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This study investigates the shoreline dynamics of a Caribbean reef-lined beach by utilizing a long-term satellite dataset spanning 75 years and a short-term, high-frequency dataset captured by a fixed camera over 3 years. An array of statistical methods, including ARIMA models, are employed to examine the impact of storms and potential cyclical influences on the shoreline dynamics. The findings indicate that significant storm events trigger a substantial retreat of the vegetation limit, followed by a slow recovery. Given the current frequency of such major events, complete recovery may take several decades, resulting in a minor influence of cyclones on the long-term erosion trend, which remains moderate. The short-term shoreline evolution is primarily driven by the annual cyclicity of the still water level, which generates an annual oscillation—an insight not previously reported. In the context of climate change, alterations to sea-level rise and cyclone frequency could disrupt the observed dynamic equilibrium at different timescales. Such changes could result in an alteration of existing cyclicities, disturbance of recovery periods, increased long-term shoreline retreat rates, and potentially affect overall coastal resilience over time.

This study investigates the shoreline dynamics of a Caribbean reef-lined beach by utilizing a long-term satellite dataset spanning 75 years and a short-term, high-frequency dataset captured by a fixed camera over 3 years. An array of statistical methods, including ARIMA models, are employed to examine the impact of storms and potential cyclical influences on the shoreline dynamics. The findings indicate that significant storm events trigger a substantial retreat of the vegetation limit, followed by a slow recovery. Given the current frequency of such major events, complete recovery may take several decades, resulting in a minor influence of cyclones on the long-term erosion trend, which remains moderate. The short-term shoreline evolution is primarily driven by the annual cyclicity of the still water level, which generates an annual oscillation—an insight not previously reported. In the context of climate change, alterations to sea-level rise and cyclone frequency could disrupt the observed dynamic equilibrium at different timescales. Such changes could result in an alteration of existing cyclicities, disturbance of recovery periods, increased long-term shoreline retreat rates, and potentially affect overall coastal resilience over time. [ABSTRACT FROM AUTHOR]

Swash motions are important for the design and assessment of beach protection projects, while the limitation of insightful observations in the swash zone still exists. An automatic identification method based on video imagery is developed to monitor and extract instantaneous swash motions in the laboratory. The method increases video sampling frequency and improves image enhancement in identification. The improved method fits well with the results of the manual method. The incident band roll-off of the swash spectrum in the experiment is consistent with those observed on natural beaches. Results have shown that on the barred beach, water depths influence the peak frequency in the incident band and cause a multi-peak swash spectrum. A large incident wave period causes a low peak frequency but high peak energy in the swash spectrum. Large incident wave height results in wider energy coupling, making swash to be saturated and more energy in swash energy. The existence of a barred beach promotes swash energy transferring from a high frequency to a low frequency. [ABSTRACT FROM AUTHOR]

Background: The growing interest in mineral resources of the deep sea, such as seafloor massive sulphide deposits, has led to an increasing number of exploration licences issued by the International Seabed Authority. In the Indian Ocean, four licence areas exist, resulting in an increasing number of new hydrothermal vent fields and the discovery of new species. Most studies focus on active venting areas including their ecology, but the non-vent megafauna of the Central Indian Ridge and South East Indian Ridge remains poorly known. In the framework of the Indian Ocean Exploration project in the German license area for seafloor massive sulphides, baseline imagery and sampling surveys were conducted yearly during research expeditions from 2013 to 2018, using video sledges and Remotely Operated Vehicles. New information: This is the first report of an imagery collection of megafauna from the southern Central Indian- and South East Indian Ridge, reporting the taxonomic richness and their distribution. A total of 218 taxa were recorded and identified, based on imagery, with additional morphological and molecular confirmed identifications of 20 taxa from 89 sampled specimens. The compiled fauna catalogue is a synthesis of megafauna occurrences aiming at a consistent morphological identification of taxa and showing their regional distribution. The imagery data were collected during multiple research cruises in different exploration clusters of the German licence area, located 500 km north of the Rodriguez Triple Junction along the Central Indian Ridge and 500 km southeast of it along the Southeast Indian Ridge. [ABSTRACT FROM AUTHOR]

Swash motions are important for the design and assessment of beach protection projects, while the limitation of insightful observations in the swash zone still exists. An automatic identification method based on video imagery is developed to monitor and extract instantaneous swash motions in the laboratory. The method increases video sampling frequency and improves image enhancement in identification. The improved method fits well with the results of the manual method. The incident band roll-off of the swash spectrum in the experiment is consistent with those observed on natural beaches. Results have shown that on the barred beach, water depths influence the peak frequency in the incident band and cause a multi-peak swash spectrum. A large incident wave period causes a low peak frequency but high peak energy in the swash spectrum. Large incident wave height results in wider energy coupling, making swash to be saturated and more energy in swash energy. The existence of a barred beach promotes swash energy transferring from a high frequency to a low frequency.

