High-resolution Sidescan Sonar Research Articles

Mapping and Recording of Ancient Shipwrecks by Using Marine Remote Sensing Techniques: Case Studies From Turkish Coasts

Within the context of the “Shipwreck Inventory Project of Turkey (SHIPT),” numerous acoustic remote sensing and photogrammetric surveys have been carried out along the coast of Turkey with the aim of detecting, mapping and documenting underwater cultural heritage. During the surveys, many ancient shipwreck sites have been discovered thanks to advanced technologies such as high-resolution side-scan sonar (SSS), sub-bottom profiler (SBP), and remotely operated vehicle (ROV). Once acoustic anomalies have been located, shipwreck sites have been verified by ROV and documented by 3D photogrammetric survey. Analysis of the collected data confirmed that the survey design and data acquisition parameters are the most important criteria for obtaining best quality image. Performing high-resolution remote sensing and photogrammetric survey for shipwrecks using optimal data collection techniques provides rapid results, decreasing time and budget and increasing the quantity of underwater cultural heritage that can be recorded. This paper discusses proper survey stages for the rapid, effective, high quality detection and recording of the shipwrecks using advanced technology. Acoustic images of shipwrecks comparing cargo, period, and form are also introduced in this paper, for the first time, which provide data on interpreting anomalies accurately for further exploration and monitoring surveys.

Archeological Assessment of Two Naval Battlefields in Çeşme and Sinop, Turkey

A marine survey was conducted to reveal the maritime cultural heritage of the naval battlefields of Cesme (1770) and Sinop (1853). The seafloor of the battle sites was mapped using a high-resolution side-scan sonar revealing the location of shipwreck remains and some potential sites of interest. The findings associated with the battles were identified by comparing their locations with historical charts and documents. Sonar imaging indicated that this cultural heritage has been heavily damaged by modern fishing and anchoring activities, as well as by natural sedimentation. Using an interdisciplinary approach that combined archeology, history, and geophysics, these two lesser known naval battlefields were studied scientifically for the first time as maritime cultural heritage sites and a preliminary interpretation of the findings is presented in this paper. Aside from their historical importance, these battlefields have great archeological value, because they harbor the last known samples of warships from the eighteenth and nineteenth centuries located on Turkish coasts. Considering that these rare cultural material remains are under threat, new regulations were suggested for both their protection and management and the site was brought to the attention of the authorities.

Limitations of Boulder Detection in Shallow Water Habitats Using High-Resolution Sidescan Sonar Images

Stones and boulders in shallow waters (0–10 m water depth) form complex geo-habitats, serving as a hardground for many benthic species, and are important contributors to coastal biodiversity and high benthic production. This study focuses on limitations in stone and boulder detection using high-resolution sidescan sonar images in shallow water environments of the southwestern Baltic Sea. Observations were carried out using sidescan sonars operating with frequencies from 450 kHz up to 1 MHz to identify individual stones and boulders within different levels of resolution. In addition, sidescan sonar images were generated using varying survey directions for an assessment of range effects. The comparison of images of different resolutions reveals considerable discrepancies in the numbers of detectable stones and boulders, and in their distribution patterns. Results on the detection of individual stones and boulders at approximately 0.04 m/pixel resolution were compared to common discretizations: it was shown that image resolutions of 0.2 m/pixel may underestimate available hard-ground settlement space by up to 42%. If methodological constraints are known and considered, detailed information about individual stones and boulders, and potential settlement space for marine organisms, can be derived.

Spatial Extent and Volume of the Shoreface Depositional Platform on the Upper Shoreface of the Glaciated Rhode Island South Shore

The extent and distribution of benthic geologic habitats on the upper shoreface (from the shoreline extending offshore to > 10-m water depth) was mapped along the 33-km-long Rhode Island south shore (RISS) in 2015–2016 using a combination of high-resolution side-scan sonar, seismic reflection profiles, surface sediment samples, and underwater video imagery. Modern (Holocene) sediment is contained largely in the shoreface depositional platform (SDP), the constructional, seaward sloping portion of the upper shoreface extending from the intertidal beach, offshore. The SDP varies in thickness and width along the RISS, with a mean thickness of 0.7 m and a mean width of 260 m. Maximum thickness (< 3 m) and width (750 m) was adjacent to a 1-km-long jetty system, supporting a net easterly longshore sediment transport along the RISS. The distribution and type of sedimentary environments on the uppermost shoreface here is largely related to the antecedent (glacial) geology. No clear correlation exists between decadal-scale shoreline change and the volume of sediment in the SDP, removing a potential metric for modelling shoreline change here and potentially for other glaciated shorefaces. The complex nature of the shoreface along the RISS, with abundant cobble to boulder gravel outcrop, makes the concept of an equilibrium profile here problematic at best.

