Moving Water Surface Research Articles

A Novel Image Recovery from Moving Water Surface Using Multi-Objective Bispectrum Method

Nowadays, the image degradation field suffers from several challenges while processing underwater color images including color distortion and image blurring due to the scattering media. Moreover, to get appropriate multi-frame super-resolution images, there is essential for recovering a better quantity of images. Traditionally, the shift among images is directly evaluated when considering the under-sampled Low-Resolution (LR) images. On the other hand, the high-frequency LR image faces unreliability owing to the aliasing consequences of sub-sampling, but it will also degrade the recovery accuracy. This task design implements a novel image recovery model from the moving water surface by adopting the multi-objective adaptive higher-order spectral analysis. Image pre-processing, lucky region selection, and image recovery are the three main phases of this model. The bicoherence method and dice coefficient method are adopted for performing the lucky region selection. Finally, the adoption of the multi-objective adaptive bispectra method is used for performing the image recovery from the moving water surface. The improved Adaptive Fitness-oriented Random number-based Galactic Swarm Optimization (AFR-GSO) algorithm is used for optimizing the constraints of the bispectrum method. The experimental results verify the enrichment of image quality by the proposed model over the existing techniques.

АНАЛІЗ КОСМІЧНИХ СИСТЕМ ІДЕНТИФІКАЦІЇ РУХОМИХ НАДВОДНИХ ОБ’ЄКТІВ

The governing documents assume the creation in Ukraine by 2025 of a state integrated system of water surface and underwater environment of the Black and Azov seas and the basins of the Dnipro and Danube rivers, as well as a system of operational (combat) control, communication, intelligence and surveillance (C4ISR) of the Armed Forces of Ukraine. Both systems will function in the interests of the Naval Forces of Ukraine and will enable receiving operational data on the water surface environment for the purpose of protecting the sovereignty and territorial integrity of Ukraine, as well as countering illegal activities within the exclusive (maritime) economic zone of Ukraine. The article considers the possibility of using space systems for moving water surface objects identification as part of the targeted water surface environment detection systems. The mentioned space systems allow to simultaneously solve all three tasks inherent in water surface environment detection systems, i.e. detection, identification and observation of moving water surface objects. In the article, moving water surface objects should be understood as manned or unmanned sea and riverine single and group objects capable of moving on the water surface. Currently, similar space systems are already used by the EU, the USA, as well as other maritime states. The abovementioned systems enable the performance of the tasks of covering the water surface environment at significant distances from the coastline under any weather conditions and at different times of the day. At the same time, there are no risks for personnel and technical means of surveillance. The article contains a description of the specified space systems, as well as an overview of the spacecraft used to relay on-board navigational information. It should be noted that at the current stage, similar space systems are also used to detect, identify and track air and ground moving objects. Keywords: water surface environment; exclusive (maritime) economic zone; space system; radio line; navigation information; AIS; LRIT; COSPAS-SARSAT; SSAS; VMS.

Hyperparameter tuning-based triple correlation for spectral analysis-enabled image recovery from moving water surface

Hyperparameter tuning-based triple correlation for spectral analysis-enabled image recovery from moving water surface

Correction to: Adaptive Higher‑Order Spectral Analysis for Image Recovery Under Distortion of Moving Water Surface Using Dragonfly‑Colliding Bodies Optimization

Correction to: Adaptive Higher‑Order Spectral Analysis for Image Recovery Under Distortion of Moving Water Surface Using Dragonfly‑Colliding Bodies Optimization

Wall similarity in turbulent boundary layers over wind waves

The structure of the steady boundary layer in the airflow over young wind waves is studied in detail using extensive data accumulated in our laboratory as well as in additional laboratory facilities and in field measurements. Following the approach adopted in studies of turbulent flow over solid rough surfaces, the coupling between the spatial evolution of wind waves and wind velocity profiles over the water is analysed. The roughness of the moving water surface under wind is not constant; wind waves that constitute the roughness elements are unsteady, random and three-dimensional. The effective water surface roughness increases with airflow velocity as well as with downstream distance. Nevertheless, the existence of wall similarity as observed in a flow over solid surfaces is demonstrated; a fully rough boundary layer is obtained for young wind waves at diverse operational conditions. This approach enables quantitative study of the coupling between the airflow and local wind wave characteristics.

