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The Surface Waves Investigation and Monitoring instrument (SWIM) provides the directional wave spectrum within the wavelength range of 23–500 m, corresponding to a frequency range of 0.056–0.26 Hz in deep water. This frequency range is narrower than the 0.02–0.485 Hz frequency range of buoys used to validate the SWIM nadir Significant Wave Height (SWH). The modulation transfer function used in the current version of the SWIM data product normalizes the energy of the wave spectrum using the nadir SWH. A discrepancy in the cut-off frequency/wavelength ranges between the nadir and off-nadir beams can lead to an overestimation of off-nadir cut-off SWHs and, consequently, the spectral densities of SWIM wave spectra. This study investigates such errors in SWHs due to the wavelength cut-off effect using buoy data. Results show that this wavelength cut-off error of SWH is small in general thanks to the high-frequency extension of the resolved frequency range. The corresponding high-frequency cut-off errors are systematic errors amenable to statistical correction, and the low-frequency cut-off error can be significant under swell-dominated conditions. By leveraging the properties of these errors, we successfully corrected the high-frequency cut-off SWH error using an artificial neural network and mitigated the low-frequency cut-off SWH error with the help of a numerical wave hindcast. These corrections significantly reduced the error in the estimated cut-off SWH, improving the bias, root-mean-square error, and correlation coefficient from 0.086 m, 0.111 m, and 0.9976 to 0 m, 0.039 m, and 0.9994, respectively. [ABSTRACT FROM AUTHOR]

The Surface Waves Investigation and Monitoring instrument (SWIM) provides the directional wave spectrum within the wavelength range of 23–500 m, corresponding to a frequency range of 0.056–0.26 Hz in deep water. This frequency range is narrower than the 0.02–0.485 Hz frequency range of buoys used to validate the SWIM nadir Significant Wave Height (SWH). The modulation transfer function used in the current version of the SWIM data product normalizes the energy of the wave spectrum using the nadir SWH. A discrepancy in the cut-off frequency/wavelength ranges between the nadir and off-nadir beams can lead to an overestimation of off-nadir cut-off SWHs and, consequently, the spectral densities of SWIM wave spectra. This study investigates such errors in SWHs due to the wavelength cut-off effect using buoy data. Results show that this wavelength cut-off error of SWH is small in general thanks to the high-frequency extension of the resolved frequency range. The corresponding high-frequency cut-off errors are systematic errors amenable to statistical correction, and the low-frequency cut-off error can be significant under swell-dominated conditions. By leveraging the properties of these errors, we successfully corrected the high-frequency cut-off SWH error using an artificial neural network and mitigated the low-frequency cut-off SWH error with the help of a numerical wave hindcast. These corrections significantly reduced the error in the estimated cut-off SWH, improving the bias, root-mean-square error, and correlation coefficient from 0.086 m, 0.111 m, and 0.9976 to 0 m, 0.039 m, and 0.9994, respectively.

In this note, a wave simulation method based on the wave spectrum is proposed, and the wave simulation is transformed into external interference to verify the necessity of using variable encounter angle real wave interference. Firstly, A wave simulation method based on wave spectrum and equidistant method is proposed and demonstrated. Secondly, wave modeling is transformed into interference force related to the encounter angle by fully considering the real marine environment. Furthermore, a trajectory tracking controller with variable encounter angles and the actual sea state is designed using the disturbance modeling method. Finally, the necessity and authenticity of considering varying encounter angles and real sea conditions in the motion control of unmanned surface vehicles (USVs) are proved by simulation. [ABSTRACT FROM AUTHOR]

Modeling a nonlinear ocean wave is one of the primary concerns in ocean engineering and naval architecture to perform an accurate numerical study of wave-structure interactions. The high-order spectral (HOS) method, which can simulate nonlinear waves accurately and efficiently, was investigated to see its capability for nonlinear wave generation. An open-source (distributed under the terms of GPLv3) project named "HOS-ocean" was used in the present study. A parametric study on the "HOS-ocean" was performed with three-hour simulations of long-crested ocean waves. The considered sea conditions ranged from sea state 3 to sea state 7. One hundred simulations with fixed computational parameters but different random seeds were conducted to obtain representative results. The influences of HOS computational parameters were investigated using spectral analysis and the distribution of wave crests. The probability distributions of the wave crest were compared with the Rayleigh (first-order), Forristall (second-order), and Huang (empirical formula) distributions. The results verified that the HOS method could simulate the nonlinearity of ocean waves. A set of HOS computational parameters was suggested for the long-crested irregular wave simulation in sea states 3 to 7.

