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N. Gracias
Underwater Robotics Research Center (CIRS), Computer Vision and Robotics Institute (VICOROB), University of Girona, Parc Científic i Tecnològic UdG C/Pic de Peguera 13, 17003 Girona, Spain

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Journal article
Published: 05 March 2021 in Sensors
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This paper proposes a 3D object recognition method for non-coloured point clouds using point features. The method is intended for application scenarios such as Inspection, Maintenance and Repair (IMR) of industrial sub-sea structures composed of pipes and connecting objects (such as valves, elbows and R-Tee connectors). The recognition algorithm uses a database of partial views of the objects, stored as point clouds, which is available a priori. The recognition pipeline has 5 stages: (1) Plane segmentation, (2) Pipe detection, (3) Semantic Object-segmentation and detection, (4) Feature based Object Recognition and (5) Bayesian estimation. To apply the Bayesian estimation, an object tracking method based on a new Interdistance Joint Compatibility Branch and Bound (IJCBB) algorithm is proposed. The paper studies the recognition performance depending on: (1) the point feature descriptor used, (2) the use (or not) of Bayesian estimation and (3) the inclusion of semantic information about the objects connections. The methods are tested using an experimental dataset containing laser scans and Autonomous Underwater Vehicle (AUV) navigation data. The best results are obtained using the Clustered Viewpoint Feature Histogram (CVFH) descriptor, achieving recognition rates of 51.2 % , 68.6 % and 90 % , respectively, clearly showing the advantages of using the Bayesian estimation ( 18 % increase) and the inclusion of semantic information ( 21 % further increase).

ACS Style

Khadidja Himri; Pere Ridao; Nuno Gracias. Underwater Object Recognition Using Point-Features, Bayesian Estimation and Semantic Information. Sensors 2021, 21, 1807 .

AMA Style

Khadidja Himri, Pere Ridao, Nuno Gracias. Underwater Object Recognition Using Point-Features, Bayesian Estimation and Semantic Information. Sensors. 2021; 21 (5):1807.

Chicago/Turabian Style

Khadidja Himri; Pere Ridao; Nuno Gracias. 2021. "Underwater Object Recognition Using Point-Features, Bayesian Estimation and Semantic Information." Sensors 21, no. 5: 1807.

Journal article
Published: 10 December 2020 in Water
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Seagrasses are valuable coastal ecosystems that protect the seabed from waves and currents. They are threatened by predominately anthropogenic activities which are causing their decline in many regions, often converting large continuous meadows into highly fragmented ones with gaps or bare sand interspersed within the meadows. To evaluate the impact fragmentation is having on the meadows’ capacity to attenuate waves, the hydrodynamics in four meadows with different fragmentation were studied by measuring wave velocity and turbulent kinetic energy. In our study area, as gap size increases, both the turbulent kinetic energy and wave velocity increase in the center of the gaps. However, although wave attenuation varied between the different fragmentation levels, no clear trend was found for wave attenuation or the level of fragmentation. Simply put, neither wave velocity nor turbulent kinetic energy presented significant trends with the fragmentation levels of the canopy on larger scales. Therefore, within the spatial and temporal limitation of this study, fragmentation on a landscape scale did not affect the hydrodynamics within the gaps. Furthermore, as with hydrodynamics, sedimentation rates also increased with gap size, but did not show differences at the landscape level with the fragmentation levels of the meadows.

ACS Style

Teresa Serra; Nuno Gracias; Iris E. Hendriks. Fragmentation in Seagrass Canopies Can Alter Hydrodynamics and Sediment Deposition Rates. Water 2020, 12, 3473 .

AMA Style

Teresa Serra, Nuno Gracias, Iris E. Hendriks. Fragmentation in Seagrass Canopies Can Alter Hydrodynamics and Sediment Deposition Rates. Water. 2020; 12 (12):3473.

Chicago/Turabian Style

Teresa Serra; Nuno Gracias; Iris E. Hendriks. 2020. "Fragmentation in Seagrass Canopies Can Alter Hydrodynamics and Sediment Deposition Rates." Water 12, no. 12: 3473.

Journal article
Published: 14 November 2019 in ISPRS Journal of Photogrammetry and Remote Sensing
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Improvements in structure-from-motion techniques are enabling many scientific fields to benefit from the routine creation of detailed 3D models. However, for a large number of applications, only a single camera is available for the image acquisition, due to cost or space constraints in the survey platforms. Monocular structure-from-motion raises the issue of properly estimating the scale of the 3D models, in order to later use those models for metrology. The scale can be determined from the presence of visible objects of known dimensions, or from information on the magnitude of the camera motion provided by other sensors, such as GPS. This paper addresses the problem of accurately scaling 3D models created from monocular cameras in GPS-denied environments, such as in underwater applications. Motivated by the common availability of underwater laser scalers, we present two novel approaches which are suitable for different laser scaler configurations. A fully unconstrained method enables the use of arbitrary laser setups, while a partially constrained method reduces the need for calibration by only assuming parallelism on the laser beams and equidistance with the camera. The proposed methods have several advantages with respect to existing methods. By using the known geometry of the scene represented by the 3D model, along with some parameters of the laser scaler geometry, the need for laser alignment with the optical axis of the camera is eliminated. Furthermore, the extremely error-prone manual identification of image points on the 3D model, currently required in image-scaling methods, is dispensed with. The performance of the methods and their applicability was evaluated both on data generated from a realistic 3D model and on data collected during an oceanographic cruise in 2017. Three separate laser configurations have been tested, encompassing nearly all possible laser setups, to evaluate the effects of terrain roughness, noise, camera perspective angle and camera-scene distance on the final estimates of scale. In the real scenario, the computation of 6 independent model scale estimates using our fully unconstrained approach, produced values with a standard deviation of 0.3%. By comparing the values to the only other possible method currently usable for this dataset, we showed that the consistency of scales obtained for individual lasers is much higher for our approach (0.6% compared to 4%).

