scholarly journals Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems

2021 ◽  
Vol 13 (10) ◽  
pp. 1874
Author(s):  
Isaac Rodríguez-Padilla ◽  
Bruno Castelle ◽  
Vincent Marieu ◽  
Philippe Bonneton ◽  
Arthur Mouragues ◽  
...  
Keyword(s):  
Optical Flow ◽  
Wave Breaking ◽  
Surf Zone ◽  
High Energy ◽  
Energy Conditions ◽  
Surface Currents ◽  
Pass Filter ◽  
Current Profiler ◽  
Low Pass

This paper examines the potential of an optical flow video-based technique to estimate wave-filtered surface currents in the nearshore where wave-breaking induced foam is present. This approach uses the drifting foam, left after the passage of breaking waves, as a quasi-passive tracer and tracks it to estimate the surface water flow. The optical signature associated with sea-swell waves is first removed from the image sequence to avoid capturing propagating waves instead of the desired foam motion. Waves are removed by applying a temporal Fourier low-pass filter to each pixel of the image. The low-pass filtered images are then fed into an optical flow algorithm to estimate the foam displacement and to produce mean velocity fields (i.e., wave-filtered surface currents). We use one week of consecutive 1-Hz sampled frames collected during daylight hours from a single fixed camera located at La Petite Chambre d’Amour beach (Anglet, SW France) under high-energy conditions with significant wave height ranging from 0.8 to 3.3 m. Optical flow-computed velocities are compared against time-averaged in situ measurements retrieved from one current profiler installed on a submerged reef. The computed circulation patterns are also compared against surf-zone drifter trajectories under different field conditions. Optical flow time-averaged velocities show a good agreement with current profiler measurements: coefficient of determination (r2)= 0.5–0.8; root mean square error (RMSE) = 0.12–0.24 m/s; mean error (bias) =−0.09 to −0.17 m/s; regression slope =1±0.15; coherence2 = 0.4–0.6. Despite an underestimation of offshore-directed velocities under persistent wave breaking across the reef, the optical flow was able to correctly reproduce the mean flow patterns depicted by drifter trajectories. Such patterns include rip-cell circulation, dominant onshore-directed surface flow and energetic longshore current. Our study suggests that open-source optical flow algorithms are a promising technique for coastal imaging applications, particularly under high-energy wave conditions when in situ instrument deployment can be challenging.

Observations of the Particle Size Distribution and Concentration in a Coastal System using an In Situ Laser Analyzer

2002 ◽  
Vol 36 (1) ◽  
pp. 59-69 ◽  
Author(s):  
Teresa Serra ◽  
Xavier Casamitjana ◽  
Jordi Colomer ◽  
Timothy C. Granata
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Water Column ◽  
Size Distribution ◽  
Posidonia Oceanica ◽  
High Energy ◽  
Suspended Particles ◽  
Energy Conditions ◽  
Coastal System

An in situ laser particle size analyzer (LISST-100, Sequoia Scientific, Inc.) has been used to study the particle size distribution and concentration of biological and non biological particles in the water column of a Mediterranean coastal system. Two field campaigns have been carried out during low and high energy conditions of the flow, caused by the passage of a storm front. For the low energy period, the water column remained stratified, whereas for the high energetic period the water column was warmer and well mixed. The first study dealt with the distribution of particles near the bottom of the coastal area. Here, two regions were taken into account. The first region was a sea-grass meadow of Posidonia oceanica and the second region was a barren sand area. The second study dealt with the determination of the vertical distribution of suspended particles in the whole water column of the system. The results showed a decrease in the vertical concentration of suspended particles in the water column with the passage of the storm front, which was associated with advection of warm water mass rather than by vertical mixing. In contrast, vertical resuspension determined the fate of suspended particles at the bottom of the water column and an increase of their concentration was found.

scholarly journals BATHYMETRY INVERSION IN THE SURF ZONE VIA ASSIMILATION OF REMOTELY SENSED WAVE BREAKING ENERGY DISSIPATION

2020 ◽  
pp. 26
Author(s):  
Francisco Soto ◽  
Patricio Catalan
Keyword(s):  
Wave Breaking ◽  
Surf Zone ◽  
Remote Sensing Data ◽  
Depth Measurement ◽  
Unique Data ◽  
Uncertain Model ◽  
Data Source ◽  
Breaking Energy ◽  
Spurious Signals

