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Shipwrecks are an integral part of our maritime archaeological landscape and are associated with diverse societal and cultural interests, yielding significant management challenges. Coupled hydrodynamic and geomorphological processes significantly impact the effective in situ preservation of these fragile sites. In this study, we assess sediment budget change and hydrodynamic triggers at metal‐hulled shipwrecks lost between 1875 and 1918, all located in the tidally dominated Irish Sea at depths between 26 and 84 m. This is conducted using time‐lapse, multibeam echosounder surveys at multiannual, annual, and weekly time steps, supported by sediment grain‐size analysis, modeled ocean currents, and shallow seismic data. Results indicate significant changes at all time steps for sites located in sand‐dominated environments, whereas the seabed around shipwrecks settled in multimodal sediments shows virtually no change outside of measurement errors (±30 cm). Variability in geomorphic change is attributed to local environmental factors, including bed shear stress, sediment supply, and spatial barriers to scour. We demonstrate that individual wrecks in similar shelf sea regions can be in very different equilibrium states, which has critical implications for the in situ management of underwater cultural heritage. [ABSTRACT FROM AUTHOR]

Near-death experiences (NDEs) are usually characterized as pleasant or positive experiences, but little research to date has involved quantification of the sentiment contained in experiencers' descriptions of their NDEs. In this study, I undertook an automated method of obtaining a corpus of 557 NDE narratives by web scraping and then using lexicon-based sentiment analysis to assign a sentiment score to each narrative. The results showed that NDEs are more often associated with positive sentiment than negative sentiment, with twice as many narratives receiving a positive overall sentiment score as a negative one. Although just under 3% of the sample contained descriptions of wholly unpleasant NDEs, many NDE narratives contained at least some negative sentiment, usually associated with the circumstances of the NDE but sometimes with the experience itself, most commonly involving the decision to return or 'go back' to the body. Future researchers should consider using aspect level sentiment analysis with a modified lexicon to more accurately quantify the sentiment contained in NDE narratives. [ABSTRACT FROM AUTHOR]

Scour processes play a critical role in the preservation status of submerged historic shipwrecks. Erosion of sediment leads to enhanced exposure of archaeological sites to physical, chemical and biological processes. Current methods for identifying erosional and depositional features at wreck sites are based primarily on visual interpretation of data, which is labour-intensive and entirely subjective. The increasing availability of high-resolution multibeam echosounder–derived digital elevation models (DEMs) of historic wreck sites allows for an entirely new level of detailed interrogation and analyses of the geomorphological features associated with these. In this study, we present a residual relief modelling method for the semi-automated extraction of such depositional and erosional features at wreck sites. Relief modelling is supplemented with a breakpoint classification approach, with final separation supported by DEM visualisation enhancement techniques. We applied the method to three World War I shipwreck sites and evaluated it against traditional manual vectorisation techniques. The results suggest that the semi-automated modelling method is robust, time-effective and capable of quantifying the products of scour processes with increased objectivity. Our method holds great potential for the objective characterisation of erosional and depositional patterns and processes at wreck sites, which have important implications for site formation studies and in situ preservation of underwater cultural heritage. [ABSTRACT FROM AUTHOR]

Conservation of historic shipwrecks is prohibitively expensive and in situ preservation and recording are the preferred archaeological approaches. Non-destructive high-definition 3D imaging is therefore essential for recording and managing submerged historic shipwrecks. Multibeam echosounders (MBES), the standard tool for hydrographic survey, can produce point clouds to image complex 3D structures. However, wreck imaging is often done using MBES in traditional survey mode optimised for morphological characterisation of the seafloor. This does not necessarily provide high-definition imagery required by archaeologists. This study demonstrates key factors influencing high-definition MBES imaging of wrecks through a controlled field experiment. Results show that optimal high-definition 3D imaging is achieved through maximising the pulse rate, narrowing the angular sector, using the highest frequency and shortest pulse lengths, applied to at least 3 to 5 overlapping centreline-parallel and offset passes with additional perpendicular/oblique lines. Variations in survey design are demonstrated to exert strong controls on sounding density and distribution, with high-density on horizontal and vertical wreck surfaces enabled by a combination of overlapping passes and offset lines. Adoption of this method would result in more widespread high-definition 3D imaging of wrecks to benefit archaeological research and develop effective mitigation strategies to minimise loss of the fragile underwater resource. [ABSTRACT FROM AUTHOR]