ACS Style

Klemen Istenič; Nuno Gracias; Aurélien Arnaubec; Javier Escartín; Rafael Garcia. Automatic scale estimation of structure from motion based 3D models using laser scalers in underwater scenarios. ISPRS Journal of Photogrammetry and Remote Sensing 2019, 159, 13 -25.

AMA Style

Klemen Istenič, Nuno Gracias, Aurélien Arnaubec, Javier Escartín, Rafael Garcia. Automatic scale estimation of structure from motion based 3D models using laser scalers in underwater scenarios. ISPRS Journal of Photogrammetry and Remote Sensing. 2019; 159 ():13-25.

Chicago/Turabian Style

Klemen Istenič; Nuno Gracias; Aurélien Arnaubec; Javier Escartín; Rafael Garcia. 2019. "Automatic scale estimation of structure from motion based 3D models using laser scalers in underwater scenarios." ISPRS Journal of Photogrammetry and Remote Sensing 159, no. : 13-25.

Journal article
Published: 14 October 2019 in Sensors
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This paper addresses the problem of object recognition from colorless 3D point clouds inunderwater environments. It presents a performance comparison of state-of-the-art global descriptors,which are readily available as open source code. The studied methods are intended to assistAutonomous Underwater Vehicles (AUVs) in performing autonomous interventions in underwaterInspection, Maintenance and Repair (IMR) applications. A set of test objects were chosen as beingrepresentative of IMR applications whose shape is typically known a priori. As such, CAD modelswere used to create virtual views of the objects under realistic conditions of added noise and varyingresolution. Extensive experiments were conducted from both virtual scans and from real data collectedwith an AUV equipped with a fast laser sensor developed in our research centre. The underwatertesting was conducted from a moving platform, which can create deformations in the perceived shapeof the objects. These effects are considerably more difficult to correct than in above-water counterparts,and therefore may affect the performance of the descriptor. Among other conclusions, the testing weconducted illustrated the importance of matching the resolution of the database scans and test scans,as this significantly impacted the performance of all descriptors except one. This paper contributes tothe state-of-the-art as being the first work on the comparison and performance evaluation of methodsfor underwater object recognition. It is also the first effort using comparison of methods for dataacquired with a free floating underwater platform.

ACS Style

Khadidja Himri; Pere Ridao; Nuno Gracias. 3D Object Recognition Based on Point Clouds in Underwater Environment with Global Descriptors: A Survey. Sensors 2019, 19, 4451 .

AMA Style

Khadidja Himri, Pere Ridao, Nuno Gracias. 3D Object Recognition Based on Point Clouds in Underwater Environment with Global Descriptors: A Survey. Sensors. 2019; 19 (20):4451.

Chicago/Turabian Style

Khadidja Himri; Pere Ridao; Nuno Gracias. 2019. "3D Object Recognition Based on Point Clouds in Underwater Environment with Global Descriptors: A Survey." Sensors 19, no. 20: 4451.

Journal article
Published: 07 September 2019 in Remote Sensing
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Rapid developments in the field of underwater photogrammetry have given scientists the ability to produce accurate 3D models which are now increasingly used in the representation and study of local areas of interest. This paper addresses the lack of systematic analysis of 3D reconstruction and navigation fusion strategies, as well as associated error evaluation of models produced at larger scales in GPS-denied environments using a monocular camera (often in deep sea scenarios). Based on our prior work on automatic scale estimation of SfM-based 3D models using laser scalers, an automatic scale accuracy framework is presented. The confidence level for each of the scale error estimates is independently assessed through the propagation of the uncertainties associated with image features and laser spot detections using a Monte Carlo simulation. The number of iterations used in the simulation was validated through the analysis of the final estimate behavior. To facilitate the detection and uncertainty estimation of even greatly attenuated laser beams, an automatic laser spot detection method was developed, with the main novelty of estimating the uncertainties based on the recovered characteristic shapes of laser spots with radially decreasing intensities. The effects of four different reconstruction strategies resulting from the combinations of Incremental/Global SfM, and the a priori and a posteriori use of navigation data were analyzed using two distinct survey scenarios captured during the SUBSAINTES 2017 cruise (doi: 10.17600/17001000). The study demonstrates that surveys with multiple overlaps of nonsequential images result in a nearly identical solution regardless of the strategy (SfM or navigation fusion), while surveys with weakly connected sequentially acquired images are prone to produce broad-scale deformation (doming effect) when navigation is not included in the optimization. Thus the scenarios with complex survey patterns substantially benefit from using multiobjective BA navigation fusion. The errors in models, produced by the most appropriate strategy, were estimated at around 1 % in the central parts and always inferior to 5 % on the extremities. The effects of combining data from multiple surveys were also evaluated. The introduction of additional vectors in the optimization of multisurvey problems successfully accounted for offset changes present in the underwater USBL-based navigation data, and thus minimize the effect of contradicting navigation priors. Our results also illustrate the importance of collecting a multitude of evaluation data at different locations and moments during the survey.

