3D Sonar Research Articles

Classification of 3D Sonar Point Clouds derived Underwater using Machine and Deep Learning (CANUPO and RandLA-Net) Approaches

Classification of 3D Sonar Point Clouds derived Underwater using Machine and Deep Learning (CANUPO and RandLA-Net) Approaches

A Method for the Interpretation of Sonar Data Recorded during Autonomous Underwater Vehicle Missions

Abstract Image acquisition from autonomous underwater vehicles (AUVs) is useful for mapping objects on the seabed. However, there are few studies on the interpretation of data collected with side-scan sonar during autonomous underwater vehicle missions. By recording the seabed with 3D multibeam sonar, a large number of survey points can be obtained. The collected data are processed using applications based on remote sensing image processing. The data collected during AUV missions (or other sonar carriers) needs to be pre-processed to reach the proper effectiveness level. This process includes corrections of signal amplification (Time Varying Gain, or TVG) and geometric distortions of sonar images (Slant Range Corrections). It should be mentioned that, when carrying out the interpretation process for structures on the sea floor, sonar users need to understand the process of visualising seabed projections and depressions, as well as the resolution limitations of the sonar sensors.

Research on dynamic ocean surface simulation based on 3D sonar image

The motion state of the ocean surface is changeable and has special irregularity. It is impossible to describe these characteristics in detail, which leads to the low accuracy of simulation for the sea surface. A simulation method of realistic dynamic ocean surface based on 3D sonar image algorithm is proposed. The number of adjacent points iteration of two adjacent images is calculated, and all the dynamic shallow surface sonar images are matched and combined. According to the edge coordinate information between the nearest adjacent images, the overlapping part between the two sonar image frames is analyzed. The two frames of sonar images beyond the threshold range of overlap are registered by ICP algorithm, The simulation of the dynamic ocean surface with the statistical model and FFT based wave generation method is carried out. The simulation results show that the research method of 3D sonar image algorithm is more accurate and can achieve more real simulation results.

Improving performance of three-dimensional imaging sonars through deconvolution

Three-dimensional (3D) imaging sonars are becoming increasingly important for ocean investigation and exploitation. To date, 3D imaging sonars employ a conventional beamforming technique popularly to reconstruct underwater 3D acoustical images. However, angular resolution of the conventional beamforming is limited, which is usually determined by array aperture. Sidelobe levels of the conventional beamforming are also relatively high. These two issues of the conventional beamforming: limited angular resolution and high sidelobe levels limit the performance improvement of 3D imaging sonars. High-resolution imaging algorithms with low sidelobe levels have rarely been investigated in 3D sonars. This paper applies a high-resolution imaging algorithm to improve 3D sonars. We demonstrate that the outputs of the conventional 3D beamforming in a 3D sonar can be formulated as a convolution of the beam pattern of the 2D array employed and the backscattering function of imaging objects, both in the far and near field. Based on the demonstration, the popular deconvolution algorithm in aeroacoustics is applied to deconvolve the conventional beamforming outputs in 3D sonars to improve the spatial resolution and suppress the sidelobes. Both the simulation and experiment verify that using the deconvolution algorithm help improve the angular resolution by more than two times and reduce the average sidelobe level by 20 dB.

Damage detection of underwater foundation of a Chinese ancient stone arch bridge via sonar-based techniques

The underwater bridge foundation is critical for the structural safety of bridges, especially the ancient ones. Generally, there is no accurate design details stored for most ancient bridges and the damage detection process must be Nondestructive Testing (NDT). This paper applied sonar-based techniques to the damage detection of the underwater foundation of a Chinese ancient stone arch bridge. A multi-beam sounder was used to measure the river bottom topography of the bridge bottom. The bottom sediment and submerged obstacles of the bridge with both sides were scanned to investigate the state of the wooden stake exposed and the appearance of strip stone foundation. The scour situation of the underwater foundation in combination with the results of multi-beam sounding was analyzed. The underwater foundation was scanned by the underwater 3D sonar imaging technology. The testing results show that: (1) It is inferred that the bottom of Gongchen bridge was originally filled with wooden piles. Due to river erosion and ship bottom scraping, the upper part of the wooden piles in the middle hole of the bridge are damaged to some extent; (2) Because of the influence of passing ships, the riverbed of the middle hole of the bridge was sunken, and the wooden piles of the middle hole are seriously damaged, which affects the stability of the expanded foundation of the strip stone; (3) The height difference of the riverbed between the middle hole and the two side holes is obvious, and the significant lateral pressure was generated. Thus, it is easy to cause instability of the wooden pile foundation; (4) The striated stone foundations of the east and west bridge piers of the middle hole are damaged due to the impact of passing ships, partial collapse and defect. In order to avoid instability, repair and reinforcement should be carried out as soon as possible; (5) The sonar-based techniques can detect the damage of underwater bridges structures, so as to provide an important reference for the safety analysis of the bridge structure.