In this work, a data assimilation approach treating bathymetry as an uncertain model parameter, is introduced where direct dissipation estimates from remote sensing data are the unique data source. Two dimensional wave breaking dissipation fields are retrieved on a wave-by-wave basis with the algorithms of Daz et al. (2018), who were able to reliably estimate breaking dissipation by removing spurious signals affecting electro-optical and microwave data. After a six hour application, the system was able to retrieve improved bathymetric estimates, without any in situ depth measurement. A prominent feature of this approach is its ability to reliably capture the amplitude and position of nearshore sandbars.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/Y7mgiSvmRYc

Hybrid Low Pass and De-Trending Filter for Robust Position Estimation of Quadcopters

2016 ◽  
Author(s):  
Shatadal Mishra ◽  
Wenlong Zhang
Keyword(s):  
Optical Flow ◽  
Weighted Average ◽  
Position Estimation ◽  
High Frequency Oscillation ◽  
Flight Tests ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Least Squares Fit ◽  
Low Pass ◽  
Velocity Information

In this paper, a hybrid low-pass and de-trending (HLPD) filtering technique is proposed to achieve robust position estimates using an optical flow based sensor which calculates velocity information at a rate of 400 Hz. In order to filter out the high-frequency oscillation in the velocity information, a standard low-pass filter is implemented. The low-pass filter successfully eliminates sudden jumps and missing data-points, which prevents unprecedented maneuvers and mid-air crashes. The integrated position estimate has the accumulated drift which occurs due to electrical signal and temperature fluctuations together with other environmental factors which affect the data acquisition from the optical flow sensor. A recursive linear least squares fit is performed for the drift model and de-trending is applied to the integrated position signal. The performance of the proposed estimator is validated by comparing with model-identification based weighted average (MI-WA) position estimator, which is commonly used in quadcopters for position estimation. Simulation and experimental flight tests are conducted and the results show that the flight performance of HLPD filter is better than the extensively used MI-WA position filter in hover and square pattern flight tests.

scholarly journals Self-organization mechanisms for the formation of nearshore crescentic and transverse sand bars

2002 ◽  
Vol 465 ◽  
pp. 379-410 ◽  
Author(s):  
M. CABALLERIA ◽  
G. COCO ◽  
A. FALQUÉS ◽  
D. A. HUNTLEY
Keyword(s):  
Surf Zone ◽  
Sediment Concentration ◽  
High Energy ◽  
Feedback Mechanism ◽  
Energy Conditions ◽  
Wave Refraction ◽  
Sand Bars ◽  
Coastal Marine ◽  
Planar Slope ◽  
First Time

The formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow-water equations and on a simplified sediment transport parameterization. By assuming normally approaching waves and a saturated surf zone, rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed. Two types of bedforms appear: one is a crescentic bar pattern centred around the breakpoint and the other, herein modelled for the first time, is a transverse bar pattern. The feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations. Basically, the waves stir up the sediment and keep it in suspension with a certain cross-shore distribution of depth-averaged concentration. Then, a current flowing with (against) the gradient of sediment concentration produces erosion (deposition). It is shown that inside the surf zone, these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms. Numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro-morphodynamic input conditions to which of the patterns develops. It is suggested that crescentic bar growth would be favoured by high-energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment. In intermediate conditions mixed patterns may occur.

scholarly journals Dynamics of Excitation and Inhibition in the Light-Adapted Limulus Eye in situ

1971 ◽  
Vol 58 (1) ◽  
pp. 1-19 ◽  
Author(s):  
Marguerite Biederman-Thorson ◽  
John Thorson
Keyword(s):  
Steady State ◽  
Lateral Inhibition ◽  
Low Frequency ◽  
Dynamic Responses ◽  
Relaxation Processes ◽  
Pass Filter ◽  
Generator Potential ◽  
Low Pass Filter ◽  
Low Pass