Geological implications of acoustic imagery of the recent seabed textures in the Eastern Harbor, Alexandria

Acoustical geophysical devices depend on sound source to transmit sound waves that reflected, diffracted or scattered off the sea bed. The frequency used by each device controls the output information that related to the sea floor properties. The present study aims to get a recent mapping of the seabed texture mostly related to acoustic imagery, sediment analysis, and video images. High resolution side scan sonar has been used for mapping the seafloor of the Eastern Harbor, Alexandria, Egypt. Four different acoustic patterns were recognized: (a) the pattern of strong backscatter related to coarse sand, (b) the pattern of weak backscatter confined to mud and fine sand, (c) patches of strong and weak backscatter and d) the pattern with isolated reflections that belong to rock outcrops and boulders. The various wavelengths of sand ripples are identifiable that depend on their wavelength and amplitude. The presence of mega ripples in the front of the main EL-Boughaz outlet at the middle of Eastern Harbor indicates bed load transport of sediment during high energy conditions (storms). The current action on the sea bottom produced current ripples which are either straight or sinus. They are usually irregular-crested, showing no bifurcation.

A Study of Operation Methods for Application of Safety Inspection of Underwater Structures using High Resolution Side Scan Sonar

A Study of Operation Methods for Application of Safety Inspection of Underwater Structures using High Resolution Side Scan Sonar

Refining the link between the Holocene development of the Mississippi River Delta and the geologic evolution of Cat Island, MS: implications for delta-associated barrier islands

Abstract The geologic evolution of barrier islands is profoundly influenced by the nature of the deposits underlying them. Many researchers have speculated on the origin and evolution of Cat Island in Mississippi, but uncertainty remains about whether or not the island is underlain completely or in part by deposits associated with the past growth of the Mississippi River delta. In part, this is due to a lack of comprehensive geological information offshore of the island that could augment previous stratigraphic interpretations based on terrestrial borings. An extensive survey of Cat Island and its surrounding waters was conducted, including shallow-water geophysics (e.g., high-resolution chirp seismic, side-scan sonar, and swath and single-beam bathymetry) and both terrestrial and marine vibracoring. High-resolution seismic data and vibracores from south and east of the island show two horizontally laminated silt units; marine radiocarbon dates indicate that they are St. Bernard delta complex (SBDC) deposits. Furthermore, seismic data reveal that the SBDC deposits taper off toward the southern shoreline of Cat Island and to the west, morphology consistent with the distal edge of a delta complex. The sedimentology and extent of each unit suggest that the lower unit may have been deposited during an earlier period of continuous river flow while the upper unit may represent reduced or sporadic river flow. OSL dates from the island platform (beneath beach ridge complexes) indicate three stages of terrestrial evolution: island emergence resulting from relative sea-level rise (~ 5400 ybp) island aggradation via littoral transport (~ 2500–4000 ybp) and island degradation due to delta-mediated changes in wave direction (present– ~ 3600 ybp). Finally, the combination of terrestrial and marine data shows that portions of Cat Island that are lower in elevation than the central part of the island are younger and are likely underlain by a thin layer of deltaic sediments. This underscores the potential for increased future vulnerability of barrier islands that develop adjacent to major river delta complexes.