Baited Remote Underwater Video Stations (BRUVS) complemented with fishing methods were used to describe the fish assemblage and its seasonal pattern in two marine inlets from Patagonia. The combined results for BRUVS and fishing sessions identified 13 fish species. Our results agree with the biogeographic schemes proposed for the southern Southwest Atlantic. The fish species belonging to the Argentine Biogeographic Province presented a seasonal pattern with a peak of maximum abundance (Notorynchus cepedianus and Galeorhinus galeus) or were recorded during warm months only (Mustelus schmitti, Myliobatis goodei, and M. ridens), coinciding with the general latitudinal pattern expected for fish species richness. The use of BRUVS in this study allowed for the assessment of different fish species and wide range of sizes, from large sharks (N. cepedianus) to small cryptic species (Patagonotothem sp.). However, three of 13 species were only recorded by fishing methods, like it was the case for M. ridens. The record of M. ridens is the first in Patagonian waters, extending its distribution for c. 180 km south of the previously known southern limit. This study contributes to filling large data gaps along the Southwest Atlantic regarding the description and understanding of the temporal dynamics of fish assemblages in particular environments within protected areas.

Baited Remote Underwater Video Stations (BRUVS) complemented with fishing methods were used to describe the fish assemblage and its seasonal pattern in two marine inlets from Patagonia. The combined results for BRUVS and fishing sessions identified 13 fish species. Our results agree with the biogeographic schemes proposed for the southern Southwest Atlantic. The fish species belonging to the Argentine Biogeographic Province presented a seasonal pattern with a peak of maximum abundance (Notorynchus cepedianus and Galeorhinus galeus) or were recorded during warm months only (Mustelus schmitti, Myliobatis goodei, and M. ridens), coinciding with the general latitudinal pattern expected for fish species richness. The use of BRUVS in this study allowed for the assessment of different fish species and wide range of sizes, from large sharks (N. cepedianus) to small cryptic species (Patagonotothem sp.). However, three of 13 species were only recorded by fishing methods, like it was the case for M. ridens. The record of M. ridens is the first in Patagonian waters, extending its distribution for c. 180 km south of the previously known southern limit. This study contributes to filling large data gaps along the Southwest Atlantic regarding the description and understanding of the temporal dynamics of fish assemblages in particular environments within protected areas. [ABSTRACT FROM AUTHOR]

Kim, J. and Kim, J., 2020. Estimation of water surface flow velocity using coastal video imagery by visual tracking with deep learning. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 522-526. Coconut Creek (Florida), ISSN 0749-0208. This paper describes the method of flow velocity estimation of water surface in video imagery by tracking waves using deep neural network for visual object tracking with unsupervised learning. The model of deep neural network consists of two stages for scene separation and image registration to extract waves only and track the propagated waves, respectively. The dataset of video imagery acquired at Anmok beach of south Korea has been used to training the model and it learns the behavior of propagated waves. The performance of model is evaluated by measuring image similarity using test dataset. And the estimated flow velocity of water surface in propagated waves is compared with the flow from conventional image processing method of particle image velocity. The results show that our proposed approach with deep learning method is very promising to measure and predict coastal waves especially in the surf zone. [ABSTRACT FROM AUTHOR]

Runup is defined as the added water level above the still water level by waves. Accurate estimation of runup is essential for coastal protection, coastal management and hazard prediction. A video-based research was carried out in Gisborne and Mahia (New Zealand) to validate previously developed runup models in a New Zealand context and present locally adjusted models based on available models. A wave runup dataset containing 14 runup time series was produced. 5 previous models were tested with field observation. Among these models, the model proposed by Homan (1986) provides the most accurate predictions of 2% R . A locally adjusted model based on Homan (1986) yields improved results ( R² = 82%). For Gisborne and Mahia, 2% R is best parameterized by beach slope. A new model parameterized beach slope produces even better results ( R² = 83%). With information of beach slopes, it can be easily applicated to beaches around Gisborne and Mahia. [ABSTRACT FROM AUTHOR]