Spatio‐temporal characteristics of small‐scale wave–current ripples on the Ameland ebb‐tidal delta

AbstractEbb‐tidal deltas are highly dynamic environments affected by both waves and currents that approach the coast under various angles. Among other bedforms of various scales, these hydrodynamics create small‐scale bedforms (ripples), which increase the bed roughness and will therefore affect hydrodynamics and sediment transport. In morphodynamic models, sediment transport predictions depend on the roughness height, but the accuracy of these predictors has not been tested for field conditions with strongly mixed (wave–current dominated) forcing. In this study, small‐scale bedforms were observed in the field with a 3D Profiling Sonar at five locations on the Ameland ebb‐tidal delta, the Netherlands. Hydrodynamic conditions ranged from wave dominated to current dominated, but were mixed most of the time. Small‐scale ripples were found on all studied parts of the delta, superimposed on megaripples. Even though a large range of hydrodynamic conditions was encountered, the spatio‐temporal variations in small‐scale ripple dimensions were relatively small (height 0.015 m, length 0.11 m). Also, the ripples were always highly three‐dimensional. These small dimensions are probably caused by the fact that the bed consists of relatively fine sediment. Five bedform height predictors were tested, but they all overestimated the ripple heights, partly because they were not created for small grain sizes. Furthermore, the predictors all have a strong dependence on wave‐ and current‐related velocities, whereas the ripple heights measured here were only related to the near‐bed orbital velocity. Therefore, ripple heights and lengths in wave–current‐dominated, fine‐grained coastal areas ( mm) may be best estimated by constant values rather than values dependent on the hydrodynamics. In the case of the Ameland ebb‐tidal delta, these values were found to be m and m. ©2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Overgrazing of Seagrass by Sea Urchins Diminishes Blue Carbon Stocks

Seagrasses are among the Earth’s most efficient ecosystems for sequestering carbon, but are also in global decline, risking carbon they have accumulated over geological timescales. One contributor to this global decline is seagrass overgrazing by sea urchins; however, it is unknown how this may affect stocks of “blue carbon” by damaging the seagrass root systems that stabilise the carbon-rich sediments of seagrass meadows. To fill this knowledge gap, we used aerial and sonar mapping plus soil carbon measures to investigate a seagrass urchin overgrazing event in Southeast Australia and quantified the concomitant impacts on blue carbon stocks. We found that seagrass loss significantly diminished local organic carbon stocks. The decline was also rapid: areas grazed within the preceding 6 months showed a 35% loss of blue carbon, which continued even after urchins had left the area (46% loss after 3 years). High-resolution 3D sonar reconstructions revealed that urchin overgrazing of seagrass caused erosion of the top 30 ± 20 cm of sediment within the 26,892 m2 barren: the equivalent of 8100 ± 5400 m3 of sediment. To calculate the additional CO2 emissions from this erosion, we assumed between 50 and 90% of the seagrass carbon stock (11.7 ± 1.24 t Corg ha−1 in the top 10 cm) would be remineralised, resulting in the release of between 57.8 and 104 tonnes of CO2 equivalents due to sea urchin overgrazing-induced erosion. This study adds to a growing body of evidence that seagrass loss leads to erosion and concomitant loss of blue carbon stocks.