ACS Style

Klemen Istenič; Nuno Gracias; Aurélien Arnaubec; Javier Escartín; Rafael Garcia. Scale Accuracy Evaluation of Image-Based 3D Reconstruction Strategies Using Laser Photogrammetry. Remote Sensing 2019, 11, 2093 .

AMA Style

Klemen Istenič, Nuno Gracias, Aurélien Arnaubec, Javier Escartín, Rafael Garcia. Scale Accuracy Evaluation of Image-Based 3D Reconstruction Strategies Using Laser Photogrammetry. Remote Sensing. 2019; 11 (18):2093.

Chicago/Turabian Style

Klemen Istenič; Nuno Gracias; Aurélien Arnaubec; Javier Escartín; Rafael Garcia. 2019. "Scale Accuracy Evaluation of Image-Based 3D Reconstruction Strategies Using Laser Photogrammetry." Remote Sensing 11, no. 18: 2093.

Research article
Published: 03 June 2019 in Aquatic Conservation: Marine and Freshwater Ecosystems
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In the Mediterranean Sea, gorgonians are among the main habitat‐forming species of benthic communities on the continental shelf and slope, playing an important ecological role in coral gardens. In areas where bottom trawling is restricted, gorgonians represent one of the main components of trammel net bycatch. Since gorgonians are long‐lived and slow‐growing species, impacts derived from fishing activities can have far‐reaching and long‐lasting effects, jeopardizing their long‐term viability. Thus, mitigation and ecological restoration initiatives focusing on gorgonian populations on the continental shelf are necessary to enhance and speed up their natural recovery. Bycatch gorgonians from artisanal fishermen were transplanted into artificial structures, which were then deployed at 85 m depth on the outer continental shelf of the marine protected area of Cap de Creus (north‐west Mediterranean Sea, Spain). After 1 year, high survival rates of transplanted colonies (87.5%) were recorded with a hybrid remotely operated vehicle. This pilot study shows, for the first time, the survival potential of bycatch gorgonians once returned to their habitat on the continental shelf, and suggests the potential success of future scaled‐up restoration activities.

ACS Style

Maria Montseny; Cristina Linares; Núria Viladrich; Alejandro Olariaga; Marc Carreras; Narcís Palomeras; Nuno Gracias; Klemen Istenič; Rafael Garcia; Stefano Ambroso; Andreu Santín; Jordi Grinyó; Josep‐Maria Gili; Andrea Gori. First attempts towards the restoration of gorgonian populations on the Mediterranean continental shelf. Aquatic Conservation: Marine and Freshwater Ecosystems 2019, 29, 1278 -1284.

AMA Style

Maria Montseny, Cristina Linares, Núria Viladrich, Alejandro Olariaga, Marc Carreras, Narcís Palomeras, Nuno Gracias, Klemen Istenič, Rafael Garcia, Stefano Ambroso, Andreu Santín, Jordi Grinyó, Josep‐Maria Gili, Andrea Gori. First attempts towards the restoration of gorgonian populations on the Mediterranean continental shelf. Aquatic Conservation: Marine and Freshwater Ecosystems. 2019; 29 (8):1278-1284.

Chicago/Turabian Style

Maria Montseny; Cristina Linares; Núria Viladrich; Alejandro Olariaga; Marc Carreras; Narcís Palomeras; Nuno Gracias; Klemen Istenič; Rafael Garcia; Stefano Ambroso; Andreu Santín; Jordi Grinyó; Josep‐Maria Gili; Andrea Gori. 2019. "First attempts towards the restoration of gorgonian populations on the Mediterranean continental shelf." Aquatic Conservation: Marine and Freshwater Ecosystems 29, no. 8: 1278-1284.

Regular paper
Published: 26 March 2019 in International Journal of Intelligent Robotics and Applications
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Image registration is one of the most fundamental steps in optical mapping from mobile platforms. Lately, image registration is performed by detecting salient points in two images and matching their descriptors. Robust methods [such as Random Sample Consensus (RANSAC)] are employed to eliminate outliers and compute the geometric transformation between the coordinate frames of images, typically a homography when the images contain views of a flat area. However, the image registration pipeline can sometimes provide a sufficient number of wrong inliers within the error bounds even when images do not overlap at all. Such mismatches occur especially when the scene has repetitive texture and shows structural similarity. Such pairs prevent the trajectory (thus, a mosaic) from being estimated accurately. In this paper, we propose to utilize closed-loop constraints for identifying mismatches. Cycles appear when the camera revisits an area that was imaged before, which is a common practice especially for mapping purposes. The proposed method exploits the fact that images forming a cycle should have an identity mapping when all the homographies between images in the cycle are multiplied. Our proposal obtains error statistics for each matched image pair extracting several cycle bases. Then, by using a previously trained classifier, it identifies image pairs by comparing error histograms. We present experimental results with different image sequences.

ACS Style

Armagan Elibol; Nak Young Chong; Hyunjung Shim; Jinwhan Kim; Nuno Gracias; Rafael Garcia. Mismatched image identification using histogram of loop closure error for feature-based optical mapping. International Journal of Intelligent Robotics and Applications 2019, 3, 196 -206.