Application of MA-ATI SAR for Estimating the Direction of Moving Water Surface Currents in Pi-SAR2 Images

A multiaperture along-track interferometric synthetic aperture radar (MA-ATI SAR) theory was proposed to obtain velocity vectors of moving objects. This theory utilizes two antennas to estimate two velocity components (aft- and fore-looking directions) by multi/sublook processing. The moving direction can then be calculated by the two velocity components. Combining it with the conventional range velocity estimation, the velocity vector can be estimated. In order to validate its methodology, the present study applies MA-ATI SAR to airborne polarimetric interfereometric SAR-2 (Pi-SAR2) for estimating the directions of moving water surface currents of rivers. The results were in good agreement with the true moving directions. The estimated accuracy showed the direction error of approximately 20° for the three cases out of four. One case showed the higher error, since there may be complicated flow patterns. The findings of this study have implications for the applicability of the MA-ATI method to an airborne SAR system.

Airborne Feature Matching Velocimetry for surface flow measurements in rivers

A new airborne river surface flow measurement technique is presented, called Airborne Feature Matching Velocimetry (AFMV). It uses matchings of characteristic image features for orthorectification and velocimetry. Riparian matching points with an arbitrarily chosen base image serve to find individual projective transformation matrices to stabilize airborne video recordings. Transformed matching points’ distances of feature shifts between subsequent video frames lead to surface velocity vectors. To test this approach, a riverine moving water surface was recorded by an airborne video camera. Results are compared to (i) image frames rectified by 3D photogrammetry and (ii) related velocimetry results obtained by Particle Image Velocimetry (PIV). Generally, both time averaged and instantaneous surface velocities obtained by AFMV are shown to be of almost equal quality to the PIV approach. AFMV gives slightly less spatially-dense results in poorly textured areas, but clearly outperforms the 3D photogrammetry reference method in relation to computational power. Thus, the new method bears the potential to provide almost real-time instantaneous airborne river surface flow measurements.

Peculiarities of development and extinguishing fires at the objects where liquified petroleum gas is stored

The possibility of using sprayed water jets is established, primarily radial air jets, in vertical and horizontal planes in order to reduce the temperature of the burning Liquefied Petroleum Gas, starting from the cut-off of its expiration into free space. Various technical means of supplying water in a spray and spray nozzles for their creation, which are used in solving the problem of reducing the temperature of the burning Liquefied Petroleum Gas are viewed. It has been established that the active phase of the sprayed water jet is most effective (0,5-0,75 of the lengths), which, acting under the cut of the flame is crushed to a finely dispersed phase under the influence of a high-speed gas jet. As can be seen from the above, the heating rate of the finely dispersed water phase is increased up to the gaseous state, which leads to a decrease of the temperature of the flame in its middle combustion zone. Consequently, in the flame temperature will be much lower than the temperature of the flame cone, and, as a result, close to the extinction temperature. The authors recommend the use of modern jet-forming devices to realize this goal – nozzles NRT-5, NRT-10, NRT-20, NRS, as well as hand nozzles of the kind RSK-50, RS-А, RS-B, PROTEK. In order to cool, for example, one horizontal ground steel tank on both sides, it is necessary to use at least two hydraulic guns, which will act as maneuvering. In this case, the flow of water from the hydraulic gun with a diameter of the nozzle 25 mm will be from 16 to 18 liters per second. Therefore, the task is to find, calculate and experimentally prove the efficiency of the thermal screen, which is created in the form of a moving water surface that can effectively protect a particular physical object from the thermal impact of the heat zone. In order to reduce the flow of water to cool the tanks, the authors suggest using the NRS to create radial (flat) water jets. Application of such a nozzle allows to increase the area of simultaneous cooling of the maximum surface area per unit time due to the expansion of the angle of the spray jet spark. The water consumption does not exceed 13 liters per second.

