In this paper, the issue that the underwater unmanned vehicle (UUV) with a sonar array achieves the passive detection of vessel targets by detecting the tones radiated from the targets is considered. ...The multi-beam low-frequency analysis and recording method is widely applied in a manned sonar system. The sonar operator provides an auxiliary decision to extract the target tones from the multiple beams output. However, the complexity of the multi-dimensional information fusion makes it difficult to apply the multi-beam processing in the unmanned sonar system. Aiming at this problem, we introduce the self-adjusting characteristics of adaptive line enhancer to a time domain broadband beamformer and then propose a self-steering broadband beamformer. The proposed beamformer can adaptively steer the main beam to the direction-of-arrival (DOA) of the tonal target. There is no need to pre-form the multiple beams. The complexity of the UUV-based tone detection is reduced. Theoretical derivation and simulation experiments verify that the main beam of the proposed beamformer can track the DOA of tonal target which is rapidly changing. Meanwhile, the tonal interferences as well as the wide-band noise are well suppressed.
The Exploration Vessel (E/V) Nautilus is an efficient 68-meter ship, with berthing for 17 permanent crew members in addition to 33 berths for rotating members of the Nautilus Corps of Exploration. ...The ship is equipped with remotely operated vehicles (ROVs), acoustic mapping sonars, and various other state-of-the-art technologies. Nautilus has a data lab for processing digital data, as well as a wet lab for processing physical samples. As part of the Ocean Exploration Trust's effort to share expeditions with the world, we utilize telepresence technology to stream live video from the ROVs and various locations aboard the ship in real time to the Nautilus Live website.
The Cabo Verde Archipelago is related to a mantle plume located close to the rotational pole of the African Plate. It consists of islands and seamounts arranged in a horseshoe‐shaped pattern open to ...the west, thus forming two volcanic chains, each with a weak east‐west age progression. High‐resolution swath bathymetry of 12 Cabo Verde seamounts is used here to assign each seamount to its pre‐shield, shield or post‐shield evolutionary stage, respectively. The eastern seamounts exhibit degraded and partially eroded morphologies, and are mainly in their post‐shield stage. A new 40Ar‐39Ar date for Senghor Seamount at 14.872 ± 0.027 Ma supports old ages for the eastern seamounts. The western seamounts generally exhibit younger volcanic‐edifice‐construction morphologies, showing fresh effusive and explosive volcanics, including rarely observed deep‐water explosive volcanism in the Charles Darwin Volcanic Field. Furthermore, the two previously unknown seamounts Sodade and Tavares in the westernmost termini of both volcanic chains exhibit pristine volcanic morphologies, in agreement with present‐day volcanism and seismic activity recorded from the western seamounts. The islands and seamounts rest on three submarine platforms to the east, northwest and southwest, respectively. Taken together, the seamount and island data suggest a shift in igneous activity from the eastern to the other platforms at about 8–6 Ma. However, the complex evolution pattern for both volcanic chains includes the simultaneous occurrence of pre‐shield or shield edifices at any time, followed by erosional and rejuvenation stages. The new seamount data still demonstrate ongoing westward submarine‐growth in both volcanic chains.
Plain Language Summary
The Cabo Verde volcanic islands and seamounts are located in the central Atlantic Ocean, ∼570 km off the west coast of Africa. They form a horseshoe‐shaped archipelago with two volcanic chains, which were formed by the African plate moving very slowly over a mantle hotspot (the Cabo Verde Plume). Both the northern and southern volcanic chains show weak east‐to‐west age progressions from ∼26 million years to the present day. This study uses underwater topographic data and observations/rock sampling via remotely operated vehicles from 12 submarine volcanic seamounts, including two previously unknown seamounts, collected during four research cruises in the Cabo Verde Archipelago. Geomorphology is used to classify each seamount as being in its pre‐shield, shield or post‐shield evolutionary stage, respectively. Cabo Verde islands and seamounts rest on three submarine morphological platforms, reflecting westward jumps of the main igneous activity, and also confirming the westward migration of the Cabo Verde hotspot beneath both volcanic chains.