AMA Style

Armagan Elibol, Nak Young Chong, Hyunjung Shim, Jinwhan Kim, Nuno Gracias, Rafael Garcia. Mismatched image identification using histogram of loop closure error for feature-based optical mapping. International Journal of Intelligent Robotics and Applications. 2019; 3 (2):196-206.

Chicago/Turabian Style

Armagan Elibol; Nak Young Chong; Hyunjung Shim; Jinwhan Kim; Nuno Gracias; Rafael Garcia. 2019. "Mismatched image identification using histogram of loop closure error for feature-based optical mapping." International Journal of Intelligent Robotics and Applications 3, no. 2: 196-206.

Journal article
Published: 11 October 2018 in IFAC-PapersOnLine
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This paper presents a navigation and mapping system for an autonomous underwater vehicle (AUV) while operating near a man-made underwater environment. The objective is to recognize objects (or object parts) and use these as landmarks for simultaneous localization and mapping (SLAM). This approach is intended as the first step towards autonomous object manipulation, to be carried out at a later stage. The approach contains two main components: Object recognition from range data, and feature-based semantic SLAM. For the first component we propose an automatic method for the recognition and location of 3D objects using 3D point clouds as input, extracted from a laser scanner. Since it is common in inspection maintenance and repair (IMR) applications to have access to the 3D models of the objects of interest, the proposed method assumes a priori knowledge of the 3D models of these objects. In typical man-made environments, such objects can be distinct components of a structure, such as valves, pipes and wet-mateable connectors. The object recognition is based on recently proposed global descriptors for point clouds, that allow a compact description of the object shape, which is independent of the object view point. Once an object is recognized, its pose with respect to the AUV is determined using an ICP-based method. The second component of the approach is a feature based SLAM algorithm that uses the recognized objects as landmarks to improve the AUV navigation. The paper presents preliminary results obtained with the Girona 500 AUV, equipped with a fast laser scanner recently developed at the University of Girona. Tests conducted in a controlled environment (water tank) illustrate the suitability of the approach.

ACS Style

K. Himri; P. Ridao; N. Gracias; A. Palomer; N. Palomeras; R. Pi. Semantic SLAM for an AUV using object recognition from point clouds. IFAC-PapersOnLine 2018, 51, 360 -365.

AMA Style

K. Himri, P. Ridao, N. Gracias, A. Palomer, N. Palomeras, R. Pi. Semantic SLAM for an AUV using object recognition from point clouds. IFAC-PapersOnLine. 2018; 51 (29):360-365.

Chicago/Turabian Style

K. Himri; P. Ridao; N. Gracias; A. Palomer; N. Palomeras; R. Pi. 2018. "Semantic SLAM for an AUV using object recognition from point clouds." IFAC-PapersOnLine 51, no. 29: 360-365.

Reference work
Published: 21 May 2018 in Encyclopedia of Robotics
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ACS Style

Nuno Gracias; Pere Ridao; Rafael García; Marc Carreras. Vision for the Marine Environment. Encyclopedia of Robotics 2018, 1 -9.

AMA Style

Nuno Gracias, Pere Ridao, Rafael García, Marc Carreras. Vision for the Marine Environment. Encyclopedia of Robotics. 2018; ():1-9.

Chicago/Turabian Style

Nuno Gracias; Pere Ridao; Rafael García; Marc Carreras. 2018. "Vision for the Marine Environment." Encyclopedia of Robotics , no. : 1-9.

Report
Published: 27 March 2018 in Coral Reefs
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Annual coral bleaching events, which are predicted to occur as early as the next decade in the Florida Keys, are expected to cause catastrophic coral mortality. Despite this, there is little field data on how Caribbean coral communities respond to annual thermal stress events. At Cheeca Rocks, an inshore patch reef near Islamorada, FL, the condition of 4234 coral colonies was followed over 2 yr of subsequent bleaching in 2014 and 2015, the two hottest summers on record for the Florida Keys. In 2014, this site experienced 7.7 degree heating weeks (DHW) and as a result 38.0% of corals bleached and an additional 36.6% were pale or partially bleached. In situ temperatures in summer of 2015 were even warmer, with the site experiencing 9.5 DHW. Despite the increased thermal stress in 2015, only 12.1% of corals were bleached in 2015, which was 3.1 times less than 2014. Partial mortality dropped from 17.6% of surveyed corals to 4.3% between 2014 and 2015, and total colony mortality declined from 3.4 to 1.9% between years. Total colony mortality was low over both years of coral bleaching with 94.7% of colonies surviving from 2014 to 2016. The reduction in bleaching severity and coral mortality associated with a second stronger thermal anomaly provides evidence that the response of Caribbean coral communities to annual bleaching is not strictly temperature dose dependent and that acclimatization responses may be possible even with short recovery periods. Whether the results from Cheeca Rocks represent an aberration or a true resilience potential is the subject of ongoing research.

ACS Style

Brooke E. Gintert; Derek P. Manzello; Ian C. Enochs; Graham Kolodziej; Renée Carlton; Arthur C. R. Gleason; Nuno Gracias. Marked annual coral bleaching resilience of an inshore patch reef in the Florida Keys: A nugget of hope, aberrance, or last man standing? Coral Reefs 2018, 37, 533 -547.

AMA Style

Brooke E. Gintert, Derek P. Manzello, Ian C. Enochs, Graham Kolodziej, Renée Carlton, Arthur C. R. Gleason, Nuno Gracias. Marked annual coral bleaching resilience of an inshore patch reef in the Florida Keys: A nugget of hope, aberrance, or last man standing? Coral Reefs. 2018; 37 (2):533-547.

