Scan Sonar Research Articles

An Interpretable Multi-Model Machine Learning Approach for Spatial Mapping of Deep-Sea Polymetallic Nodule Occurrences

AbstractHigh-resolution mapping of deep-sea polymetallic nodules is needed (a) to understand the reasons behind their patchy distribution, (b) to associate nodule coverage with benthic fauna occurrences, and (c) to enable an accurate resource estimation and mining path planning. This study used an autonomous underwater vehicle to map 37 km2 of a geomorphologically complex site in the Eastern Clarion–Clipperton Fracture Zone. A multibeam echosounder system (MBES) at 400 kHz and a side scan sonar at 230 kHz were used to investigate the nodule backscatter response. More than 30,000 seafloor images were analyzed to obtain the nodule coverage and train five machine learning (ML) algorithms: generalized linear models, generalized additive models, support vector machines, random forests (RFs) and neural networks (NNs). All models ML yielded similar maps of nodule coverage with differences occurring in the range of predicted values, particularly at parts with irregular topography. RFs had the best fit and NNs had the worst spatial transferability. Attention was given to the interpretability of model outputs using variable importance ranking across all models, partial dependence plots and domain knowledge. The nodule coverage is higher on relatively flat seafloor ( < 3°) with eastward-facing slopes. The most important predictor was the MBES backscatter, particularly from incident angles between 25 and 55°. Bathymetry, slope, and slope orientation were important geomorphological predictors. For the first time, at a water depth of 4500 m, orthophoto-mosaics and image-derived digital elevation models with 2-mm and 5-mm spatial resolutions supported the geomorphological analysis, interpretation of polymetallic nodules occurrences, and backscatter response.

Three-Dimensional Reconstruction and Visualization of Underwater Bridge Piers Using Sonar Imaging.

The quality of underwater bridge piers significantly impacts bridge safety and long-term usability. To address limitations in conventional inspection methods, this paper presents a sonar-based technique for the three-dimensional (3D) reconstruction and visualization of underwater bridge piers. Advanced MS1000 scanning sonar is employed to detect and image bridge piers. Automated image preprocessing, including filtering, denoising, binarization, filling, and morphological operations, introduces an enhanced wavelet denoising method to accurately extract the foundation contour coordinates of bridge piers from sonar images. Using these coordinates, along with undamaged pier dimensions and sonar distances, a model-driven approach for a 3D pier reconstruction algorithm is developed. This algorithm leverages multiple sonar data points to reconstruct damaged piers through multiplication. The Visualization Toolkit (VTK) and surface contour methodology are utilized for 3D visualization, enabling interactive manipulation for enhanced observation and analysis. Experimental results indicate a relative error of 13.56% for the hole volume and 10.65% for the spalling volume, demonstrating accurate replication of bridge pier defect volumes by the reconstructed models. Experimental validation confirms the method's accuracy and effectiveness in reconstructing underwater bridge piers in three dimensions, providing robust support for safety assessments and contributing significantly to bridge stability and long-term safety assurance.

CORAL-Catamaran for Underwater Exploration: Development of a Multipurpose Unmanned Surface Vessel for Environmental Studies.

CORAL (Catamaran fOr UndeRwAter expLoration) is a compact, unmanned catamaran-type vehicle designed and developed to assist the scientific community in exploring marine areas such as inshore regions that are not easily accessible by traditional vessels. This vehicle can operate in different modalities: completely autonomous, semi-autonomous, or remotely assisted by the operator, thus accommodating various investigative scenarios. CORAL is characterized by compact dimensions, a very low draft and a total electric propulsion system. The vehicle is equipped with a single echo-sounder, a 450 kHz Side Scan Sonar, an Inertial Navigation System assisted by a GPS receiver and a pair of high-definition cameras for recording both above and below the water surface. Here, we present results from two investigations: the first conducted in the tourist harbour in Pozzuoli Gulf and the second in the Riomaggiore-Manarola marine area within the Cinque Terre territory (Italy). Both surveys yielded promising results regarding the potentiality of CORAL to collect fine-scale submarine elements such as anthropic objects, sedimentary features, and seagrass meadow spots. These capabilities characterize the CORAL system as a highly efficient investigation tool for depicting shallow bedforms, reconstructing coastal dynamics and erosion processes and monitoring the evolution of biological habitats.