The dynamics of spike discharge in eccentric cell axons from the in situ lateral eye of Limulus, under small sinusoidal modulation of light to which the eye is adapted, are described over two decades of light intensity and nearly three decades of frequency. Steady-state lateral inhibition coefficients, derived from the very low-frequency response, average 0.04 at three interommatidial spacings. The gain vs. frequency of a singly illuminated ommatidium is described closely from 0.004 to 0.4 cps by the linear transfer function s0.25; this function also accounts approximately for the measured phase leads, the small signal adaptation following small step inputs, and for Pinter's (1966) earlier low-frequency generator potential data. We suggest that such dynamics could arise from a summation in the generator potential of distributed intensity-dependent relaxation processes along the dendrite and rhabdome. Analysis of the dynamic responses of an eccentric cell with and without simultaneously modulated illumination of particular neighbors indicates an effect equivalent to self-inhibition acting via a first-order low-pass filter with time constant 0.42 sec, and steady-state gain near 4.0. The corresponding filters for lateral inhibition required time constants from 0.35 to 1 sec and effective finite delay of 50–90 msec.

scholarly journals Beach Morphodynamic Response to a Submerged Reef

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 340 ◽  
Author(s):  
Douglas Duarte Nemes ◽  
Francisco Fabián Criado-Sudau ◽  
Marcos Nicolás Gallo
Keyword(s):  
Wave Energy ◽  
Wave Breaking ◽  
Seasonal Cycle ◽  
High Energy ◽  
Morphological Features ◽  
Energy Conditions ◽  
Vector System ◽  
Coastal Processes ◽  
Physical Mechanisms ◽  
Physical Functions

To develop beach engineering, the submerged structure’s primary physical functions have to be understood. This study focuses on submerged structures in order to understand the strategy of reduced wave energy, stabilizing the shoreline and not generating erosion or adversely modifying coastal processes. Important developments have been made since the 1990s, taking into account the functions of recreational amenity. However, non-dimensional models cannot explain the physical mechanisms that generate accretion or erosion morphological features in the lee of the submerged structure. The present study aims to collaborate with the understanding of the mechanism of beach response to a submerged structure. For this, 26 surveys were made using topographic, Lagrangian, and Eulerian hydrodynamic measures during one seasonal cycle of a beach system from Rio de Janeiro (Brazil) with a natural submerged reef or rocky bank V-shape in the plan. This beach system is energetic and intermediate when referring to wave energy conditions and beach states, respectively. The wave breaking vector system on the rocky bank’s geometry was examined in the intermediate and dissipative beach morphodynamic organization. The variability of the wave breaking vector system determines the establishment, deformation, and erosion features in the lee of the structure. During high-energy waves, the submerged structure’s hydrodynamic and morphodynamic processes are transparent. When the submerged structure combines with the dissipative beach state, the surfing wave conditions are improved. These results provide the dimensional and positional references for an engineering proposal for a beach system.

In Situ Measurement of Algae Concentration Based on Pseudorandom Sequence Modulation

2014 ◽  
Vol 675-677 ◽  
pp. 271-274 ◽  
Author(s):  
Chao Yi Shi ◽  
Yu Jun Zhang ◽  
Gao Fang Yin ◽  
Nan Jing Zhao ◽  
Jing Bo Duan ◽  
...  
Keyword(s):  
Measurement System ◽  
Correlation Coefficients ◽  
Modulation Method ◽  
Pseudorandom Sequence ◽  
Theory Analysis ◽  
Pass Filter ◽  
Excitation Light ◽  
Low Pass Filter ◽  
Low Pass

We employed a method based on pseudorandom sequence modulation to suppress the system noise and sunlight interference for in situ measurement of algae concentration. Based on the theory analysis of the pseudorandom sequence modulation method, we established a measurement system. The excitation light was modulated by m sequence. The induced modulated fluorescence was demodulated by AD630 and then narrow-band filtered by a two-order Butterworth low-pass filter. The practical experiment results show that the linear response correlation coefficients of the measurement system reach up to 0.999 weather in a low concentration range (0~10μg/L) or in the whole concentration range (0.5~100μg/L).