Web cameras are transforming coastal environmental monitoring. Improvements in camera technology and image processing capabilities, paired with decreases in cost, enable widespread use of camera systems by researchers, managers and first responders for a growing range of environmental monitoring applications. Applications are related to transportation and commerce, preparedness, risk reduction and response, and stewardship of coastal resources. While web cameras are seemingly ubiquitous, operators often follow unique installation procedures and collect, store, and process imagery data in various ways. These inconsistencies significantly limit the ability for imagery data to be shared and utilized across research and operational disciplines. Similar to the early days of other remote sensing networks like High Frequency Radar, the benefits and downstream application of coastal imagery data can be greatly enhanced through centralized data access and standardization of data collection, analysis and dissemination. The NOAA National Ocean Service Web Camera Applications Testbed (WebCAT) was launched in 2017 in partnership with SECOORA, as a public-private partnership to address this coastal ocean observing standardization need. WebCAT is a pilot project relying on the private sector expertise of Surfline, Inc., to install and operate several web cameras capable of meeting the short-term needs of diverse users including NOAA, USGS, state health agencies, academia and others. The project aims to determine operational imagery collection, storage, processing, access, and archival requirements that will foster collaboration across research and operational user communities. Seven web cameras have been installed at six locations along the southeast United States coast (from Florida to North Carolina) for purposes including: counting animals on the beach and migrating right whales, identifying rip currents, validating wave runup models, and understanding human use of natural resources. Here we present a review of the state of coastal imagery data and an overview of the WebCAT project. Goals of an upcoming community workshop will also be presented along with our vision for how WebCAT can motivate a future sustained operational web camera network.

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.

Two separate efforts to characterize epibenthic communities in the northern Bering and Chukchi seas using video imagery from a drop camera system have now been completed. In the initial phase in 2008, we acquired video imagery from the USCGC Healy while drifting on station during the multidisciplinary Bering Sea Program and used cluster analysis and non-metric multidimensional scaling to identify epibenthic assemblage types and associated sediment characteristics based upon along-track epifaunal counts. We also quantified the areal density of easily recognizable organisms such as brittle stars (Ophiura sp.) and sea stars, which were abundant and easily identified. While sampling was not extensive enough to rigorously compare the density of epifauna with trawling data available from prior years, our observations confirmed the characteristics of epifaunal communities sampled through much more labor-intensive trawling. Densities of epifauna that could be readily enumerated were of the same order of magnitude in both types of observations. During the second phase in 2016 and 2017 of video observations from the CCGS Sir Wilfrid Laurier , we improved the quality of imagery, and obtained seafloor video footage from each station in the internationally coordinated sampling grid in the Distributed Biological Observatory (DBO). This grid lies in the productive waters of the northern Bering and Chukchi seas. Quantitative analysis was not undertaken in this second phase, but the imagery confirms the presence of specific organismal community assemblages that can be related to environmental factors such as sediment grain size and water mass identity that are available from other project data collected during the Bering Sea and DBO projects. For example, sandier sediments typically had diverse epifaunal communities including filter feeders as significant community components. In muddier sediments, deposit feeders such as brittle stars predominated. All the second phase video footage has been posted in both abbreviated form on the video-sharing website youtube.com, and longer (10 min per station) versions are freely downloadable from a Google Drive server. Future videography may help identify changes in epibenthic diversity and community composition and could be successfully evaluated with crowd-sourced citizen science and/or more traditional scientific documentation. [ABSTRACT FROM AUTHOR]

Abstract Reflected waves account for a significant part of the nearshore energy budget and influence incoming waves, nearshore circulation and sediment transport. The use of swash parameters to estimate wave reflection is investigated at three different beaches ranging from highly reflective to dissipative. It is observed that it is essential to account for swash processes when estimating reflection, in particular at intermediate and reflective beaches with a steep beachface. Our results show that runup asymmetry in uprush/backwash can be used as a proxy for dissipation in the swash zone: larger asymmetry values indicating greater dissipation. In our dataset, a reflection predictor based on runup asymmetry has better skill in comparison to empirical predictors based on surf similarity, because runup is a process that integrates both surf and swash zone wave transformation. Runup asymmetry behaves as a swash similarity parameter and reflects an equilibrium between swash period, slope and dissipation. Highlights • Link between swash parameters and wave reflection investigated at three different beaches. • Asymmetry in uprush/backwash can be considered a proxy for swash dissipation. • Evidence of equilibrium between runup asymmetry, period and slope. [ABSTRACT FROM AUTHOR]

In this Special Issue “Application of Remote Sensing Methods to Monitor Coastal Zones” nine original research papers were published, with topics covering a wide range of ranging of remote sensing applications including coastal topography, bathymetry, land cover, and nearshore hydrodynamics [...]