Oil droplets transport due to irregular waves: Development of large-scale spreading coefficients

The movement of oil droplets due to waves and buoyancy was investigated by assuming an irregular sea state following a JONSWAP spectrum and four buoyancy values. A technique known as Wheeler stretching was used to model the movement of particles under the moving water surface. In each simulation, 500 particles were released and were tracked for a real time of 4.0h. A Monte Carlo approach was used to obtain ensemble properties. It was found that small eddy diffusivities that decrease rapidly with depth generated the largest horizontal spreading of the plume. It was also found that large eddy diffusivities that decrease slowly with depth generated the smallest horizontal spreading coefficient of the plume. The increase in buoyancy resulted in a decrease in the horizontal spreading coefficient, which suggests that two-dimensional (horizontal) models that predict the transport of surface oil could be overestimating the spreading of oil.

An investigation of channel flow with a smooth air–water interface

Experiments and numerical simulation are used to investigate fully developed laminar and turbulent channel flow with an air–water interface as the lower boundary condition. Laser Doppler velocimetry measurements of streamwise and wall-normal velocity components are made over a range of Reynolds number based upon channel height and bulk velocity from 1100 to 4300, which encompasses the laminar, transitional and low Reynolds numbers turbulent regimes. The results show that the airflow statistics near the stationary wall are not significantly altered by the air–water moving interface and reflect those found in channel flows. The mean statistics on the water interface side largely exhibit results similar to simulated Poiseuille–Couette flow (PCF) with a solid moving wall. For second-order statistics, however, the simulation and experimental results show some discrepancies near the moving water surface, suggesting that a full two-phase simulation is required. A momentum and energy transport tubes analysis is investigated for laminar and turbulent PCFs. This analysis builds upon the classical notion of a streamtube and indicates that part of the energy from the pressure gradient is transported towards the stationary wall and is dissipated as heat inside the energy tubes, while the remainder is transmitted to the moving wall. For the experiments, the airflow energy is transmitted towards the water to overcome the drag force and drive the water forward; therefore, the amount of energy transferred to the water is higher than the energy transferred to a solid moving wall.

Construction Set: Structural Concept for Joaquín Sorolla Railway Station in Valencia

The structure of Joaquín Sorolla railway station in Valencia is based on a modular construction concept. Like a Meccano or a “construction set”, it is composed of identical elements prepared to be bolt-connected together.In structural terms, the “mushroom” or “umbrella” type is considered. Simply formed by a central column with a cantilever roof, it is a classical typology in structural engineering. The main innovative features of the project are the successive sequence of the different modules – with and without column – and the height transition from the platforms to the hall, considering a similar “umbrella” type structure but inclined.This structural concept is supported by its refined details: first, the bolted connections between modules and secondly identifying the shape of the central connection between the diagonal beams of the modules, which identify the butt joint itself.Viewed from the underneath, the modules offer a strong structural composition of an expressive, modular coffered ceiling, intended to become the representative image of the station. In the formalization of the structure, the paintings of Joaquin Soralla have been a source of inspiration, particularly the painting of “Boy playing with a boat”. The light treatment, mirrored and reflected in the moving water surface, is of particular importance in this picture. The brush strokes in the picture draw the luminous atmosphere of Mediterranean beaches and the white steel structure of the station, with its refined elements and details, representing the boat the child is playing with, define a welcoming iconic symbol for Valencia.

