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The coast of Bahia state is the longest along the Brazilian coastline, and there are significant knowledge gaps concerning its estuarine fish fauna. Thus, there is a need to provide extensive coverage of the estuarine ichthyofauna of Bahia to provide an updated checklist of its fishes, which could function as a database for the management of such biodiversity. Therefore, this study aimed to characterize three different important estuarine systems (Camamu, Todos os Santos Bay, and Caravelas) in Bahia to contribute information on the ichthyofauna in shallow areas of the state. We recorded 29 orders, 54 families, 101 genera, and 147 species of fish. The families with the highest number of species were Sciaenidae and Carangidae, with twelve and nine species, respectively, followed by Gobiidae and Engraulidae, each with eight species. In terms of abundance in the northern region, the orders Atheriniformes (28.80%), Pleuronectiformes (15.92%), Clupeiformes (14.20%), and Gerreiformes (13.91%) predominated. In the Central region, Gerreiformes (21.55%), Tetraodontiformes (17.94%), Gobiiformes (12.83%), and Clupeiformes (8.94%) were the most representative. In the southern region, the orders Clupeiformes (57.48%), Mugiliformes (14.09%), Atheriniformes (4.10%), Lutjaniformes (3.97%), Gerreiformes (3.60%), and Carangiformes (2.23%) predominated. The region was characterized by a high representation of guilds of marine migrant species, followed by marine, estuarine, and freshwater visitors. [ABSTRACT FROM AUTHOR]

This paper introduces a unified model for layered rotating shallow‐water (RSW) and quasi‐geostrophic (QG) equations, based on the intrinsic relationship between these two sets of equations. We propose a novel formulation of the QG equations as a projection of the RSW equations. This formulation uses the same prognostic variables as RSW, namely velocity and layer thickness, thereby restoring the proximity of these two sets of equations. It provides direct access to the ageostrophic velocities embedded within the geostrophic velocities resolved by the QG equations. This approach facilitates the study of differences between QG and RSW using a consistent numerical discretization. We demonstrate the effectiveness of this formulation through examples including vortex shear instability, double‐gyre circulation, and a simplified North Atlantic configuration. Plain Language Summary: In this paper, we present a straightforward way to connect two important sets of ocean equations: the layered rotating shallow‐water (RSW) equations and the quasi‐geostrophic (QG) equations. We consider a unified method to formulate the QG equations as a projection of the RSW equations. This method uses the same variables as the RSW equations, making it easier to understand how these two sets of equations relate to each other. Our approach also provides direct access to important velocity information that is usually hidden in the QG equations. This allows us to study the differences between the QG and RSW equations using the same numerical techniques. We show the benefits of our model with two examples: a vortex shear instability and a double‐gyre configuration. This work provides a useful tool for the understanding of ocean dynamics. Developing a unified numerical framework for nested models can greatly simplify oceanographic modeling and enhance accuracy. Key Points: Introduces QG equations as a projection of rotating shallow‐water (RSW) equations using the same prognostic variablesAllows consistent nested numerical methods for both QG and RSW equationsSuccessfully tested on vortex shear instability, double‐gyre circulation, and a simplified North Atlantic configuration [ABSTRACT FROM AUTHOR]

Fish habitats and reproduction can be significantly altered downstream of hydroelectric power plants operated by hydropeaking and resulting in rapid and frequent changes in river hydrodynamic conditions. To mitigate the impacts, it is necessary to maintain the habitat quality through operational measures. The microhabitat method, coupling 1 D or 2 D hydraulic simulations to biological models, is a useful tool to assess the evolution of hydromorphological parameters and fish habitats and define these mitigation measures. Calibration of the hydraulic model must be carried out carefully because the model must accurately reproduce hydraulic conditions from low to high flows. The objective is therefore to evaluate the sensitivity of the habitat value as a function of the type of calibration and the friction law for shallow habitats. The analysis is performed by estimating the uncertainty in fish habitat values resulting from Strickler's law or Nikuradse's law. The study is carried out on a river in the French Pyrenees based on the modeling of 2 stations with different cross-sectional shapes, one with progressive overflow and the other without these phenomena. Thanks to field measurements at low and high flowrates, the calibration process showed that the friction coefficient can be multiplied by 2. Two dimensionnal simulations give similar results to those obtained with 1 D when the flow remains unidirectional but differ for areas with high overflows. Calibration and models can lead to different conclusions regarding the estimation of habitat modifications due to hydropeaking operation and the definition of base flow and maximum turbine discharge. [ABSTRACT FROM AUTHOR]

Shallow-water mooring chains of floating offshore wind turbines pose challenges such as nonlinear tension characteristics, high cost and prominent fatigue issues, which seriously hinder the large-scale use of floating wind power. Based on the hydrological and meteorological data of an offshore wind farm in the South China Sea, a sensitivity analysis of the mooring chain fatigue of a semi-submersible floating offshore wind turbine in shallow water was conducted with different environmental loads and mooring chain design parameters. It was found that mooring fatigue is mainly caused by the wave condition within diagonal distribution of the wave dispersion diagram. The mooring chain fatigue calculated using the main monochromatic wave was more conservative than that calculated using the wave scatter diagram with a difference of about 28%. The mooring fatigue calculated using turbulent wind spectrum was greater than that calculated using steady wind. In contrast, waves are the main source of mooring fatigue, and the second-order wave force has an undeniable impact on the mooring fatigue of a semi-submersible floating offshore wind turbine, which accounts for approximately 26% of wave-induced mooring fatigue. In addition, the current-induced mooring fatigue should not be neglected, although its effect is not as large as that caused by the wave or wind loads. An increase in the cross-sectional diameter and the length of a mooring chain, as well as a reasonable clump weight arranged, all contribute to improving the fatigue life of mooring chains in shallow water, which provide useful technical references for the optimization of mooring lines fatigue in shallow-water areas. [ABSTRACT FROM AUTHOR]