The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. −40 m) are recorded at c. 13.5 and 11.5k cal a bp. Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp. Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions. [ABSTRACT FROM AUTHOR]

Species distribution models (SDMs) are commonly used to model the spatial structure of species in the marine environment, however, most fail to account for detectability of the target species. This can result in underestimates of occupancy, where nondetection is conflated with absence. The site occupancy model (SOM) overcomes this failure by treating occupancy as a latent variable of the model and incorporates a detection submodel to account for variability in detection rates. These have rarely been applied in the context of marine fish and never for the multiseason dynamic occupancy model (DOM). In this study, a DOM is developed for a designated species of concern, cusk (Brosme brosme), over a four‐season period. Making novel use of a high‐resolution 3‐dimensional hydrodynamic model, detectability of cusk is considered as a function of current speed and algae cover. Algal cover on the seabed is measured from video surveys to divide the study area into two distinct regions: those with canopy forming species of algae and those without (henceforth bottom types). Modeled estimates of the proportion of sites occupied in each season are 0.88, 0.45, 0.74, and 0.83. These are significantly greater than the proportion of occupied sites measured from underwater video observations which are 0.57, 0.28, 0.43, and 0.57. Individual fish are detected more frequently with increasing current speed in areas lacking canopy and less frequently with increasing current speed in areas with canopy. The results indicate that, where possible, SDM studies for all marine species should take account of detectability to avoid underestimating the proportion of sites occupied at a given study area. Sampling closed areas or areas of conservation often requires the use of nonphysical, low impact sampling methods like camera surveys. These methods inherently result in detection probabilities less than one, an issue compounded by time‐varying features of the environment that are rarely accounted for marine studies. This work highlights the use of modeled hydrodynamics as a tool to correct some of this imbalance. Detection of marine fish is often not considered when mapping their distributions. This study considers detectability as a function of hydrodynamics and bottom type. Findings show how considering detection probability affects occupancy estimates for marine fish in an area of conservation for a priority species. [ABSTRACT FROM AUTHOR]

Introduction: International reports suggest there have been prehospital delays for time-sensitive emergencies like stroke and TIA during the COVID-19 pandemic. The aim was to investigate the impact of the COVID-19 pandemic on ambulance times and emergency call volume for adults with suspected stroke and TIA in Ireland. Method: We conducted a retrospective cohort study of patients ≥ 18 years with suspected stroke/TIA, based on data from the National Ambulance Service. We included all cases assigned code 28 (suspected stroke/TIA) by the emergency call-taker, from 2018-2021. We compared ambulance times and emergency call volume by week, the four COVID-19 waves (defined by the Health Protection Surveillance Centre) and annually. The COVID-19 period was from March 1, 2020 - December 19, 2021 and the pre-COVID-19 period January 1, 2018 - February 29, 2020. Continuous variables were compared with t-tests and categorical variables with Pearson's χ2 tests. Results: 40,012 cases were included: 20,281 in the pre-COVID-19 period and 19,731 in the COVID-19 period. Mean patient age significantly decreased between the two periods, from 71 years (±16.5) to 69.8 years (±17.1); p<0.001. Mean ambulance response time increased between the two periods from 17 minutes 31 seconds to 18 minutes 59 seconds (p<0.001). The number of cases with symptom onset to emergency call time of >4 hours significantly increased from 5,581 to 6,060 during the COVID-19 period (p<0.001). Mean calls/day increased from 25.1/day to 30.1/day during the COVID-19 period. Conclusion: Early findings from the study suggest an increase in call volume for stroke/TIA between the COVID-19 and pre-COVID-19 periods. An increase in response times during the same periods was also found. We concluded that longer symptom-to-call times indicate a change in healthcare-seeking behavior. Sustaining high levels of compliance with stroke code protocols is crucial during healthcare crises. Future research will involve further analysis including controlling for confounders. [ABSTRACT FROM AUTHOR]