Concept of Autonomous Underwater Vehicle Docking Using 3D Imaging Sonar

Concept of Autonomous Underwater Vehicle Docking Using 3D Imaging Sonar

Methodology for Processing of 3D Multibeam Sonar Big Data for Comparative Navigation

Autonomous navigation is an important task for unmanned vehicles operating both on the surface and underwater. A sophisticated solution for autonomous non-global navigational satellite system navigation is comparative (terrain reference) navigation. We present a method for fast processing of 3D multibeam sonar data to make depth area comparable with depth areas from bathymetric electronic navigational charts as source maps during comparative navigation. Recording the bottom of a channel, river, or lake with a 3D multibeam sonar data produces a large number of measuring points. A big dataset from 3D multibeam sonar is reduced in steps in almost real time. Usually, the whole data set from the results of a multibeam echo sounder results are processed. In this work, new methodology for processing of 3D multibeam sonar big data is proposed. This new method is based on the stepwise processing of the dataset with 3D models and isoline maps generation. For faster products generation we used the optimum dataset method which has been modified for the purposes of bathymetric data processing. The approach enables detailed examination of the bottom of bodies of water and makes it possible to capture major changes. In addition, the method can detect objects on the bottom, which should be eliminated during the construction of the 3D model. We create and combine partial 3D models based on reduced sets to inspect the bottom of water reservoirs in detail. Analyses were conducted for original and reduced datasets. For both cases, 3D models were generated in variants with and without overlays between them. Tests show, that models generated from reduced dataset are more useful, due to the fact, that there are significant elements of the measured area that become much more visible, and they can be used in comparative navigation. In fragmentary processing of the data, the aspect of present or lack of the overlay between generated models did not relevantly influence the accuracy of its height, however, the time of models generation was shorter for variants without overlay.

In Situ Observations of Ripples on the Surf Zone of a Beach

Kim, M.J.; Lee, S.H.; Baek, Y.S.; Do, J.D.; Lim, H.S., and Lee, H.J., 2019. In situ observations of ripples on the surf zone of a beach. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 36-40. Coconut Creek (Florida), ISSN 0749-0208.Ripple migration was observed on the surf zone of a beach in the eastern coast of Korea. A 3D sonar sensor and a current meter were placed together on a sand bar in water depth of 3.4 m for about 10 days in the spring of 2017. Bedloads were calculated from the records of ripple geometry and migration and were compared with estimates from a sediment transport model (SEDTRANS96). The ripples observed ranged in height (Hr) and length (Lr) from 0.5 to 8.9 cm and from 11.4 to 125.3 cm, respectively. They were highly dependent on the wave height (Hs) and thus wave-induced current speed (Uc). The largest ripples (Hr = 3.64 cm, Lr = 51.43 cm) occurred during the arrival of waves of 1 m height, the highest waves in the measurement period. At this time, the current and ripple migration speeds (Uc and Ur) were 4.08 cm/s and 17.13 cm/h, respectively. Therefore, the bedload was estimated as 5.785 kg/h/m. However, as Hs decreased to 0.5 m, the size and Ur of the ripples and Uc decreased simultaneously. At the wave height of 0.5 m, the values of Hr, Lr, Uc, and Ur were 1.97 cm, 18.82 cm, 2.72 cm/s, and 0.26 cm/h, respectively. The resulting bedload was estimated as 0.047 kg/h/m. A comparison of the measured and modeled bedloads indicated a model overestimation by a factor of 6–8. The model used the default values of 1 cm and 10 cm for ripple height and length, respectively. The rather large discrepancy may have been derived mainly from inaccuracy in estimating bed shear stress as well as ripple geometry. Therefore, this study emphasizes the importance of in situ ripple observations to place reasonable constraints on modeled bedloads.

Control laws to avoid collision with three dimensional obstacles using sensors

Collision avoidance in 3D environments is important to the problem of planning safe trajectories for an autonomous vehicle. Existing literature on collision avoidance assumed that obstacle shapes are known a priori and modeled obstacles as spheres or bounding boxes. However, in 3D environments, an obstacle shape is unknown to the autonomous vehicle, and the vehicle detects an obstacle boundary using 3D sensors, such as 3D sonar. In this paper, we introduce control laws for collision avoidance, considering scenarios where a vehicle detects arbitrarily shaped and non-convex obstacles using sensors. Moreover, our control laws are designed considering motion constraints, such as the maximum turn rate and the maximum speed rate of the vehicle. The effectiveness of our control laws is verified using MATLAB simulations.