Chicago/Turabian Style

Brooke E. Gintert; Derek P. Manzello; Ian C. Enochs; Graham Kolodziej; Renée Carlton; Arthur C. R. Gleason; Nuno Gracias. 2018. "Marked annual coral bleaching resilience of an inshore patch reef in the Florida Keys: A nugget of hope, aberrance, or last man standing?" Coral Reefs 37, no. 2: 533-547.

Conference paper
Published: 12 November 2017 in Advances in Intelligent Systems and Computing
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This paper presents the use of omnidirectional cameras on underwater robots for the rapid high-resolution mapping of shipwrecks in marine archaeology applications. In collaboration with the University of Zadar, the methodology was recently demonstrated on the Gnalić shipwreck during the Breaking the Surface 2016 workshop held in Biograd na Moru (Croatia). The robot was programmed to survey the shipwreck and the data collected was used to build 360\(^\circ \) panoramic videos, topological panoramic maps and 3D optical reconstructions. The paper describes a recently built multicamera system comprising 5 compact, high resolution video cameras. It outlines the methodology used, reports the results obtained, and discusses the challenges that marine archaeology poses to underwater robotics, as well as the contribution that this technology may bring to the archaeology community.

ACS Style

Josep Bosch; Nuno Gracias; Pere Ridao; David Ribas; Klemen Istenič; Rafael Garcia; Irena Radic Rossi. Immersive Touring for Marine Archaeology. Application of a New Compact Omnidirectional Camera to Mapping the Gnalić shipwreck with an AUV. Advances in Intelligent Systems and Computing 2017, 183 -195.

AMA Style

Josep Bosch, Nuno Gracias, Pere Ridao, David Ribas, Klemen Istenič, Rafael Garcia, Irena Radic Rossi. Immersive Touring for Marine Archaeology. Application of a New Compact Omnidirectional Camera to Mapping the Gnalić shipwreck with an AUV. Advances in Intelligent Systems and Computing. 2017; ():183-195.

Chicago/Turabian Style

Josep Bosch; Nuno Gracias; Pere Ridao; David Ribas; Klemen Istenič; Rafael Garcia; Irena Radic Rossi. 2017. "Immersive Touring for Marine Archaeology. Application of a New Compact Omnidirectional Camera to Mapping the Gnalić shipwreck with an AUV." Advances in Intelligent Systems and Computing , no. : 183-195.

Journal article
Published: 01 August 2017 in Marine Geology
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ACS Style

Giuliana Panieri; Stefan Bünz; Daniel J. Fornari; Javier Escartin; Pavel Serov; Pär Jansson; Marta E. Torres; Joel Johnson; Wei-Li Hong; Simone Sauer; Rafael Garcia; Nuno Gracias. An integrated view of the methane system in the pockmarks at Vestnesa Ridge, 79°N. Marine Geology 2017, 390, 282 -300.

AMA Style

Giuliana Panieri, Stefan Bünz, Daniel J. Fornari, Javier Escartin, Pavel Serov, Pär Jansson, Marta E. Torres, Joel Johnson, Wei-Li Hong, Simone Sauer, Rafael Garcia, Nuno Gracias. An integrated view of the methane system in the pockmarks at Vestnesa Ridge, 79°N. Marine Geology. 2017; 390 ():282-300.

Chicago/Turabian Style

Giuliana Panieri; Stefan Bünz; Daniel J. Fornari; Javier Escartin; Pavel Serov; Pär Jansson; Marta E. Torres; Joel Johnson; Wei-Li Hong; Simone Sauer; Rafael Garcia; Nuno Gracias. 2017. "An integrated view of the methane system in the pockmarks at Vestnesa Ridge, 79°N." Marine Geology 390, no. : 282-300.

Proceedings article
Published: 01 June 2017 in OCEANS 2017 - Aberdeen
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This work presents advances towards the development of the Deep Vision system, consisting of a stereo camera setup attached to a trawl, which will make it possible to identify and measure the fish passing through without bringing them aboard the boat. This identification and measuring task requires a preprocessing in which the specimens should be segmented from the image background. Several lighting artifacts such as non-uniform illumination, shadows and reflections are some of the challenges to be addressed during the segmentation procedure. This paper describes the segmentation pipeline used to segment the fish from the background in an efficient and robust way.

ACS Style

R. Prados; R. Garcia; N. Gracias; L. Neumann; Havard Vagstol. Real-time fish detection in trawl nets. OCEANS 2017 - Aberdeen 2017, 1 -5.

AMA Style

R. Prados, R. Garcia, N. Gracias, L. Neumann, Havard Vagstol. Real-time fish detection in trawl nets. OCEANS 2017 - Aberdeen. 2017; ():1-5.

Chicago/Turabian Style

R. Prados; R. Garcia; N. Gracias; L. Neumann; Havard Vagstol. 2017. "Real-time fish detection in trawl nets." OCEANS 2017 - Aberdeen , no. : 1-5.