Marine habitat mapping provides information on seabed substrata and faunal community structure to users including research scientists, conservation organizations, and policy makers. Full-coverage acoustic data are frequently used for habitat mapping in combination with video ground-truth data in either a supervised or unsupervised classification. In this investigation, video ground-truth data with a camera footprint of 1 m² were classified to level 4 of the European Nature Information System habitat classification scheme. Acoustic data with a horizontal resolution of 1 m² were collected over an area of 130 km² using a multibeam echosounder, and processed to provide bathymetry and backscatter data. Bathymetric derivatives including eastness, northness, slope, topographic roughness index, vector rugosity measure, and two measures of curvature were created. A feature selection process based on Kruskal-Wallis and post hoc pairwise testing was used to select environmental variables able to discriminate ground-truth classes. Subsequently, three datasets were formed: backscatter alone (BS), backscatter combined with bathymetry and derivatives (BSDER), and bathymetry and derivatives alone (DER). Two classifications were performed on each of the datasets to produce habitat maps: maximum likelihood supervised classification (MLC) and ISO Cluster unsupervised classification. Accuracy of the supervised habitat maps was assessed using total agreement, quantity disagreement, and allocation disagreement. Agreement in the unsupervised maps was assessed using the Cramer's V coefficient. Choice of input data produced large differences in the accuracy of the supervised maps, but did not have the same effect on the unsupervised maps. Accuracies were 46, 56, and 49% when calculated using the sample and 52, 65, and 51% when using an unbiased estimate of the population for the BS, BSDER, and DER maps, respectively. Cramer's V was 0.371, 0.417, and 0.366 for the BS, BSDER, and DER maps, respectively. [ABSTRACT FROM AUTHOR]

We present early to Mid-Holocene paleo-geographic reconstructions for the Ramore Head area (Northern Ireland). This coastal area is characterized by Mesolithic occupation (c. 10-6 ka) and preserved early-Mid-Holocene peats both on- and offshore. This paper improves on previous reconstructions by employing a backstripping methodology, which removes accumulated recent deposits from identified buried paleo-landsurfaces instead of using modern topography as an analogue to the past landscape. Paleo-landsurfaces are identified offshore from seismic profiles supplemented by cores, and onshore through legacy borehole records. The paleo-landsurface can be traced offshore to depths of −2 to −19 m and is buried by <5 m of modern sediment. It extends onshore under the coastal town of Portrush and is buried <2.5-10 m below modern ground level. The identified paleo-landsurface is combined with sea-level curves from recent Glacio-Isostatic-Adjustment models to reconstruct marine transgression during the early-Mid-Holocene. Comparison is also made with reconstructions based on modern topography. Together, the identified paleo-landsurfaces and revised reconstructions can assist future site prospection on- and offshore and delimit high-potential areas for heritage management. Revised reconstructions also allow placement of extant archaeology into a more accurate context of landscape change and help develop insights into local-scale site location patterns. [ABSTRACT FROM AUTHOR]

ABSTRACT Aim To investigate the effect of climatic, historical and spatial variables on species richness patterns in freshwater fish. Location North America and Europe. Methods Regional species lists were used to document the spatial richness patterns. Three realms, Europe and Pacific and Atlantic North America, were identified. The numbers of species, by habitat, migration and distributional range categories, were calculated and the contributions of regional mean and seasonal temperature and rainfall, historical (realm, glaciation), and spatial (area, elevational range) variables to predicting richness were assessed using boosted regression trees, model-averaging and spatially explicit models. Results The latitudinal temperature gradient is stronger than that for rainfall in the Atlantic realm whereas the rainfall gradient in Europe is independent of the temperature gradient. Species richness is more strongly correlated with temperature than rainfall, and the effects are stronger in the Atlantic realm than in Europe. The influence of environmental variables differs between habitat specialist and generalist species. Climate, particularly maximum monthly temperature, is the best predictor of richness in rivers whereas climate variables are less important than historical/spatial variables for diadromous species. Main conclusions Freshwater fish richness differences between realms follow differences in spatial climatic trends. The contributions of climatic, historical and spatial predictor variables vary with ecology: temperature is a better predictor than rainfall in river-dwellers. The richness gradient is driven more by physiological than by energetic constraints on species. The importance of history is probably underestimated because of correlations with climate variables. [ABSTRACT FROM AUTHOR]