Coastal lagoons are important wetland sites for migratory species and the local flora and fauna population. The Stagnone Lagoon is a coastal lagoon located on the west edge of Sicily between the towns of Marsala and Trapani. The area is characterized by salt-harvesting plants and several archaeological sites and is affected by microtidal excursion. Two mouths allow exchange with the open sea: one smaller and shallower in the north and one larger and deeper in the south. This study aims to understand the lagoon's hydrodynamics, in terms of circulation and involved forces. The circulation process appears to be dominated mainly by tide excursions and wind forces. Wind velocity, water levels, and water velocity were recorded during different field campaigns in order to obtain a benchmark value. The hydrodynamic circulation has been studied with a 2DH (two-dimensional in the horizontal plane) unstructured mesh model, calibrated with data collected during the 2006 field campaign and validated with the data of the 2007 campaign. Rapid changes in averaged velocity have been found both in Vx and Vy components, showing the strong dependence on seiches. This study tries to identify the main factor that domains the evolution of the water circulation. Sensitivity analyses were conducted to estimate the correct energy transfer between the forcing factors and dissipating ones. A Gauckler–Strickler roughness coefficient between 20 and 25 m1/3/s is found to be the most representative in the lagoon. To enhance the knowledge of this peculiar lagoon, the MIKE 21 model has been used, reproducing all the external factors involved in the circulation process. Nash–Sutcliffe coefficient of efficiency (NSE) values up to 0.92 and 0.79 are reached with a Gauckler–Strickler coefficient equal to 20 m1/3/s related to water depth and the Vy velocity component. The Vx velocity component NSE has never been satisfying, showing the limits of the 2D approach in reproducing the currents induced by local morphological peculiarities. Comparing the NSE value of water depth, there is a loss of up to 70% in model predictivity capability between the southern and the northern lagoon areas. This study aims to support the local decision-makers to improve the management of the lagoon itself. [ABSTRACT FROM AUTHOR]

The high spatial resolution and wide applicability of multi-spectral remote sensing make it significant for estimating shallow water depth. In areas with mixed substrates, determining the contribution of substrate reflection to the sensor's received signal can effectively enhance the precision of multi-spectral remote sensing bathymetry. Therefore, this paper proposes a Two Factors constrained Quasi-Analytical Algorithm (TF-QAA). Firstly, the algorithm considers the spectral variation of the mixed substrates. Secondly, a robust correlation between inherent optical parameters and water depth is established in this study, which is used to enforce a linear relationship constraint on the initially estimated water depth. Sentinel-2 image data was used to verify the algorithm in the Antelope Reef area of the South China Sea. The best result from images taken at different times indicates that the TF-QAA method has the average absolute error (MAE) of 0.92 m, the root mean square error (RMSE) of 1.20 m, the average relative error (MRE) of 10.6%, and the correlation coefficient (R2) of 0.97. The results suggest that the algorithm is effective for Case 1 water, providing a novel approach for extensive bathymetric mapping in shallow water areas of islands, with or without LiDAR-measured depth data. [ABSTRACT FROM AUTHOR]

A set of planar motion mechanism experiments of the Duisburg Test Case Post-Panamax container model executed in a towing tank with shallow depth is applied to train a neural network to analyse the ability of the proposed model to learn the effects of different depth conditions on ship's manoeuvring capabilities. The motivation of the work presented in this paper is to contribute an alternative and effective approach to model non-linear systems through artificial neural networks that address the manoeuvring simulation of ships in shallow water. The system is developed using the Levenberg–Marquardt backpropagation training algorithm and the resilient backpropagation scheme to demonstrate the correlation between the vessel forces and the respective trajectories and velocities. Sensitivity analyses were performed to identify the number of layers necessary for the proposed model to predict the vessel manoeuvring characteristics in two different depths. The outcomes achieved with the proposed system have shown excellent accuracy and ability in predicting ship manoeuvring with varying depths of shallow water. [ABSTRACT FROM AUTHOR]

One of the promising strategies for the improvement of the resistance characteristics and energy efficiency of a ship is trim optimization. Most of the studies conducted so far regarding trim optimization deal with unrestricted water. The effect of trim on the total resistance and its components for the KRISO Container Ship model in confined and shallow water is investigated using computational fluid dynamics. Numerical simulations of resistance tests with and without the free surface effects using two turbulence models are carried out for even keel and four trims in restricted water. A verification study is conducted for the total resistance, sinkage, and trim in terms of grid resolutions and time steps to assess the numerical uncertainty. The numerical results are validated against the experimental ones available in the literature. Performing the double body simulations enabled the analysis of the effect of trim on the resistance components. The numerical results pointed out that by adjusting the trim a reduction in the total resistance in confined and shallow water can be obtained. [ABSTRACT FROM AUTHOR]

The maneuverability of ships is influenced by several factors, including ship design, size, propulsion system, hull shape, and external conditions such as wind, waves, and currents. The size, shape, and arrangement of the hull, rudder, and propeller are decisive for maneuverability. Hydrodynamic forces such as bank effect and squat significantly impact the maneuverability of large ships in narrow channels. With the increasing trend of building ever-larger ships, the demand to evaluate the maneuvering performance of the ship at the design stage has become more critical than ever. Both experimental and computational methods are used to obtain accurate maneuvering characteristics of vessels. In this study, the methods for predicting ship maneuvering characteristics are analyzed using a systematic review based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA). This article contributes to a deeper understanding of the hydrodynamic capabilities of ships and identifies possible future challenges in the field of ship hydrodynamics. The findings inform educators and the shipping industry about the importance of predicting the maneuvering performance of ships, with an emphasis on the education and training of seafarers needed to make timely decisions in critical situations. [ABSTRACT FROM AUTHOR]

This article focuses on the design of semi-implicit schemes that are fully well-balanced for the one-dimensional shallow water equations, that is, schemes that preserve all smooth steady states of the system and not just water-at-rest equilibria. The proposed methods outperform standard explicit schemes in the low-Froude regime, where the celerity is much larger than the fluid velocity, eliminating the need for a large number of iterations on large time intervals. In this work, splitting and relaxation techniques are combined in order to obtain fully well-balanced semi-implicit first and second order schemes. In contrast to recent Lagrangian-based approaches, this one allows the preservation of all the steady states while avoiding the complexities associated with Lagrangian formalism. [ABSTRACT FROM AUTHOR]

It is necessary to maintain maneuverability for ship navigation in shallow water, such as channels, ports and other confined waters. In this study, a turning circle maneuver with 35° rudder deflection and a 20/5 zigzag maneuver for KVLCC2 in shallow waters are tested numerically to directly predict the maneuverability of the ship in shallow water. A viscous in-house CFD solver is applied with the dynamic overset grid approach. The impacts of the water depth on the ship's maneuverability in terms of turning and zigzag competence are evaluated, and the underlying mechanism is analyzed. The numerical method is validated by comparing it with experimental data on the turning indices, which shows good agreement. It is demonstrated that the turning capability become worse with a smaller depth–draft ratio, thus resulting in a lower yaw rate and a greater steady turning diameter. However, the drift angle and lateral speed are reduced with a smaller depth–draft ratio for zigzag maneuvers, but the overshoot angle and turn lag vary with the water depth non-monotonically. [ABSTRACT FROM AUTHOR]

A high-speed advancing ship will cause significant squats in shallow water, which could increase the risk of grounding. To this end, a program based on the Rankine higher-order boundary element method (HOBEM) is developed to investigate a high-speed displacement ship with a transom stern moving in shallow water. The nonlinear free surface condition is satisfied by adopting an iterative algorithm on the real free surface. The transom condition is considered by implementing a modified transom condition. Computations of wave-making resistance, sinkage and trim in deep water are first performed, and satisfactory agreement is achieved by comparing with the experimental results; the simulations are then extended to the shallow water case. It indicates that the present method can provide a suitable balance of practicability and robustness, which can be considered as an efficient tool for the guidance in ship design stage. [ABSTRACT FROM AUTHOR]