A Multi-Scale Fusion Strategy for Side Scan Sonar Image Correction to Improve Low Contrast and Noise Interference

Side scan sonar images have great application prospects in underwater surveys, target detection, and engineering activities. However, the acquired sonar images exhibit low illumination, scattered noise, distorted outlines, and unclear edge textures due to the complicated undersea environment and intrinsic device flaws. Hence, this paper proposes a multi-scale fusion strategy for side scan sonar (SSS) image correction to improve the low contrast and noise interference. Initially, an SSS image was decomposed into low and high frequency sub-bands via the non-subsampled shearlet transform (NSST). Then, modified multi-scale retinex (MMSR) was employed to enhance the contrast of the low frequency sub-band. Next, sparse dictionary learning (SDL) was utilized to eliminate high frequency noise. Finally, the process of NSST reconstruction was completed by fusing the emerging low and high frequency sub-band images to generate a new sonar image. The experimental results demonstrate that the target features, underwater terrain, and edge contours could be clearly displayed in the image corrected by the multi-scale fusion strategy when compared to eight correction techniques: BPDHE, MSRCR, NPE, ALTM, LIME, FE, WT, and TVRLRA. Effective control was achieved over the speckle noise of the sonar image. Furthermore, the AG, STD, and E values illustrated the delicacy and contrast of the corrected images processed by the proposed strategy. The PSNR value revealed that the proposed strategy outperformed the advanced TVRLRA technology in terms of filtering performance by at least 8.8%. It can provide sonar imagery that is appropriate for various circumstances.

Object Detection in Side Scan Sonar Images using Local Binary Pattern features

Object Detection in Side Scan Sonar Images using Local Binary Pattern features

Assessing the importance of sediment characterization on seabed embedment predictions of cylindrical objects

The prediction of object embedment into the seabed is important for the deployment and efficacy of submerged sensors and sensor networks, as well as for other applications such as unexploded ordnance risk assessment, subaquatic search and rescue efforts, or anchors and moorings. The embedment of objects into the seabed during placement depends on the strength parameters of the seabed sediment. However, a detailed characterization of seabed strength can be complex and costly since quality seabed samples and/or in situ testing are required. This study evaluates the importance of a detailed geotechnical seabed sediment characterization over seabed classification from geoacoustic surveying or accepting unknown seabed conditions for the prediction of seabed embedment of cylindrical objects. Monte Carlo simulation was applied to model the uncertainty of sediment strength parameters. The results suggest that prior knowledge of the general sediment type (e.g., fine-grained versus coarse-grained as determined from side scan sonar imaging) significantly improves the precision of the embedment predictions over unknown conditions, reducing the coefficient of variation (CV) in prediction of percent embedment (PE) by about 50 % to 65 %. Performing a detailed geotechnical testing of sediment strength represented a further improvement by 15 % to 35 % over the knowledge of sediment type. Both the mean and standard deviation of PE in fine-grained sediments are at least about 3 times the values for coarse-grained sediments indicating a wider distribution of PE with deeper embedment for cohesive fine-grained soils. The embedment behavior is a function of the method of deployment (free fall with a certain speed versus placement with no speed) in stiff cohesive sediments but is less relevant in soft sediments since PE values are always greater than 100 % (i.e., full embedment). Similarly, in cohesionless sediments, PE is always less than 50 %.

Sonarlogger: Enabling long-term underwater sonar observations

Coastal seas are under increasing pressure from extreme weather events and sea level rise, resulting in impacts such as changing hydrodynamic conditions, coastal erosion, and marine heat waves. To monitor changes in coastal marine habitats, such as reefs and macrophytes meadows, which add to the resilience of our coasts, consistent, medium- to long-term seafloor observations are needed. This project aims to deliver repeated, high-frequency sonar surveys on a stationary seabed mooring of a specific target area over a period of up to several months. A new stand-alone subsea system, the Sonarlogger, based on a battery pack, low-power logger and a high-resolution scanning sonar, was developed. It allows for long-term deployments with a customisable battery pack, WI-FI download and configurable sleep state. The system has been tested for over 130 days in dynamic coastal environments off the Belgian coast. Combined with auxiliary sensors, such as for measuring currents, waves and turbidity, this system enables comprehensive studies of morphologic changes and changing benthic ecosystems. Moreover, this system has the capacity to provide measurements of coastal environments during storms, where conventional systems may fall short, providing insights into event-based changes of the seafloor.