Near-seabed (<50 m) sediments were studied throughout the Irish sector of the Rockall Trough (ca. 123,000 km) based on a combined analysis of shallow seismic (3.5 kHz) and multibeam swath data acquired by the Irish National Seabed Survey and reprocessed here at higher resolution. The detailed identification of seven acoustic facies served to classify the Rockall Trough into six main sedimentary provinces, incorporating the well-known Feni Drift, Donegal-Barra Fan and Rockall Bank mass flow. In the northern part of the study area, extensive mass transport deposits from both flanks of the trough are the dominant depositional features. Debris flow deposits formed by ice streaming of the British-Irish ice sheet characterise most of the Donegal-Barra Fan, whereas turbidite deposition occurs towards the toe of the fan. On the western margin of the trough, the post-glacial Rockall Bank mass flow deposit displays a rough topography with no acoustic penetration. Several failure scarps are visible on the flank of the bank where the mass flow originated, and pass downslope into large sediment lobes and smaller debris flow deposits. Smaller-scale mass transport deposits were also discovered close to some canyons indenting the eastern slope. High seismic penetration characterises the Feni contourite drift deposit, and precise mapping of its geographical extent shows that it is considerably wider than previously reported. The sediment waves that drape this drift are interpreted as predominantly relict features, and their varied geometry suggests a complex oceanographic regime. In the deeper part of the trough, the data reveal novel evidence of the widespread occurrence (about 12,000 km) of distinct seismic and backscatter signatures indicating the possible presence of fluid escape structures within fine-grained sediments of mixed contouritic, hemipelagic and turbiditic origin. Sediment overloading and increased pore pressure resulting from extensive mass wasting to the north of the area is a likely cause of dewatering-rooted fluid migration towards the seabed, but further investigations are required to confirm the nature and origin of such fluids in the Rockall Trough. [ABSTRACT FROM AUTHOR]

The Maidens (including the North and Outer Klondyke) are a group of bedrock extrusions about 14 km northeast of Larne, off the coast of Northern Ireland (central point for Maidens Complex: 54°57'50.0, 25°42'20.0). Multibeam echosounder data have been combined with extensive ground-truthing to produce broad-scale substratum and biotope maps for the site. The bathymetry was used to derive rasters of slope gradient, rugosity, aspect, and fine- and broad-scale benthic position index which were used for further analyses with Principal Components Analysis. Ground-truthing data were used to create sample signatures and a Maximum Likelihood Analysis performed to classify the surfaces according to that signature. The supervised classifications generated distributions for three broad-scale substrata and habitat biotopes (six level three biotopes, four level four and one level five biotope). The maps provide critical information and distributions that greatly facilitate the conservation, management and monitoring of a proposed Special Area of Conservation. [ABSTRACT FROM AUTHOR]

A 1:30,000 substratum map for an area off the north coast of Ireland is presented. The study area is bounded in the south by the Causeway coastline and in the north by the following coordinates: top left corner (6°43'36''W, 55°17'N) and top right corner (6°27'W, 55°17'N). This mapping has been made possible through the availability of full seafloor coverage multibeam swath bathymetry and backscatter data (both gridded to 1 m), together with ground-truthing data collected over the past 40 years. Bathymetry data were used to generate terrain indices such as slope, rugosity, aspect, fine- and broad-scale Benthic Position Index, whilst the backscatter data were interpreted visually, subjected to an unsupervised classification process using QTC Multiview, and combined with the bathymetry-derived parameters into a clustermap in ArcGIS. The resulting maps allowed us to divide the seabed into 10 distinct acoustic classes, which, linked to sediment samples, diver surveys, underwater video-tows and remotely operated vehicle surveys, were converted into a substratum map. This is the most accurate seafloor substratum map to date for the north coast of Ireland and could form the basis for more in-depth geological, biological and hydrodynamic studies of this highly dynamic coastline. [ABSTRACT FROM AUTHOR]

This paper outlines work currently being undertaken to reconstruct submerged archaeological landscapes off the north coast of Ireland. This research uses the recently-completed Joint Irish Bathymetric Survey (JIBS), which has provided full-coverage high-resolution multibeam bathymetric data for the sea-bed off the north coast. This data has been examined for evidence of past sea-level change and been used to produce palaeo-geographic reconstructions of the past landscape, which in turn have facilitated the identification of ten areas of high archaeological potential. The results presented here will form the basis of a future programme of archaeological survey and prospection. © 2010 The Authors [ABSTRACT FROM AUTHOR]