The holographic signal-processing method for a single vector scalar receiver (VSR) in the high-frequency band in shallow water is developed in the paper. The aim of this paper is to present the results of the theoretical analysis, numerical modeling, and experimental verification of holographic signal processing for a noise source by the VSR. The developed method is based on the formation of the 2D interferogram and 2D hologram of a noise source in a shallow-water waveguide. The 2D interferograms and 2D holograms for different channels of the VSR (P sound pressure and V X and V Y vibration velocity components) are considered. It is shown that the 2D interferogram consists of parallel interference fingers in the presence of a moving noise source. As a result, the 2D hologram contains focal points located on a straight line, and the angular distribution of the holograms has the main extreme value. It is shown in the paper that the holographic signal-processing method allows detecting the source, estimating the source bearing, and filtering the useful signal from the noise. The results of the source detection, source bearing estimation, and noise filtering are presented within the framework of experimental data processing and numerical modeling. [ABSTRACT FROM AUTHOR]

The low-power underwater acoustic modem is usually an important component of the Underwater Wireless Sensor Network (UWSN). Network nodes have predetermined energy resources that will not be replenished during the life of the node. In shallow waters, multipath propagation is constantly occurring and for the modem to work effectively, solutions to overcome them must be used, which will also meet the important criterion of energy efficiency. The article presents the concept of a low-power underwater modem using Multiple Frequency-Shift Keying (MFSK) modulation and the fast frequency- hopping spread spectrum technique. In order to determine the performance of the modem, simulation tests were carried out using the Watermark simulator using the measured impulse responses of channels in shallow waters. [ABSTRACT FROM AUTHOR]

Shallow water passive source localization is an essential problem in underwater detection and localization. Traditional matched-field processing (MFP) methods are sensitive to environment mismatches. Many neural network localization methods still have room for improvement in accuracy if they are further adjusted to underwater acoustic characteristics. To address these problems, we propose a deep learning localization method via improved input features and network structure, which can effectively estimate the depth and the closest point of approach (CPA) range of the acoustic source. Firstly, we put forward a feature preprocessing scheme to enhance the localization accuracy and robustness. Secondly, we design a deep learning network structure to improve the localization accuracy further. Finally, we propose a method of visualizing the network to optimize the estimated localization results. Simulations show that the accuracy of the proposed method is better than other compared features and network structures, and the robustness is significantly better than that of the MFP methods. Experimental results further prove the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In shallow-water ocean-bottom cable (OBC) seismic data, the ineffectiveness of conventional surface-related multiple elimination (SRME) methods due to poor seabed records is addressed. This research utilizes the seismic wavefield received by multiple cables from a single shot gather to predict shallow water multiple models for that shot gather. Initially, the seismic data within a finite aperture around a seismic trace in the time domain shot gather is treated as the known seismic wavefield. This seismic wavefield is then extrapolated along the water layer to this seismic trace, following the Fresnel diffraction principle. The extrapolated data becomes the shallow water multiple model for this seismic trace. This process is repeated for each trace in the shot gather to obtain the shallow water multiple model of the entire shot gather. Forward modeling tests have shown that smaller data apertures can effectively avoid the impact of spatial aliasing on multiple model prediction. To address the overlap of primary waves and shallow water multiples in deep seismic data, which have lower dominant frequencies, the multiple model data is used as a known seismic wavefield and extrapolated along the water layer again. This produces second-order and higher-order multiple models. Applying this model to suppress multiple waves can minimize primary waves loss. This entirely data-driven approach necessitates solely water depth information, imposing no additional conditions. Both forward modeling and real seismic data testing validate the efficacy of this method in shallow water. [ABSTRACT FROM AUTHOR]

This paper introduces a model-independent passive source localization method, employing asynchronous distributed hydrophones in shallow water. Based on the frequency invariability of the acoustic field, assuming the correct source range information, the warped spectra of received signals at distributed hydrophones exhibit identical shapes. Subsequently, a cost function is formulated to mutually align the warped spectra, with its maximum point indicating the source location. The proposed method can locate the source in two-dimensional horizontal space without requiring either angle- or time-synchronization information. Numerical simulations are conducted to demonstrate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

A method is presented to calculate the vibrations of an ice shelf floating in shallow water under different boundary conditions. One condition is that there is no flux, which reduces all calculations and the other is that there is no pressure at the seaward end of the ice shelf. The effect of these boundary conditions is investigated in detail, and the modes of vibration are also determined. Motion simulations of the system are presented for the potential velocity of the water and the vertical displacement of the ice shelf. These are found through a numerical method, which reduces all calculations to matrix multiplication. The underlying motion is shown to be very complex and difficult to interpret from single-point response measurements. The motion of more realistic ice shelves can be expected to be even more complicated. [ABSTRACT FROM AUTHOR]

The current time-domain solution methods for the wavefield equations of a single medium do not apply to the wavefield equations of shallow water seismic with a fluid–elastomer coupling. To solve this problem, based on the explicit central difference method and implicit Newmark method, the explicit–explicit method, implicit–implicit method, and explicit–implicit method time-domain expressions for the local solution are derived, and the time-domain expressions for the explicit and implicit methods in the global solution are derived.The stability and computational efficiency of different time-domain solving methods for the shallow water seismic wavefield equations are theoretically analyzed. The numerical results are compared with the simulation data from the multiphysics field simulation software COMSOL 6.0, and the numerical stability, computational efficiency and accuracy of the different solving methods are also analyzed theoretically. The results show that the implicit method in the global solution is relatively optimal among the methods proposed in this paper, which ensures numerical stability at the larger step size for improving the computational efficiency and considers the higher computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

Shallow water bathymetric information is important for human life because it has a strong influence on phenomena and dynamics in coastal areas. Conventional bathymetric mapping methods are capable of obtaining high-precision accuracy, but require expensive and complex resources. Specifically, in shallow waters, survey instruments have difficulty obtaining adequate depth data due to the many obstacles that must be overcome. Remote sensing-based shallow water bathymetry called as Satellite-Derived Bathymetry (SDB) is a reasonable and efficient choice. Technological developments enable SDB data processing to be much more efficient in terms of time and storage by utilizing cloud-based platforms such as Google Earth Engine (GEE). Spatial and temporal resolution is still a challenge in SDB, so in this condition PlanetScope with daily temporal resolution capabilities is an optimistic choice. However, this image falls into a relatively new image category. In this study we tested the performance of Sentinel-2A imagery and new PlanetScope imagery bands. The existence of the new sensor owned by PlanetScope allows an increased choice of SDB data sources with high spatial and temporal resolution that is better than the general datasets currently available. There are four additional channels are Coastal Blue, Green I, Yellow, and Red Edge. Assessment is needed to test the capabilities of each new channel using empirical methods via the Stumpf algorithm. Based on accuracy assessment observations, the Sentinel-2A channel combination is still better in terms of accuracy and determination, because it is able to represent the depth in the study area up to 70%. The potential use of PlanetScope's new channels for SDB applications can still be seen in the combination of the Coastal Blue and Yellow channels. This channel combination is still able to represent 47% of the depth variations in the study area. [ABSTRACT FROM AUTHOR]