Exploration and identification of ancient Roman shipwreck located at Quseir, Red Sea

Recent marine geophysical investigations in front of the Myos Hormos Port (also known as Quseir al-Qadim) on the Red Sea coast of Egypt indicated the existence of an ancient Roman shipwreck, among other features on the seafloor. The study showed that side scan sonar imaging is a powerful technique for classifying the seafloor and detecting submerged targets among other seafloor features with resembling acoustic signatures. Integrating bathymetric data with sonar imageries displayed the seafloor topography in front of the ancient port where reef habitats were dominant. The Autonomous Underwater Vehicle was efficient in mapping closed and near-shore areas like bays. This vehicle provided high-resolution bathymetric and sonar data for the semi-closed bay area located at the entrance of the ancient port. Acoustic measurements were done for the sunken shipwreck using sonar software, and a structural model was established for the ∼ 32 m long sunken ship. The model suggested the presence of a pile of shipload gathered around the shipwreck. Results can contribute to the development of Egypt's tourism industry by promoting underwater cultural heritage preservation, as the discovery of an ancient Roman shipwreck is a significant finding that can attract tourists worldwide.

Sonar image intelligent processing in seabed pipeline detection: review and application

Subsea pipelines rely primarily on imaging sonar for detection and identification. We analyze the imaging principles of side scan sonar, multi-beam sonar, synthetic aperture sonar, seafloor penetrating sonar and forward-looking sonar. We discuss their effectiveness in detecting seabed pipelines, as well as their limitations in image recognition capabilities. As intelligent algorithms have become increasingly important in the field of image processing, we review the sonar image intelligent detection and recognition algorithms in the past six years and summarize the internal principles and application effects of classic algorithms such as Scale-Invariant Feature Transform, K-means algorithm, and constant false-alarm rate that currently show good application prospects. Simultaneously, we review the particular strengths exhibited by these algorithms, such as contour feature extraction, image segmentation and clustering, target recognition under background noise, etc. The research on intelligent processing of sonar images opens up a new way to solve the difficult problem of the seabed targets detection and recognition.

Unsupervised terrain reconstruction from side scan sonar constrained to the imaging mechanism

Unsupervised terrain reconstruction from side scan sonar constrained to the imaging mechanism

Scanning Sonar Data From an Underwater Robot With Ground Truth Localization

Scanning Sonar Data From an Underwater Robot With Ground Truth Localization

Improving Yolo5 for Real-Time Detection of Small Targets in Side Scan Sonar Images

Improving Yolo5 for Real-Time Detection of Small Targets in Side Scan Sonar Images

Assessment and Characterization of Woji Creek Riverbed in Port Harcourt, Rivers State, Nigeria, Utilizing Side Scan Sonar Technology

Woji Creek plays a crucial role in vessel navigation, supports diverse flora and fauna habitats, and sustains local livelihoods. However, human activities and natural events have led to changes in its riverbed over time. Given its significance for coastal stability and geomorphology, there is a pressing need to classify, evaluate, and ensure its environmental sustainability. The primary objective of this study is to employ side scan sonar technology to classify and assess the riverbed of Woji Creek in Port Harcourt, Nigeria. The study aims to classify the riverbed, analyze water depth variations, evaluate navigational suitability, and determine turbidity levels within the creek. To achieve these objectives, the methodology involved acquiring Side-Scan Sonar (SSS) and Sub-bottom profile data. These datasets underwent backscatter processing to create geocoded backscatter images. Feature points were extracted and matched from these images to derive riverbed classification, depth categories, water volume distribution, and river turbidity analysis. The riverbed classification revealed the presence of three primary sediment types: Clayey Silty Sand, Silty Clay, and Silty Sand, each with distinct implications for navigation. Shallow, Moderate, Deep, and Very Deep areas were identified within Woji Creek, each influencing navigational conditions. Additionally, the water volume distribution analysis provided essential insights into depth limitations and route planning.
 Moreover, the assessment of river turbidity identified low, moderate, and high turbidity zones, reflecting water clarity and suspended particle levels. These findings serve as invaluable decision support tools for navigation planning and management in Woji Creek, offering comprehensive insights into the riverbed, depth suitability, volume distribution, and water quality. Leveraging this data can enhance strategic decision-making processes and contribute to the sustainable management of this vital waterway.

Long-term morphological and sedimentological changes caused by bottom trawling on the northern Catalan continental shelf (NW Mediterranean)