Proceedings article
Published: 01 June 2017 in OCEANS 2017 - Aberdeen
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Accurate and detailed 3-dimensional (3D) models of the underwater environment are becoming increasingly important in modern marine surveys, since they convey immense information that can be easily interpreted. Techniques such as bundle adjustment (BA) and structure from motion (SfM), which jointly estimate sparse 3D points of the scene and camera poses, have gained popularity in underwater mapping applications. However, for large-area surveys these methods are computationally expensive and not intended for online application. This paper proposes an SfM pipeline based on solving the BA problem in an incremental and efficient way. Furthermore, the new system can provide not only the solution of the optimization (camera trajectory along time and the 3D points of the environment), but also the estimate of the uncertainty associated with the 3D reconstruction. This system is able to produce results in mission-time, i.e. while the robot is in the water or very shortly afterwards. Such quick availability is of great importance during survey operations as it allows data quality assessment in-situ, and eventual replanning of missions in case of need.

ACS Style

Klemen Istenic; Viorela Ila; Lukas Polok; Nuno Gracias; Rafael Garcia. Mission-time 3D reconstruction with quality estimation. OCEANS 2017 - Aberdeen 2017, 1 -9.

AMA Style

Klemen Istenic, Viorela Ila, Lukas Polok, Nuno Gracias, Rafael Garcia. Mission-time 3D reconstruction with quality estimation. OCEANS 2017 - Aberdeen. 2017; ():1-9.

Chicago/Turabian Style

Klemen Istenic; Viorela Ila; Lukas Polok; Nuno Gracias; Rafael Garcia. 2017. "Mission-time 3D reconstruction with quality estimation." OCEANS 2017 - Aberdeen , no. : 1-9.

Research article
Published: 23 February 2017 in Geochemistry, Geophysics, Geosystems
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Microbathymetry data, in situ observations, and sampling along the 13°20′N and 13°20′N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high‐angle fault, scarps show extensive mass wasting that reduces their slope. Flexural rotation further lowers scarp slope, hinders mass wasting, resulting in morphologically complex chaotic terrain between the breakaway and the denuded corrugated surface. Extension and drag along the fault plane uplifts a wedge of hangingwall material (apron). The detachment surface emerges along a continuous moat that sheds rocks and covers it with unconsolidated rubble, while local slumping emplaces rubble ridges overlying corrugations. The detachment fault zone is a set of anostomosed slip planes, elongated in the along‐extension direction. Slip planes bind fault rock bodies defining the corrugations observed in microbathymetry and sonar. Fault planes with extension‐parallel stria are exposed along corrugation flanks, where the rubble cover is shed. Detachment fault rocks are primarily basalt fault breccia at 13°20′N OCC, and gabbro and peridotite at 13°30′N, demonstrating that brittle strain localization in shallow lithosphere form corrugations, regardless of lithologies in the detachment zone. Finally, faulting and volcanism dismember the 13°30′N OCC, with widespread present and past hydrothermal activity (Semenov fields), while the Irinovskoe hydrothermal field at the 13°20′N core complex suggests a magmatic source within the footwall. These results confirm the ubiquitous relationship between hydrothermal activity and oceanic detachment formation and evolution.

ACS Style

Javier Escartín; Catherine Mevel; Sven Petersen; Diane Bonnemains; Mathilde Cannat; Muriel Andreani; N. Augustin; Antoine Bezos; Valérie Chavagnac; Yujin Choi; Marguerite Godard; K. Haaga; C. Hamelin; Benoit Ildefonse; J. Jamieson; B. John; Thomas Leleu; C. J. MacLeod; M. Massot-Campos; P. Nomikou; J. A. Olive; Marine Paquet; Céline Rommevaux-Jestin; M. Rothenbeck; A. Steinfuhrer; M. Tominaga; L. Triebe; R. Campos; N. Gracias; Rafael Garcia. Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N, Mid Atlantic Ridge). Geochemistry, Geophysics, Geosystems 2017, 18, 1451 -1482.

AMA Style

Javier Escartín, Catherine Mevel, Sven Petersen, Diane Bonnemains, Mathilde Cannat, Muriel Andreani, N. Augustin, Antoine Bezos, Valérie Chavagnac, Yujin Choi, Marguerite Godard, K. Haaga, C. Hamelin, Benoit Ildefonse, J. Jamieson, B. John, Thomas Leleu, C. J. MacLeod, M. Massot-Campos, P. Nomikou, J. A. Olive, Marine Paquet, Céline Rommevaux-Jestin, M. Rothenbeck, A. Steinfuhrer, M. Tominaga, L. Triebe, R. Campos, N. Gracias, Rafael Garcia. Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N, Mid Atlantic Ridge). Geochemistry, Geophysics, Geosystems. 2017; 18 (4):1451-1482.

Chicago/Turabian Style

Javier Escartín; Catherine Mevel; Sven Petersen; Diane Bonnemains; Mathilde Cannat; Muriel Andreani; N. Augustin; Antoine Bezos; Valérie Chavagnac; Yujin Choi; Marguerite Godard; K. Haaga; C. Hamelin; Benoit Ildefonse; J. Jamieson; B. John; Thomas Leleu; C. J. MacLeod; M. Massot-Campos; P. Nomikou; J. A. Olive; Marine Paquet; Céline Rommevaux-Jestin; M. Rothenbeck; A. Steinfuhrer; M. Tominaga; L. Triebe; R. Campos; N. Gracias; Rafael Garcia. 2017. "Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N, Mid Atlantic Ridge)." Geochemistry, Geophysics, Geosystems 18, no. 4: 1451-1482.