Active listening in 3D auditory scenes

As an animal moves in its natural environment, to seek food, track targets, and steer around obstacles, its distance and direction to objects continuously change, invoking dynamic feedback between 3D scene representation, attention, and action-selection. Animals that rely on active sensing provide powerful systems to investigate neural underpinnings of sensory-guided behaviors, as they produce the very signals that inform motor actions. Echolocating bats, for example, transmit sonar signals and process auditory information carried by echoes to guide behavioral decisions for spatial orientation. Further, the bat adapts its echolocation signal design in response to 3D spatial information computed from echo returns, and therefore, the directional aim and temporal patterning of its calls provide a window into the animal’s attention to objects in its surroundings. In addition, the bat actively controls pinna position and head movements to enhance auditory cues about 3D target position. These adaptive behaviors require an interface between auditory processing and motor commands, and our research findings implicate the midbrain superior colliculus in sensory-guided spatial orienting behaviors. This talk will review behavioral and neurobiological studies of 3D sonar scene analysis in the echolocating bat, an animal whose active control over acoustic signals provides a window into its perceptual world.

Robotic system for off-shore infrastructure monitoring

ABSTRACTIn this paper, a novel modular reconfigurable mobile inspection robotic system is presented. The system consists of two underwater robotic platforms, including a tracked mobile robot for moving on rough terrain and a remotely operated vehicle robot for free underwater operation. Applications of the system include structural monitoring of off-shore infrastructure made of steel, concrete or other materials. The system is equipped with a 3D sonar, high-definition cameras and laser sensors to navigate underwater and locate structural defects. Mathematical models of the tracked robot are derived for operation underwater. Operation and verification of the ROV vision system is shown. The system sensing equipment is capable of performing simultaneous localisation and mapping tasks, thus an algorithm for navigation and localisation of defects based on sensor fusion is proposed and discussed.

3D Sonar Measurements in Wakes of Ships of Opportunity

Abstract The aim of this work is to test the potential capabilities of 3D sonar technology for studying small-scale processes in the near-surface layer of the ocean, using the centerline wake of ships of opportunity as the object of study. The first tests conducted in Tampa Bay, Florida, with the 3D sonar have demonstrated the ability of this technology to observe the shape of the centerline wake in great detail starting from centimeter scale, using air bubbles as a proxy. An advantage of the 3D sonar technology is that it allows quantitative estimates of the ship wake geometry, which presents new opportunities for validation of hydrodynamic models of the ship wake. Three-dimensional sonar is also a potentially useful tool for studies of air-bubble dynamics and turbulence in breaking surface waves.

Spherical Acoustic Lens for 3D Imaging SONAR

The states of the structures within a harbor after underwater construction or after a disaster are mainly visually checked and confirmed by divers. A new method that is independent of the water turbidity is desired to replace this direct diver necessity. In this study, we propose a spherical acoustic lens consisting of two or more concentric layers for use in a real-time three-dimensional imaging SONAR, which has many advantages. It does not require electronic circuitry for the beam forming, and it has a wide field of view and can simultaneously collect signals from various directions. The acoustical characteristics of the spherical lens are analyzed under conditions in which the speed of sound of the lens materials by using a finite difference time domain (FDTD) method. The results show that the spherical lens has a narrower receive beam profile and a higher receive gain than conventional compound lenses consisting of three aspheric lens.

1P1-A15 自律型水中ロボットへの搭載を想定した小型3次元ソーナーの開発 : テストシステムの設計と基礎実験

To develop a small-size 3D sonar for Autonomous Underwater Vehicles, a test system, which consists by a T-type acoustic transducer array and signal processing units, is constructed. The signal processing units are controlled by a laptop PC, and can generate a special waveform to transmit, and record multi channel signals for post processing simultaneously. In this paper the design of the acoustic transducer array and the results of fundamental experiments in a test tank are described.

C301 水中でのリアル・タイム三次元音響映像

The EchoScope Real Time 3D sonar generates instantaneous 3D images. Every 3D data set is the result of a single acoustic transmitter pulse, hence movement of the sonar head does not distort the data. All data points based on the same transmitter pulse are consistent. An acoustic volume is insonified by the transmitter pulse and the echoes are detected by using a 2D array of 1600 hydrophones. Phase and amplitude are used for parallel generation of 4096 receiver beams (New version: 16384) and 2D lateral images are generated in range slices.The resulting 3D data set contains intensity as well as 3D co-ordinates (x, y and z). These co-ordinates are automatically georeferenced through a GPS receiver and a heading sensor. The Echoscope is also equipped with a roll & pitch sensor.

Ideas for Underwater 3D Sonar Range Sensing and Environmental Modelling

A 3D spatial grid for exploiting the range and direction information inherent in sonar range data is presented. Special attetntion is given to the realtime performance of this representation, i.e. it should be a feasible way of representing the 3D range data acquired by an operating AUV.