Applications of (video-based) depth inversion in the near-shore coastal environment are growing in numbers. Video-based capabilities in nearshore monitoring are improving and coastal monitoring programs are expanding due to greater availability and reduced costs. Video-derived beach (state) indicators such as beach width, bar position and wave and current parameters are supplemented by accurate depth estimations through inversion. Video-based depth inversion knows two main approaches, a spectral and temporal method of celerity estimation. The two methods have so far never been compared as video-systems are often tailored for the chosen celerity estimation method. Here, a spectral and temporal method are compared using controlled synthetic datasets obtained using the SERRE1D Boussinesq model to estimate celerity and invert depth. The assessment is carried out on a set of wave boundary conditions with over linear and barred bottom profile. Both methods invert depth with a similar accuracy for the most realistic JONSWAP cases. An evident correlation is found between wave skewness, non-linearity and depth estimation error linked to the limits of the linear dispersion relation. A residual ’sensing’ error is linked to method-based parameters and a changing wave shape as incident waves propagate inshore. The inversion-error can be reduced significantly including a wave height dependent non-linear correction. Importantly, a method-based error is introduced for the temporal method to increase the suitability for data assimilation. Likewise, the spectral method has its own existing depth-error estimation to feed into the Kalman Filter. However, these method-based error estimates show very weakly or no relation to the observed error between estimated cross-shore profile and bottom profile used for the model input. [ABSTRACT FROM AUTHOR]

Different methods can be used to measure the time and distance of travel of a fire and thus its speed. The selection of a particular method will depend on the experimental objectives, design, scale, location (in the laboratory or field), required accuracy and resources available. In this study, measurements from ocular observation (directly by eye), visible spectrum video imagery and thermocouple instrumentation were used to compare their performance in quantifying the time of arrival and rate of spread of a fire burning across a eucalypt forest litter fuel bed in a combustion wind tunnel. All methods gave similar results, but there were some significant differences depending on the dryness of the fuel and speed of the wind. [ABSTRACT FROM AUTHOR]

The present work investigates cross-shore shoreline migration as well as its alongshore variability (with deformation) on timescales of days to years using 6 years of time-averaged video images. The variability of the shoreline is estimated through empirical statistical methods with comprehensive reference to three scales of variability. At the meso-to macro-tidal barred Biscarrosse beach, shoreline responds in decreasing order at seasonal (winter/summer cycles, 52%), event (storms, 28%) and inter-annual scales. Whereas seasonal evolution is dominated by wave climate modulation, short-term evolution is influenced by tidal range and surf-zone sandbar characteristics. The influence of tide range and sandbars increases when timescale decreases. This is even more the case for the alongshore deformation of the shoreline which is dominated by short-term evolution. An EOF analysis reveals that the first mode of shoreline change time series is associated with cross-shore migration and explains 58% of the shoreline variability. The rest of the modes are associated to deformation which explain 42% of shoreline variability. [ABSTRACT FROM AUTHOR]

Recent research into rip currents has revealed the existence of multiple circulation patterns, meaning that no single escape strategy is appropriate in all situations. Rip circulation is influenced by surfzone morphology, which can be inferred from wave breaking patterns in video imagery. Wave breaking often occurs over the bars adjacent to the rip channel, with little breaking over the seaward end of the rip. However, under varying wave and tide conditions, breaking can also occur at the seaward extent of rip channels. Here, we use this difference as a novel wave dissipation parameter to classify a rip channel as either ‘open’ or ‘closed’ in terms of rip-head wave breaking. A 4-day field study provided Lagrangian rip current data at a macrotidal, dissipative beach monitored by a coastal imaging system. Using this new parameter, rip channels that were identified as closed exhibited a 31% increase in current speeds and 43% increase in horizontal vorticity compared to open channels. The transition between open and closed channels occurred over a single tidal cycle, which altered surfzone retention rates. Closed channels promoted surfzone retention, with < 25% of drifters exiting the surfzone. In comparison, open channels were more conducive to exchange, with exit rates up to 91%. Analysis of the Royal National Lifeboat Institution lifeguard rip incident database showed that open rips were disproportionately represented in the occurrence of rescue events, and calculated here to be twice as dangerous as closed rips. The use of this new open/closed parameter could be used by surf lifesaving organisations, and may have implications for the cross-shore exchange of sediment and pollutants. [ABSTRACT FROM AUTHOR]

