Single-beam Data Research Articles

Bedform evolution and dynamics of a geostrophic current-swept shelf, northern KwaZulu-Natal, South Africa

When compared to tide-dominated shelves, shelves swept by geostrophic flows are relatively understudied, yet geostrophic currents have the potential to construct substantial current-generated shelf bedforms. This paper examines the evolution of a series of bedforms encountered along the narrow Agulhas Current-swept northern KwaZulu-Natal shelf. Their evolution is placed in the context of progressive current impingement and variation in flows associated with the postglacial transgression and culminating in the present-day highstand.Ultra-high resolution seismic reflection, multibeam, side-scan sonar and single beam data sets reveal several bedform scales and morphologies; wave ripples and shoreface-connected ridges are associated only with the inner shelf, and 2D and 3D very large dunes are more cosmopolitan and span the entire shelf sector. The inner shelf is marked by rock outcrop (aeolianite), surrounded by sandy sediment, grading seaward into sediment starved bedforms associated with bioclastic gravels. Where sufficient sediment exists in local depocenters, very large dunes form discontinuous fields along the outer shelf.The seismic stratigraphy of the outer shelf reflects the effects of postglacial flooding by rising sea levels and increasing current impingement by the Agulhas Current. The Holocene wave ravinement surface is overlain by flat-lying strata (early dune development and dune amalgamation with first current exposure), in turn covered by hummocky, sub-horizontal aggrading beds (amalgamation), overlain by inclined cross-bedded packages (lee faces of the bedforms formed during migration and full current interaction).Morphometric analyses show that for both the inner and outer shelf, no relationships exist between water depth, wavelength and spacing. Height to spacing (H/L) relationships are weak but nevertheless show a broadly positive trend. Bedform heights are lower on the inner shelf compared to the outer shelf, but bedform spacing is greater on the inner shelf, with a 40% overlap in H/L indices observed between the two areas. The departures in overlap can be linked to the competing offshore Agulhas Current and the inshore wave-dominated processes. Bedforms of the inner shelf plot below the global H/L mean and can be related to the more infrequent incursions of the Agulhas Current core. At the time of survey, the Agulhas Current was likely situated well offshore, resulting in reduced current activity in the survey area resulting in rounding of the dune crests, degradation of the dune crests and trough infilling. On the outer shelf, the H/L values plot above the mean global trend, suggesting vertical accretion due to the faster currents. Crest rounding and downlapping of the upstream lee faces onto the downstream stoss faces indicate dune degradation, which is related to a seaward location of the Agulhas Current at the time of survey.

Detached breakwaters, yes or not? A modelling approach to evaluate and plan their removal

Detached breakwaters have been widely employed as a measure against beach erosion and for coastal protection. However, this type of structures may cause different critical issues, and the advantages are not always evident. Water stagnation, rip currents development in the gaps between multiple structures, and obstruction of the natural panorama are well-recognised issues. However, their removal is always problematic because it is generally associated with rapid erosion of the beach and high costs. This work proposes a modelling approach to obtain a preliminary evaluation of a theoretical removal intervention and discusses its possible consequences. The study case is the Moneglia beach, a tourist beach located on the eastern Ligurian coast, NW Italy. The beach is characterised by the presence of three detached breakwaters, arranged over the entire length of the beach. A dataset consisting of LiDAR data, multibeam data, single-beam data and DGPS data was used to obtain an accurate digital elevation model (DEM) of the study area. Subsequently, the XBeach model was used to simulate three scenarios: i) state-of-the-art scenario (S0), ii) detached breakwaters removal scenario (S1), iii) detached breakwaters removal scenario + nourishment (S1N). The S1 scenario was implemented to evaluate the beach morphodynamic response in the case of a removal intervention. S1N was implemented to simulate a beach recovery plan through a beach nourishment intervention. Once the S1N final scenario was obtained, XBeach was implemented to get a comparison with the sea flooding hazard in the S0 and S1 scenarios. The sea flooding hazard assessment was performed considering storm events with a return time of 50 and 100 years, respectively. The results showed both the potential of the XBeach model as a tool and the sustainability of a theoretical detached breakwater removal intervention.

