Multibeam Sonar Research Articles

Organizing and visualizing point clouds with continuous levels of detail

Point clouds contain high detail and high accuracy geometry representation of the scanned Earth surface parts. To manage the huge amount of data, the point clouds are traditionally organized on location and map-scale; e.g. in an octree structure, where top-levels of the tree contain few points suitable for small scale overviews and lower levels of the tree contain more points suitable for large scale detailed views. The drawback of this solution is that it is based on discrete levels, causing visual artifacts in the form of data density shocks when creating the commonly used perspective views. This paper presents a method based on an optimized distribution of points over continuous levels, avoiding the visualization shocks. The traditional distribution ratio’s of data amounts over discrete levels of raster or vector data is considered the reference. How to convert this to point clouds with continuous levels (still benefiting from the proven advantages of the data distribution in discrete levels for efficient access at a wide range of scales)? In our solution, for each point a cLoD (continuous Level of Detail) value is computed and added as dimension to the point. A SFC (Space Filling Curve)-based nD data clustering technique can be used to organize the points, so that they can be efficiently queried. It should be noted that also other multi-dimensional indexing and clustering techniques could be applied to realize continuous levels based on the cLoD value. Besides the mathematical foundation of the approach also several implementations are described, varying from a 3D web-browser based solution to an augmented reality point cloud app in a mobile phone. The cLoD enables interactive real-time visualization using perspective views without data density shocks, while supporting continuous zoom-in/out and progressive data streaming between server and client. The described cLoD based approach is generic and supports different types of point clouds: from airborne, terrestrial, mobile and indoor laser scanning, but also from dense matching optical imagery or multi-beam echo soundings.

Assessment of the Effects of Sensors Misalignment of a Multi-Beam Hydrographic Survey

A hydrographic survey vessel shows three -dimensional movements (Roll, Pitch and Heave) misalignment with respect to the vessel reference unit (VRU) due to environmental effects, such as wind, current, other vessel wakes, etc. These motions if ignored, cause errors in measured depth and in the positioning of the sounding. Hence the need of a motion sensor and gyroscope. However, the alignment of the multi-beam sonar head to the motion sensor and gyro (Octant) is critical to the accuracy of the determined depths. It is not possible to install the sonar head in perfect alignment with the motion sensor and gyroscope to the accuracy required. The synchronization of the GPS time with the Motion sensor and gyro, the latency of the position, as reported by the GPS as well as the velocity of sound in water are important parameters to account for the misalignment of the motion senor and the multi beam sonar head; this is called the Patch Test. In view of this, a patch test was done to ascertain the mounting angles of EMB 2058 Multi-beam sonar with Octan V installed onboard a survey vessel (Bitam). The result of the Patch test gives a row, pitch and heading value of -1.242˚, -4.92˚, and -0.48˚respectively. The speed of sound in water as measured ranges from; 1531.47m/s to 1531.60m/s within a minimum cast depth of 0.49m and maximum cast depth of 16.00m. The statistical analysis gives and average error of 2.642cm/m2 which was within acceptable standard as define by the International Hydrographic Organization (IHO).

Characterizing bedforms in shallow seas as an integrative predictor of seafloor stability and the occurrence of macrozoobenthic species

AbstractIn soft‐bottom marine ecosystems, bedform variation is induced by wind‐ and tidal‐driven hydrodynamics. The resulting megaripples, sand waves and sandbanks form a spatially and temporally heterogeneous seafloor landscape. The strong physical forces imposed by the migration of these bedforms are important determinants for the occurrence of different macrozoobenthic species. Quantifying the effect of these forces can help in differentiating natural‐ and anthropogenically induced physical stressors. However, large‐scale mapping of seabed morphology at high resolution using multibeam echosounder is challenging, costly and time‐consuming, especially in shallow seas, prohibiting wide swaths. Instead, their bathymetry is typically studied using single‐beam transects that are interpolated to bathymetric grids with a relatively coarse resolution (20 m). However, this leaves out information on smaller scale (<20 m) bedforms that can be ecologically relevant. In the Dutch Wadden sea, a shallow tidal system, we characterized bedform variation at high resolution using single‐beam data for the first time. We calculated a 2‐D Terrain Ruggedness Index (TRI) at sub‐meter resolution along the single‐beam transects and interpolated the results to a full 3‐D grid. We then validated the result by relating TRI to independently modeled hydrodynamic parameters and to the distribution of macrozoobenthic species. We found that TRI successfully integrates the variation of tidal‐driven bed shear stress and wave‐driven orbital velocity. In addition, we found TRI to be a good predictor of the occurrence of macrozoobenthic species. The inferred small‐scale bedforms provide valuable information for separating the relative importance of natural dynamics versus anthropogenic disturbances such as dredging and bottom trawling activities. We discuss that by repurposing already available single‐beam data in this way, bedforms can be characterized at high resolution without the need for additional equipment or mapping campaigns, yielding novel input to decision‐making on marine management and conservation.