Over the years, air lubrication technology has been widely applied to maritime vessels, demonstrating its significant energy-saving and emission-reducing effects. However, the application of this technology in inland waterway transportation faces unique challenges due to the shallower water depths, particularly during low water periods. Under such conditions, the formation of the air layer and its associated drag-reduction effects may undergo alterations. Conducting research on air lubrication technology in shallow water conditions holds great practical significance for promoting its application in inland waterway vessels. Therefore, a numerical study is undertaken to examine the impact of water depth on Air layer Drag Reduction (ALDR) to promote the use of ALDR technology on inland canal boats with shallow water depths. The object was a specific river-sea direct ship model, and a groove was created at the bottom of the model with air injection. At two distinct speeds, numerical simulations were run for four different depths: deep water, moderate water, shallow water, and ultra-shallow water. A comparative examination of the air layer morphology on the ship bottom and drag reduction was conducted to investigate the impact of water depth on ALDR and confirm the viability of using ALDR technology on shallow-water navigation boats. The results indicate that due to the change in the velocity and pressure fields at the bottom of the ship, the efficiency of drag reduction and the form of the air layer on the ship's bottom are significantly impacted by variations in water depth in restricted waters. However, the total resistance can still be significantly reduced by setting grooves on the hull with air injected in shallow waterways. Reduced frictional resistance no longer predominates the overall resistance reduction in shallow water; the proportion of the decrease in viscous pressure resistance rises and can reach up to 4.8 times the decrease in frictional resistance. The research confirms the application prospects of this technology on inland waterway transport ships. [ABSTRACT FROM AUTHOR]

Due to the blockage of seawater, seafloor displacement cannot be directly measured by space geodesy. The combination of Global Navigation Satellite Systems‐acoustic ranging (GNSS‐A) has been used to overcome the electromagnetic barrier, so that a GNSS‐determined sea surface vessel's coordinates can be transformed to seafloor benchmarks in a global reference frame. Due to the high cost and science priorities, previous GNSS‐A studies mainly targeted relatively deep water and a minimum of three transponders were used to form an array, equivalent to a precision geodetic station. With recent developments in unmanned autonomous surface vessels, low cost GNSS‐A surveys are poised to become practical. Here we demonstrate that with a carefully designed surveying trajectory, Wave Glider‐based GNSS‐A surveying of a single transponder in shallow water can provide centimeter‐level accuracy on horizontal seafloor positioning, even if the sound speed model deviates from the actual value by a few meters per second. Results from a nine‐month experiment conducted at ∼54 m water depth show that the repeatability of the seafloor horizontal positioning is better than 2 cm. When conditions allow, the acoustic observations should be collected symmetrically about the transponder and data redundancies are recommended to reduce the error associated with time‐dependent variations in sound speed. Plain Language Summary: Seafloor geodesy is important for monitoring offshore strain processes. Global Navigation Satellite Systems‐acoustic ranging (GNSS‐A) uses sound signals traveling in water as rulers to measure the distances between the sea surface vessel and the seafloor sensor (transponder), so that the GNSS‐determined sea surface vessel's coordinates can be transformed to the seafloor through triangulation. Multiple transponders deployed on the seafloor are often needed to form an array so that noise caused by irregular variations in the sound signals can be reduced. In shallow water, due to the relatively short distance, the range distortion caused by a sound signal's refraction is smaller, and the time it takes to conduct each complete cycle of survey is shorter. These conditions allow the seafloor displacements to be measured with centimeter‐level accuracy using only one transponder. Key Points: For single transponder Global Navigation Satellite Systems‐acoustic ranging in shallow water, seafloor vertical position estimation is sensitive to sound speed error and variationA geometrically symmetric surveying trajectory is preferable for error reduction in horizontal seafloor positioningSeafloor horizontal positions were measured with <2 cm repeatability at ∼54 m water depth over five repeat surveys with Wave Gliders [ABSTRACT FROM AUTHOR]

In this paper, we study the variations of holograms of a moving source in an inhomogeneous ocean waveguide. It is assumed that intense internal waves (internal solitons) are the reason for the inhomogeneities of the shallow water waveguide. The results of 3D modeling of the sound field considering horizontal refraction by internal waves are presented. In the context of 3D modeling, the interferogram (sound intensity distributions in frequency–time coordinates) and hologram (2D Fourier transform of the interferogram) of moving sources are analyzed. The hologram consists of two disjoint regions corresponding to the unperturbed field and the field perturbed by internal waves. This structure of the hologram allows for the reconstruction of the interferogram of the unperturbed field in a waveguide in the absence of intense internal waves. The error in the reconstruction of the unperturbed interferogram is estimated. [ABSTRACT FROM AUTHOR]

A data-driven method, the truncated LS-SVM, is proposed for estimating the nondimensional hydrodynamic coefficients of a nonlinear manoeuvring model. Experimental data collected in a shallow water towing tank are utilized in this study. To assess the accuracy and robustness of the truncated LS-SVM method, different test data sizes are selected as the training set. The identified nondimensional hydrodynamic coefficients are presented, as well as the corresponding parameter uncertainty and confidence intervals. The validation is carried out using the reference data, and statistical measures, such as the correlation coefficient, centred RMS difference, and standard deviation are employed to quantify the similarity. The results demonstrate that the truncated LS-SVM method effectively models the hydrodynamic force prediction problems with a large training set, reducing parameter uncertainty and yielding more convincing results. [ABSTRACT FROM AUTHOR]

The rising sea levels caused by the climate crisis are causing significant changes in the coastal environment of the Korean Peninsula, leading to increased demand for coastal erosion protection. Accurate bathymetric information is crucial for implementing effective prevention measures. However, existing methods such as the airborne light detection and ranging (LiDAR) bathymetry (ALB) and multibeam echo sounder (MBES) are not cost-effective for small-scale regions, and the single-beam echo sounder (SBES) method using manned survey vessels is challenging to use in low-water-depth areas. In this study, we aimed to develop an autonomous surface vehicle (ASV) to conduct bathymetric surveying at a very small water depth of less than 2.0 m. The survey was conducted by connecting SBES and network real-time kinematic (N-RTK) positioning data to a small, self-developed ASV. The vessel was autonomously navigated using N-RTK positioning data during most measurement operations, allowing for precise sounding intervals using a simple waypoint setting for each planned sidetrack without direct steering. The bathymetric measurements of exposed or partially exposed rocks at average water depths of 2.0 m or less could be obtained from the bathymetric surveying using the unmanned vessel and devices applied in this study. [ABSTRACT FROM AUTHOR]

