Directional Waverider Research Articles

O CLIMA DE ONDAS NA COSTA SUL DE ARRAIAL DO CABO, RJ: DISTRIBUIÇÃO DE PARÂMETROS DE ONDA

A Marinha do Brasil operou um um ondógrafo direcional WAVERIDER DATAWELL ao largo da costa sul de Arraial do Cabo, RJ, sobre uma lâmina d’água de 82 metros, entre agosto de 1988 e outubro de 1999. Os resultados do processamento preliminar das informações de onda direcional são apresentados. As séries temporais de curto termo foram consistidas e então submetidas a rotinas de cálculo do espectro direcional. As séries de parâmetros amostrais como altura significativa, período de pico, direção e espalhamento no período de pico foram sintetizadas na forma de histogramas e diagramas de ocorrência conjunta. Os resultados mostraram que a maior parte da energia provêm de ondas vindas de SSE a SSO, com períodos variando entre 11 e 13 segundos. Um segundo pico de energia vem de ESE a SSE com períodos predominando entre 7 e 9 segundos. O espalhamento das ondas vindas de S, geradas mais distante, foi ligeiramente maior do que as de SE. Isto pode estar relacionado com uma maior variabilidade espaço-temporal dos ventos nas respectivas zonas de geração.

A Two-Scale Approximation for Efficient Representation of Nonlinear Energy Transfers in a Wind Wave Spectrum. Part II: Application to Observed Wave Spectra

Abstract In Part I of this series, a new method for estimating nonlinear transfer rates in wind waves, based on a two-scale approximation (TSA) to the full Boltzmann integral (FBI) for quadruplet wave–wave interactions, was presented, and this new method was tested for idealized spectral data. Here, the focus is on comparisons of the TSA and the discrete interaction approximation (DIA) with the FBI for observed wave spectra from field measurements. Observed wave spectra are taken from a wave gauge array in Currituck Sound and a directional waverider off the coast near the Field Research Facility at Duck, North Carolina. Results show that the TSA compares much more favorably to the FBI than does the DIA, even for cases in which the parametric component of the formulation does not capture the spectral energy distribution very well. These results remain valid for the TSA estimates when the FBI results are significantly affected by the directional distribution of energy. It is also shown that although nonlinear transfers are substantially weaker in swell portions of the spectrum these interactions contribute significantly to the spectral evolution and net energy balance in long-distance swell propagation.

Variabilidade morfológica da praia do Pântano do Sul, ilha de Santa Catarina, Brasil

This work aims at analyzing some beach morphologic variability profiles which have been measured on Pântano do Sul beach, south of Santa Catarina Island. Three beach profiles have been monitored along the beach from August 2002 to August 2003 in a monthly rate. An extra profile has been measured in order to clarify the presence of megacusps. Wave characteristics in the surf zone have been monitored through visual observation in each profile. The wave regime in deep waters has also been assessed during the beach profile sampling period by using data collected by a directional wave rider buoy placed approximately 35 km from the Santa Catarina Island. The profiles morphological variations have taken place due to four main reasons: (i) the wave average energy variability among the three sectors thus reflecting the exposure level of the various parts of the beach to the incident waves. The more the beach is exposed to the waves action, the more are the variations in its sedimentary stock; (ii) high wave energy, characterized by South-Southeast swells with peak periods above 10 seconds and significant wave height above 4 m in deep waters, condition which erodes the subaereal portion of the beach; (iii) persistent low wave energy, which usually brings on sediment to the beach; (iv) the rhythmic beach morphology itself, which may trigger local variations in the beach face slope as well as in its volume among profiles measured on megacusps crests or on megacusps embayments.

Operational Wave, Current, and Wind Measurements With the Pisces HF Radar

This paper presents results of a trial of a Pisces HF radar system aimed at assessing its use as a component of a wave-monitoring network being installed around the coasts of England and Wales. The radar system has been operating since December 2003 and the trial continued to June 2005. The data have been processed in near-real time and displayed on a website. Radar measurements of the directional spectrum and derived parameters are compared with those measured with a directional waverider and with products from the Met Office, United Kingdom, operational wave model. Radar measurements of currents and winds are also compared with Met Office model products and, in the case of winds, with the QuikSCAT scatterometer. Statistics on data availability and accuracy are presented. The results demonstrate that useful availability and accuracy in wave and wind parameters are obtained above a waveheight threshold of 2 m and at ranges up to 120 km at the radar operating frequencies (7-10 MHz) used. Waveheight measurements above about 1 m can be made with reasonable accuracy (e.g., mean difference of 2.5% during January-February 2004). Period and direction parameters in low seas are often contaminated by noise in the radar signal. The comparisons provide some evidence of wave model limitations in offshore wind and swell conditions

Intercomparison of Sea-State and Zero-Crossing Parameters From the WACSIS Field Experiment and Interpretation Using Video Evidence

During the WACSIS field experiment, wave elevation time series data were collected over the period December 1997 to May 1998 on and near the Meetpost Nordwijk platform off the coast of the Netherlands from an EMI laser, a Saab radar, a Baylor Wave Staff, a Vlissingen step gauge, a Marex radar and a Directional Waverider. This paper reports and interprets, with the help of simultaneous dual video recordings of the ocean surface, an intercomparison of both single wave and sea state wave parameters.