Multiresolution Satellite-Derived Bathymetry in Shallow Coral Reefs: Improving Linear Algorithms with Geographical Analysis

da Silveira, C.B.L.; Strenzel, G.M.R.; Maida, M.; Araujo, T.C.M., and Ferreira, B.P., 2020. Multiresolution satellite-derived bathymetry in shallow coral reefs: Improving linear algorithms with geographical analysis. Journal of Coastal Research, 36(6), 1247–1265. Coconut Creek (Florida), ISSN 0749-0208.Bathymetric maps are one of the first steps for most hydrological and ecological studies of the seascape, as depth is a determinant factor in the distribution of organisms, patterns of wave exposure, and coastal circulation. The coral reefs of Tamandare-Brazil, located at Costa dos Corais marine protected area (MPA), encompass a mosaic of interconnected habitats of complex geomorphology, including coral reefs, algal, and seagrass beds. These coastal habitats are subjected to chronic impacts such as sedimentation, reef erosion, and increasing human use, leading to habitat loss. Despite their social and ecological importance and the conservation measures in place, bathymetric and habitat maps of this coast are lacking. Indeed, in situ surveys are not always feasible in shallow coral reef areas. The present study offers a detailed bathymetric mapping of the area using multiresolution satellite imagery. One Landsat-8 (December 2016) and one WorldView-03 (February 2017) imagery were used to derive medium (30-m) and high-resolution (2-m) bathymetry of the study area. Single-beam echo sounder surveys were performed to obtain field data to calibrate the depth-retrieving algorithms: linear model, ratio band model, principal component analyses of the transformed bands, and geographically weighted regressions (GWR). For both resolution datasets, results showed that the algorithms' RMS were significantly improved by the GWR technique (RMS > 0.9) because of adaptability to the bottom heterogeneity found in complex areas such as coral reefs. Specific geomorphological reef zones were recognizable in the resulting bathymetric maps, such as intrareef lagoon, reef crest, fore-reef, and reef flat. This research concluded that affordable methods such as single-beam data coupled with satellite imagery through GWR can provide the required inputs for mapping shallow areas with complex relief. Such results may be further used to habitat mapping, necessary to inform the multiple-use zonation foreseen in MPA management plans.

Estimating bed material fluxes upstream and downstream of a controlled large bifurcation ‐ the Mississippi‐Atchafalaya River diversion

AbstractBed material transport at river bifurcations is crucial for channel stability and downstream geomorphic dynamics. However, measurements of bed material transport at bifurcations of large alluvial rivers are difficult to make, and standard estimates based on the assumption of proportional partitioning of flow and bedload transport at bifurcations may be erroneous. In this study, we employed a combined approach based on observed topographic change (erosion/deposition) and bed material transport predicted from a one‐dimensional model to investigate bed material fluxes near the engineering‐controlled Mississippi‐Atchafalaya River diversion, which is of great importance to sediment distribution and delivery to Louisiana's coast. Yang's (1973) sediment transport equation was utilized to estimate daily bed material loads upstream, downstream, and through the diversion during 2004–2013. Bathymetric changes in these channels were assessed with single beam data collected in 2004 and 2013. Results show that over the study period, 24% of the Mississippi River flow was diverted into the Atchafalaya River, while the rest remained in the mainstem Mississippi. Upstream of the diversion, the bed material yield was predicted to be 201 million metric tons (MT), of which approximately 35 MT (i.e., 17%) passed through the bifurcation channel to the Atchafalaya River. The findings from this study reveal that in the mainstem Mississippi, the percentage of bed material diversion (83%) is larger than the percentage of flow diversion (76%); Conversely, the diversion channel receives a disproportionate amount of flow (24%) relative to bed material supply (17%). Consequently, severe bed scouring occurred in the controlled Outflow Channel to the Atchafalaya River, while riverbed aggradation progressed in the mainstem Mississippi downstream of the diversion structures, implying reduced flow capacity and potential risk of a high backwater during megafloods. The study demonstrates that Yang's sediment transport equation provides plausible results of bed material fluxes for a highly complicated large river diversion, and that integration of the sediment transport equation with observed morphological changes in riverbed is a valuable approach to investigate sediment dynamics at controlled river bifurcations.