This paper describes Phase 1 of the project 'Archaeological Applications of the Joint Irish Bathymetric Survey (JIBS) Data', analysing bathymetric and backscatter data derived from multibeam surveys off the north coast of Ireland. In particular, the usability of the data for shipwreck detection, identification and site characterization is explored. In Phase 1, the data was screened for anomalous sea-bed features, which were subsequently described, catalogued and categorized according to their archaeological potential and cross-referenced against existing records. A planned second phase of this project will examine each anomaly in greater detail together with the local and regional hydrodynamic conditions. © 2010 The Authors [ABSTRACT FROM AUTHOR]

Please clickhereto download the map associated with this article. Multibeam echosounder data collected by the Irish National Seabed Survey (INSS) between 2000 and 2001 in the Rockall Trough have been used by many projects to analyze the geomorphology and the sedimentary processes of the margins of the Trough. However, due to the low spatial resolution of 150–250 m and the amount of artefacts still embedded in the publicly available data, many geomorphological features have been overlooked. This paper shows that the same multibeam dataset can provide more detailed information on seabed processes when the latest hydrographic and backscatter post-processing techniques are used to reduce data artefacts and improve data quality and spatial resolution. The resulting map, presented here at a scale of 1:450,000, is based on a semi-automatic and manual interpretation of geomorphological features highlighted using a new and improved 30 m bathymetric grid and a multibeam backscatter mosaic obtained using the GEOCODER post-processing algorithm. Overall, the map shows a complex sedimentological scenario where the Rockall Bank Mass Flow failure, the Donegal-Barra trough-mouth fan, along slope structures such as the Feni Contourite Drift and the Porcupine moat dominate the Rockall Trough flanks and basin floor. Smaller features such as canyon and gully systems, escarpments, coral mounds, volcanic mounds and iceberg scours have also been mapped in detail. In addition, the interpretation of the backscatter mosaic allows for the first time the identification of depositional lobes generated by downslope mass transport and canyon drainage systems, particularly where these features completely lose their bathymetric expression. [ABSTRACT FROM PUBLISHER]

McGonigle, C., Brown, C. J., and Quinn, R. 2010. Insonification orientation and its relevance for image-based classification of multibeam backscatter. – ICES Journal of Marine Science, 67: 1010–1023.The use of multibeam echosounders (MBES) for mapping benthic habitat has gained widespread acceptability. Multibeam backscatter imagery provides an objective tool for scientists and managers to chronicle the extent and condition of the benthic resource. However, there are no standardized methods describing how best to process backscatter data to derive meaningful segmentations, although several acquisition parameters have been identified as having the capacity to affect the classification result. This research attempts to determine how the orientation at which a feature is insonified can affect classification outcome using commercially available software (QTC-Multiview), and to evaluate this significance related to vessel speed as a proxy for data density. A complex 2-km2 area of Stanton Banks, UK, was selected as the test site for the study. The area was insonified using a Kongsberg Simrad EM1002 MBES at perpendicularly opposing orientations, at two different vessel speeds within the same 24-h period. The classifications displayed 53% (k = 0.396) similarity at 4 m s−1 and 49% (k = 0.342) at 2 m s−1 from opposing orientations. Common orientations at different speeds were 68% (k = 0.583) similar (east–west) and 53% (k = 0.384; north–south). Most of the variation was in topographically complex areas, which coincided with shallow depths (<60 m). Meteorological and oceanographic conditions at the time the data were collected were evaluated as having had the potential to influence the outcome of the classifications. Interpretation of the results suggests that the orientation at which insonification occurs has a greater ability to influence the classification result than vessel speed using an image-based technique. [ABSTRACT FROM PUBLISHER]

Efforts to develop a procedurally robust method for automated classification of multibeam backscatter have taken a variety of approaches (e.g., image-based, textural, angular range analysis). For image-based classification, little research has focused on the roles of operational parameters of vessel and sonar system in affecting the final classification. Repeat multibeam surveys (2005 and 2006) conducted at the same area with different sounding densities were classified using QTC-Multiview. Comparison of class areas revealed 78% agreement between classifications derived from the two surveys. Cross-tabulation of ground truth video and class demonstrate 71% agreement in the low-density survey and 77% for the high-density. Differences between classifications are primarily attributed to variation in along track data density, errors in the compensation process, and/ or insufficient quality control of the input data. Natural change detection at the scales observed was determined not to be practically discernable from the errors associated with the classification process. [ABSTRACT FROM AUTHOR]