In this paper, a numerical assessment of the effect of shallow water on the total resistance of the solar catamaran SolarCat is carried out using computational fluid dynamics within the software package STAR–CCM+. The unsteady viscous fluid flow was modelled based on the Reynolds-averaged Navier–Stokes (RANS) equations with the application of the k − ω SST ( k − ω Shear Stress Transport) turbulence model. The RANS equations were discretized by the finite volume method, and the position of the free surface is determined by the volume of fluid method. In shallow water conditions, a mesh morphing algorithm is applied. Numerical simulations were carried out for the deep water and limited depths corresponding to h / T = 7. 6 , h / T = 4 , and h / T = 2 at two speeds. The verification study was carried out and the total numerical uncertainty was calculated for the total resistance and sinkage of the catamaran. A detailed analysis of the flow around the catamaran was carried out. [ABSTRACT FROM AUTHOR]

Numerical simulation is used to study the possibility of remote acoustic monitoring of underwater keels in ice-covered shallow-water waveguides. A statistically average hummock for the Arctic region is considered, with a keel draft of 8 m, located in a waveguide with a depth of 40 m. It is assumed that the ridge of the hummock is perpendicular to the acoustic track, the length of which is 10 km. A point broadband source and a vertical receiving array are used, which are necessary for extracting the mode amplitudes. It is shown that mode coupling due to the keel manifests itself quite distinctly in modulation of the mode amplitudes in a broad frequency band. A methodology for analyzing this modulation by constructing cepstrograms (spectrograms from the spectrum) is proposed. The cepstrograms reveal dispersion curves corresponding to pairs of coupled modes. Then, from the location of the dispersion curves on the cepstrogram, it is possible to estimate the location of the keel on the track. [ABSTRACT FROM AUTHOR]

Despite the high accuracy of conventional acoustic hydrographic systems, measurement of the seabed along coastal belts is still a complex problem due to the limitations arising from shallow water. In addition to traditional echo sounders, airborne LiDAR also suffers from high application costs, low efficiency, and limited coverage. On the other hand, remote sensing offers a practical alternative for the extraction of depth information, providing fast, reproducible, low-cost mapping over large areas to optimize and minimize fieldwork. Satellite-derived bathymetry (SDB) techniques have proven to be a promising alternative to supply shallow-water bathymetry data. However, this methodology is still limited since it usually requires in situ observations as control points for multispectral imagery calibration and bathymetric validation. In this context, this paper illustrates the potential for bathymetric derivation conducted entirely from open satellite data, without relying on in situ data collected using traditional methods. The SDB was performed using multispectral images from Sentinel-2 and bathymetric data collected by NASA's ICESat-2 on two areas of relevant interest. To assess outcomes' reliability, bathymetries extracted from ICESat-2 and derived from Sentinel-2 were compared with the updated and reliable data from the BathyDataBase of the Italian Hydrographic Institute. [ABSTRACT FROM AUTHOR]

To describe demographic findings, typical injuries and functional neurological outcomes in patients with cervical trauma and tetraplegia sustained after diving into shallow water. A retrospective study was performed including all patients treated in BG Klinikum Hamburg suffering from tetraplegia after jumping into shallow water between 1st June 1980 and 31st July 2018. One hundred and sixty patients with cervical spinal injuries and tetraplegia following a dive into shallow water were evaluated. Of these, 156 patients (97.5%) were male. The mean age was 24.3 years ± 8.1 and the accidents occurred most often in inland waters (56.2%) and mostly between May and August (90.6%). In all cases there was one vertebra fractured, whereas in 48.1% of cases, two vertebrae were severed. In the majority of cases (n = 146), a surgical procedure was performed. Overall, the mean hospital stay was 202 days (±72, range: 31–403) and one patient died. On admission, 106 patients (66.2%) showed a complete lesion according to AIS A, with incomplete lesions in the remaining 54 patients (AIS B: n = 25 [15.6%], AIS C: n = 26 [16.3%], AIS D: n = 3 [1.9%]). In two thirds of the patients, the level of paralysis on admission was at the level of segments C4 (31.9%) or C5 (33.7%). Seventeen patients (10.6%) needed prehospital resuscitation. In 55 patients (34.4%), the neurological findings improved during the course of inpatient treatment and rehabilitation. Sixty-eight patients (42.5%) developed pneumonia, of which 52 patients (76.5%) were ventilated. In addition, 56.5% of patients with paralysis levels C0–C3 required ventilation, whereas only 6.3% of patients with paralysis levels C6–C7 were affected. Three patients (1.9%) were discharged from hospital with continuous ventilation. Overall, 27.4% of all AIS A patients, 56% of all AIS B patients and 46.2% of all AIS C patients improved neurologically, with 17% of all patients being able to walk. The consequences of a cervical spine injury after diving into shallow water are severe and lifelong. Functionally, patients may benefit from care in a specialised centre, both in the acute phase and during rehabilitation. The more incomplete the primary paralysis, the greater the possibility of neurological recovery. [ABSTRACT FROM AUTHOR]

The Lie symmetry analysis is applied for the study of a modified one-dimensional Saint–Venant system in which the density depends on the average temperature of the fluid. The geometry of the bottom we assume that is a plane, while the viscosity term is considered to be nonzero, as the gravitational force is included. The modified shallow water system is consisted by three hyperbolic first-order partial differential equations. The admitted Lie symmetries form a four-dimensional Lie algebra, the A3,3 ⊕ A1. However, for the viscosity free model, the admitted Lie symmetries are six and form the A5,19 ⊕ A1 Lie algebra. For each Lie algebra we determine the one-dimensional optimal system and we present all the possible independent reductions provided by the similarity transformations. New exact and analytic solutions are calculated for the modified Saint–Venant system. [ABSTRACT FROM AUTHOR]

This work presents an investigation of ice shelf vibration using a model based on shallow water approximation. The study focused on the effect of changes in the draft on the vibration of the ice shelf and presents both time-domain and frequency-domain results. The model used a radiation condition for energy propagation into the ice shelf. Furthermore, an energy balance relation was derived to investigate the energy flow within the system. Results show that changes in the draft can significantly impact the ice shelf's vibration and that the energy flow within the system is affected by the geometry of the ice shelf. Results are presented for the interaction of wave packets in the time domain with the ice shelf. These show that energy is reflected and transmitted by the ice shelf and that the motion of the wave packets is very different in the ice shelf than in the open water. Overall, this study provides insight into the dynamics of ice shelf vibration and highlights the importance of considering changes in the draft and using the time domain when modelling these phenomena. [ABSTRACT FROM AUTHOR]