Bottom trawling is a fishing method that involves towing of nets along the seafloor to catch demersal species. The dragging of trawling gears along the seafloor results in scraping and ploughing of the surficial sediments, leading to the formation of turbid plumes of resuspended sediments and causing measurable changes in the seabed morphology. High-resolution multibeam data, side scan sonar, sediment grain size and vessel tracking data have been used to investigate the impact of bottom trawling on the seafloor morphology and surficial sediments of the northern Catalan continental shelf (NW Mediterranean), providing new insights into the impact of this anthropogenic activity on the seafloor. Multibeam data evidenced the occurrence of large-scale erosive features as a consequence of repeated scouring by fishing gears in localized areas. They are characterized by elongated (70-300 m wide and up to 8 km long) channelized areas of high backscatter with variable incision (from 0.2 m to 1.2 m). The spatial distribution of these morphologies shows a similar pattern to that observed in the fishing intensity, with maximum values in the areas of increased trawling intensity, corresponding to the main fishing grounds. Side scan sonar data also shows higher densities of trawl marks in these areas than in the surroundings. Sediment cores collected on these features show an upward-coarsening trend in the first 4-5 cm of the core, suggesting that part of the finer fraction resuspended by trawling is winnowed, increasing the sand content of the surface sediment. The identification of such large erosive morphologies in the main fishing grounds evidences that repeated trawling over the same fishing ground during decades can result in deep excavation of the seafloor, leading to permanent large-scale morphological changes. Furthermore, the evolution of these erosive features over a 13-year interval points towards long recovery periods after the cessation of trawling activities.

Large gravitational collapse structure on a rocky coast (Kvarner, NE Adriatic Sea)

The studied rock collapse structure is located on the Liburnian coast (Rijeka Bay, channel zone of the NE Adriatic). The relief of the southern part of this coast, with a length of 6.5 km, is a large escarpment with very steep to vertical slopes reaching heights of 100 m above sea level, as a result of tectonic movements along the Kvarner fault zone. These events probably led to a sudden relaxation of the highly fractured rock mass. The progressive expansion occurred at locations where previously favourably oriented faults and fissures had formed a polygonal rock collapse resembling a rock-slide which is the focus of this study. Another aim of this study is to reconstruct and explain the complex morphological evolution of the studied landslide, from the pre-failure deformations, through the failure itself, to post-failure displacements, as well as possible future instabilities. Recent techniques to survey the instability, location and to analyse the evolution of the rupture surface and its dimensions were combined (Unmanned Aerial Vehicle, Side Scan Sonar and Remotely Operated Vehicles). The estimated total volume of displaced rock mass is 950,000 m3. The lower part of the instability phenomenon was submerged during the Holocene sea level rise. Since then, a large part of the displaced rock mass has been in a stable position, with sporadic rock falls. However, given unfavourable orientation and discontinuity characteristics, as well as unfavourable environmental influences, possible instabilities might also be expected in the future.

Seabed characterization of the Trindade island shelf, Brazil

This paper presents the first mapping of bedform morphological features on the Trindade Island shelf, with the goal of identifying and defining them.By using a side scan sonar, collecting seabed samples, and taking submarine photographs, five different morphological types were identified on this shelf: an erosive type: (i) characterized by the dispersion of rocks and rock blocks; and four depositional types: (ii) one formed by calcareous algal reefs, (iii) one composed by rhodoliths, (iv) one formed by medium sands with large symmetrical wave ripples, (v) and the last one formed by fine sands with asymmetrical wave ripples. The main result is a morphological map of the Trindade Island shelf, which shows the occurrence of these five seabed units.To further understand the sedimentological factors that affect the island shelf, we also examined the sediments that were collected for this study. Our results show that the amount of carbonate-formed grains on the collected sand sediments is higher than the amount of grains formed by the volcanoclastic ones, generated by the disaggregation of the main building on Trindade Island. The sediments formed by bioclastic grains are more frequently found in the coarser fractions than in the finer fractions when compared to lithic ones.

Underwater Wireless Sensor Network-Based Delaunay Triangulation (UWSN-DT) Algorithm for Sonar Map Fusion

Abstract Robust and fast image recognition and matching is an important task in the underwater domain. The primary focus of this work is on extracting subsea features with sonar sensor for further Autonomous Underwater Vehicle navigation, such as the robotic localization and landmark mapping applications. With the assistance of high-resolution underwater features in the Side Scan Sonar (SSS) images, an efficient feature detector and descriptor, Speeded Up Robust Feature, is employed to seabed sonar image fusion task. In order to solve the nonlinear intensity difference problem in SSS images, the main novelty of this work is the proposed Underwater Wireless Sensor Network-based Delaunay Triangulation (UWSN-DT) algorithm for improving the performances of sonar map fusion accuracy with low computational complexity, in which the wireless nodes are considered as underwater feature points, since nodes could provide sufficiently useful information for the underwater map fusion, such as the location. In the simulated experiments, it shows that the presented UWSN-DT approach works efficiently and robustly, especially for the subsea environments where there are few distinguishable feature points.