Key Points
We present bathymetrical maps of 12, in part previously uncharted Cabo Verde seamounts
Geomorphology reflects various evolutionary seamount stages and relative ages. Four older seamounts indicate late Quaternary sea level lowstands
Islands and seamounts rest on three morphological platforms, indicating westward jumps of the main igneous activity
The maritime industry has been continuously transforming the nature of its business and striving to embrace technology in many aspects. In this context, autonomous technologies have been receiving ...momentum with a potential to revolutionise the landscape of shipping industry. After conducting a comprehensive literature review on the issues facing by the short sea shipping (SSS) industry, a model is developed to explore the potential savings of removing crew and use of autonomous technologies through a Continuously Unmanned Ship (CUS) that is operated by a Shore Control Centre (SCC). The analysis shows that autonomous technologies are viable to the challenges that the shipping industry is facing in terms of crew costs and skill shortage. To validate this statement, a case study is selected and various scenarios were tested based on relevant operational and financial considerations, including crew arrangement, cargo utilisation levels and shore wage coefficients. The results suggest that the savings occur in demand-uncertain markets and where a network of vessels are operated via a control centre. While autonomous technology use in shipping holds promise, there remain several limitations that this research addresses in terms of implementation, commercial attractiveness, risk profile, legislative, workforce planning and port operations.
The aim of this research was to assess marine litter abundance and its effects on the benthic fauna in an area of the central Mediterranean Sea exploited by fisheries using fish aggregating devices ...(FAD). The study was carried out by means of a remotely-operated vehicle (ROV). Derelict fishing gear, mainly FAD ropes, represented the main source of marine debris, contributing 96.2% to the overall litter. About 47% of debris items (mostly FAD ropes) entangled colonies of the protected black coral Leiopathes glaberrima. The results of this research will assist in the monitoring of “impact/harm” to the coral and other benthic communities, as recommended by the Marine Strategy Framework Directive and by the Integrated Monitoring and Assessment Programme. Preventive and mitigation measures (i.e., biodegradable fishing gear, onboard technology to locate and retrieve gear, reception and/or payment for old/retrieved gear, and introduction of no-take zones) to reduce the problem are discussed.
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•Seafloor marine litter was quantified in an area heavily exploited by FADs fishery.•Debris density recorded, from 250 to 400 m depth, was 4.63 items/100 m2.•Derelict fishing gear, mainly FAD ropes, represented 96.2% of the overall litter.•Marine litter severely impacted habitats and species of conservation concern.•The black coral Leiopathes glaberrima resulted severely damaged by entanglement.
In challenging environments, feature-based visual SLAM encounters frequent failures in frame tracking, introducing unknown poses to robotic applications. This paper introduces an immediate approach ...for recovering untracked camera poses. Through the retrieval of key information from elapsed untracked frames, lost poses are efficiently restored with a short time consumption. Taking account of reconstructed poses and map points during local optimizing, a denser local map is constructed around ambiguous frames to enhance the further SLAM procedure. The proposed method is implemented in a SLAM system, and monocular experiments are conducted on datasets. The experimental results demonstrate that our method can reconstruct the untracked frames in nearly real time, effectively complementing missing segments of the trajectory. Concurrently, the accuracy and robustness for subsequent tracking are improved through the integration of recovered poses and map points.
Mobility of teleoperated unmanned ground vehicles can be significantly compromised under large communication delays, if the delays are not compensated. This article considers a recently developed ...delay compensation theory and presents its first empirical evaluation in improving mobility and drivability of a high-speed teleoperated vehicle under large delays. The said delay compensation theory is a predictor-based framework. Two realizations of this framework are considered: a model-free realization that relies only on model-free predictors, and a blended realization, where the heading predictions from the model-free predictor are blended with those from a steering-model-based feedforward predictor for a more accurate prediction of the vehicle heading. A teleoperated track-following task is designed in a human-in-the-loop simulation platform. This platform is used to compare the teleoperation performance with and without the predictor-based framework under both constant and varying delays. Through repeated measurement analysis of variance, it is concluded that the predictor-based framework is effective in achieving a higher vehicle speed, more accurate lateral control, and better drivability as indicated by the three performance metrics of track completion time, track keeping error, and steering control effort, respectively. In addition, it is shown that the blended architecture can lead to further improvements in these metrics compared to using the model-free predictors alone. The analysis also shows that there is no statistically significant difference between constant and varying delay cases in the designed experiment, nor there is any direct relation between drivers' skill level and level of improvement in metrics.