Book chapter
Published: 10 February 2017 in Computer Vision in Vehicle Technology
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Deep sea exploration, requires the use of underwater vehicles. Initially, such vehicles were operated by a pilot while carrying one or more scientists. These limitations have led to the development of unmanned underwater vehicles (UUVs), which represent a safer alternative since no human personnel need to dive into the ocean. UUVs can be classified into remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs). Acquiring optical images with an AUV is an even more dangerous endeavor since the robot needs to get very close to the seafloor, which may lead to accidents that range from hitting the seafloor to being trapped by a fishing net. When acquiring images of the ocean floor, the main challenges are caused by the special transmission properties of the light in the underwater medium. The term dehazing addresses restoration of images compromising atmospheric haze, which is essentially an effect of light scattering. Vision-based navigation is a dead-reckoning process.

ACS Style

Rafael Garcia; Nuno Gracias; Tudor Nicosevici; Ricard Prados; Natalia Hurtos; Ricard Campos; Javier Escartin; Armagan Elibol; Ramon Hegedus; Laszlo Neumann; Atsushi Imiya; Tomas Pajdla; Jose M. Álvarez; Antonio M. López. Exploring the Seafloor with Underwater Robots. Computer Vision in Vehicle Technology 2017, 75 -99.

AMA Style

Rafael Garcia, Nuno Gracias, Tudor Nicosevici, Ricard Prados, Natalia Hurtos, Ricard Campos, Javier Escartin, Armagan Elibol, Ramon Hegedus, Laszlo Neumann, Atsushi Imiya, Tomas Pajdla, Jose M. Álvarez, Antonio M. López. Exploring the Seafloor with Underwater Robots. Computer Vision in Vehicle Technology. 2017; ():75-99.

Chicago/Turabian Style

Rafael Garcia; Nuno Gracias; Tudor Nicosevici; Ricard Prados; Natalia Hurtos; Ricard Campos; Javier Escartin; Armagan Elibol; Ramon Hegedus; Laszlo Neumann; Atsushi Imiya; Tomas Pajdla; Jose M. Álvarez; Antonio M. López. 2017. "Exploring the Seafloor with Underwater Robots." Computer Vision in Vehicle Technology , no. : 75-99.

Book chapter
Published: 10 February 2017 in Computer Vision in Vehicle Technology
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Underwater vehicles, either remotely operated or autonomous, have enabled a growing range of applications over the last two decades. This chapter addresses the creation of 2D mosaics, which is currently the most widely used method for organizing underwater imagery in mapping and inspection applications. Building a 2D mosaic is a task that involves two main steps. From a geometrical point of view, the acquired images should be aligned and warped accordingly into a single common reference frame. Even when navigation data are available, performing a topology estimation step is required to guarantee recovering accurate estimates of the vehicle path, and its value becomes even higher when dealing with large-scale surveys involving hundreds of thousands of images. The image registration problem consists of finding an appropriate planar transformation, which allows aligning in two or more 2D images taken from different viewpoints.

ACS Style

Nuno Gracias; Rafael Garcia; Ricard Campos; Natalia Hurtos; Ricard Prados; Asm Shihavuddin; Tudor Nicosevici; Armagan Elibol; Laszlo Neumann; Javier Escartin; Atsushi Imiya; Tomas Pajdla; Jose M. Álvarez; Antonio M. López. Application Challenges of Underwater Vision. Computer Vision in Vehicle Technology 2017, 133 -160.

AMA Style

Nuno Gracias, Rafael Garcia, Ricard Campos, Natalia Hurtos, Ricard Prados, Asm Shihavuddin, Tudor Nicosevici, Armagan Elibol, Laszlo Neumann, Javier Escartin, Atsushi Imiya, Tomas Pajdla, Jose M. Álvarez, Antonio M. López. Application Challenges of Underwater Vision. Computer Vision in Vehicle Technology. 2017; ():133-160.

Chicago/Turabian Style

Nuno Gracias; Rafael Garcia; Ricard Campos; Natalia Hurtos; Ricard Prados; Asm Shihavuddin; Tudor Nicosevici; Armagan Elibol; Laszlo Neumann; Javier Escartin; Atsushi Imiya; Tomas Pajdla; Jose M. Álvarez; Antonio M. López. 2017. "Application Challenges of Underwater Vision." Computer Vision in Vehicle Technology , no. : 133-160.

Journal article
Published: 01 September 2016 in Earth and Planetary Science Letters
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Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault's base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 Mw 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.

ACS Style

Javier Escartín; Frédérique Leclerc; Jean-Arthur Olive; Catherine Mevel; Mathilde Cannat; Sven Petersen; Nico Augustin; Nathalie Feuillet; Christine Deplus; Antoine Bezos; Diane Bonnemains; Valérie Chavagnac; Yujin Choi; Marguerite Godard; Kristian A. Haaga; Cédric Hamelin; Benoit Ildefonse; John W. Jamieson; Barbara E. John; Thomas Leleu; Christopher J. MacLeod; Miquel Massot-Campos; Paraskevi Nomikou; Marine Paquet; Céline Rommevaux-Jestin; Marcel Rothenbeck; Anja Steinführer; Masako Tominaga; Lars Triebe; Ricard Campos; Nuno Gracias; Rafael Garcia; Muriel Andreani; Géraud Vilaseca. First direct observation of coseismic slip and seafloor rupture along a submarine normal fault and implications for fault slip history. Earth and Planetary Science Letters 2016, 450, 96 -107.