Repeated mapping of reefs constructed by Sabellaria spinulosa Leuckart 1849 at an offshore wind farm site

Sabellaria spinulosa reefs are considered to be sensitive and of high conservation status. This article evaluates the feasibility of using remote sensing technology to delineate S. spinulosa reefs. S. spinulosa reef habitats associated with the Thanet Offshore Windfarm site were mapped using high resolution sidescan sonar (410kHz) and multibeam echo sounder (<1m2) data in 2005 (baseline), 2007 (pre-construction baseline) and 2012 (post-construction). The S. spinulosa reefs were identified in the acoustic data as areas of distinct irregular texturing. Maps created using acoustic data were validated using quantitative measures of reef quality, namely tube density (as a proxy for the density of live S. spinulosa), percentage cover of S. spinulosa structures (both living and dead) and associated macrofauna derived from seabed images taken across the development site. Statistically significant differences were observed in all physical measures of S. spinulosa as well the number (S) and diversity (H׳) of associated species, derived from seabed images classified according to the presence or absence of reef, validating the use of high resolution sidescan sonar to map these important biogenic habitats. High precision mapping in the early stages allowed for the micro-siting of wind turbines in a way that caused minimal damage to S. spinulosa reefs during construction. These habitats have since recovered and expanded in extent. The surveys undertaken at the Thanet Offshore Windfarm site demonstrate the importance of repeat mapping for this emerging industry, allowing habitat enhancement to be attributed to the development whilst preventing background habitat degradation from being wrongly attributed to the development.

Surficial geology and geophysical investigations of the Capers Inlet, South Carolina (USA) 7.5-Minute Quadrangle

Surficial geology and geophysical investigations of the Capers Inlet, South Carolina (USA) 7.5-Minute Quadrangle is a compilation of geological and geophysical data collected in the Caper's Inlet Quadrangle, situated along the central coastline of South Carolina, USA. The 1:24,000 scale map area encompasses marine environments in the shallow nearshore and offshore (constituting approximately 80% of the study area) and terrestrial barrier island and Pleistocene upland environments (20% of the study area). The geologic map was compiled by overlaying existing topographic maps with data from high-resolution sidescan sonar, subbottom profiler, and GPR surveys supplemented with surficial sediment grabs and vibracore samples. These data were collected in 2009 and early 2010 for an MSc thesis project conducted through the Department of Geology and Environmental Geosciences at the College of Charleston, South Carolina. The resulting maps illustrate the spatial variability of surficial seafloor geology in the area, with sediment distribution ranging from a coarse shell hash to fine-grained mud. The shallow stratigraphy is characterized by a thin layer of modern sediment overlying the boundary between the Quaternary and Tertiary as well as the presence of several paleochannels in the backbarrier and shallow offshore. By portraying both seafloor geology and shallow stratigraphy, maps and accompanying information provide scientists and coastal managers with a better understanding of the relationship that exists between stratigraphy, sediment distribution, and geomorphology in the area.

Benthic Geologic Habitats of Shallow Estuarine Environments: Greenwich Bay and Wickford Harbor, Narragansett Bay, Rhode Island, U.S.A

Abstract Oakley, B.A.; Alvarez, J.D., and Boothroyd, J.C., 2012. Benthic geologic habitats of shallow estuarine environments: Greenwich Bay and Wickford Harbor, Narragansett Bay, Rhode Island, U.S.A. An integrated mapping approach using high-resolution side-scan sonar, surface sediment grab samples, digital aerial and orthophotography, and underwater video imagery was used to map Holocene sediment cover and Late Wisconsinan glacial outcrop in two shallow embayments in Narragansett Bay, Rhode Island, U.S.A. The use of side-scan sonar to characterize the seafloor has become common in a variety of different marine environments. Challenges remain in classifying side-scan or other acoustic data into a naming convention that is useful to scientists and managers. We characterize the benthic geologic habitats of these areas utilizing a flexible naming convention that combines information about geologic processes, morphologic form, particle size, biota, and anthropogenic impacts. Benthic geologic habitats were sep...

Sidescan sonar imagery of widespread fossil and active cold seeps along the central Chilean continental margin

The central Chilean subduction zone between 35°S and 37°S was investigated in order to identify, document and possibly understand fluid flow and fluid venting within the forearc region. Several areas were mapped using multibeam bathymetry and backscatter, high-resolution sidescan sonar, chirp subbottom profiling and reflection seismic data. On a subsequent cruise ground-truthing observations were made using a video sled. In general, this dataset shows surprisingly little evidence of fluid venting along the mid-slope region, in contrast to other subduction zones such as Central America and New Zealand. There were abundant indications of active and predominantly fossil fluid venting along the upper slope between 36.5°S and 36.8°S at the seaward margin of an intraslope basin. Here, backscatter anomalies suggest widespread authigenic carbonate deposits, likely the result of methane-rich fluid expulsion. There is unpublished evidence that these fluids are of biogenic origin and generated within the slope sediments, similar to other accretionary margins but in contrast to the erosional margin off Central America, where fluids have geochemical signals indicating an origin from the subducting plate.