In unmanned vehicles, LiDARs and GPS/INSs are the most popular sensors to achieve perception and positioning. Precise calibration of the extrinsic parameters between the LiDAR and the GPS/INS is ...necessary for a successful implementation of sensor fusion. The extrinsic transformation between the LiDAR and GPS/INS is 6D (<inline-formula> <tex-math notation="LaTeX">x </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">y </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">z </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">yaw </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">pitch </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">roll </tex-math></inline-formula>), but the motion of a vehicle is mainly 3D (<inline-formula> <tex-math notation="LaTeX">x </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">y </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">yaw </tex-math></inline-formula>). The problem is to calculate the 6D extrinsic parameters with the limitation of 3D motion (plane constraint). The solution to this problem has been breaking the plane constraint by designing specific vehicle motions. This paper proposes a new method, a trajectory-based hand-eye calibration method, which makes full use of the large range of unmanned vehicles. The trajectories with large and small ranges are used to solve the rotation and translation, respectively. It is proved that the extrinsic parameters can be solved when the trajectory range of the unmanned vehicle is sufficiently large. The method proposed is tested with simulation, custom and KITTI datasets, and compared with the state-of-the-art methods. The results demonstrate that the accuracy and efficiency of the method proposed are comparable to the state of the art methods.
Abstract To improve the perception ability of unmanned boats on water targets and improve the autonomous collision avoidance function of unmanned boats, the problem of target motion state prediction ...is studied and a method for predicting the motion state of unmanned water targets based on lidar is proposed. Firstly, a three-dimensional point cloud space model is established and the down-sampling and clutter filtering are completed through various filters. Secondly, based on European clustering target segmentation, a target tracking algorithm combined with 3D-IOU metric is proposed to achieve target tracking. Finally, the Kalman filter is introduced for denoising, combined with the iterative closest point algorithm (Iterative Closest Point, ICP) and the centroid calculation algorithm to realize the prediction of the target speed and course. After the test on the lake, the method can meet the real-time requirements, complete the accurate prediction of the target motion state and control the error at a low level. At the same time, this method can also lay the foundation for the development of subsequent autonomous navigation tasks of unmanned vehicles.
Seafloor litter has been studied both on the continental shelves (by trawling during 24 years) and in canyons (by ROV) of the French Mediterranean sea Water (FMW). On the continental shelf, mean ...densities range from 49.63 to 289.01 items/km2. The most abundant categories were plastic, glass/ceramics, metals and textiles. Trend analysis shows a significant increase in plastic quantities during the study period. Plastics accumulate at all depths, with heavier items being found in deeper areas, while the continental slope-break appears as a clean area. The spatial distribution of litter revealed the influence of geomorphologic factors, anthropic activities, shipping route, river inputs. All the canyons are affected by debris but coastal canyons (Ligurian Sea and Corsica) were more impacted than offshore canyons in the Gulf of Lion. The FMW appears to be highly polluted with regard to values found in other areas, but lower than those observed in the Eastern Mediterranean.
•Time series of 23 years of seafloor litter data collected from bottom trawl surveys.•Use of three years of litter data collected in canyons from Remotely Operated Vehicle.•Marine litter assessment for the Gulf of Lion and eastern Corsica areas.•Spatial analyses allowing the identification of hot spots and temporal trends.•On the continental shelf, annual mean densities range from 49.63 to 289.01 items/km2.•The most common litter categories are plastics, glass/ceramic, metals and textiles.
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