The increasing demand for goods that can be transported by sea and the reduction in transportation costs have led to a trend toward larger ships. The increase in ship capacity leads to an increase in ship length and, thus, a decrease in transportation costs. The maneuverability of large ships in shallow water when calling at ports is becoming increasingly difficult. This is due to the discrepancy between increasing ship dimensions and unchanged waterway structures such as approach channels, harbors, and ports. The maneuverability of a vessel in shallow waters is different from the maneuverability in deep waters. The reasons for this are due to the shallow water effect. Shallow water affects the maneuverability of ships due to hydrodynamic forces caused by the current, shallower depth under the keel and proximity to the shore. It is a major challenge both for shipbuilders to design such vessels and for shipowners to have trained and well-educated officers who can navigate large vessels in shallow waters. This article presents the effects of shallow waters on large ship maneuvering and mathematical models that have been used to predict ship behavior under the influence of these forces. [ABSTRACT FROM AUTHOR]

Reef composition and diversity of coral reef fishes play an essential role in the ecosystem. The reef fish diversity is a crucial indicator of the health level of coral reef ecosystems. The benefit of fish diversity in coral reef ecosystems is to describe ecological services. This research intended to determine reef fish diversity among stations at different depths, consisting of shallow water and reef slope. Research sampling was done in July 2018 and July 2019 in Tunda Island waters at eight stations billowing the coral distribution pattern. Collected data of reef fishes were by using Underwater Visual Census (UVC) on Belt Transects Method at 250 m² transect area (50 meters of length and 2.5 m on either side). The result showed 69 reef fishes in shallow water and 67 species on the reef slope. The total of fish species ware from 13 families consisting of Acanthuridae, Apogonidae, Blenniidae, Chaetodontidae, Ephippidae, Haemulidae, Labridae, Lutjanidae, Nemipteridae, Pomacentridae, Pseudochromidae, Scaridae and Serranidae. The community services structure of coral reef fishes is included in the moderate community stability category with an H’ value ranging from 1.19- 1.60 in shallow water and 1.23-1.44 at reef slope, respectively. Diversity in coral reef fish communities might be associated with species' spatial distribution over the reef habitat's physical structure, but these patterns could be highly scaledependent. In general, it could be said that the higher the coral reef diversity, the higher the reef fish diversity. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the hydrodynamic effect of the condition of the tank bottom, e.g., false bottom vs true bottom, on the KCS container ship under static drift and static rudder configurations in shallow water (depth-draught ratio H/T = 1.2) using viscous CFD simulation with rigorous validations. The results of the grid sensitivity study for static drift in shallow water with a false/true bottom show that the grid convergence for forces, moment, sinkage, and trim are rather difficult to achieve in the solutions with the true bottom. Among the static drift cases, the computational results of forces, moment, sinkage, and trim generally show good agreement with the experimental data, provided that identical bottom configuration between the experiment and the simulation is set. Parametric study for the effect of gap size between the side wall of the towing tank and the side edge of the false bottom quantifies that the gap size of 10% ship length is still not narrow enough to approximate lateral force and yaw moment of the KCS as if it were in true bottom condition using false bottom. On the tank bottom, negative pressure magnitude and its region become larger and wider, respectively, for the true bottom than those of the false bottom at non-zero drift angle. This yields a difference in the wave profile along the hull at the suction side which results in the increase of lateral force and yaw moment with true bottom compared to those with a false bottom. The vortical structure developed between the hull and the tank bed is also affected by the difference in pressure magnitude and its distribution on the tank bed. Among the static rudder cases, the difference in pressure distribution is quite localized in the stern vicinity at the port and starboard of the hull. Yet it yields 7–10% difference in hull-rudder interaction coefficients with true bottom compared to those with false bottom although the blockage effect to the tank width is less apparent than the static drift configuration. In consequence, the shallow water effects are more pronounced using true bottom than false bottom at static drift and static rudder conditions. The present study indicates the importance of replicating the tank bottom condition in the CFD simulation similar to the experiment. [ABSTRACT FROM AUTHOR]

To investigate the effect of a false bottom on a ship in shallow water, viscous CFD simulations of the KRISO Container Ship (KCS) under pure yaw motion at H/T = 1.2 are carried out using the in-house flow solver "NAGISA" with the in-house overset grid assembler "UP_GRID", both developed at NMRI. Validations of forces and moment over one yaw motion period show that inertial contributions are significant in the surge and sway forces, while they are almost negligible in the yaw moment. The sway force in the present study is dominated by the inertial force, and thus, it must be deducted when the effect of a false bottom is investigated. Yaw-related linear hydrodynamic coefficients for false bottoms show more than a 25% difference compared to the values for true bottoms yet changing the tank bottom configuration does not affect the course stability index for the ship used in the present study. Throughout the local flow analysis, negative pressure and its propagated region are more pronounced in the true bottom than in the false bottom, which strongly influences the pressure distribution on the hull surface. The hull with a true bottom is subjected to a larger suction force from the tank bottom on its fore to the side tangential region than that with a false bottom. Vortical structures around the hull are also affected by the tank bottom configuration. [ABSTRACT FROM AUTHOR]

Theoretical studies of wave processes in rotating astrophysical plasma are discussed, with a particular emphasis on new theoretical models of astrophysical plasma such as the magnetohydrodynamic shallow water approximation and anelastic approximation, together with the frequently-used Boussinesq approximation. In addition to the traditional approximation for Coriolis force, effects are discussed, which are caused by its non-traditional representation that accounts for the horizontal rotation component. Linear waves in such plasma are described in detail, and their dispersion properties are discussed. An overview of instabilities in astrophysical plasma is given, which are caused by nonlinear effects. [ABSTRACT FROM AUTHOR]

Bathymetric surveys of shallow waters are increasingly necessary for navigational safety and environmental studies. In situ surveys with floating acoustic sensors allow the collection of high-accuracy bathymetric data. However, such surveys are often unfeasible in very shallow waters in addition to being expensive and requiring specific sectorial skills for the acquisition and processing of raw data. The increasing availability of optical images from Uncrewed Aerial Vehicles, aircrafts and satellites allows for bathymetric reconstruction from images thanks to the application of state-of-the-art algorithms. In this paper, we illustrate a bathymetric reconstruction procedure involving the classification of the seabed, the calibration of the algorithm for each class and the subsequent validation. We applied this procedure to high-resolution, UAV-derived orthophotos, aircraft orthophotos and Sentinel-2 Level-2A images of two marinas along the western Ligurian coastline in the Mediterranean Sea and validated the results with bathymetric data derived from echo-sounder surveys. Our findings showed that the aircraft-derived bathymetry is generally more accurate than the UAV-derived and Sentinel-2 bathymetry in all analyzed scenarios due to the smooth color of the aircraft orthophotos and their ability to reproduce the seafloor with a considerable level of detail. [ABSTRACT FROM AUTHOR]