Wave conditions around islands in the South China Sea (SCS) are of significant interest due to their importance for marine operations and coastal engineering. Understanding and accurately predicting wave characteristics in this region are crucial. In this study, the third-generation wave model WAVEWATCH III is employed to examine wave conditions around islands in the SCS. According to the water depth and significant wave height, the sea state around the island was classified into two categories: typhoon sea state and moderate sea state. Several popular wind input–dissipation source terms (ST2, ST4 and ST6) are used to assess the typhoon sea state and the moderate sea state separately. The results are validated by field wave data. ST4 and ST6 show good performance in significant wave height for moderate sea states, while ST2 is good at the mean wave period. For the typhoon sea state, ST2 gives the best results in significant wave height with larger correlation coefficients and a smaller RMSE. The above results provide valuable insights into the effects of different source terms on the accuracy of wave simulations for different sea states. The spatial distribution of the significant wave heights is also demonstrated with ST2, which may be useful for assessing the wave conditions of marine structures from the large scale of the SCS to the island scale of the Yongle Atoll. [ABSTRACT FROM AUTHOR]

The Pearl River Estuary is a typical estuary region in southern China, and the study of surface wave occurrence and characteristics is of great importance for shipping management, nearshore engineering, and monitoring shoreline changes and other human activities. Long-term and continuous observational data are critical for achieving a better understanding of waves. In this study, the wave measurements based on a high-precision wave gauge were analyzed and observation data over approximately two years at a sampling frequency of 2 Hz were obtained. The wave system in the Pearl River Estuary was found to deviate from the assumption of a stationary stochastic process similar to that in the open ocean, due to the effects of abnormal waves caused by human activities. Therefore, traditional distribution functions such as Rayleigh and Weibull were not suitable for accurately fitting the main wave parameters ( H s , T p , etc.), particularly in the tail. Consequently, abnormal wave signals were extracted from all wave sets, and through the comparison and analysis of the wave spectral features, it was determined that these abnormal waves are caused by the ship wakes. The spectral characterization of these waves was performed to determine the characteristics of different ship wake processes. Ship wakes in the Pearl River Estuary are an important part of the wave system, and their wave height is significantly larger than the normal wave. Based on the spectral characteristics of ship wakes, this study proposed some news characteristics of ship wakes in the main channel of the Pearl River Estuary. [ABSTRACT FROM AUTHOR]

Spectral wave modelling is widely used to simulate large-scale wind–wave processes due to its low computation cost and relatively simpler formulation, in comparison to phase-resolving or hydrodynamic models. However, some applications require a time-domain representation of sea waves. This article proposes a methodology to transform the wave spectrum into a time series of water surface elevation for applications that require a time-domain representation of ocean waves. The proposed method uses a generated phase spectrum and the inverse Fourier transform to turn the wave spectrum into a time series of water surface elevation. The consistency of the methodology is then verified. The results show that it is capable of correctly transforming the wave spectrum, and the significant wave height of the resulting time series is within 5% of that of the input spectrum.

Wave energy is a promising renewable resource for its reliability and power density, and many technological milestones have been achieved. Significant efforts are made to design and optimize Wave Energy Converters (WECs); however, analyses are often limited to simplified conditions. Among such restrictive assumptions, waves are frequently described utilizing monodirectional spectra, thus leading to approximate evaluations, also in terms of absorbed power. In real sea conditions, the waves are multidirectional, and the analysis as a 2D superposition of multiple wave components should be investigated. In particular, linear waves can be analyzed as a sum of sine waves characterized by different amplitudes, frequencies, phases and directions. The case study device analyzed in this paper is PeWEC (Pendulum Wave Energy Converter), a rotating mass device that converts energy based on pitch motion, moored through a spread catenary mooring system. The sea states investigated are those of the island of Cyprus. The spectrum is defined as the combination between the JONSWAP frequency spectrum and the cos-2s directional spectrum. To compute the sea elevation components the Deterministic Amplitude Scheme (DAS) method is used. The forcing acting on the device, the mooring loads and the device motions are examined and compared to quantify the error produced by the monodirectional approximations. The time domain solver OrcaFlex is employed to investigate the interaction of the waves with the moored hull. Compared with the multidirectional analysis, the monodirectional approximation generates an overestimation of the pitch by 5% and of the surge by 3%, highlighting the importance of taking spreading into account if the device is directional.

