A new online tool for visualization of volumetric data

This work was sponsored by the Engineering and Physical Sciences Research Council (EPSRC) UK, the Medical Research Council (MRC) UK and the Wellcome Trust

Real-time Image Generation for Compressive Light Field Displays

With the invention of integral imaging and parallax barriers in the beginning of the 20th century, glasses-free 3D displays have become feasible. Only today—more than a century later—glasses-free 3D displays are finally emerging in the consumer market. The technologies being employed in current-generation devices, however, are fundamentally the same as what was invented 100 years ago. With rapid advances in optical fabrication, digital processing power, and computational perception, a new generation of display technology is emerging: compressive displays exploring the co-design of optical elements and computational processing while taking particular characteristics of the human visual system into account. In this paper, we discuss real-time implementation strategies for emerging compressive light field displays. We consider displays composed of multiple stacked layers of light-attenuating or polarization-rotating layers, such as LCDs. The involved image generation requires iterative tomographic image synthesis. We demonstrate that, for the case of light field display, computed tomographic light field synthesis maps well to operations included in the standard graphics pipeline, facilitating efficient GPU-based implementations with real-time framerates.United States. Defense Advanced Research Projects Agency. Soldier Centric Imaging via Computational CamerasNational Science Foundation (U.S.) (Grant IIS-1116452)United States. Defense Advanced Research Projects Agency. Maximally scalable Optical Sensor Array Imaging with Computation ProgramAlfred P. Sloan Foundation (Research Fellowship)United States. Defense Advanced Research Projects Agency (Young Faculty Award

Understanding coastal morphodynamic patterns from depth-averaged sediment concentration

This review highlights the important role of the depth-averaged sediment concentration (DASC) to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern: beach cusps, surf zone transverse and crescentic bars, and shoreface-connected sand ridges. We present a formulation and methodology, based on the knowledge of the DASC (which equals the sediment load divided by the water depth), that has been successfully used to understand the characteristics of these features. These sand bodies, relevant for coastal engineering and other disciplines, are located in different parts of the coastal zone and are characterized by different spatial and temporal scales, but the same technique can be used to understand them. Since the sand bodies occur in the presence of depth-averaged currents, the sediment transport approximately equals a sediment load times the current. Moreover, it is assumed that waves essentially mobilize the sediment, and the current increases this mobilization and advects the sediment. In such conditions, knowing the spatial distribution of the DASC and the depth-averaged currents induced by the forcing (waves, wind, and pressure gradients) over the patterns allows inferring the convergence/divergence of sediment transport. Deposition (erosion) occurs where the current flows from areas of high to low (low to high) values of DASC. The formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features, but the physical mechanisms for their migration, their finite-amplitude behavior and their decay can also be explored

Field experiments of beach scarp erosion during oblique wave, stormy conditions (Normandy, France)

International audienceA field-based experimental study of beach scarp morphodynamic evolution was conducted on the shoreface of a macrotidal sandy beach subject to storms combined with spring tide events (Luc-sur-Mer, France). Both video and in-situ measurements on an artificial berm are used to understand beach scarp evolution over one tide during stormy conditions. Image time stacks are used to analyze the swash action on the beach scarp and topo-graphical data of the scarp are recorded with a terrestrial scanner laser to quantify the morphodynamic response of the beach scarp to wave action. This work provides a new and unique dataset about beach scarp changes and berm morphology in particular under rising tide and oblique wind-wave conditions. During one stormy event, the berm was completely destroyed. However, contrasting alongshore changes were measured during the erosive phase with different crest and foot scarp retreats and eroded volumes between the west and the east side of the berm. The beach in front of the scarp also shows a contrasting residual evolution, indicating an evident longshore sediment transport on the study area as a consequence of incident oblique wave conditions. A strong connection between beach evolution and beach scarp changes is clearly identified. The scarp erosion increases on the west side of the berm when the beach level is lowered and reduces when the beach surface rises on the east side. The beach slope and foreshore elevation as a result of a longshore sediment transport between east and west profiles, influence swash activity. Overall, water depth and swash activity became progressively different along the scarp during the experiment. Swash measurements indicate that the presence of the beach scarp strongly influences the swash motion. At high tide, the reflection of the uprush on the scarp front induces a collision between the reflected backwash and the following uprush dynamic. These collisions reduce and sometimes stop the motion of the following uprush, reducing the incoming swash excursion. Consequently, the scarp presence modifies the swash interaction that normally appears on a planar beach surface. With a beach scarp, the swash energy level is substantially attenuated and its spectrum is characterized by a large band. The number of uprush impacts on the scarp front calculated from video images reaches about 25 per 5 min. In spite of the swash energy attenuation due to swash/swash interactions, these impacts provoke the berm destruction in about two hours. However, the onshore migration of the swash zone induced by the rising tide appears to be important to explain scarp destruction, compensating the attenuated swash activity due to backwash-uprush interactions