Detection of Stones in Marine Habitats Combining Simultaneous Hydroacoustic Surveys

Exposed stones in sandy sublittoral environments are hotspots for marine biodiversity, especially for benthic communities. The detection of single stones is principally possible using sidescan-sonar (SSS) backscatter data. The data resolution has to be high to visualize the acoustic shadows of the stones. Otherwise, stony substrates will not be differentiable from other high backscatter substrates (e.g., gravel). Acquiring adequate sonar data and identifying stones in backscatter images is time consuming because it usually requires visual-manual procedures. To develop a more efficient identification and demarcation procedure of stone fields, sidescan sonar and parametric echo sound data were recorded within the marine protected area of “Sylt Outer Reef” (German Bight, North Sea). The investigated area (~5.900 km2) is characterized by dispersed heterogeneous moraine and marine deposits. Data from parametric sediment echo sounder indicate hyperbolas at the sediment surface in stony areas, which can easily be exported. By combining simultaneous recorded low backscatter data and parametric single beam data, stony grounds were demarcated faster, less complex and reproducible from gravelly substrates indicating similar high backscatter in the SSS data.

The Southwest Indian Ocean Bathymetric Compilation (swIOBC)

AbstractWe present a comprehensive regional bathymetric data compilation for the southwest Indian Ocean (swIOBC) covering the area from 4°S to 40°S and 20°E to 45°E with a spatial resolution of 250 m. For this, we used multibeam and singlebeam data as well as data from global bathymetric data compilations. We generated the swIOBC using an iterative approach of manual data cleaning and gridding, accounting for different data qualities and seamless integration of all different kinds of data. In comparison to existing bathymetric charts of this region, the new swIOBC benefits from nearly four times as many data‐constrained grid cells and a higher resolution, and thus reveals formerly unseen seabed features. In the central Mozambique Basin a surprising variety of landscapes were discovered. They document a deep reaching influence of the Mozambique Current eddies. Details of the N‐S trending Zambezi Channel could be imaged in the central Mozambique Basin.

Automatic Mexico Gulf Oil Spill Detection from Radarsat-2 SAR Satellite Data Using Genetic Algorithm

In this work, a genetic algorithm is exploited for automatic detection of oil spills of small and large size. The route is achieved using arrays of RADARSAT-2 SAR ScanSAR Narrow single beam data obtained in the Gulf of Mexico. The study shows that genetic algorithm has automatically segmented the dark spot patches related to small and large oil spill pixels. This conclusion is confirmed by the receiveroperating characteristic (ROC) curve and ground data which have been documented. The ROC curve indicates that the existence of oil slick footprints can be identified with the area under the curve between the ROC curve and the no-discrimination line of 90%, which is greater than that of other surrounding environmental features. The small oil spill sizes represented 30% of the discriminated oil spill pixels in ROC curve. In conclusion, the genetic algorithm can be used as a tool for the automatic detection of oil spills of either small or large size and the ScanSAR Narrow single beam mode serves as an excellent sensor for oil spill patterns detection and surveying in the Gulf of Mexico.

Automatic Detection of Oil Spill Disasters Along Gulf of Mexico Using RADARSAT-2 SAR Data

In this work, the genetic algorithm is utilised for automatic detection of oil spills under wind speed conditions larger than 20 ms−1. The procedure is implemented using sequences of RADARSAT-2 SAR ScanSAR Narrow single beam data acquired in the Gulf of Mexico. The study demonstrates that implementing crossover allows for generation of accurate oil spills pattern. This conclusion is confirmed by the receiver–operating characteristic (ROC) curve. The ROC curve indicates that the existence of oil slick footprints can be identified with the area under the ROC curve and the no-discrimination line of 85 %, which is greater than that of other surrounding environmental features. In conclusion, the genetic algorithm can be used as a tool for the automatic detection of oil spills and the ScanSAR Narrow single beam mode serves as an excellent sensor for oil spill detection and surveying under wind speed larger than 20 ms−1.