Application of Remote Sensing Techniques to Identification of Underwater Airplane Wreck in Shallow Water Environment: Case Study of the Baltic Sea, Poland

Multibeam echo sounders (MBES), side-scan sonars (SSS), and remotely operated vehicles (ROVs) are irreplaceable devices in contemporary hydrographic works. However, a highly reliable method of identifying detected wrecks is visual inspection through diving surveys. During underwater research, it is sometimes hard to obtain images in turbid water. Moreover, on-site diving operations are time-consuming and expensive. This article presents the results of the remote sensing surveys that were carried out at the site of a newly discovered wreck, in the southern part of the Baltic Sea (Poland). Remote sensing techniques can quickly provide a detailed overview of the wreckage area and thus considerably reduce the time required for ground truthing. The goal of this paper is to demonstrate the process of identification of a wreck based on acoustic data, without involving a team of divers. The findings, in conjunction with the collected archival documentation, allowed for the identification of the wreck of a Junkers Ju-88, a bomber from World War II.

Intuitively visualizing spatial data from biogeographic assessments: A 3-dimensional case study on remotely sensing historic shipwrecks and associated marine life

Biogeographic assessments aim to determine spatial and temporal distributions of organisms and habitats to help inform resource management decisions. In marine systems, rapid technological advances in sensors employed for biogeographic assessments allow scientists to collect unprecedented volumes of data, yet it remains challenging to visually and intuitively convey these sometimes massive spatial or temporal data as actionable information in geographically relevant maps or virtual models. Here, we provide a case study demonstrating an approach to bridge this data visualization gap by displaying coastal ocean data in a 3D, interactive online format. Our case study documents a workflow that provides resource managers, stakeholders, and the general public with a platform for direct exploration of and interaction with 3D data from hydrographically mapping shipwrecks and marine life on the continental shelf of North Carolina, USA. We simultaneously mapped shipwrecks and their associated fish using echosounders. A multibeam echosounder collected high-resolution multibeam bathymetry of the shipwrecks and detected the broad extent of fish schools. A calibrated splitbeam echosounder detected individual fish and fish schools. After processing the echosounder data, we built an interactive, online 3D data visualization web application complemented by multimedia and story text using ESRI geographic information systems. The freely available visual environment, called “Living Shipwrecks 3D,” allows direct engagement with the biogeographic assessment data in a customizable format. We anticipate that additional interactive 3D data applications can be constructed using a similar workflow allowing seamless exploration of complex spatial data used in biogeographic assessments.

Pre-rig mobilization hazard evaluation in offshore oil and gas prospect drilling: A case study of TM field, offshore Niger Delta

TM Field, located offshore Niger Delta in the Gulf of Guinea (Nigeria), has been evaluated for potential drilling hazards prior to the drilling of a proposed oil well. This is in a region where potential hazards that could inhibit successful drilling exercise have not been adequately studied. The study adopted the modern technique of offshore geohazard evaluation that relies mainly on suites of geophysical and shallow geological investigations which include ocean bathymetry using multi-beam echo sounder, side-scan sonar, sub-bottom profiler, magnetic, and 2D-high resolution seismic reflection surveys. The results were integrated to draw inferences about the risk potential of the field. From the bathymetric survey, water depths were found to range from 345 m to 650 m LAT, with seabed relief being 305 m. Water depth at the proposed well location was found to be approximately 450 m and the seabed was found to slope in the northwestern direction. Seafloor gradient was computed as 0.05 across the whole area. Two shallow sub-surface stratigraphic units, labelled A and B, were delineated. Unit A was directly beneath the seafloor and seemed to be composed mainly of clayey/silty sand. Its thickness ranged from 6 m to 70 m across the study area. Unit B appeared to be a layer of sand and its total thickness was not fully delineated. Observable kinks and displacements at the flanks of seabed undulations/depressions on sub-bottom profiler sections suggested that the depressions may be fault-controlled. On the map generated from the marine magnetic data, a magnetic fault was delineated and this appeared to be coincident with the shallower of the two buried faults on the cross-line seismic section cutting through the proposed well-head location. Interpreted seismic reflection data presented this fault as being inactive. Most of the faults mapped, especially the buried ones, appeared to be inactive except a few. Regions with mapped amplitude anomalies are to be avoided during rig-mobilization operations. Though engineering conditions are expected to vary vertically since layers occur as intercalation, significant lateral variation is not expected within uniform layers of bed. Risk of punch-through associated with clayey formation is expected to be low because the geologic layers are not uniformly and entirely clay. The proposed well-head location was found to be free of potential hazard sources.