Side scan sonar data quantification for seabed classification in Yos Sudarso Bay, Jayapura

Side Scan Sonar (SSS) is an instrument that is usually used in surveys to perform seabed imaging. SSS was able to show two-dimensional images of the seabed with contour, topographic, and target conditions simultaneously. This technology is capable of distinguishing seabed types such as rocks, sand, or others. In addition, the usefulness of this technology can also detect the existence of marine pipes and cables, shallow structures of the seabed, dredges, environmental studies, military, archaeology, fisheries, and mining. The aims of this research were to identify and interpret the seabed, measure the acoustic backscatter (dB) and amplitude (mV) of the seabed substrate, and compute SSS data using Continuous Wavelet Transform (CWT) in the Yos Sudarso Bay, Jayapura. Processing data was performed by radiometric Beam Angle Correction (BAC), Automatic Gain Control (AGC), and geometric (bottom tracking) corrections using SonarWiz 7 software. Pre-processed SSS data were then converted to XtfToSegy and the amplitude values were exported by SeiSee software, and CWT was calculated using Matlab. Amplitude data was visualized using Microsoft Excel to display a relation between amplitude, time, and CWT graph. The results of seabed detection were three areas of sand and one coral target. The amplitude value of sand 1 ranged from 4319 to 30976 mV with the = backscatter value was -17.10 dB. The amplitude value of sand 2 ranged from 1411 to 12288 mV with the backscatter value was -18.79 dB. The amplitude value of sand 3 ranged from 1391.625 to 12032 mV with the backscatter value was -18.70 dB. The amplitude of the coral ranged from 24960 to 32640 mV with the backscatter value was -2.30 dB. The CWT analysis results show that the yellow-coloured coral’s energy represents a rougher and harder object. The energy generated from the blue-coloured sand represents the object has smooth and non-hardening characteristics.

Bathymetry mapping for pioneer ship voyages using side scan sonar in Sembulang Waters, Riau Islands

The SSS C-MAX CM2 Tow fish instrument is an acoustic instrument that operates at a frequency of 325 kHz with a maximum sounding distance of 200 m towing cable length of 50 m, producing images and textures within a large area. This study aimed to process data from the SSS C-max CM2 measurement survey to obtain MSL and LLWL tidal corrected bathymetry data, which is used to create a sailing map for pioneer ships in Sembulang Waters, Riau Islands. The SSS data acquisition was carried out on March 15 - 18, 2021, in Sembulang Waters using a 5GT vessel with a Batam State Polytechnic team. Tidal data was taken using a tidal board placed at Sembulang Pier. SSS data processing used Sonar Wiz 7 licensed software obtained from Pushidrosal with the application of several geometric and radiometric corrections. Geometric corrections included layback, bottom tracking, and slant range correction. Radiometric correction consists of Beam angle Correction (BAC), Automatic Gain Control (AGC), Time-Varying Gain (TVG), and Empirical Gain Normalization (EGN). Tidal data was processed using the Admiralty method. SSS data was exported into .csv format for making topographic maps of the seabed based on the depth and width of the ideal shipping lane based on the specifications of traditional fishing vessels used at the research site. The actual depth value of the Sembulang Waters ranges from 0.5 meters to 27.7 meters. The depth of the waters towards the east is getting deeper. The depth value of the Sembulang Waters in LLWL conditions ranges from 0 meters to 26.5086 meters, shows that several locations need to be avoided for ships sailing area and need to be dredging for the safety of ships ≥ 5GT.

Assessing the effect of onshore and offshore Wave Energy Converters on seafloor integrity combining image-based and acoustic methods

The European Atlantic Ocean offers great opportunities for the development of projects for renewable energy extraction, and the Marine Renewable Energy sector is developing different technologies for energy converters, including Wave Energy Converters. Besides, the European Commission is adopting measures and politics to increase the installed capacity of ocean energy. However, there are still uncertainties on the potential environmental effects of wave energy converters, which led regulators and stakeholders to perceive their operation as a risky activity. To overcome the non-technological barriers that could hinder the development of marine renewable energies, and improve the knowledge on the impacts on the seafloor integrity (among others), SafeWAVE project set an Environmental Research Demonstration Strategy based on the collection, processing, modelling, analysis and sharing of environmental data collected in Aguçadoura (Portugal), Armintza (Spain) and Le Croisic (France) representing different types of technology, locations and project scales. Video recordings were carried out, using Remotely Operated Vehicles, to identify the environmental impacts of the moorings on the seafloor morphology. That information was completed by side scan sonar campaigns using an Autonomous Underwater Vehicle. The video recordings were useful also to assess the attraction effect of the moorings to epibenthic invertebrates and fishes, whereas the side scan sonar provided quantitative information on the area affected by physical alteration (<1% of the total area occupied by the devices at Armintza and Le Croisic).