A direct estimation of longshore currents using in-situ instruments is difficult and costly, and often limited to punctual measurements over short durations. Video remote sensing systems offer an alternative when drifting features, like foam induced by breaking waves or other streaks, are visible. In this paper we describe a method based on the application of the Radon transform on longshore spatio-temporal images. The sinogram from the Radon transform is used to find the angle of the drifting, further converted into current. Our approach is first tested using synthetic fields created using anisotropic Gaussian random currents and waves. Comparison is also made with in-situ currents from the Grand Popo 2014 experiment in Benin (Gulf of Guinea, West Africa). Results show an overall good agreement (O(30%)) in the swash, surf and inner shelf zones while the method offers best skills in the surf zone (17%) where the drifting foam induced by wave breaking is evident. The width of the Radon peak is found to be a good proxy of accuracy. This remote sensing method allows a long term monitoring of the longshore current and its cross-shore structure, which brings new perspectives in quantifying sediment drift variability. [ABSTRACT FROM AUTHOR]

Identifying the factors driving community dynamics in hydrothermal vent communities, and in particular biological interactions, is challenged by our ability to make direct observations and the difficulty to conduct experiments in those remote ecosystems. As a result, we have very limited knowledge on species׳ behaviour and interactions in these communities and how they in turn influence community dynamics. Interactions such as competition or predation significantly affect community structure in vent communities, and video time-series have successfully been used to gain insights in biological interactions and species behaviour, including responses to short-term changes in temperature or feeding strategies. In this study, we combined in situ and ex situ approaches to characterise the behaviour and interactions among two key species encountered along the Mid-Atlantic Ridge (MAR): the shrimp Mirocaris fortunata and the crab Segonzacia mesatlantica. In situ, species small-scale distribution, interactions and behaviour were studied using the TEMPO observatory module deployed on the seafloor at the base of the active Eiffel Tower edifice in the Lucky Strike vent field as part of the EMSO-Açores MoMAR observatory. TEMPO sampled 2 min of video four times a day from July 2011 to April 2012. One week of observations per month was used for ‘long-term’ variations, and a full video data set was analysed for January 2012. In addition, observations of crab and shrimp individuals maintained for the first time under controlled conditions in atmospheric pressure (classic tank) and pressurised (AbyssBox) aquaria allowed better characterisation and description of the different types of behaviour and interactions observed in nature. While the identified in situ spatial distribution pattern was stable over the nine months, both species displayed a significant preference for mussel bed and anhydrite substrata, and preferentially occupied the area located directly in the fluid flow axis. The aggregation behaviour of M. fortunata resulted in the occurrence of numerous intraspecific interactions mainly involving the use of two pairs of sensory organs (antenna/antennule) and fleeing behaviours when in contact or close to individuals of S. mesatlantica . The higher level of passiveness observed in the ex situ artificial environment compared to the in situ environment was attributed to the lack of stimulation related to low densities of congeners and/or of sympatric species compared to the natural environment and the absence of continuous food supply, as both species displayed a significant higher level of activity during feeding time. This result emphasises the role of food supply as a driver of species distribution and behaviour. Direct in situ observations using cameras deployed on deep-sea observatories, combined with experimental set-up in pressurised aquaria, will help investigators understand the factors influencing community dynamics and species biology at vents as well as their underlying mechanisms. [ABSTRACT FROM AUTHOR]

Sandbar straightening on natural beaches is known to occur following storm events. However, on a typical south-west Western Australia beach, sandbar straightening is observed under low amplitude wind-sea forcing in summer and remains alongshore-variable following high wave events associated with winter storms. During summer, diurnal variations in wave height and direction are associated with a strong sea breeze cycle. At the peak of the sea breeze the local wind-sea approaches the beach obliquely, driving strong alongshore currents. The occurrence of the seasonal, obliquely-incident wind-sea provides the opportunity for testing the role of the wave angle on sandbar straightening. The location of the bar crest is observed using time exposure video images and the alongshore variability is quantified using the standard deviation of the sandbar position. The role of wave incidence angle on alongshore-variability is highlighted, as the sandbar straightens in the presence of oblique wave forcing associated with summer sea breezes, and remains alongshore-variable with normally incident wave forcing. The transition from alongshore-variable to alongshore-uniform also depends on the antecedent bathymetry, in particular the distance between the shore and the bar crest. When the sandbar is further offshore, alongshore variability persists in the presence of strong sea breezes. [ABSTRACT FROM AUTHOR]

The use of variance images for runup and shoreline detection is analyzed in this work. A methodology based on the variance images is first motivated with synthetic time stacks and then confirmed with real images. A total of 55 time stack images from five different cameras at three video stations (in Spain and New Zealand) were digitized and used for the study. These images include different tide and wave conditions. From the time stack images we: 1) obtained the mean shoreline position and maximum runup manually digitizing the water/sand interface and, 2) computed the variance function. The variance function is shown to have a particular cross-shore shape, with two characteristic positions which allow us to satisfactorily recover the mean shoreline position and maximum runup obtained in the first step. Variance images were shown to be useful both for detecting mean shoreline, and for evaluating runup, providing a potential alternative for timex images. The method did not work well when runup occurred within the groundwater seepage face. [ABSTRACT FROM AUTHOR]