Multibeam-echosounder Accuracy Verification Experimental Method and Initial Results

In the past, the multibeam-echosounder (MBES), which performs seafloor depth measuring, detection, and hydrographic surveying, has been used only for observation targets that far exceed the error level. However, AUV and sea surface platform surveys, which have high positioning accuracy, is beginning to be used to the increasing needs for high-accuracy monitoring, e.g., hydrographic surveys, harbor surveys, seafloor detection such as shipwrecks, and exploration of resources, volcanoes, and faults. The significance of properly recognizing and evaluating errors of the MBES is increasing. In this study, we describe a method of acquiring the MBES observation data in the tank space precisely measured by the total stations to verify the accuracy. According to the method proposed in this study, it is feasible to evaluate the accuracy of a device itself on the order of cm. We also report the results of the actual experiment as follows; the ranging accuracy directly under the MBES was about 1–1.5 cm regardless of the distance and depends on the pulse length (T=30µs): the accuracy was worse than expected when the beam angle changed: the seafloor detection accuracy, which depends on the angular resolution, was about twice the footprint. The above experimental findings are not completely consistent with theoretical predictions and require further research, which contributes to the prediction of accuracy and detection performance.

A comparison of different acoustic methods for sedimentary classification of King George Bay, Antarctica

Multibeam sonar and high-resolution seismic mapping are marine geophysical techniques frequently employed to map the distribution and type of marine sediments. Both techniques involve the transmission and reception of acoustic pulses reflected by the seafloor and typically generate consistent and satisfactory results at a relatively low-cost relative to direct sampling. However, mainly due to their operational peculiarities (frequency range, beam width, etc.), each method generates some discrepancies regarding sedimentary distribution for the same area. Here, we compare three well-established marine geophysical techniques (Multibeam Echosounder (MBES) bathymetry and backscatter intensity, Sub-Bottom Profiler (SBP) echo-characterization, defined as the acoustic response of marine sediments as a function of its sedimentological properties, and seismic amplitude) applied to characterize seabed geology, analyzing comparing the results observed from each method. The study area is the glaciomarine environment of King George Bay, South Shetland Islands, Antarctica. We demonstrate that each method responds to specific characteristics of the seafloor, mainly because of divergent interactions between the acoustic signal and morphological features at different scales and sedimentological interfaces. Despite some consistencies, considerable mismatches in terms of classification approaches are apparent. Nevertheless, we show how these different classification approaches can be interpreted together to enable more precise geological understandings.

The Relationship Between Submarine Melt and Subglacial Discharge From Observations at a Tidewater Glacier

AbstractAt tidewater glacier termini, ocean‐glacier interactions hinge on two sources of freshwater—submarine melt and subglacial discharge—yet these freshwater fluxes are often unconstrained in their magnitude, seasonality, and relationship. With measurements of ocean velocity, temperature and salinity, fjord budgets can be evaluated to partition the freshwater flux into submarine melt and subglacial discharge. We apply these methods to calculate the freshwater fluxes at LeConte Glacier, Alaska, across a wide range of oceanic and atmospheric conditions during six surveys in 2016–2018. We compare these ocean‐derived fluxes with an estimate of subglacial discharge from a surface mass balance model and with estimates of submarine melt from multibeam sonar and autonomous kayaks, finding relatively good agreement between these independent estimates. Across spring, summer, and fall, the relationship between subglacial discharge and submarine melt follows a scaling law predicted by standard theory (melt ∼ discharge1/3), although the total magnitude of melt is an order of magnitude larger than theoretical estimates. Subglacial discharge is the dominant driver of variability in melt, while the dependence of melt on fjord properties is not discernible. A comparison of oceanic budgets with glacier records indicates that submarine melt removes 33%–49% of the ice flux into the terminus across spring, summer, and fall periods. Thus, melt is a significant component of the glacier's mass balance, and we find that melt correlates with seasonal retreat; however, melt does not appear to directly amplify calving.