Wave conditions around islands in the South China Sea (SCS) are of significant interest due to their importance for marine operations and coastal engineering. Understanding and accurately predicting wave characteristics in this region are crucial. In this study, the third-generation wave model WAVEWATCH III is employed to examine wave conditions around islands in the SCS. According to the water depth and significant wave height, the sea state around the island was classified into two categories: typhoon sea state and moderate sea state. Several popular wind input–dissipation source terms (ST2, ST4 and ST6) are used to assess the typhoon sea state and the moderate sea state separately. The results are validated by field wave data. ST4 and ST6 show good performance in significant wave height for moderate sea states, while ST2 is good at the mean wave period. For the typhoon sea state, ST2 gives the best results in significant wave height with larger correlation coefficients and a smaller RMSE. The above results provide valuable insights into the effects of different source terms on the accuracy of wave simulations for different sea states. The spatial distribution of the significant wave heights is also demonstrated with ST2, which may be useful for assessing the wave conditions of marine structures from the large scale of the SCS to the island scale of the Yongle Atoll.

There is a wide consensus within the polar science, meteorology, and oceanography communities that more in situ observations of the ocean, atmosphere, and sea ice are required to further improve operational forecasting model skills. Traditionally, the volume of such measurements has been limited by the high cost of commercially available instruments. An increasingly attractive solution to this cost issue is to use instruments produced in-house from open-source hardware, firmware, and postprocessing building blocks. In the present work, we release the next iteration of our open-source drifter and wave-monitoring instrument, which follows these solution aspects. The new design is significantly less expensive (typically by a factor of 5 compared with our previous, already cost-effective instrument), much easier to build and assemble for people without specific microelectronics and programming competence, more easily extendable and customizable, and two orders of magnitude more power-efficient (to the point where solar panels are no longer needed even for long-term deployments). Improving performance and reducing noise levels and costs compared with our previous generation of instruments is possible in large part thanks to progress from the electronics component industry. As a result, we believe that this will allow scientists in geosciences to increase by an order of magnitude the amount of in situ data they can collect under a constant instrumentation budget. In the following, we offer (1) a detailed overview of our hardware and software solution, (2) in situ validation and benchmarking of our instrument, (3) a fully open-source release of both hardware and software blueprints. We hope that this work, and the associated open-source release, will be a milestone that will allow our scientific fields to transition towards open-source, community-driven instrumentation. We believe that this could have a considerable impact on many fields by making in situ instrumentation at least an order of magnitude less expensive and more customizable than it has been for the last 50 years, marking the start of a new paradigm in oceanography and polar science, where instrumentation is an inexpensive commodity and in situ data are easier and less expensive to collect. [ABSTRACT FROM AUTHOR]

The paper is devoted to further development of an accelerated method for simulation of the two-dimensional surface waves at infinite depth with the use of a two-dimensional model derived with simplifications of the three-dimensional equations for potential periodic deep-water waves. A 3D full wave model (FWM) is based on a numerical solution of a 3D Poisson equation written in the surface-fitted coordinates for a nonlinear component of the velocity potential. For sufficient vertical resolution used for the Poisson equation, the 3D model provides very high accuracy. The simplified model is based on the 2D Poisson equation written for a free surface. This exact equation contains both the first and second derivatives of the velocity potential, i.e., it is unclosed. The analysis of the accurate solutions for the 3D velocity potential obtained with the 3D model shows that those variables are linearly connected to each other. This property allows us to obtain a 2D equation for the first derivative of the velocity potential (i.e., vertical velocity on surface), which gives the closed 2D formulation for a 3D problem of two-dimensional waves. The previously developed scheme was not universal since the parameters of the closure scheme had to be adjusted to the specific setting. The current paper offers a new formulation of a closing scheme based on the integral parameters of wave field. The method of closing the equations, as well as the numerical parameters, were chosen on the basis of the multiple numerical experiments with the full nonlinear wave model (FWM) and selection of a suitable closing scheme. That is why the given model can be called Heuristic Wave Model (HWM). The connection between the first and second variables is not precise; hence, the method as a whole cannot be exact. However, the derived 2D model is able to reproduce different statistical characteristics of the 2D wave field with good accuracy. The main advantage of the model developed is its high performance exceeding that of 3D model by about two decimal orders. [ABSTRACT FROM AUTHOR]