Increasing the accessibility of acoustic data through global access and imagery

Abstract The National Oceanographic and Atmospheric Administration (NOAA) uses water column sonar data to assess physical and biological characteristics from the ocean surface to the seabed. Acoustic surveys produce large volumes of data that can deliver valuable information beyond their original collection purpose if the data are properly managed, discoverable, and accessible to the public. NOAA's National Centers for Environmental Information, in partnership with NOAA's National Marine Fisheries Service and the University of Colorado, have created a national archive for water column sonar data to help achieve these goals. Through these efforts, over 21 TB of sonar data are now publicly available. Raw sonar files are difficult to interpret due to their size, complexity, and proprietary format. In order for users to understand the quality and composition of large volumes of archived data more easily, several visualization products were explored. Three processing methods were applied to multifrequency single-beam data (Simrad EK60) collected off the US northwest coast between 2007 and 2013. One method illustrates these complex data in a single image using a novel colour scale [multifrequency single-beam imaging (MFSBI)], another examines the nautical area scattering coefficients between two frequencies (ΔNASC), and the third indices the data into acoustic classifications [multifrequency indicator (MFI)]. The ability to apply the algorithms efficiently to multiyear datasets was explored. MFSBI proved effective at conveying the composition of the data and was easily adaptable to automated processing. ΔNASC, which required manual seabed corrections, illustrated a generalized pattern for changes in the water column across the shelf. MFI provided an empirically based statistical approach but will require more effort in the near term to evaluate and assess the accuracy and precision of each classification. Overall, spatio-temporal patterns of the acoustic backscatter identified large interannual variations in composition with the continental shelf break often playing a key role in attracting biological assemblages.

Fourier-Transform Infrared Absorption Spectroscopy in Binary Hydrocarbon-Alcohol Single Droplet Evaporation

Broadband absorption spectroscopy, by way of FTIR, was used to investigate the vapor cloud of a single millimeter sized liquid droplet suspended by a syringe as it evaporates at standard conditions. Single beam data were collected every 8 seconds resulting in a time-resolved record. Species concentrations were tracked using their resonant absorption peaks and correlated with a multidimensional numerical model. The numerical model combined a Gaussian beam transmission through a temporally changing spherical vapor cloud with radial concentration gradients, informed by theD2law and interpreted using the Abel transform. There was fair agreement with temporal evaporation trends for single component runs. Multicomponent experiments of ethanol and isooctane showed synergistic blending effects and preferential evaporation of ethanol. Droplets were also suspended by a thermocouple to track the droplet temperature over time as they were subject to evaporative cooling. This work is the foundation of a basic technique for collecting useful data to inform a complex transport problem.

Genetic algorithm for oil spill automatic detection using synthetic aperture radar

<div> <p>This work has exploited a Genetic algorithm for oil spill automatic detection. This is implemented to sequences of RADARSAT-2 SAR  ScanSAR narrow single beam data in the Gulf of Mexico. The study shows that the implementation of crossover is generated an accurate oil slick pattern. This is confirmed by using the receiver–operational characteristics (ROC) curve. The ROC curve endorses the existence of oil slick footprints with 90%, which is larger than other surrounding environment features. It can be pronounced that ScanSAR Narrow single beam is the tremendous promise sensor for oil spill detection and survey. In conclusion, the Genetic Algorithm can be used as an automatic detection tool for oil spill.</p> </div> <p> </p>

Automatic detection of oil spills in the Gulf of Mexico from RADARSAT-2 SAR satellite data

This work aimed to design optimization procedures for oil spill footprint automatic detection from synthetic aperture radar (SAR) satellite data. The main motivation of this work is to utilize a genetic algorithm (GA) without involving post-classification image processing tools for oil spill footprint boundary shape optimizations that involve local and global optimizations. The procedures are operated using sequences of RADARSAT-2 SAR ScanSAR Narrow single beam data acquired in the Gulf of Mexico. The study shows that the GA has high performance for oil spill boundary shape automatic optimization and detection. This provides evidence with standard error of 0.12 and non-significant differences with different acquisition dates. The ScanSAR Narrow mode data shows the extremely existing of 90 % of the oil spill footprint compared to the sea surface roughness and look-alikes. It can be said that Scan SAR Narrow mode can monitor oil spill disasters. In conclusion, the GA can be used as an automatic tool for oil spill without involving other post-image processing classification.

Calibration diagnostic and updating strategy based on quantitative modeling of near-infrared spectral residuals.