In situ TEM studies of irradiation effects for materials improvement

1991 ◽  
Vol 49 ◽  
pp. 452-453
Author(s):  
Charles W. Allen
Keyword(s):  
Nuclear Reactor ◽  
Austenitic Stainless Steels ◽  
High Energy ◽  
Point Of View ◽  
In Situ Tem ◽  
Irradiation Effects ◽  
Tem Analysis ◽  
Radiation Induced ◽  
Analytical Tools

Irradiation effects studies employing TEMs as analytical tools have been conducted for almost as many years as materials people have done TEM, motivated largely by materials needs for nuclear reactor development. Such studies have focussed on the behavior both of nuclear fuels and of materials for other reactor components which are subjected to radiation-induced degradation. Especially in the 1950s and 60s, post-irradiation TEM analysis may have been coupled to in situ (in reactor or in pile) experiments (e.g., irradiation-induced creep experiments of austenitic stainless steels). Although necessary from a technological point of view, such experiments are difficult to instrument (measure strain dynamically, e.g.) and control (temperature, e.g.) and require months or even years to perform in a nuclear reactor or in a spallation neutron source. Consequently, methods were sought for simulation of neutroninduced radiation damage of materials, the simulations employing other forms of radiation; in the case of metals and alloys, high energy electrons and high energy ions.

In situ irradiation effects studies in medium- and high-voltage TEM

1995 ◽  
Vol 53 ◽  
pp. 234-235
Author(s):  
Charles W. Allen
Keyword(s):  
Cross Section ◽  
Particle Flux ◽  
Threshold Value ◽  
High Energy ◽  
Irradiation Damage ◽  
Defect Complexes ◽  
Lattice Position ◽  
Electrons And Ions ◽  
The Masses

With respect to structural consequences within a material, energetic electrons, above a threshold value of energy characteristic of a particular material, produce vacancy-interstial pairs (Frenkel pairs) by displacement of individual atoms, as illustrated for several materials in Table 1. Ion projectiles produce cascades of Frenkel pairs. Such displacement cascades result from high energy primary knock-on atoms which produce many secondary defects. These defects rearrange to form a variety of defect complexes on the time scale of tens of picoseconds following the primary displacement. A convenient measure of the extent of irradiation damage, both for electrons and ions, is the number of displacements per atom (dpa). 1 dpa means, on average, each atom in the irradiated region of material has been displaced once from its original lattice position. Displacement rate (dpa/s) is proportional to particle flux (cm-2s-1), the proportionality factor being the “displacement cross-section” σD (cm2). The cross-section σD depends mainly on the masses of target and projectile and on the kinetic energy of the projectile particle.

In situ TEM Studies of agglomeration of sub-nanometer Ru layers in Ru/C multilayers

1992 ◽  
Vol 50 (1) ◽  
pp. 256-257
Author(s):  
Tai D. Nguyen ◽  
Ronald Gronsky ◽  
Jeffrey B. Kortright
Keyword(s):  
Layered Structure ◽  
Driving Force ◽  
High Energy ◽  
Superior Performance ◽  
In Situ Tem ◽  
Rayleigh Instability ◽  
Practical Applications ◽  
Transmission Electron ◽  
Diffraction Patterns

Nanometer period Ru/C multilayers are one of the prime candidates for normal incident reflecting mirrors at wavelengths < 10 nm. Superior performance, which requires uniform layers and smooth interfaces, and high stability of the layered structure under thermal loadings are some of the demands in practical applications. Previous studies however show that the Ru layers in the 2 nm period Ru/C multilayer agglomerate upon moderate annealing, and the layered structure is no longer retained. This agglomeration and crystallization of the Ru layers upon annealing to form almost spherical crystallites is a result of the reduction of surface or interfacial energy from die amorphous high energy non-equilibrium state of the as-prepared sample dirough diffusive arrangements of the atoms. Proposed models for mechanism of thin film agglomeration include one analogous to Rayleigh instability, and grain boundary grooving in polycrystalline films. These models however are not necessarily appropriate to explain for the agglomeration in the sub-nanometer amorphous Ru layers in Ru/C multilayers. The Ru-C phase diagram shows a wide miscible gap, which indicates the preference of phase separation between these two materials and provides an additional driving force for agglomeration. In this paper, we study the evolution of the microstructures and layered structure via in-situ Transmission Electron Microscopy (TEM), and attempt to determine the order of occurence of agglomeration and crystallization in the Ru layers by observing the diffraction patterns.

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