[Introduction] According to the measured wave data of one year in the deep water area of Eastern Guangdong, this paper mainly studies the basic characteristics of annual waves in the sea area. [Method] Firstly, the eigenvalues of wave height and period were counted month by month, get the basic distribution characteristics of the whole year; Then made statistics for the wave direction, obtain the seasonal characteristics of wave direction; Furthermore, the joint distribution of wave height and period and the relationship between wave height and period were explored; Finally, the characteristics of typical typhoon waves were studied. [Result] The results showed that: (1) The annual average Hs is 1.52 m, the Hmax is 15.97 m, the highest mean value of Hs in December, January and February, the Hmax is caused by Typhoon Mangkhut; (2) Affected by monsoon season and tropical cyclone, the normal wave direction and strong wave direction are ENE and SE respectively; (3) The main wave type in the whole year is wind wave component, the correlation between wave height and period is fitted; (4) According to the measured data of typhoon wave of Mangkhut, both wave height and period have a significant increase and decrease process. Through wave spectrum analysis during the typhoon, it experienced the evolution from double-peaked spectrum to single-peaked spectrum, it shows that the wave type during typhoon is mainly wind-surge mixed wave, the peak value reached 96.74 m2/Hz at 6:00 on September 16, peak frequency is 0.07 Hz. [Conclusion] The research results of this paper can provides technical reference for the design of related marine engineering.

We consider a method for calculating the natural wave spectra of round and rectangular shielded waveguides with arbitrary dielectric filling, which is a modification of the Galerkin method and based on the representation of the wave fields of the guiding structure in the form of an expansion in the eigenfunctions of the boundary value problem for uniformly filled waveguides. An algorithm for calculating the characteristics of symmetric waves of a circular waveguide with gradient dielectric filling and a rectangular shielded waveguide with arbitrary and angular dielectric filling has been compiled.

Spectral wave modelling is widely used to simulate large-scale wind--wave processes due to its low computation cost and relatively simpler formulation, in comparison to phase-resolving or hydrodynamic models. However, some applications require a time-domain representation of sea waves. This article proposes a methodology to transform the wave spectrum into a time series of water surface elevation for applications that require a time-domain representation of ocean waves. The proposed method uses a generated phase spectrum and the inverse Fourier transform to turn the wave spectrum into a time series of water surface elevation. The consistency of the methodology is then verified. The results show that it is capable of correctly transforming the wave spectrum, and the significant wave height of the resulting time series is within 5% of that of the input spectrum. [ABSTRACT FROM AUTHOR]

The vast majority of guiding structures are described [13] by non-self-adjoint electrodynamic operators, which are understood as the totality of the differential equation and the system of boundary conditions. In [15], the conditions for the non-self-adjointness of electrodynamic operators are formulated as applied to the method of separation of variables. The indicated operators can be put in accordance with [56] integral equations. The boundary problems for cylindrical guiding structures are assigned the Volterra integral equations, using asymptotic solutions of which an a priori determination of the spectra of solutions of boundary-value problems for two-layer open and shielded waveguides is carried out.

The paper is devoted to further development of an accelerated method for simulation of the two-dimensional surface waves at infinite depth with the use of a two-dimensional model derived with simplifications of the three-dimensional equations for potential periodic deep-water waves. A 3D full wave model (FWM) is based on a numerical solution of a 3D Poisson equation written in the surface-fitted coordinates for a nonlinear component of the velocity potential. For sufficient vertical resolution used for the Poisson equation, the 3D model provides very high accuracy. The simplified model is based on the 2D Poisson equation written for a free surface. This exact equation contains both the first and second derivatives of the velocity potential, i.e., it is unclosed. The analysis of the accurate solutions for the 3D velocity potential obtained with the 3D model shows that those variables are linearly connected to each other. This property allows us to obtain a 2D equation for the first derivative of the velocity potential (i.e., vertical velocity on surface), which gives the closed 2D formulation for a 3D problem of two-dimensional waves. The previously developed scheme was not universal since the parameters of the closure scheme had to be adjusted to the specific setting. The current paper offers a new formulation of a closing scheme based on the integral parameters of wave field. The method of closing the equations, as well as the numerical parameters, were chosen on the basis of the multiple numerical experiments with the full nonlinear wave model (FWM) and selection of a suitable closing scheme. That is why the given model can be called Heuristic Wave Model (HWM). The connection between the first and second variables is not precise; hence, the method as a whole cannot be exact. However, the derived 2D model is able to reproduce different statistical characteristics of the 2D wave field with good accuracy. The main advantage of the model developed is its high performance exceeding that of 3D model by about two decimal orders.

Increasing problems due to supplying energy demand conveyed researchers to find a solution in renewable energy resources and consequently marine engineers drew attentions towards wave energy which has the merit of higher energy density than the other resources. Oscillating Water Column (OWC) is one of the most propitious devices for capturing wave energy. Researchers have studied the device under different wave height and period conditions and they investigated various geometric parameters such as front wall draft and the chamber length. However, the effects of wave spectrum type or shape has not been investigated deeply yet. Different wave spectra have been developed for different places around the world but the focus of this study is on the two well-known spectra called JONSWAP and Pierson-Moskowitz to see how the type of the spectrum can impact on inner chamber fluctuation, pressure variation and reflection response of an offshore OWC. To achieve this goal, a 1:15 scale model of an offshore OWC was constructed in National Iranian Marine Laboratory. The results show that inner chamber free surface spectrum is affected by the type of incident wave spectrum. In another word, energy content at peak frequency was approximately 50% higher when the incident wave spectrum is of JONSWAP type. However, energy corresponding to sloshing frequency and total energy content in the chamber were almost the same for both types of the spectra. Pressure spectra inside the chamber showed a similar trend as free surface elevation. Although there was a little difference in reflection response of an OWC influenced by the type of spectra, this discrepancy was more pronounced in high frequency waves.