Oblique impact of a water cone on a solid wall

The hydrodynamic problem of oblique impact of a water cone on a solid wall is investigated by the three dimensional (3D) velocity potential flow theory. The time stepping method is used in a stretched coordinate system to track the moving water surface where the fully nonlinear dynamic and kinematic boundary conditions are satisfied through an improved Eulerian method. In particular the free surface elevation and potential variation are updated at a given azimuth in each θ plane of the cylindrical coordinate system, to overcome the numerical difficulties caused by the complex variation of the 3D curved free surface. Remeshing and smoothing are applied regularly along the intersection lines of the free surface and each θ plane. Detailed convergence study with respect to a time step and element size has been undertaken and high accuracy has been achieved. Extensive simulations are made for perpendicular and oblique impacts. Detailed results for pressure and free surface profile are provided.

Experimental Study of Doppler Effect for Underwater Acoustic Communication Using Orthogonal Signal Division Multiplexing

This paper is about the underwater acoustic (UWA) communication using orthogonal signal division multiplexing (OSDM) in shallow water, whose environment is time spread and frequency spread. In this paper, the Doppler effect – Doppler shift and spread – for UWA communication using OSDM is mainly considered. The effects of Doppler shift and Doppler spread are evaluated in a test tank with a moving platform on a stable water surface and with a stable platform with a moving water surface, respectively. Doppler shift correction, which has been considered in simulation-based studies, is found to work effectively. In relation to the effect of Doppler spread, the experimental result well agrees with the simulation result. Through this study, it is confirmed that a smaller frame length is preferable because it enables the measurement of the UWA channel frequently so that it can keep up with channel changes.

Experimental Study of Doppler Effect for Underwater Acoustic Communication Using Orthogonal Signal Division Multiplexing

This paper is about the underwater acoustic (UWA) communication using orthogonal signal division multiplexing (OSDM) in shallow water, whose environment is time spread and frequency spread. In this paper, the Doppler effect – Doppler shift and spread – for UWA communication using OSDM is mainly considered. The effects of Doppler shift and Doppler spread are evaluated in a test tank with a moving platform on a stable water surface and with a stable platform with a moving water surface, respectively. Doppler shift correction, which has been considered in simulation-based studies, is found to work effectively. In relation to the effect of Doppler spread, the experimental result well agrees with the simulation result. Through this study, it is confirmed that a smaller frame length is preferable because it enables the measurement of the UWA channel frequently so that it can keep up with channel changes.

Bispectral analysis and recovery of images distorted by a moving water surface

We propose a new algorithm to recover a geometrically correct image of an object or scene from a set of images distorted by the wave motion of a water surface. Under mild conditions where the wavy surface normals weakly satisfy a Gaussian distribution, we demonstrate that the geometric distortion can be removed and a corrected image can be recovered. Our method is based on higher-order spectra analysis-in particular, the bispectrum, similar to its use in astronomical speckle imaging. In adapting this technique to imaging through or over a moving water surface, special care must be taken, and specifically tailored techniques are discussed in this paper. Our algorithm has been tested under two different scenarios: the refraction of light through a water surface (the underwater case) and the reflection of light from a water surface (the reflection case). Results in both cases have been encouraging.

Particle tracking velocimetry beneath water waves. Part II: Water waves

Particle Tracking techniques described earlier in the first part of this paper (Hering et al. 1997) were used to study the flow field beneath mechanically generated and wind induced flow fields. Experiments were conducted at three different wind/wave facilities (Heidelberg, Delft and San Diego). Particle Tracking allows an extensive study of drift velocities, wave orbital motion and turbulent Reynolds Stress beneath water waves. Monte Carlo simulations show, that the effects of the moving water surface on the calculation of mean properties of a flow can easily be avoided by Lagrangian measurements. Due to micro-scale wave breaking friction velocity profiles show a significant increase of turbulence towards the interface.

