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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.

A new approach to estimate the peak period using time stack images from a video monitoring system is presented. The method is an improvement of the one developed by Stockdon and Holman (Stockdon, H.F., Holman, R.A., 2000. Estimation of wave phase speed and nearshore bathymetry from video imagery. J. Geophys. Res. Ocean. 105, 22015–22033), (S&H) including thresholding of the image to automatically identify free foam zone in the image, improved filtering procedure and windowing of the pixel intensity series in order to avoid noisy signals and spectral leakage. Results are tested against measurements in four beaches showing an absolute error below 2 s for 75% of the analyzed images despite the variable light conditions and noisy signals. Comparison with the S&H method is given showing that the new method reduces relative error on average by 28%. These results are achieved without taking into account the camera configuration requiring only the identification of a representative amount of land pixels in order to adequately eliminate noisy signals produced by environmental light fluctuations.

As extensive efforts from consumer drone manufacturers resulted in inexpensive aircrafts that can capture high quality video imagery, drones are increasingly considered to be beneficial for scientific purposes. In the recent past, video imagery has been used to analyze waves in terms of several hydrodynamic parameters and to indicate matching coastal features. Whereas these measurements have been acquired using static cameras mounted on large poles situated at beaches, this report exploits a recently developed method using Unmanned Aerial Vehicles (UAVs) as a means to map coastal morphology. After recording aerial imagery in combination with several Ground Control Points (GCPs), several time series of georectified coastal images are compiled. Subsequently, for all of the points in a predefined grid, pixel intensities are stored throughout the time of the recording. Consequently, hydrodynamic data like wave celerity and phase are estimated, which in turn are used to invert water depths for every location in a predetermined area of interest using an algorithm called cBathy. Using reference measurements with an accuracy in the order of five centimeters, this report benchmarks the bathymetry as computed using the drone imagery by calculating the root mean squared error, the root mean squared error divided by the water depth and the mean error of three different sub areas within the area of interest. After calibrating parameters as used by the cBathy algorithm, it is shown that the best computation yielded a bathymetry with a root mean squared error of 0.37 meters for a total area of approximately 2500 square meters. It is also shown that the other datasets yield errors of approximately twice the error of the best dataset. It is shown that the total error can to a large extent be attributed to errors in the rectification part of the algorithm. The large errors and the large discrepancy between the errors make the method currently unsuitable for coastal monitoring purpose

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 characterize 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 pressurized (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. Th

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. © 2015 Elsevier B.V.

Swash oscillations on two natural beaches were measured to show that the shape and magnitude of energy spectra can be largely dependent on processes occurring inside the surfzone. The observations took place on a steep, intermediate beach on the east coast (Tairua Beach), and a low-sloping, dissipative beach located on the west coast of New Zealand (Ngarunui Beach, Raglan), and aimed at improving the understanding of the effects of wave breaking, beach slope, and nonlinear wave interactions on the swash oscillations. These problems were addressed by analysing datasets obtained from field experiments undertaken at these two sites. A field experiment at Tairua Beach showed that swash oscillations were critically dependent on the stage of the tide which controlled the degree of wave energy dissipation over the sandbar crest. Under mild, near-constant offshore wave conditions, the presence of a sandbar and the tidally-controlled water depth over its crest determined whether most of the incoming waves broke before reaching the shoreline. This forced a change in the pattern of wave energy dissipation across the surfzone between low and high tide, which was reflected by changes to swash elevation (runup) on time-scales of a few hours. Significant runup height Rs, defined as 4 times the standard deviation of the waterline time series, varied by a factor of 2 between low tide, when most of the waves were breaking over the sandbar and high tide, when the waves were barely breaking. The increase in wave energy dissipation during low tide was associated with changes in swash maxima distribution, decrease in mean swash period and increasing energy at infragravity frequencies (0.004–0.05 Hz). Bispectral analysis suggested this infragravity modulation might be connected with the presence of secondary waves at the shoreline. Swash oscillations at Tairua were not homogeneous along the beach. Alongshore variability in Rs of up to 78% was observed and was mainly driven by changes in t

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 4.3 years. 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., Postprint (published version)

Coastal inundation during storms is produced by the addition of the storm surge and the wave run-up, which depends on setup and swash, to the astronomical tide level. Here, we use video monitoring techniques to estimate the inundation at the beach of Noordwijk (The Netherlands) during the seven strongest storms in the period between 1998 and 2005. Inundation values ranged from 22 to 112 m, with considerable alongshore variation before the peak of each storm. In addition, we demonstrate that mean inundation values along the beach are well estimated using a simple parameter that includes the intertidal and the supratidal beach slope, deep-water wave height and wavelength and the surge level

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 4.3 years. 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)

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 56 (2009): 2065-2074, doi:10.1016/j.dsr.2009.06.008., 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 4.9 mm/sec., at the substratum level, in low temperature (4.5 to 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 flow rates in diffuse flow areas where such a simple linear flow/temperature relation is shown to dominate., The first part of this research was sponsored by a NOAA/NURP grant award #NA96RU0221 and NSF grant OCE-9901563 to MKT and JS. JS was also supported by a FCAR (Quebec) post-doctoral fellowship. The last part of the project was supported through the ANR DEEP OASES (ANR06 BDV005).

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 4.9 mm/s at the substratum level, in low-temperature (4.5-16.4 degrees 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.

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

The rise of large digital video archives has strengthened the need for more efficient ways of indexing video files an accessing the information contained in them. Reconnaissance platforms, such as the Predator UAV, are contributing thousands of hours of video footage that require analysis, storage, and retrieval. A process is proposed for converting a video stream into a series of mosaic and selected still images that provide complete coverage of the original video. The video mosaic images can be utilized as visual indexes into a video database. in addition, mosaic images contain information from an entire sequence of video frames to provide "at a glance" analysis capabilities. Actual reconnaissance video footage is converted to still-image representation using the proposed process and the results are discussed. Further, a web-based browse and search capability was developed to demonstrate the benefits of using the proposed process. Further, the Predator Unmanned Aerial Vehicle (UAV) system configuration is described with recommendations for placement of the video mosaic building process proposed in this research.

This study considers the implications of video datalink (VDL) on the AC-130. Gunships use infrared and low-light television sensors, and synthetic aperture radar to search for and to identify target for close air support and interdiction missions. The addition of VDL offers gunship crews the ability to employ real-time information to the cockpit/offboard targeting (RTIC/OT) technology to improve situational awareness, survivability, and operational flexibility. Also, VDL offers the joint force air component commander (JFACC) inflight tasking capability, increased reconnaissance capability, operational flexibility and situation awareness. Ultimately, VDL allows command and control elements to exercise direct control of gunship operations. These capabilities are beneficial when they provide information to the crew or to the JFACC. However, VDL used to provide direct control of gunship operations may violate the Air Force doctrinal tenet of centralized control and decentralized execution. Lessons learned from recent contingencies, leadership doctrine, academic works on leadership and management theory all suggest that direct control of tactical mission can cause decreased survivability, ineffective span of control, task saturation, tactical inflexibility, mistrust between commanders and subordinates, decreased morale, and subordinates that lack initiative. The study provides recommendations to mitigate potential problems associated with the use of VDL on gunships.