Successful rescue action at sea is based on a. o. a correct choice of rescue means and their reliability. Operational characteristics of life-saving appliances determine their performance in a given water area. Therefore they affect duration time of rescue action and decide this way on survival time of shipwrecked persons. This paper presents impact of characteristics of circular inflatable life rafts on their dynamics in a given sea environment. Particular issues dealing with raft motion were analyzed and their solutions were then presented in the form of computer programs built into MATLAB environment. The programs operate on the open choice basis–the user is requested to introduce data of a raft to be investigated. The program clearly informs which units should be used for the data. The obtained results allow to limit survivours searching area and simultaneously form the basis for working out a model of searched object drift motion. In this work the use was made of the results obtained from the KBN research project No. 4T12C03827 in which an attempt was made to analyzing capsize probability of a raft at given sea states. The raft investigated in the project is also used as a reference raft in the computer programs developed in this work.

Violante-Carvalho, N.; D'Avila, V.; Heringer Villena, H.H., and Mendonça Filippo, A.M., 2020. The Flying Anchor: An original technique for beach profile measurements in the surf zone. Journal of Coastal Research, 36(3), 654–660. Coconut Creek (Florida), ISSN 0749-0208. An original method is proposed to measure beach profiles in the surf zone. Surveying this dynamic and energetic region is usually a challenge when waves are large, which is exactly when the nearshore processes are more intense. The lack of bathymetry and wave data is indisputably a limiting factor hindering the understanding of the physics involved. Countless techniques have been proposed in the last decades to increase the temporal and spatial density of such measurements, with different degrees of success. Seeking to bring new approaches to address these issues, the proposed operation consists of launching a specially designed anchor from the beach face over the surf zone, carrying a graduated cable. When the cable is drawn taut, a pressure sensor is hand towed along the sea floor measuring the profile, as well as yielding the wave energy spectrum. The technique is efficient and fast and employs a small team at a very low cost. Some of the main limitations of the known in situ techniques, such as sea state dependency, high cost per profile, and longshore drift, are mitigated. [ABSTRACT FROM AUTHOR]

The wave spectrum provides a short-term sea state description that is used for calculations in various engineering disciplines. Accepted theoretical models are developed for oceans and specific regions and their parameters are determined to best fit the data which is usually gathered in dedicated wave measurement campaigns. Modern numerical wave model simulations of historic periods that are calibrated with available satellite altimetry measurements provide a new data source that is comprehensive in space and time. One such dataset, the WorldWaves database, is used to revise and optimize the standard wave spectrum parameters for the Adriatic Sea. Tabain’s, wave spectrum and its modal frequency relation are revised. An optimization methodology is developed to find the parameters to best describe the Adriatic Sea waves. Ultimately, the JONSWAP wave spectrum is chosen and its parameters were optimized together with the parameters of Tabain’s modal frequency relation. An improved wave spectrum definition for the Adriatic Sea is proposed named the JONSWAP-Adriatic wave spectrum. [ABSTRACT FROM AUTHOR]

A new approach for assessing the quality of Synthetic Aperture Radar (SAR) wave spectra is presented here. The algorithm addresses two specific issues, related to the 180° directional ambiguity in the propagation direction inherent to SAR measurements, and the removal of noise. In spite of several and progressive advances in the mapping and retrieval of SAR wave spectra, these issues are persistent in the existing official databases and hinder the use of these data for practical uses. This new algorithm is based on a recently developed database of long-term global wave spectral characteristics, which allows estimating the occurrence probability of every individual wave system found in the observed spectra, and that of its ambiguous pair. In addition, assuring the spatial consistency of the wave systems along track, helps obtaining more robust results. In this sense, wave spectra within a track are processed in several steps, so that wave systems with more likelihood of being correct are processed first, and consequently used to evaluate the more challenging components. Accordingly, a specific quality label is assigned to every wave system depending on the certainty achieved. An Envisat track over a challenging area with multiple crossing swells is used to illustrate the performance of the algorithm. [ABSTRACT FROM AUTHOR]