A variety of video and photographic imaging platforms are used to survey seafloor habitats and organisms beyond the effective depth of most SCUBA diving (>30 m). Each platform has benefits and shortcomings, with the most frequently limiting factors being (a) access to the most advanced instruments, (b) response of organisms, and (c) resolution of organism identification. Here, we describe the approaches used to collect, process, and analyze video imagery collected with a simple towed camera sled in the Monterey Bay National Marine Sanctuary as part of a larger, ongoing characterization project that began in 2006. We describe the details of deployment, imagery collection, postprocessing, and analyses gleaned from hundreds of hours of underwater video. Data extracted from camera sled imagery have been analyzed using multivariate model comparison techniques and have been represented in a variety of forms to support management needs and public outreach efforts. [ABSTRACT FROM AUTHOR]

Abstract: Time–exposure intensity (averaged) images are commonly used to locate the nearshore sandbar position (x b ), based on the cross-shore locations of maximum pixel intensity (x i ) of the bright bands in the images. It is not known, however, how the breaking patterns seen in Variance images (i.e. those created through standard deviation of pixel intensity over time) are related to the sandbar locations. We investigated the suitability of both Time–exposure and Variance images for sandbar detection within a multiple bar system on the southern coast of Brazil, and verified the relation between wave breaking patterns, observed as bands of high intensity in these images and cross-shore profiles of modeled wave energy dissipation (x D ). Not only is Time–exposure maximum pixel intensity location (x i-Ti ) well related to x b , but also to the maximum pixel intensity location of Variance images (x i-Va ), although the latter was typically located 15m offshore of the former. In addition, x i-Va was observed to be better associated with x D even though x i-Ti is commonly assumed as maximum wave energy dissipation. Significant wave height (Hs) and water level (η) were observed to affect the two types of images in a similar way, with an increase in both Hs and η resulting in x i shifting offshore. This η-induced x i variability has an opposite behavior to what is described in the literature, and is likely an indirect effect of higher waves breaking farther offshore during periods of storm surges. Multiple regression models performed on x i , Hs and η allowed the reduction of the residual errors between x b and x i , yielding accurate estimates with most residuals less than 10m. Additionally, it was found that the sandbar position was best estimated using x i-Ti (x i-Va ) when x b was located shoreward (seaward) of its mean position, for both the first and the second bar. Although it is unknown whether this is an indirect hydrodynamic effect or is indeed related to the morphology, we found that this behavior can be explored to optimize sandbar estimation using video imagery, even in the absence of hydrodynamic data. [Copyright &y& Elsevier]

Abstract: Groundwater seepage is known to influence beach erosion and accretion processes. However, field measurements of the variation of the groundwater seepage line (GWSL) and the vertical elevation difference between the GWSL and the shoreline are limited. We developed a methodology to extract the temporal variability of the shoreline and the wet–dry boundary using video imagery, with the overarching aim to examine elevation differences between the wet–dry boundary and the shoreline position in relation to rainfall and wave characteristics, during a tidal cycle. The wet–dry boundary was detected from 10min time-averaged images collected at Ngaranui Beach, Raglan, New Zealand. An algorithm discriminated between the dry and wet cells using a threshold related to the maximum of the red, green, and blue intensities in Hue-Saturation-Value. Field measurements showed this corresponded to the location where the water table was within 2cm of the beachface surface. Time stacks and time series of pixels extracted from cross-shore transects in the video imagery, were used to determine the location of the shoreline by manually digitizing the maximum run-up and minimum run-down location for each swash cycle, and averaging the result. In our test data set of 14 days covering a range of wave and rainfall conditions, we found 6 days when the elevation difference between the wet–dry boundary and the shoreline remained approximately constant during the tidal cycle. For these days, the wet–dry boundary corresponded to the upper limit of the swash zone. On the other 8 days, the wet–dry boundary and the shoreline decoupled with falling tide, leading to elevation differences of up to 2.5m at low tide. Elevation differences between the GWSL and the shoreline at low tide were particularly large when the cumulative rainfall in the preceding month was greater than 200mm. This research shows that the wet–dry boundary (such as often used in video shoreline-finding algorithms) is related to groundwater seepage on low-sloped, medium to fine sand beaches such as Ngaranui Beach (mean grain size ∼0.27mm, beach slope ∼1:70) and may not be a good indicator of the position of the shoreline. [Copyright &y& Elsevier]