Radar imaging of water surface flow fields

We describe the capabilities of coherent high resolution radar to observe remotely the effects of an upwelling subsurface flow on the water surface. This observation is possible because the radar radiation backscatters very strongly from surface features with dimensions similar to its wavelength, in this case X-band at 0.03 m. This technique provides imaging capability with relatively high spatial resolution (∼0.3 m) and fast time sampling (∼0.006 s) over a large surface area. The processed data reveal both the line-of-sight velocity spectrum of moving water surface features, and their water surface radar backscatter cross-section. We believe that the surface features are generated by subsurface vortices oriented normal to the surface. The vortices are advected with the bulk flow of the jet. Our radar observations of the down-stream flow from a submerged waterjet that is directed parallel to the surface are consistent with those previously measured by laser velocimetry.

Measurements of Wave Height by Visualizing Air-Side Free-Surface and Illuminating the Wetted Surface of Hull through Water

Two optical methods to measure wave profiles are proposed with some accuracy analysis and examples. Although these are independent two methods, both are new techniques to get clear lines of free-surface boundaries. The methods provide enough contrast there for the boundary to be identified accurately by the image processing manner.The one is the method to measure wave profiles along straight cutlines where the air-side of free-surface is visualized by mist of dry-ice (CO2 gas). The mist, which is put on the water surface at upstream of the circulating water channel, covers all the surface in contact by the shearing stress of the moving water surface. The laser light sheet clearly visualizes the edge boundary of the air-side.The second is for the measurement of the hull-side wave profiles by illuminating the wetted surface of the hull through the water. The surface looks brightly white as if some kinds of white paints were painted. It has enough contrast along the free-surface to be identified definitely. Because the original pictures by the both methods have clear change in contrast across the free-surface boundary, the methods can provide relatively accurate results even after image processing.Because both methods are enough simple and automatic. they can be applied for daily measurements of the wave height in the circulating water channel.

Response to self-motion in waterstriders: visual discrimination between rotation and translation

Waterstriders (Gerris paludum) often try to maintain a nearly stationary position on a moving water surface. Passive motion is restricted to 3 degrees of freedom: yaw, longitudinal, and transverse displacement. They correct for passive rotation and translation by distinct behavioral sequences. The compensatory behavior is predominantly visually controlled. 1. When waterstriders are rotated and translated simultaneously, they are able to discriminate their own rotation and translation visually. 2. They discriminate their rotation from their translation even if the visible pattern is restricted to a monocular visual field. 3. They detect rotation only if they see an extended pattern.

Turbulent air flow over the dominant component of wind-generated water waves

This paper presents a laboratory study of the dynamic properties of air flow over small wind-generated water waves. On the basis of measurements of mean velocity profiles, turbulent intensity profiles and energy spectra, the detailed structure of turbulent wind immediately above and between the crests of progressive water waves has been examined.The velocity sensor (a hot-wire anemometer) was fastened to a self-adjusting positioner to measure instantaneous air velocities at a fixed distance from a moving water surface. The waves had a dominant frequency, 2·4 Hz, and a ratio of wave celerity and air friction velocity close to one. With the aid of a digital computer, the desired parameters of air flow were obtained by a statistical technique which was developed to sample and average simultaneous recordings of water surface displacements and instantaneous air velocities.The results of the wind field measurements over representative waves indicate that, on the average, the air flow separates from the wavy water surface just behind crests, and reattaches somewhere on the windward face of the next wave. The measured turbulent quantities consistently show the characteristics of separated air flow. The separation phenomenon suggests that, without some modification, the Benjamin-Miles shearing flow mechanism is inapplicable to the growth of fully-developed small water waves, at least when the ratio of the phase speed to air friction velocity is of order unity. The observed flow configuration tends to support the separation mechanism of energy transfer originally outlined by Jeffreys and later explored further by Stewart and Deardorff.Mean properties of the turbulent air flow referred to the mean water level were obtained by continuous sampling of the air flow over many waves with a sensing probe, either at a fixed distance from the mean water level (fixed probe measurement) or at a constant distance from the moving water surface (moving probe measurement). It was found that for continuously averaged measurements, the fixed probe yielded results which deviate less from the local mean than the moving probe results. This holds for the mean velocity distributions and especially for the turbulent quantities.