The intertidal beach profile provides coastal engineers and managers with a good indication of the current state of a sandy coastline, however regular beach profile measurements are time consuming and expensive to obtain using conventional surveying methods. The potential to reconstruct the intertidal beach profile from measurements of reflected waves is tested here using three field datasets covering a different range of hydro-morphological conditions from dissipative, to reflective. The swash is found to behave as a low-pass filter on reflected waves, with a cut-off frequency that primarily depends on the swash slope. An agreement is found between video-derived swash spectrum saturation tail and the shortest reflected waves, computed from deep water directional wave measurements. By integrating this swash slope over a tidal cycle, the shape of the intertidal beach profile can be reconstructed. Our results clearly show the potential of such method to estimate complex intertidal beach profile, such as double-slope beaches. • The intertidal beach profile can be reconstructed by integrating the swash slope over a tidal cycle. • The swash behaves as a low-pass filter, with a cut-off frequency that primarily depends on the swash slope. • A good agreement is found between video-derived swash spectrum saturation tail and the shortest reflected waves. [ABSTRACT FROM AUTHOR]

The ocean surface roughness and foam coverage are the two important elements in the electromagnetic (EM) thermal emission computation. The foam contribution accounts for the air modifying the dielectric property of the water side interface layer. It can be modeled using a mixing rule of the air and water relative permittivities weighted by the air fraction and foam-free portion in the EM-influence volume, respectively. For high EM frequencies, the air fraction can be approximated by the whitecap fraction given as a function of wind speed empirically established with oceanographic observations. This simplification works very well for C band and higher frequencies but overestimates the foam effects for the L-band; the air fraction needs to be reduced compared to the whitecap fraction. Through the thermal emission analysis applied to several data sets of radiometer measurements in high winds, a function relating the air fraction and whitecap coverage is established. Incorporating the proposed function, the thermal emission model computations are in very good agreement with radiometer measurements at 1.4, 4.7, 6, 10, 18, 23, and 37 GHz with various incidence angles and both vertical and horizontal polarizations. Comparing the foam and roughness components contributing to the wind-induced thermal emission, the roughness contribution dominates over a broad wind speed range. Except for the vertical polarization near the 55° incidence angle, the roughness contribution is almost always greater than the foam contribution to well above 20 m/s wind speed, the crossover wind speed for the foam contribution to exceed roughness contribution is dependent on the frequency, incidence angle, and polarization. [ABSTRACT FROM AUTHOR]

Synthetic aperture radar (SAR) is a valuable tool to observe many oceanographic parameters of the ocean surface. The significant wave height (Hs or SWH), defined as the mean wave height of the highest one-third of waves, can be estimated using indirect relations between SAR-derived and the actual ocean wave spectra. However, multilook SAR imaging of ocean surface waves is highly affected by degraded azimuthal resolution and the random shift of scattered elements as the waves propagate off the SAR range direction. Therefore, the azimuthal displacement is found to be very low when near-range travelling ocean waves with narrow band spectrum are imaged. In this study, an improved algorithm is developed to directly estimate the significant wave height of ocean waves that propagate in the near-range direction using SARSAR imagery. The slope of the NRCS with respect to the radar wave incidence angle is derived from SAR images using an iterative scheme. A total of 69 SAR images from Sentinel-1A and 1B from 2016 to 2017, acquired near Hawaii, and in situ wave data from nearby National Data Buoy Center buoys are used to estimate Hs and validate the improved algorithm. Results show that the algorithm performs well in estimating SWH under low to moderate wind forcing conditions (4–10 ms−1). The accuracy of the SWH estimation decreases under high-wind-speed and wind-wave-dominant conditions. [ABSTRACT FROM AUTHOR]

Highlights • A hurricane risk assessment framework is introduced to identify vulnerable bridges. • The maximum sustained wind speed is selected as the intensity measure. • Uncertainties in both demand and capacity variables are considered. • The proposed framework is highly effective in assessing risk of bridge failures. Abstract Coastal bridges sustained severe damage during hurricanes Ike, Katrina, and Ivan. Reducing the impact of future hurricane events to coastal bridges requires conducting a comprehensive risk analysis. A comprehensive risk analysis of bridges enables owners to assign limited resources to the most critical bridges in the inventory through a risk-informed decision making process. This study presents a computationally efficient methodology for structural fragility analysis and risk assessment of simply supported coastal bridges vulnerable to hurricane hazard. Various sources of uncertainty associated with hurricane hazard and bridge response are identified, and thereby establishing probability distributions. The novelty of the proposed method includes the consideration of uncertainties in extreme wave heights and wave period by means of a wave spectral density distribution in the calculation of wave forces. The proposed hurricane risk analysis method was successfully applied to coastal bridges located in the state of Georgia (U.S.A). The application presents the derivation of probabilistic models of demand, capacity and hazard; and highlights the potential of the proposed framework for identification and ranking of the most vulnerable bridges. [ABSTRACT FROM AUTHOR]