The River Bann, Northern Ireland, discharges onto the high-wave energy, swell-dominated North Atlantic coast. The funnel-shaped estuary, buttressed by Tertiary basalt outcrops, is partially barred by dunes developed on a mid-Holocene gravel barrier. The meso-scale evolution of the estuary and nearshore zone therefore demonstrates the interaction of fluvial, marine and coastal processes. Echo sounder, side-scan sonar and Chirp sub-bottom profiler were used to map bathymetry, surficial sediments and sediment stratigraphy respectively. Side-scan sonar data, ground-truthed by surficial sediment sampling, yielded 3 distinct acoustic facies, interpreted as sand (90% of study area) bedrock (9%) and gravel (1%). Oblique nearshore sandwaves, (wavelength 20 - 60m, height 0.8 - 2.4m) are replaced 1.5km offshore by planar sands (20m water depth). Adjacent to the bedrock headland of Portstewart Point lies a relict shore platform (at -30m OD Belfast), likely formed during a late-Pleistocene lowstand. Individual boulders up to 1m diameter are imaged on the bedrock surface. The surface is partially overlain by active, shore parallel gravel wedges surfaced by ripple beds (wavelength 1.5m, height 1.0m) which are partially overlapped by planar sand. Repeat seasonal surveys show general onshore surface bedform migration during winter and offshore re-distribution of sediment in summer. These changes suggest that west to east tidal currents re-circulating sediment between the offshore and nearshore zones are modified seasonally by changes in wave regime and river discharge. Chirp surveys revealed two main seismic stratigraphic units, termed inshore and offshore, overlying the acoustic basement, the inshore unit being more internally complex. Four major controls on Holocene nearshore sedimentation on the north coast of Northern Ireland are suggested: (1) antecedent geological constraints, (2) sediment supply, (3) wave climate and (4) tidal current regime. Apart from antecedent geology, these controls have been, and continue to be, modified by RSL fluctuations and storm events. [ABSTRACT FROM AUTHOR]

Acoustic methods are routinely used to provide broad scale information on the geographical distribution of benthic marine habitats and sedimentary environments. Although single-frequency multibeam echosounder surveys have dominated seabed characterisation for decades, multifrequency approaches are now gaining favour in order to capture different frequency responses from the same seabed type. The aim of this study is to develop a robust modelling framework for testing the potential application and value of multifrequency (30, 95, and 300 kHz) multibeam backscatter responses to characterize sediments' grain size in an area with strong geomorphological gradients and benthic ecological variability. We fit a generalized linear model on a multibeam backscatter and its derivatives to examine the explanatory power of single-frequency and multifrequency models with respect to the mean sediment grain size obtained from the grab samples. A strong and statistically significant (p < 0.05) correlation between the mean backscatter and the absolute values of the mean sediment grain size for the data was noted. The root mean squared error (RMSE) values identified the 30 kHz model as the best performing model responsible for explaining the most variation (84.3%) of the mean grain size at a statistically significant output (p < 0.05) with an adjusted r2 = 0.82. Overall, the single low-frequency sources showed a marginal gain on the multifrequency model, with the 30 kHz model driving the significance of this multifrequency model, and the inclusion of the higher frequencies diminished the level of agreement. We recommend further detailed and sufficient ground-truth data to better predict sediment properties and to discriminate benthic habitats to enhance the reliability of multifrequency backscatter data for the monitoring and management of marine protected areas. [ABSTRACT FROM AUTHOR]

Chirp sub-bottom profilers produce high-resolution images of the near-surface. An attribute of the sea-bed reflection in chirp data are fluctuations in polarity between adjacent traces. Two models are proposed and presented to explain this: the first incorporates changes in an acoustic impedance gradient at the sea bed; the second uses changes in the thickness of the uppermost sediment layer. Mixing of adjacent traces produces a consistent polarity for the sea-bed reflector. Reflection coefficients are calculated, using amplitude information derived from single-traces, and polarity information from trace mixing, with application to a marine archaeological case study. The reflection coefficient calculated for the top of a buried 18th century wooden wreck is -0.26. [ABSTRACT FROM AUTHOR]

The original version of this article was revised: Additional correction in Table 1: please delete (') in the second column heading was incorrectly carried out. It should read "Acquisition settings test"; by this, the author meant only to delete the apostrophe symbol, not the entire second column heading. [ABSTRACT FROM AUTHOR]