Directional wave measurements from three wave sensors during the FETCH experiment

During the Flux, Etat de la mer et Télédéction en Condition de fetcH variable (FETCH) experiment, directional wave measurements were made by an airborne radar RESSAC and by two moored buoys, an Air–Sea Interaction Spar (ASIS) and a Directional Waverider. In order to define the performance and compatibility of these wave sensors with different measuring principles, a comparison of the directional measurements in a variety of meteorological conditions during the experiment is presented in this paper. It was found that within the limits of their operational ranges, the sensors agreed on the one‐dimensional spectrum and the basic parameters derived from it—significant wave height and peak frequency. The sensors reported the directional features of the wave field and the mean direction consistently, but in some cases the two buoys disagreed on the directional width of the spectrum. Most of these cases were associated with a single swell‐dominated event.

Validation and intercomparisons of wave measurements and models during the EuroROSE experiments

The objective of the EuroROSE (European Radar Ocean Sensing) project was to combine area covering ground-based remote-sensed wave and current data with high-resolution numerical forecast models to provide nowcasts and forecasts for coastal marine operators. Two experiments to test and to demonstrate the system took place: one on the coast of Norway, north of Bergen in March 2000 and the second on the north coast of Spain at Gijon in October–November 2000. Qualitative and quantitative intercomparisons of the wave measurements and wave model products from these experiments are presented. These include measurements using the Wellen Radar (WERA) high-frequency (HF) radar, the WaMoS (Wave Monitoring System) X-band radar, a directional Waverider and output from the WAM wave model. Comparisons are made of the full directional spectra and of various derived parameters. This is the first-ever intercomparison between HF and X-band radar wave measurements and between either of these and WAM. It has provided a data set covering a much wider range of storm and swell conditions than had been available previously for radar wave-measurement validation purposes and has clarified a number of limitations of the radars as well as providing a lot of very useful radar wave data for future model-validation applications. The intercomparison has led to improvements in the data quality control procedures of both WaMoS and WERA. The two radar sytems measured significant wave height with mean biases of 3% and 6%, respectively, and mean direction differences of less than 2° in both cases. Limitations in the WAM model implementation are also discussed.

Sea surface imaging with an across-track interferometric synthetic aperture radar: the SINEWAVE experiment

An across track interferometric synthetic aperture radar (InSAR) is used to image ocean waves. Across track InSAR data were acquired during the SAR INnterferometry Experiment for validation of ocean Wave imaging models (SINEWAVE) in the North Sea using an airborne X-band radar with horizontal polarization. A wind sea system was imaged at different flight levels and with different flight directions with respect to the ocean wave propagation direction. Simultaneously, ocean wave spectra were measured by a directional wave rider buoy. Thus, the experiment data comprises synthetic aperture radar (SAR) intensity, coherence, and phase images together with in situ measurements. As shown in a recent theoretical study by Schulz-Stellenfleth and Lehner (2001), across track InSAR provides distorted (bunched) digital elevation models (DEMs) of the sea surface. Using SINEWAVE data the DEM bunching mechanism is verified with in situ ocean wave measurements available for the first time. It is shown that significant waveheight as well as one-dimensional (1D) wavenumber spectra derived from bunched DEMs and buoy data are in good agreement for small nonlinearities. Peak wave directions and peak wavelength detected in bunched DEMs and SAR intensity images are compared with the buoy spectrum. Peak rotations of up to 30/spl deg/ with respect to the buoy spectrum are found depending on flight direction and flight level. Two-dimensional (2D) spectra of bunched DEMs, corresponding coherency maps, and SAR intensity images are intercompared. The signal-to-noise ratio (SNR) of bunched DEM spectra is shown to be about 5 to 10 dB higher than the SNR of SAR intensity image spectra.

A Comparison of Directional Buoy and Fixed Platform Measurements Of Pacific Swell

The performance of the Datawell Directional Waverider and the National Data Buoy Center (NDBC) 3-m discus buoy, widely used to measure the directional properties of surface gravity waves, are evaluated through comparisons to an array of six pressure transducers mounted 14 m below the sea surface on a platform in 200-m depth. Each buoy was deployed for several months within a few kilometers of the platform. The accuracy of the platform ground-truth array was verified by close agreement of wavenumber estimates with the theoretical linear dispersion relation for surface gravity waves. Buoy and array estimates of wave energy and directional parameters, based on integration of the directional moments across the frequency band of energetic swell (0.06–0.14 Hz), are compared for a wide range of wave conditions. Wave energy and mean propagation direction estimates from both buoys agree well with the platform results. However, the Datawell buoy provides significantly better estimates of directional spread and skewness than the NDBC buoy.