The wave characteristics of the eastern Guangdong offshore water were quantified based on 1-year wave observations at a water depth of 60 m. This study statistically analyzed the observed wave characteristics and quantified the variations of the wave parameters and spectrum due to Super Typhoon Mangkhut. Results showed that the dominant and strong wave directions in the northeastern South China Sea were north-eastern and eastern, respectively. The average significant wave height was in the range of 0.7–2.4 m. During Super Typhoon Mangkhut, the maximum wave height and period were 11.3 m and 10–12 s, respectively, and peak spectral density mainly varied between 0.06 and 0.1 Hz. Results of this study can provide a basis for offshore engineering design and are of great significance for marine forecasting and disaster prevention and reduction. • The wave characteristics of the eastern Guangdong offshore water were quantified based on 1-year wave observations. • The significant wave height (H 1/3) was 1.7 - 3.5 m, and maximum wave height (H max) was 11.3 m during Super Typhoon Mangkhut. • Both Jonswap and Wenshengchang spectrum can fit the measured wave spectrum well in this region during Super Typhoon Mangkhut. [ABSTRACT FROM AUTHOR]

Measured wave data covering two years simultaneously at 3 locations along the eastern Arabian Sea reveals the presence of long-period (peak wave period > 18 s) low-amplitude waves (significant wave height

The evolution of wind waves in coastal zones leads to changes in the shape of the wave spectrum. Along the coast of Kerala, due to the presence of mudbanks during the southwest monsoon, we could observe downshifting of the peak frequency in the wave spectral data. The present study aims at proving the mechanism of frequency downshifting and possible influence of the downshifting process on mudbank formation. The results of SWASH (Simulating WAves till SHore) modeling and bispectral analysis shows that frequency downshifting occurs due to the difference nonlinear triad interactions of the main frequency peak of the wave spectrum with frequencies of the infragravity range independent of the viscosity of the medium. The increase in wave dissipation accelerates frequency downshifting additionally, decreasing the wave energy in the main peak frequency. It is shown that frequency downshifting can be one of the possible wave mechanisms of mudbank formation due to essentially different wave attenuation coefficients at the beginning and end of this process. For muddy cohesive sediments, it will lead to formation with an erosive profile at first and then an accumulative profile, i.e., mudbank formation.

In order to investigate the complex hydrodynamics and associated sediment movement resulting from the ship passages in heavy shipping traffic waterways, field measurements were performed in a heavy shipping traffic waterway. Based on the collected waves, flow velocity and water turbidity data, the analyses of the ship-induced hydrodynamics and associated sediment suspension phenomena were conducted. The low-frequency primary wave and high-frequency secondary wave were more pronounced for a barge and yacht in the wave structure, respectively, and contributed more to the flow velocity fluctuations and the bottom shear stress. The ship-induced bottom shear stress can cause significant suspended sediment concentration increase, and there is a correlation between the maximum suspended sediment concentration and maximum ship-induced drawdown height, which can provide a reference for the waterway management.

We perform a critical analysis of the present approach in wave modeling and of the related results. While acknowledging the good quality of the best present forecasts, we point out the limitations that appear when we focus on the corresponding spectra. Apart from the meteorological input, these are traced back to the spectral approach at the base of the present operational models, and the consequent approximations involved in properly modeling the various physical processes at work. Future alternatives are discussed. We then focus our attention on how, given the situation, to deal today with the estimate of the maximum wave heights, both in the long term and for a specific situation. For this, and within the above limits, a more precise evaluation of the wave spectrum is shown to be a mandatory condition.

Although there have been a number of studies investigating fundamental characteristics of infragravity waves in coastal zones, a proper method of deciding period ranges that are associated with gravity or infragravity waves remains uncertain. In this study, we proposed an empirical method of separating spectral energies of gravity and infragravity waves by analyzing the wave observation data acquired off Gyeongpo beach on the Korean east coast. The fundamental principle of the suggested method is to represent the separation period discriminating gravity and infragravity waves as a function of the significant wave period, rather than a fixed value that was conventionally applied in previous studies. As a consequence of using the new method, the relationships between heights and periods of gravity and infragravity waves were more clearly identified.