AUV-based bed roughness mapping over a tropical reef

Identifying fixed bed roughness scales of hydrodynamic relevance to waves and currents is challenging around coral reefs due to their highly inhomogeneous bathymetry. In order to characterize the spatial variability in reef roughness, a quantitative analysis of high-resolution sidescan sonar backscatter is performed for the identification of distinct substrates around a tropical reef and is related to echo sounder-based roughness measurements. Data were collected in the vicinity of the Kilo Nalu Observatory on the south shore of Oahu using sidescan sonar and a narrow beam echo sounder incorporated in a REMUS-100 (Remote Environmental Monitoring UnitS) autonomous underwater vehicle (AUV). With basic statistics and principal component analysis of variables derived from the backscatter data, it is possible to discriminate between areas of rough reef, bare reef, and rippled sand. Echo sounder-derived spectral analysis did not reveal dominant length scales. However, by combining the seabed classification obtained from sidescan measurements with echo sounder data, spectral root mean square (RMS) height values of approximately 3.3 cm and 7.3 cm are assigned to the bare reef and rough reef areas, respectively, for roughness with wavelengths between 0.2 and 6 m.

Mingulay reef complex: an interdisciplinary study of cold-water coral habitat, hydrography and biodiversity

The Mingulay reef complex in the Sea of the Hebrides west of Scotland was first mapped in 2003 with a further survey in 2006 revealing previously unknown live coral reef areas at 120 to 190 m depth. Habitat mapping confirmed that distinctive mounded bathymetry was formed by reefs of Lophe- lia pertusa with surficial coral debris dating to almost 4000 yr. Benthic lander and mooring deployments revealed 2 dominant food supply mechanisms to the reefs: a regular rapid downwelling of surface water delivering pulses of warm fluorescent water, and periodic advection of high turbidity bottom waters. Closed chamber respirometry studies suggest that L. pertusa responds to seawater warming, such as that seen during the rapid downwelling events, with increases in metabolic rate. Lipid biomarker analy- sis implies that corals at Mingulay feed predominantly on herbivorous calanoid copepods. Integrating geophysical and hydrographical survey data allowed us to quantify the roles of these environmental factors in controlling biodiversity of attached epifaunal species across the reefs. Longitudinal structur- ing of these communities is striking: species richness (α) and turnover (β) change significantly west to east, with variation in community composition largely explained by bathymetric variables that are spa- tially structured on the reef complex. Vibro-cores through the reef mounds show abundant coral debris with significant hiatuses. High resolution side-scan sonar revealed trawl marks in areas south of the coral reefs where vessel monitoring system data showed the highest density of local fishing activity. The interdisciplinary approach in this study allowed us to record the food supply and hydrographic environ- ment experienced by L. pertusa and determine how it may be ecophysiologically adapted to these con- ditions. Improved basic understanding of cold-water coral biology and biodiversity alongside efforts to map and date these long-lived habitats are vital to development of future conservation policies.

Seep mounds on the Southern Vøring Plateau (offshore Norway)