AMA Style

Javier Escartín, Frédérique Leclerc, Jean-Arthur Olive, Catherine Mevel, Mathilde Cannat, Sven Petersen, Nico Augustin, Nathalie Feuillet, Christine Deplus, Antoine Bezos, Diane Bonnemains, Valérie Chavagnac, Yujin Choi, Marguerite Godard, Kristian A. Haaga, Cédric Hamelin, Benoit Ildefonse, John W. Jamieson, Barbara E. John, Thomas Leleu, Christopher J. MacLeod, Miquel Massot-Campos, Paraskevi Nomikou, Marine Paquet, Céline Rommevaux-Jestin, Marcel Rothenbeck, Anja Steinführer, Masako Tominaga, Lars Triebe, Ricard Campos, Nuno Gracias, Rafael Garcia, Muriel Andreani, Géraud Vilaseca. First direct observation of coseismic slip and seafloor rupture along a submarine normal fault and implications for fault slip history. Earth and Planetary Science Letters. 2016; 450 ():96-107.

Chicago/Turabian Style

Javier Escartín; Frédérique Leclerc; Jean-Arthur Olive; Catherine Mevel; Mathilde Cannat; Sven Petersen; Nico Augustin; Nathalie Feuillet; Christine Deplus; Antoine Bezos; Diane Bonnemains; Valérie Chavagnac; Yujin Choi; Marguerite Godard; Kristian A. Haaga; Cédric Hamelin; Benoit Ildefonse; John W. Jamieson; Barbara E. John; Thomas Leleu; Christopher J. MacLeod; Miquel Massot-Campos; Paraskevi Nomikou; Marine Paquet; Céline Rommevaux-Jestin; Marcel Rothenbeck; Anja Steinführer; Masako Tominaga; Lars Triebe; Ricard Campos; Nuno Gracias; Rafael Garcia; Muriel Andreani; Géraud Vilaseca. 2016. "First direct observation of coseismic slip and seafloor rupture along a submarine normal fault and implications for fault slip history." Earth and Planetary Science Letters 450, no. : 96-107.

Journal article
Published: 26 July 2016 in Sensors
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We present an approach for navigating in unknown environments while, simultaneously, gathering information for inspecting underwater structures using an autonomous underwater vehicle (AUV). To accomplish this, we first use our pipeline for mapping and planning collision-free paths online, which endows an AUV with the capability to autonomously acquire optical data in close proximity. With that information, we then propose a reconstruction pipeline to create a photo-realistic textured 3D model of the inspected area. These 3D models are also of particular interest to other fields of study in marine sciences, since they can serve as base maps for environmental monitoring, thus allowing change detection of biological communities and their environment over time. Finally, we evaluate our approach using the Sparus II, a torpedo-shaped AUV, conducting inspection missions in a challenging, real-world and natural scenario.

ACS Style

Juan David Hernández; Klemen Istenič; Nuno Ricardo Estrela Grácias; Narcís Palomeras; Rafael García Campos; Eduard Vidal; Eduard Vidal Garcia; Marc Carreras. Autonomous Underwater Navigation and Optical Mapping in Unknown Natural Environments. Sensors 2016, 16, 1174 .

AMA Style

Juan David Hernández, Klemen Istenič, Nuno Ricardo Estrela Grácias, Narcís Palomeras, Rafael García Campos, Eduard Vidal, Eduard Vidal Garcia, Marc Carreras. Autonomous Underwater Navigation and Optical Mapping in Unknown Natural Environments. Sensors. 2016; 16 (8):1174.

Chicago/Turabian Style

Juan David Hernández; Klemen Istenič; Nuno Ricardo Estrela Grácias; Narcís Palomeras; Rafael García Campos; Eduard Vidal; Eduard Vidal Garcia; Marc Carreras. 2016. "Autonomous Underwater Navigation and Optical Mapping in Unknown Natural Environments." Sensors 16, no. 8: 1174.

Journal article
Published: 28 May 2016 in Journal of Intelligent & Robotic Systems
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One of the most important features of mobile robots is their capability to gather data from areas beyond human reach. This capability has increased the demand for the use of robots undertaking exploration tasks, which has naturally led to the need for efficient methods to process the obtained data. Image mosaicing is a useful tool for obtaining a high-resolution visual representation of a large area that has been explored using optical sensors. In this paper, we present an efficient image mosaicing approach that utilizes submapping methods to obtain a map of a surveyed area with reduced computational effort. The approach uses a modified agglomerative hierarchical clustering method to form submaps according to similarity information obtained through feature descriptor matching, and takes advantage of this submapping to reduce the computation and time costs. Comparative results on real challenging underwater datasets are presented.

ACS Style

Armagan Elibol; Jinwhan Kim; Nuno Gracias; Rafael Garcia. Fast Underwater Image Mosaicing through Submapping. Journal of Intelligent & Robotic Systems 2016, 85, 167 -187.

AMA Style

Armagan Elibol, Jinwhan Kim, Nuno Gracias, Rafael Garcia. Fast Underwater Image Mosaicing through Submapping. Journal of Intelligent & Robotic Systems. 2016; 85 (1):167-187.

Chicago/Turabian Style

Armagan Elibol; Jinwhan Kim; Nuno Gracias; Rafael Garcia. 2016. "Fast Underwater Image Mosaicing through Submapping." Journal of Intelligent & Robotic Systems 85, no. 1: 167-187.