Abstract: This paper introduces a semi-automatic computer algorithm designed to detect rip current channels in video imagery. As a case study, this method is applied to 3.3years of video data from an embayed beach to demonstrate the link between antecedent surf zone morphology, wave energy and up/down transitions in beach state. An objective measure of rip channel change was developed to define six significant rip reconfiguration events and relate these events to wave energy. Over the period of study no complete resets of the nearshore morphology occurred. The analysis indicates that direct correlation of rip patterns with the instantaneous wave conditions is not a useful way to demonstrate how rips and waves interact. The average wave energy over a period of ten days, combined with storm duration were good indicators of rip channel change, demonstrating that in general, beach morphology responds with a time lag to changes in forcing. Rip channels with a short cross-shore length and narrow alongshore spacing responded faster to changes in wave conditions than rips with a long cross-shore length and wider alongshore spacing. To force changes in the rip morphology, longer rip channels required wave events of higher energy and/or a longer duration. Offshore islands protect the beach under certain wave approach angles, sometimes resulting in a dual-width surf zone, which was narrow at the sheltered end and wide at the exposed end of the beach. The wider surf zone end was characterised by three dominant and persistent rip channels, whereas the narrow surf zone section contained a number of smaller rips which evolved rapidly under wave forcing. Our observations demonstrate the importance of rip channel size in controlling the response time of nearshore morphology. [Copyright &y& Elsevier]

Abstract: The dynamics of single submerged sandbars of two artificial embayed beaches (La Barceloneta and Bogatell, Barcelona, NW Mediterranean) has been studied with a video-recorded data set of 4.3years. The alongshore-averaged cross-shore migration, the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions, alongshore sediment transport and shoreline variability. In general, the submerged bars follow the general cyclic morphological behaviour observed in natural beaches, switching among the four intermediate morphodynamic states, but the studied beaches can be arrested during long periods of low wave conditions. The dominant up-state transition in Barcelona beaches during storms is the transition toward the rhythmic bar and beach state, the complete morphodynamic reset (longshore bar and trough state) only occurring during extreme wave events. The cross-shore migration of bars is dominated by the weekly and interannual components. The interannual component shows an onshore bar migration trend at both beaches, in contrast with the net offshore migration observed in multibarred open beaches. Bar disposition is located progressively seaward in the dominant alongshore transport direction (i.e., oblique with respect to the shoreline). At La Barceloneta beach, shoreline and barline orientations change consistently and a significant correlation between the accumulated alongshore sediment transport and the associated change in bar orientation has been found, suggesting that alongshore transport can play a significant role in barline orientation. Finally, bar sinuosity increases during eastern storms in both beaches. This indicates that the formation of crescentic bars occurs for approximately shore-normal waves. Some of the differences observed in bar morphology and mobility in the two studied beaches are related to their different level of protection with respect to the incident waves (beach indentation). [Copyright &y& Elsevier]

Abstract: Numerous attempts have been made over the last thirty years to estimate fluid flow rates at hydrothermal vents, either at the exit of black smoker chimneys or within diffuse flow areas. In this study, we combine two methods to accurately estimate fluid flow velocities at diffuse flow areas. While the first method uses a hot film anemometer that performs high-frequency measurements, the second allows a relatively rapid assessment of fluid flow velocity through video imagery and provides in situ data to calibrate the sensor. Measurements of flow velocities on hydrothermal diffuse flow areas were obtained on the Mid-Atlantic Ridge (MAR). They range from 1.1 to 4.9mm/s at the substratum level, in low-temperature (4.5–16.4°C) diffuse flow areas from the Tour Eiffel sulfide edifice. A strong correlation was observed between fluid flow velocities and temperature, supporting the possible use of temperature as a proxy to estimate the flow rates in diffuse flow areas where such a simple linear flow/temperature relation is shown to dominate. [Copyright &y& Elsevier]

Abstract: The response to a shoreface nourishment of the two-bar system at Noordwijk (the Netherlands) is analyzed based on a daily data set of time-exposure video images collected during about 6 years, complemented with topographic and bathymetric surveys. The 1.7 Mm3 nourishment, implemented as a 3 km alongshore bump seaward of the outer bar, migrated more than 300 m onshore in 4 years before losing its integrity. Furthermore, the nourishment interrupted the autonomous seaward migration of both bars for the entire duration of the study period and, allaying earlier fears, did not intensify the three-dimensional patterns in the bars, such as the crescentic plan-shape and rip channels. The nourishment did result in clear head effects on both flanks, with the bar becoming discontinuous and the flank section decaying or becoming attached to an offshore-located bar, while the section of bar landward of the nourishment became attached to a landward-located bar. This sequence of morphologies is known as bar switching. Each switching episode took almost one year to complete and can therefore not be ascribed to individual wave events. We suspect that shoreface nourishments enhance the possibility of bar switching by creating alongshore variability in the position and depth of the outer bar and in its cross-shore migration rate and direction. The Noordwijk nourishment did not influence the shoreline position as its trend did not undergo distinctive variations after 1998. Differences in the response of the Noordwijk sandbars to the shoreface nourishment compared with other Dutch nourishments are attributed to the location and size (volume per unit length) of the nourishment with respect to the sandbars and to the median grain size of the nourished material. [Copyright &y& Elsevier]