Séquences d'évolution morphodynamique des barres intertidales d'une plage macrotidale : l'exemple d'Omaha beach (Normandie, France)

The present paper deals with the morphodynamics of intertidal bars on Omaha beach, a macrotidal beach located along the Normandy coastline. During two years (defined here as medium-term time-scale), a monthly topographic monitoring has been conducted on this beach. An analysis of the morphological evolution of the ridge and runnel systems is performed and correlated to the forcing conditions (waves and tide) recorded on the lower foreshore. Our results allow to distinguish some morphodynamical evolution sequences with one stage of accretion and one stage of destruction of the bars. In order to discriminate these two stages, an energetic criterion is used. Accretion stages correspond to long periods of fair weather conditions (significant wave height, H-s 1 m). The destructive processes are modulated by tide level and pre-existing morphology. Our results show also a medium-term morphodynamic variability along the beach profile. Indeed, the upper beach bars are much more mobile than the lower beach ones. The drainage channel dynamic is also highlighted as a destabilizing factor which weakens the bar resistance to storm activity. Moreover, the construction and the evolution of intertidal bars correspond to short-term reorganisations of an intertidal sand volume which seems to be quite stable over a medium-term period.Cet article traite de la morphodynamique des barres intertidales présentes sur la plage macrotidale Omaha beach située sur la côte du Calvados en Normandie. Durant deux années, ces systèmes, localement dénommés plages à barres et bâches, ont fait l'objet d'un suivi topographique à un pas de temps mensuel défini comme moyen-terme. L'analyse combinée de l'évolution morphologique et des enregistrements des conditions de forçage, vagues et marée sur la basse plage, montre l'existence de séquences d'évolution morphodynamique comprenant chacune une phase d'accrétion et une phase de destruction des barres sableuses. Afin de les distinguer, un critère énergétique, basé sur l'intensité de l'agitation, est utilisé. Les phases d'accrétion correspondent à de longues périodes de faible agitation (hauteur significative de la houle, Hs 1 m) lors de tempêtes, dont l'action érosive est modulée par le niveau tidal et la morphologie antécédente. À moyen terme, l'ensemble des résultats montre des disparités de comportement morphodynamique de l'estran, les barres étant plus mobiles sur la partie supérieure du profil que sur la partie inférieure. Une dynamique de chenaux de drainage est mise en évidence. C'est un facteur de déstabilisation des barres qui fragilise leur résistance à l'action des tempêtes. De plus, la présence des barres et leur évolution morphologique est la traduction topographique de réorganisations d'un stock sableux intertidal stable à moyen terme

Stage and rate of formation of a complex spit in a megatidal environment Zustand und Formungsrate eines komplexen Nehrungshakensystems in einem Makrogezeiten-Ästuar Etapes et rythmes de formation d'une flèche sédimentaire à crochets multiples en environnement mégatidal

International audienceThe Pointe d'Agon is a complex spit located on the west coast of the Cotentin (Normandy, France), evolving across the megatidal Regnéville inlet. This spit has on its distal part several well defined hooks. Using aerial photographs covering half a century makes it possible to monitor the formation of a new hook in a two stage process. The influence on the shoreline of the swash bar located on the ebb delta can be highlighted. Longshore transport is disturbed by the bar and its onshore migration. Updrift of the bar, this disturbance leads to the advance of the shoreline. On the downdrift side, an erosion zone results from the decrease of sediment supplied by longshore transport as the bar and the tombolo that formed prior to its attachment to the beach act as natural breakwater. The northward migration of the outlet channel leads to the formation of a sand platform which in turn changes the orientation of the shoreline axis from SE to SSE, initialising the formation of a new spit. The welding of the bar and the resumption of the north-south longshore transport regulate the shoreline and spit axis towards SE. The lengthening and shape of the Agon spit seems to be controlled by the migration of swash bars on the ebb delta of Regnéville inlet. These bars influence the sediment flux and shoreline mobility over a timescale of several years. Bar migration takes approximately 12 years but formation of hook spit has taken 26 years during the recent period. In addition, this study underlines the specific characteristics of the morphology of a megatidal sandy coast and its influence on swash bar migration. An increase of the migration rate is observed near the upper beach in accordance with the reflective profile of this part of beach which is typical for these megatidal environments

Morphodynamic of beach scarps on a macrotidal coast during high water level events (Normandy, France)

Although there are numerous studies on the morphology and physical processes affecting the dune's scarp and many conceptual models describing beach scarps on microtidal and mesotidal environments (Sunamura, 1985a ; Short, 1999), really quantitative informations about the beach scarp formation is lacking, especially along tidal environments where the tide controls the level of wave attack. However, Sherman and Nordstrom (1985) give a qualitative description of beach scarp formations and evolution based on field observations but without data set