicate that wind direction is better taken into account above 13.5°. Moreover, an auxiliary parameter related to wave slope, such as wave steepness, would help to improve retrieval performance. Significant wave height data are of secondary use, but an implementation with real wave age information might not significantly improve wind speed retrieval. To improve the performance of Hs and wave period retrieval, auxiliary information, such as wind speed, wave steepness, or wave age, is needed. Finally, multivariable empirical models are proposed. [ABSTRACT FROM AUTHOR]