A considerable portion of the variability in nearshore sandbars is related to changes in the plan shape of quasi-rhythmic alongshore non-uniform features, such as rip channels and crescentic shapes. These changes may include changes in their alongshore length, cross-shore amplitude and alongshore position. Here, we use complex empirical orthogonal eigenfunction analysis to quantify these changes from a 3.4-year data set of almost daily time-exposure images of the double-barred coast at Noordwijk (Netherlands).The observed alongshore non-uniform features had alongshore lengths between 380 and approximately 3000 m and lifetimes in the order of months, considerably longer than the characteristic time scale of individual wave events. Transitions from one feature to another were mostly gradual, resulting from an alongshore differential growth in amplitude. Abrupt transitions, that is, the existing features disappeared entirely and were subsequently replaced by different features, were barely observed and did not always take place during high-energy wave events. The amplitude of the non-uniform features varied between 0 and 30 m on a weekly to monthly scale, unrelated to variations in the wave height. In addition, the features migrated back and forth along the shore with typical rates of O(10 m/day) on weekly scales with the rates increasing with an increase in the alongshore component of the wave power. On the whole our observations suggest that alongshore non-uniform sandbar variability is governed by free behaviour rather than by the direct forcing of the prevailing wave conditions. [Copyright &y& Elsevier]

Changes in nearshore sandbar morphology comprise of an alongshore uniform and non-uniform component. The former reflects the overall on/offshore migration, while the latter expresses changes in quasi-rhythmic non-uniformities, such as crescentic plan shapes. Here we focus on the alongshore-uniform component, quantified from a 3.4-year data set of daily time-exposure video images of the double barred nearshore at Noordwijk, Netherlands. The high temporal resolution and the long duration of the data set allowed us to quantify the cross-shore bar migration at weekly, seasonal and inter-annual time scales and, accordingly, to compare the contribution of all three components to the total variability in cross-shore bar position. The maximum observed offshore-directed weekly, seasonal and inter-annual bar migration rates were 10, 0.5 and 0.2 m/day. Maximum onshore rates at weekly and seasonal scales were 8 and 0.5 m/day, while onshore migration at the inter-annual scale was not observed. The inter-annual bar migration dominated the bar crest variability over time spans longer than 10–13 months, whereas changes on the weekly scale were the dominant source of variability on time spans shorter than 7–10 months. Seasonal bar migration only dominated the bar crest variability at the outer bar on time spans between 7 and 13 months. In general, Noordwijk appears to be a site with a strong inter-annual signal, with limited seasonal variability, and with fluctuations at weekly scales that are long compared to the characteristic time scale of individual events, suggesting a response to sequences of events rather than to individual events. [Copyright &y& Elsevier]

The remote sensing of the sea surface is commonly regarded as a logistically simple and cost-effective way of obtaining long-term (>years) time series of nearshore sandbar location. In this paper, we demonstrate that, similar to video imagery, time-exposure X-band (∼3 cm wave length) radar images contain alongshore, breaking-related high-intensity bands that can be used to compute the location of the underlying sandbar crests. Analysis of time-exposure X-band images and bathymetric surveys collected at Egmond aan Zee, Netherlands shows that the radar-based bar crest location, defined as the cross-shore location of maximum radar intensity, differs from the in situ surveyed crest location by a distance of O(10 m). This difference, Δx¯radar, depends linearly on the offshore water level, consistent with model predictions in which the radar intensity is assumed to behave as the energy of the surface roller. The model additionally suggests a dependence of Δx¯radar on the offshore wave height when the wave field across the bar is non-saturated. In general, such wave conditions did not result in radar images with sufficient contrast to determine the bar crest location and, accordingly, the wave-height dependence was not observed clearly in the field. Because of the dependence of Δx¯radar on the offshore water level, time series of radar-based bar crest location show artificial variability when the images are collected at different water levels. Various techniques for correcting this variability are discussed. [Copyright &y& Elsevier]

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 (r 2) = 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 ; coherence 2 = 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. [ABSTRACT FROM AUTHOR]