Acoustic seabed characterization with autonomous underwater vehicles

Autonomous underwater vehicles (AUVs) have been proven to be useful platforms to for acoustic seabed surveys with a variety of sonar systems. In this talk, results from two recent field experiments will be presented. One of the experiments was conducted in the New England shelf and upper slope areas using an AUV equipped with a towed hydrophone array and a 3.5 kHz sound source. The objective was to study the fine grained sediment (mud) layer on the shelf and the mutli-layer sub-bottom stratigraphy on the upper slope. The highlight of this first experiment is on the internal reflections from the mud layer at lower grazing angles, as well as the sub-bottom layering structure near a submarine landslide site. The other experiment took place at the Atlantis II Seamounts, and a deep water AUV was utilized with payloads including a multibeam echosounder, a sidescan sonar, a sub-bottom profiler, and a still image camera. The objective was to investigate the seafloor condition on the seamount summit plateau, of which the area is about 15 km × 5 km. Survey results showing sediment distributions and benthic marine life habitats will be presented. [Work supported by the Office of Naval Research.]

How prevalent is acoustic scattering from oceanic microstructure?

Any oceanic environment with spatial gradients in sound speed and density can result in acoustic scattering hot spots. These acoustic hotspots can be rapidly evolving and vary in their spatial heterogeneity. Here, we review acoustic scattering models for turbulence and present data collected with a variety of split-beam and multi-beam echosounders illustrating the range of environments and spatial scales associated with scattering from physical microstructure, including shear instabilities in estuarine environments, non-linear internal waves on the continental shelf, strong interface scattering due to double-diffusion, scattering from strong gradients or interfaces, and turbulent microstructure at the New England shelf break front. The theoretical acoustic scattering formulations for different types of physical microstructure are applied to these different environments, and recommendations are made for optimal frequency bands to sample the different types of physical microstructure and the optimal measurements for inference of parameters that describe the physical microstructure. Limitations imposed on detection and quantification of scattering from the physical microstructure due to sources including suspended sediment, bubbles, and biological targets, are also discussed. [Work supported by the ONR.]

Sonar Observation of Heat Flux of Diffuse Hydrothermal Flows

AbstractPrevious work using multibeam sonar to map diffuse hydrothermal flows is extended to estimate the heat output of diffuse flows. In the first step toward inversion, temperature statistics are obtained from sonar data and compared to thermistor data in order to set the value of an empirical constant. Finally, a simple model is used to obtain heat‐flux density from sonar‐derived temperature statistics. The method is applied to data from the Cabled Observatory Vent Imaging Sonar (COVIS) deployed on the Ocean Observatories Initiative's Regional Cabled Array at the ASHES vent field on Axial Seamount. Inversion results are presented as maps of heat‐flux density in MW/m2 and as time series of heat‐flux density averaged over COVIS' field of view.

A Characterisation of Benthic Currents from Seabed Bathymetry: An Object-Based Image Analysis of Cold-Water Coral Mounds

Seabed sedimentary bedforms (SSBs) are strong indicators of current flow (direction and velocity) and can be mapped in high resolution using multibeam echosounders. Many approaches have been designed to automate the classification of such SSBs imaged in multibeam echosounder data. However, these classification systems only apply a geomorphological contextualisation to the data without making direct assertions on the velocities of benthic currents that form these SSBs. Here, we apply an object-based image analysis (OBIA) workflow to derive a geomorphological classification of SSBs in the Moira Mounds area of the Belgica Mound Province, NE Atlantic through k-means clustering. Cold-water coral reefs as sessile filter-feeders benefit from strong currents are often found in close association with sediment wave fields. This OBIA provided the framework to derive SSB wavelength and wave height, these SSB attributes were used as predictor variables for a multiple linear regression to estimate current velocities. Results show a bimodal distribution of current flow directions and current speed. Furthermore, a 5 k-means classification of the SSB geomorphology exhibited an imprinting of current flow consistency which altered throughout the study site due to the interaction of regional, local, and micro scale topographic steering forces. This study is proof-of-concept for an assessment tool applied to vulnerable marine ecosystems but has wider applications for applied seabed appraisals and can inform management and monitoring practice across a variety of spatial and temporal scales. Deriving spatial patterns of hydrodynamic processes from widely available multibeam echosounder maps is pertinent to many avenues of research including scour predictions for offshore structures such as wind turbines, sediment transport modelling, benthic fisheries, e.g., scallops, cable route and pipeline risk assessment and habitat mapping.