Multidisciplinary study of seep-related structures on Southern Vøring Plateau has been performed during several UNESCO/IOC TTR cruises on R/V Professor Logachev. High-resolution sidescan sonar and subbottom profiler data suggest that most of the studied fluid discharge structures have a positive relief at their central part surrounded by depression. Our data shows that the present day fluid activity is concentrated on the top of these “ seep mounds”. Number of high hydrocarbon (HC) gas saturated sediment cores and 5 cores with gas hydrate presence have been recovered from these structures. δ 13C of methane (between −68 and −94.6‰ VPDB) and dry composition of the gas points to its biogenic origin. The sulfate depletion generally occurs within the upper 30–200 cm bsf and usually coincides with an increase of methane concentration. Pore water δ 18O ranges from 0.29 to 1.14‰ showing an overall gradual increase from bottom water values (δ 18O ∼ 0.35‰). Although no obvious evidence of fluid seepage was observed during the TV surveys, coring data revealed a broad distribution of living Pogonophora and bacterial colonies on sea bottom inside seep structures. These evidences point to ongoing fluid activity (continuous seepage of methane) through these structures. From other side, considerable number and variety of chemosynthetic macro fauna with complete absence of living species suggest that present day level of fluid activity is significantly lower than it was in past. Dead and subfossil fauna recovered from various seep sites consist of solemyid ( Acharax sp.), thyasirid and vesicomyid (cf. Calyptogena sp.) bivalves belonging to chemosymbiotic families. Significant variations in δ 13C (−31.6‰ to −59.2‰) and δ 18O (0.42‰ and 6.4‰) of methane-derived carbonates collected from these structures most probably related to changes in gas composition and bottom water temperature between periods of their precipitation. This led us to ideas that: (1) seep activity on the Southern Vøring Plateau was started with large input of the deep thermogenic gas and gradually decries in time with increasing of biogenic constituent; (2) authigenic carbonate precipitation started at the near normal deep sea environments with bottom water temperature around +5 °C and continues with gradual cooling up to negative temperatures recording at present time.

Improving Coral Reef Habitat Mapping of the Puerto Rico Insular Shelf Using Side Scan Sonar

Use of high resolution (0.1m) side-scan sonar for generating detailed benthic maps (4 m2 mapping unit) in coral reef environments was investigated by collecting imagery over 60 km2 of the Puerto Rico insular shelf, from shoreline to shelfedge. Visual interpretation of acoustic imagery resulted in 21 different habitat types classified within broad categories of unconsolidated sediment (7), consolidated bottom (6), and vegetated areas (8). Detailed maps showed the amount, size, and spatial distribution of habitats across the shelf. Qualitative and quantitative benthic characterizations showed habitats to be biologically distinct and ecologically relevant at multiple scales. Image collection was cost effective and amenable to small-boat use.

計量魚群探知機による海底地質判別に関する研究

Despite the significance of the geologic map of seabed classification, geological survey using high resolution side-scan sonar is not widely utilized in fisheries due to its high cost. Therefore a new algorithm for the analysis of echo sounder data measured by quantitative echo-sounders is presented in this paper so that it can be applicable to the seabed classification to make geologic maps in fisheries. The present algorithm is based on the Discrete Wavelet Transform in the analysis of reflections to draw out significant differences among different textures or materials on the seabed from their waveforms. In this paper, the development of the present algorithm is described using data obtained by two experiments carried out on the coasts of Hokkaido and Okinawa using quantitative echo-sounders. The results show that the present method can classify sand and silt seabed from others by the maximum values of wavelet power on a low frequency level in the discrete wavelet analysis and show that the present algorithm is applicable to the seabed classification for the creation of geologic maps in fisheries.

Giant iceberg plow marks at more than 1 km water depth offshore West Greenland

During a recent (2006) cruise of RV ‘Dana’ high resolution side-scan sonar and sub-bottom profiling was carried out on selected shelf and slope transects offshore Disko Bugt, central West Greenland. Available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c. 1100 m water depth. The newly acquired side-scan sonar data reveal the presence of giant iceberg plow marks extending (sub)parallel to the slope between about 800 and 1085 m water depth. The height difference between bottom of the scours and rim crest is up to 40 m. The largest plow marks are about 750 m wide. To date no observed modern icebergs including those from Antarctica have drafts in excess of c. 500 m. Taking into account maximum glacial sea level lowering of c. 120 m, the paleo-iceberg keel depth was at least 950 m. Due to the presence of the relatively shallow (< 700 m) sill of Davis Strait to the south, calving of these paleo-icebergs is thought to have occurred from an ice margin in the Baffin Bay region (Jakobshavn Isbræ paleo-ice stream?). The depth of occurrence (> 1000 m) and dimensions of the plow marks are concluded to be exceptional, and comparable to glacial scouring features reported from the Arctic Ocean.