The relationship between modal elevation angle and the relative arrival time between modes, derived from exploiting modal dispersion, provides source information that is less susceptible to environmental influences. However, the standard method based on modal dispersion has limitations for application. To overcome this, we propose a hybrid method for passive source ranging of low-frequency underwater acoustic-pulse signals in a range-independent shallow-water waveguide. Our method leverages deep learning, utilizing the intermediate results from the standard method as inputs, and short-time conventional beamforming to transform signals received by a vertical line array into a beam-time-domain sound-intensity map. The source range is estimated using an attention-based regression model with a ResNet backbone that has been trained on the beam-time-domain sound-intensity map. Our experimental results demonstrate the superiority of the proposed method, with a mean relative-error reduction of 71%, mean root-squared error reduction of 2.25 km, and an accuracy of 85%, compared to matched-field processing. [ABSTRACT FROM AUTHOR]

The possibility of controlling localized fields in multimode shallow water waveguides based on the principle of interference invariance was studied. Within the framework of the numerical experiments in a wide frequency range of 100–350 Hz and range intervals of 10–100 km, the possibilities of focusing the sound field by wavefront reversal and controlling of the focusing of the focal spot by frequency tuning in shallow water waveguides was analyzed. The focal spot scanning was carried out by frequency tuning with a fixed distribution of the sound field at receiving and transmitting vertical antenna apertures. A comparative analysis of the features of focusing and focal spot control for summer and winter stratification of the water layer was carried out. It is shown that the parameters of the focal spot during frequency tuning were more stable in the winter waveguide. It is demonstrated that the sound frequency tuning had a piecewise continuous character and was carried out on a domain of one continuous track and jump-passing on the other track in accordance with the waveguide interference fringes in the range–frequency domain. [ABSTRACT FROM AUTHOR]

Natural marine soundscapes are being threatened by increasing anthropic noise, particularly in shallow coastal waters. To preserve and monitor these soundscapes, understanding them is essential. Here, we propose a new method for semi-supervised categorization of shallow marine soundscapes, with further interpretation of these categories according to concurrent environmental conditions. The proposed methodology uses a nonlinear mapping of short-term spectrograms to a two-dimensional space, followed by a density-based clustering algorithm to identify similar sound environments. A random forest classifier, based on additional environmental data, is used to predict their occurrence. Finally, explainable machine learning tools provide insight into the ecological explanation of the clusters. This methodology was tested in the Belgian part of the North Sea, and resulted in clearly identifiable categories of soundscapes that could be explained by spatial and temporal environmental parameters, such as distance to the shore, bathymetry, tide or season. Classifying soundscapes facilitates their identification, which can be useful for policy making or conservation programs. Soundscape categorization, as proposed in this work, could be used to monitor acoustic trends and patterns in space and time that might provide useful indicators of biodiversity and ecosystem functionality change. [ABSTRACT FROM AUTHOR]

We present an experimental study of gravity currents (GCs) with internal stratification in a semicircular channel in the inertial–buoyancy and Boussinesq regime. Forty tests were performed with a denser volume of fluid (brine advancing in a fresh water ambient fluid) in lock-release. The lock contains an internal stratification, with a layer of density ρ L overlain by a layer of density ρ U , where ρ a < ρ U < ρ L and ρ a is the density of the ambient fluid. The experiments cover both a full depth and a partial depth configurations. The measurements consist of marking the front position of the currents as a function of the time from release, t. Two lateral video-cameras were used to detect the flow profile. Also local instantaneous density and velocity profiles data were collected in a fixed section downstream of the gate, in order to give further details and a better description of the physical phenomenon. The data of front speed and current thickness were compared to a theoretical model (Zemach and Ungarish, 2021) based on (i) a Boussinesq flow; (ii) large Reynolds number; (iii) current advancing in shallow water conditions; and (iv) negligible ambient fluid dynamics. The system of equations and boundary conditions allow the prediction of the motion of the GC, in particular the position and speed of the nose x N t and u N t . The agreement of theory and experiments is fairly good, especially for the full depth configuration. The partial depth configuration experiments are less accurately reproduced by the theory, and require a correction coefficient of the Froude number at the front, that accounts for the deviations of the realistic system from the free-slip and sharp non-entraining interface in the control volume about the head. • Gravity currents with initial internal stratification in a non-rectangular cross-section propagate according to a simple model. • Experiments in full depth and partial depth configurations in a circular cross-section channel are reasonably well reproduced by the model. • Comparison refers to front speed and buoyancy fluxes and density profiles are estimated. [ABSTRACT FROM AUTHOR]

Over many years, there has been great practical interest in how solid bodies interact with and skim on liquid layers. In the present investigation, the focus is on the important role of body mass and shape in such skimming motions. Considering a thin two-dimensional solid body that impacts obliquely and then rebounds on a shallow inviscid water layer, we develop a mathematical model to predict quantitatively the duration and evolution of the body and fluid motions and indeed the success or failure of the whole skim. In the current setting, the shallow water layer thickness is small relative to the representative body length. The combined roles of increased mass and shape are found to be crucial, governed by a similarity solution. The relationship C ~M2/3 between scaled body curvature and mass is identified and highlighted. In particular, increased convex curvature of the underbody is found to alter the interactive pressure in such a way that it inhibits the occurrence of a super-elastic response in the exit vertical velocity and height of the body, and in effect enables a much heavier body to skim successfully provided the above relationship is maintained. [ABSTRACT FROM AUTHOR]

The consideration of shallow water effects has gained in importance regarding inland operations. The interaction between the keel and the riverbed affects the hydrodynamic characteristics of marine vessels. The highly complex nature of the interference phenomenon in catamarans makes the shallow water problem more complicated as compared to monohulls. Hence, catamarans are very sensitive to speed changes, as well as to other parameters, such as the shallow water effects. This makes the design of catamarans more challenging than their monohull equivalents. At lower Froude numbers, the higher importance of the frictional resistance makes the greater wetted surface of the catamaran a disadvantage. However, at higher speeds, there is the potential to turn their twin hulls into an advantage. This study aims to investigate the wave-making resistance of a zero-carbon fast passenger ferry operating in shallow water. The URANS (unsteady Reynolds-averaged Navier–Stokes) method was employed for resistance simulations. Then, the double-body approach was followed to decompose the residual resistance into viscous pressure and wave-making resistance with the help of the form factors of the vessel calculated at each speed. The characteristics of the separated wave-making resistance components were obtained, covering low, medium, and high speeds. Significant findings have been reported that contribute to the field by providing insight into the resistance components of a fast catamaran operating in shallow waters. [ABSTRACT FROM AUTHOR]