There is no geophysical evidence for the Mahuika Crater on the continental shelf southwest of New Zealand

ABSTRACT This study examines new bathymetric and geophysical evidence that questions the existence of the Mahuika Crater: a proposed impact depression 20.2 km wide lying on the continental shelf ∼250 km SW of New Zealand. Multibeam echo sounder and sub-bottom profiler data across the published location of the crater were collected and synthesised with existing bathymetric data for the wider region to assess the validity of such a claim. We conclude that there is no geophysical basis for the existence for the Mahuika impact crater in the region, the initial presumption of a crater was unsubstantiated, and is a myth propagated in the literature.

Mesophotic Reefs of the Largest Brazilian Coastal Protected Area: Mapping, Characterization and Biodiversity

Mesophotic reefs are poorly known worldwide despite their great ecological relevance and management importance for coral reef conservation strategies. To aid in filling this gap, we conducted a pioneering, large-scale survey, covering a total of around 315 miles in length, in the largest Brazilian coastal Marine Protected Area (MPA) Costa dos Corais. From the digital bathymetry model (30 to 50 m depth) generated by a multibeam echo sounder, we selected areas of greater geomorphological diversity for a detailed investigative expedition of mesophotic ecosystems. Various sampling techniques were used: single-beam echo sounders for detailing the relief, a remotely operated underwater vehicle (ROV) for habitat type investigation, baited remote underwater video (BRUV) for collecting images of the fish community, and scuba diving to perform transects describing the benthic and fish community. We analyzed reef environments from 20 to 68 m deep. As a result, we present the mapping and geomorphological characterization of two compartments of mesophotic reefs at 21–45 m depth and an image library of mesophotic ecosystems with the species description and indications of whether it is a new record in the region. Biodiversity data were collected covering eight species of sponges, with greater abundance for Ircinia spp., Aplysina spp., and Xestospongia muta; eight from corals, mainly Siderastrea spp. And Montastrea cavernosa; and 68 species of reef fish, with the Labridae family (including Scarinae—11 species) being the richest. Our results demonstrate the importance of mesophotic reefs for MPA Costa dos Corais reef biodiversity and, with that, the need to protect these areas through the application of local conservation strategies, such as the creation of “no-take zones”.

Categorizing Active Marine Acoustic Sources Based on Their Potential to Affect Marine Animals

Marine acoustic sources are widely used for geophysical imaging, oceanographic sensing, and communicating with and tracking objects or robotic vehicles in the water column. Under the U.S. Marine Mammal Protection Act and similar regulations in several other countries, the impact of controlled acoustic sources is assessed based on whether the sound levels received by marine mammals meet the criteria for harassment that causes certain behavioral responses. This study describes quantitative factors beyond received sound levels that could be used to assess how marine species are affected by many commonly deployed marine acoustic sources, including airguns, high-resolution geophysical sources (e.g., multibeam echosounders, sidescan sonars, subbottom profilers, boomers, and sparkers), oceanographic instrumentation (e.g., acoustic doppler current profilers, split-beam fisheries sonars), and communication/tracking sources (e.g., acoustic releases and locators, navigational transponders). Using physical criteria about the sources, such as source level, transmission frequency, directionality, beamwidth, and pulse repetition rate, we divide marine acoustic sources into four tiers that could inform regulatory evaluation. Tier 1 refers to high-energy airgun surveys with a total volume larger than 1500 in3 (24.5 L) or arrays with more than 12 airguns, while Tier 2 covers the remaining low/intermediate energy airgun surveys. Tier 4 includes most high-resolution geophysical, oceanographic, and communication/tracking sources, which are considered unlikely to result in incidental take of marine mammals and therefore termed de minimis. Tier 3 covers most non-airgun seismic sources, which either have characteristics that do not meet the de minimis category (e.g., some sparkers) or could not be fully evaluated here (e.g., bubble guns, some boomers). We also consider the simultaneous use of multiple acoustic sources, discuss marine mammal field observations that are consistent with the de minimis designation for some acoustic sources, and suggest how to evaluate acoustic sources that are not explicitly considered here.