Fluid mud dynamics in the Weser estuary turbidity zone tracked by high-resolution side-scan sonar and parametric sub-bottom profiler

Fluid mud in estuarine turbidity maximum zones (TMZ) can pose considerable navigation risks due to potentially substantial reductions in nautical depth, coupled with an inherent difficulty of detection by conventional echo-sounders. Despite intensive research efforts, however, our knowledge about the spatial and temporal dynamics of fluid mud is still not sufficient. In this study, the combined use of a side-scan sonar (Sportscan®, Imagenex) and a parametric sub-bottom profiler (SES-2000®, Innomar Technology GmbH) has proved successful for high-resolution fluid mud detection and volumetric quantification in an estuarine environment. In 2004 and 2005, repeated surveys were conducted in the navigation channel of the upper meso- to lower macrotidal Weser estuary TMZ (German North Sea coast) at different tidal stages and river discharges. Current velocity data were simultaneously collected by 1,200-kHz broadband ADCP (RDInstruments) measurements. Ground-truthing was carried out by means of grab sampling and gravity coring, adapted to fluid mud conditions. It was found that fluid mud occurrence in the Weser estuary is highly variable on time scales of a few hours and spatial scales of several metres. The riverbed is characterised by sand and mud deposits, and a complex morphology including subaqueous dunes and smooth bed deposits intermittently overlain by fluid mud. Thus, a continuous, coherent fluid mud body covering the entire TMZ riverbed was not observed. Rather, spatial distribution was patchy and highly dependent on suspended particulate matter (SPM) concentrations in the water column, as a result of which local fluid mud deposits varied in thickness from centimetres to metres. The formation of fluid mud was largely restricted to slack water, although slack-water conditions were not necessarily associated with large-scale fluid mud appearance. Advective SPM transport of resuspended fluid mud seems to be the most plausible explanation for the high spatial variability observed, even between two successive tides. The amount of fluid mud deposited and resuspended in the course of a tidal cycle can reach several 10s of tons even in small riverbed depressions.

Lights, camera and acoustics: Assessing macrobenthic communities at a dredged material disposal site off the North East coast of the UK

This study presents the results of a trial assessment based on a combination of sampling techniques at a dredged material disposal site located off the North East coast of the UK, over 2001 to 2004. The site was surveyed with a high-resolution sidescan sonar system producing a mosaic with 100% coverage of the survey area. Benthic communities and sediments were ground-truthed using a Hamon grab with a video camera. Additionally, the area was also sampled in 2003 with a Sediment Profile Imaging (SPI) camera, which complemented other techniques by providing in situ information on sediment quality, and biogenic activities. An assessment is made of the benefits of combining the results from conventional methods, principally using grab samples, with those from acoustic techniques and optical imaging devices to determine seafloor and macrobenthic conditions. This information has the potential to contribute to the enhancement of routine monitoring programmes within UK waters.

Slope failure, mass flow and bottom current processes in the Rockall Trough, offshore Ireland, revealed by deep-tow sidescan sonar

The margins of the Rockall Trough, currently the focus of oil and gas exploration interest, incorporate an environmentallyimportant and lightly studied shelf region. To address the paucity of information within this region an extensive high resolution sidescan sonar survey was carried out in the Irish sector of the Rockall Trough in June/July 1998. This valuable natural laboratory contains information on slope stability, sediment transport, nutrient upwelling, bottom current, and biological activity at a shelf/slope/basin-floor transition. Detailed information on the nature of many of these processes can be provided from shallow geophysical techniques. The TRIM (TOBI Rockall Irish Margins) project (Shannon et al., 2001), funded by the Irish Petroleum Infrastructure Programme (Rockall Studies Group), acquired 3100 line-km of TOBI sidescan sonar and 3700 km of 3.5 kHz profiler data along the margins of the Rockall Trough (Figure 1). This project followed on from the earlier reconnaissance AIRS (Atlantic Irish Regional Survey) survey conducted over the entire southern Rockall Trough region, using the lower resolution surface towed sonar side-scan system known as GLORIA (Unnithan et al., 2001). The TOBI sidescan system, developed at the Southampton Oceanography Centre (Flewellen et al., 1993), is deep-towed at 300-400 m above the seafloor. It transmits at a frequency of 32 kHz and samples the acoustic response of the seabed and shallow sedimentary structure to a centimetre to metre depth scale. This acoustic response therefore reflects not only the backscattering properties of the seabed but also the shallow detailed structure of sediments formed by recent sedimentological processes.