An ocean surface wave retrieval algorithm, Parameterized First-guess Spectrum Method (PFSM), which was initially developed for C-band Synthetic Aperture Radar (SAR), is modified to extract wave parameters from X-band TerraSAR-X (TS-X) images. Wave parameters, including significant wave height (SWH) and mean wave period (MWP) were extracted from nine TS-X HH-polarization images and were compared to in situ buoy measurements. The range of these wave retrievals is from 1 to 5 m of SWH and from 2 to 10 s of MWP. The retrieval accuracy could reach 80%. After that, a total of 16 collected TS-X HH-polarization images were used to invert wave parameters and then the retrieval results were compared to the operational WAVEWATCH-III wave model results. The SAR and in situ buoy wave comparison shows a 0.26 m Root-Mean-Square Error (RMSE) of SWH and a 19.8% of Scatter Index (SI). The SAR and WAVEWATCH-III model comparison yields slightly worse results with an RMSE of 0.43 m of SWH and a 32.8% of SI. For MWP, the SAR and buoy comparison shows the RMSE is 0.45 s with an SI of 26%, which is better than the results from the SAR and WAVEWATCH-III model comparison. Our results show that the PFSM algorithm is suitable to estimate wave parameters from X-band TS-X data.

Spectral properties near the dominant wave region influence significantly the surface roughness relevant to ocean remote sensing employing low-frequency microwave sensors. The critical parameters characterizing dominant waves are wind speed and dimensionless spectral peak frequency, which is the inverse wave age. The dimensionless spectral peak frequency can be expressed as an equivalent dimensionless fetch or duration. The connection between dominant waves and surface roughness is the spectral slope. This paper presents a surface wave spectral model designed for low-frequency microwave remote sensing, with special emphasis on tropical cyclone (TC) applications. The key elements of the spectral model are: 1) a general spectral function with coefficients accommodating a variable spectral slope and 2) a parametric function connecting the spectral slope and wind speed, which is established with the mean square slope (MSS) observations obtained inside hurricanes by the global positioning system reflectometry technique. In order to make use of the MSS observations inside hurricanes, parametric models of the spatial distributions of wind speed and dimensionless spectral peak frequency inside TCs are developed. The parametric models are based on the wind and wave similarity relationships derived from analyses of hurricane hunter measurements. [ABSTRACT FROM AUTHOR]

Based on the linear random wave solutions of water wave equations in finite water depth, a theoretical statistical distribution of the wave-induced drift is derived. The parameters involved in the distribution can be determined by the water depth and the wave spectrum of ocean waves. As an illustrative example, we consider a simple wind-generated sea and the parameters are calculated for typical wind speeds and water depths by using Phillips spectrum. The behaviours of the distribution and the effects of wind speed and water depth on the distribution are investigated. [ABSTRACT FROM AUTHOR]

The substructures of offshore wind turbines are subjected to different types of hydrodynamic loads from sea states. The wave forces exerted by irregular breaking waves are one of the serious concerns because of the uncertainties involved in defining the breaking wave and the resulting force calculations. In the present study, irregular breaking wave forces on a vertical pile structure are investigated using an open-source Computational Fluid Dynamics (CFD) model REEF3D. The Level Set Method (LSM) is used for modelling the free surface. The Bretschneider spectrum is used for the irregular wave generation. This is validated in the numerical wave tank by comparing the numerical wave spectrum with the experimental wave spectrum. The wave free surface is calculated at three wave gauge locations and compared with experiments. It is observed that the peak of spectral wave density is higher for the wave gauge located besides the cylinder due to shoaling, wave run up and reflections from the cylinder and the peak of spectral wave density is lower for the wave gauge located behind the cylinder due to wave breaking. Further, simulations are performed to study the wave forces on a monopile due to the depth-limited breaking waves. A good match is observed with the experimental and numerical results. Numerical wave energy spectra at different locations along the tank are compared to study the changes in the wave surface elevations due to the interaction of irregular breaking waves with a monopile. The statistical parameters for free surface elevation and wave forces are further investigated. The free surface features around the monopile during its interaction with waves are also studied. [ABSTRACT FROM AUTHOR]

More than three decades of observations of tropical cyclone wind and wave fields have resulted in a detailed understanding of wave-growth dynamics, although details of the physics are still lacking. These observations are presented in a consistent manner, which provides the basis to be able to characterize the full wave spectrum in a parametric form throughout tropical cyclones. The data clearly shows that an extended fetch model can be used to represent the maximum significant wave height in such storms. The shape stabilizing influence of nonlinear interactions means that the spectral shape is remarkably similar to fetch-limited cases. As such, the tropical cyclone spectrum can also be described by using well-known parametric models. A detailed process is described to parameterize the wave spectrum at any point in a tropical cyclone. [ABSTRACT FROM AUTHOR]