An Efficient Method for Detection and Quantitation of Underwater Gas Leakage Based on a 300-kHz Multibeam Sonar

In recent years, multibeam sonar has become the most effective and sensitive tool for the detection and quantitation of underwater gas leakage and its rise through the water column. Motivated by recent research, this paper presents an efficient method for the detection and quantitation of gas leakage based on a 300-kHz multibeam sonar. In the proposed gas leakage detection method based on multibeam sonar water column images, not only the backscattering strength of the gas bubbles but also the size and aspect ratio of a gas plume are used to isolate interference objects. This paper also presents a volume-scattering strength optimization model to estimate the gas flux. The bubble size distribution, volume, and flux of gas leaks are determined by matching the theoretical and measured values of the volume-scattering strength of the gas bubbles. The efficiency and effectiveness of the proposed method have been verified by a case study at the artificial gas leakage site in the northern South China Sea. The results show that the leaking gas flux is approximately between 29.39 L/min and 56.43 L/min under a bubble radius ranging from 1 mm to 12 mm. The estimated results are in good agreement with the recorded data (32–67 L/min) for gas leaks generated by an air compressor. The experimental results demonstrate that the proposed method can achieve effective and accurate detection and quantitation of gas leakages.

Seabed Classification Using Multibeam Echosounder Measurement Data

Multibeam Echosounder (MBES) utilizes acoustic waves emitted to the seafloor through a transmitter or transducer and records its reflective. The information obtained by MBES are depth data and the scattering value of the acoustic signal reflected by the object or the seabed, called backscatter. Acoustic backscatter can be used to classify objects or the seabed such as shipwrecks or seabed sediments. This study focuses on seabed classification using an acoustic backscatter obtained from the measurement at Alur Pelayaran Barat Surabaya (APBS). The data used in this research are acoustic backscatter from bathymetry data extraction and ground truth data of sediments. This study found the fine sand sediments with backscatter value −15.56 dB, and clayey silt sediments with backscatter value −24.36 dB. The correlations between backscatter and seabed sediments in study area were classified into four classes, clay class sediments with backscatter intensity range [(−33.81) – (−28)] dB, clayey silt class sediments with backscatter intensity range [(−27.99) – (−23)] dB, sandy silt backscatter intensity range [(−22.9) – (−18)] dB, and sand class sediments with backscatter intensity range [(−17.99) – (−10)] dB. Based on the results data are known in the study area of seabed conditions dominated by sediments type sandy silt.

A Case Study of Completely Buried Wind-Power Cable Detection Using 3D Acoustic Imaging

As offshore wind power is renewable energy produced through the installation and operation of large-scale offshore infrastructure, risk management is crucial in power platforms. Safety accidents caused by external factors during the operation of submarine power cables can lead to enormous costs, thus necessitating the monitoring of burial depth and route information of cables. In this study, we developed a 3D acoustic imaging method that obtains information on the route and depth of completely buried power cables. An acoustic source-based engineering ocean seismic 3D (EOS3D) system has been used to detect buried objects in the subsurface because conventional sonars, such as multi-beam echo sounder (MBES) and side-scan sonar (SSS), which are used to analyze seafloor characteristics, have limitations in detecting completely buried cables in the subsurface. Field data were obtained as 8-channel data using a chirp source (2–8 kHz) designed to obtain a 25 × 25 cm horizontal spatial resolution from real-time kinematic (RTK) positioning. The image stack method was proposed to effectively detect buried cables, with the vertical gradient analyzed using signals decomposed into representative bin sizes and low-mid-high-frequency components. The acoustic anomalies of buried objects, identified as export cables and protectors, were processed into images using the proposed image stack method and gradient analysis. This case study of buried wind power cables using 3D acoustic imaging could be utilized in burial assessment survey (BAS)-data acquisition, processing/analysis processes, and operation and management of buried cables.

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.