A reliable synchronization system of the transmitted data frame has a significant impact on the efficiency of the underwater communication system. This applies in particular to communication systems dedicated to work in shallow waters, where the phenomenon of multipath permanently occurs. To overcome these difficulties, the concept of a synchronization system consisting of two broadband signals of opposite monotonicity was presented. The method of receiving these signals has been described in detail. The stochastic channel model with Rician fading and the Watermark simulator was used to test the efficiency of the synchronization system in the underwater multipath channel. [ABSTRACT FROM AUTHOR]

Short-term changes in shallow bathymetry affect the coastal zone, and therefore their monitoring is an essential task in coastal planning projects. This study provides a novel approach for monitoring shallow bathymetry changes based on drone multispectral imagery. Particularly, we apply a shallow water inversion algorithm on two composite multispectral datasets, being acquired five months apart in a small Mediterranean sandy embayment (Chania, Greece). Initially, we perform radiometric corrections using proprietary software, and following that we combine the bands from standard and multispectral cameras, resulting in a six-band composite image suitable for applying the shallow water inversion algorithm. Bathymetry inversion results showed good correlation and low errors (<0.3 m) with sonar measurements collected with an uncrewed surface vehicle (USV). Bathymetry maps and true-color orthomosaics assist in identifying morphobathymetric features representing crescentic bars with rip channel systems. The temporal bathymetry and true-color data reveal important erosional and depositional patterns, which were developed under the impact of winter storms. Furthermore, bathymetric profiles show that the crescentic bar appears to migrate across and along-shore over the 5-months period. Drone-based multispectral imagery proves to be an important and cost-effective tool for shallow seafloor mapping and monitoring when it is combined with shallow water analytical models. [ABSTRACT FROM AUTHOR]

The effects of the free surface on the behavior of inclined dense jets in shallow ambient were investigated in detail. The hybrid turbulence model scale-adaptive simulation (SAS), coupled with the volume of fluid (VOF) multiphase model, was used to detect the complex interaction of the jet and the free surface as well as displacements of the free surface and induced waves. The simulation results had reasonable accuracy compared with experimental data for dilution, geometrical characteristics, and complex structures of the jet, except the trend of return point dilution, which the increase of Froude number results in fluctuations in it. Moreover, it was shown that the dilution and geometrical quantities have the same trend whether the Froude number increases in the constant depth, or the depth level decreases in the constant Froude number, except the return point dilution, which is more sensitive to depth than to Froude number variation. The generation of waves due to the impingement of the jet on the free surface leads to more detrainment, and causes the emergence of an area with low dilution value beneath the jet on the bed before the return point. In addition, analyzing the three-dimensional (3D) concentration contours demonstrated that in shallower depths, the so-called lateral plumes impact the bed over a wider area. Therefore, based on the effects of waves and lateral plumes, the so-called return plate seems to give a better understanding of the environmental impacts of the jet on the bed than does the traditional return point. [ABSTRACT FROM AUTHOR]

Accurate shallow water bathymetry data are essential for coastal construction and management, marine traffic, and shipping. With the development of remote sensing satellites and sensors, the satellite-derived bathymetry (SDB) method has been widely used for bathymetry in shallow water areas. However, traditional satellite bathymetry requires in-situ bathymetric data. Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) with the advanced high-resolution topographic laser altimeter system (ATLAS) provides a new technical tool and makes up for the shortcomings of traditional bathymetric methods in shallow waters. In this study, a new method is proposed to automatically detect photons reflected from the shallow seafloor with ICESat-2 altimetry data. Two satellite bathymetry models were trained, to obtain shallow water depth from Sentinel-2 satellite images. First, sea surface and seafloor signal photons from ICESat-2 were detected in the Oahu (in the U.S. Hawaiian Islands) and St. Thomas (in the U.S. Virgin Islands) sampling areas, to obtain water depths along the surface track. The results show that the RMSE is between 0.35 and 0.71 m and the R2 is greater than 0.92, when compared to the airborne LiDAR bathymetry (ALB) data in the field. Second, the ICESat-2 bathymetric points from Oahu Island are used to train the Back Propagation (BP) neural network model and obtain the SDB. The RMSE is between 0.97 and 1.43 m and the R2 is between 0.90 and 0.96, which are better than the multi-band ratio model with RMSE of 1.03–1.57 m and R2 of 0.89–0.95. The results show that the BP neural network model can effectively improve bathymetric accuracy, when compared to the traditional multi-band ratio model. This approach can obtain shallow water bathymetry more easily, without the in-situ bathymetric data. Therefore, it extends to a greater extent with the free ICESat-2 and Sentinel-2 satellite data for bathymetry in shallow water areas, such as coastal, island and inland water bodies. [ABSTRACT FROM AUTHOR]

We present a novel 3D implementation of a horizontal axis tidal turbine (HATT) in the shallow water hydrostatic code SHYFEM. The uniqueness of this work involves the blade element momentum (BEM) approach: the turbine is parameterized by applying momentum sink terms in the x and y momentum equations. In this way, the turbine performance is the result of both the flow conditions and the turbine's geometric characteristics. For these reasons, the model is suitable for farm-layout studies, since it is able to predict the realistic behavior of every turbine in a farm, considering the surrounding flow field. Moreover, the use of a shallow water code, able to reproduce coastal morphology, bathymetry wind, and tide effects, allows for studying turbine farms in realistic environments. [ABSTRACT FROM AUTHOR]

The vibroacoustic behavior of a vibrating infinitely-long thin three-dimensional cylindrical shell immersed in a perfect underwater acoustic waveguide is predicted using an analytical method. Vibration is induced by a point force excitation on the surface of the shell that is ingested into the equations of motion modeled using Flügge's shell theory. Radiated acoustic pressures are then investigated in relation to an influence from the acoustic boundaries of an underwater acoustic waveguide. The waveguide, which simulates a simplified shallow water environment, is composed of an upper free surface and a lower rigid floor. Its influence is modeled with the image-source method. Graf's addition theorem is employed to reconcile the coordinate systems of the infinite image sources in the fluid–structure coupling analytical expressions. Predictions of the near-field acoustic pressure are obtained by a direct numerical evaluation of the inverse Fourier integral, while the far-field acoustic pressure uses the stationary phase method. Axial directivities are of interest as the longitudinal length of the 3D shell imposes an additional dimension to the most commonly used 2D models in the literature to which radiated acoustic waves can dissipate energy. The far-field sound propagation from the shell in different fluid domain configurations is also shown. • Vibroacoustic behavior of a 3D vibrating cylindrical shell immersed in shallow water is presented. • Analytical formulations for both near- and far-field radiated acoustic pressures are developed. • A comparison is made between the typical simplified 2D setting and present 3D model. • Far-field pressures are presented as axial directivities to showcase the effect of the longitudinal direction. • Effects of different waveguide configurations on the far-field sound propagation of the shell are compared. [ABSTRACT FROM AUTHOR]