A diagnostic and updating strategy is explored for multivariate calibrations based on near-infrared spectroscopy. For use with calibration models derived from spectral fitting or decomposition techniques, the proposed method constructs models that relate the residual concentrations remaining after a prediction to the residual spectra remaining after the information associated with the calibration model has been extracted. This residual modeling approach is evaluated for use with partial least-squares (PLS) models for predicting physiological levels of glucose in a simulated biological matrix. Residual models are constructed with both PLS and a hybrid technique based on the use of PLS scores as inputs to support vector regression. Calibration and residual models are built with both absorbance and single-beam data collected over 416 days. Effective models for the spectral residuals are built with both types of data and demonstrate the ability to diagnose and correct deviations in performance of the calibration model with time.

Utilization of a genetic algorithm for the automatic detection of oil spill from RADARSAT-2 SAR satellite data

In this work, a genetic algorithm is applied for the automatic detection of oil spills. The procedure is implemented using sequences from RADARSAT-2 SAR ScanSAR Narrow single-beam data acquired in the Gulf of Mexico. The study demonstrates that the implementation of crossover allows for the generation of an accurate oil spill pattern. This conclusion is confirmed by the receiver-operating characteristic (ROC) curve. The ROC curve indicates that the existence of oil slick footprints can be identified using the area between the ROC curve and the no-discrimination line of 90%, which is greater than that of other surrounding environmental features. In conclusion, the genetic algorithm can be used as a tool for the automatic detection of oil spills, and the ScanSAR Narrow single-beam mode serves as an excellent sensor for oil spill detection and survey.

Seabed Mixed Sediment Classification with Multi-beam Echo Sounder Backscatter Data in Jiaozhou Bay

The multi-beam echo sounder system can not only obtain high-precision seabed bathymetry data, but also obtain high-resolution seabed backscatter strength data. A number of studies have applied acoustic remote sensing method to classify seabed sediment type with multi-beam backscatter strength data, and obtained better classification results than the traditional sediment sampling method. However, these studies mainly focus on the single type sediment classification or seabed mixed sediment classification using single beam data, not multi-beam echo sounder data. Based on backscatter strength data by a high-frequency (300 kHz) Simrad EM3000 multi-beam echo sounder and seabed sediment sampling data of Jiaozhou Bay in Qingdao, China, we establish the relation model between seabed backscatter strength and sediment type characteristics after data processing and corrections. The purpose of data processing is to diminish or weaken the influence of local bottom slope and near nadir reflection on backscatter strength data. Processed backscatter strength data through corrections and compensations can better characterize the features of the seabed sediments. Applying the back propagation neural network method based on genetic algorithm, we present a fast and accurate seabed classification method in this paper which could identify not just a single type of sediment-like rock, sand but also mixed types of sediment like sand gravel, clayey silt and sand-silt-clay.

An evaluation of compiled single-beam bathymetry data as a basis for regional sediment and biotope mapping

Abstract Maps of surficial sediment distribution and benthic habitats or biotopes provide invaluable information for ocean management and are at the core of many seabed mapping initiatives, including Norway's national offshore mapping programme MAREANO (www.mareano.no). Access to high-quality multibeam echosounder data (bathymetry and backscatter) has been central to many of MAREANO's mapping activities, but in order to maximize the cost-effectiveness of future mapping and ensure timely delivery of scientific information, seabed mappers worldwide may increasingly need to look to existing bathymetry data as a basis for thematic maps. This study examines the potential of compiled single-beam bathymetry data for sediment and biotope mapping. We simulate a mapping scenario where full coverage multibeam data are not available, but where existing bathymetry datasets are supplemented by limited multibeam data to provide the basis for thematic map interpretation and modelling. Encouraging results of sediment interpretation from the compiled bathymetry dataset suggest that production of sediment grain size distribution maps is feasible at a 1:250 000 scale or coarser, depending on the quality of available data. Biotope modelling made use of full-coverage predictor variables based on (i) multibeam data, and (ii) compiled single-beam data supplemented by limited multibeam data. Using the same response variable (biotope point observations obtained from video data), the performance of the respective models could be assessed. Biotope distribution maps based on the two datasets are visually similar, and performance statistics also indicate there is little difference between the models, providing a comparable level of information for regional management purposes. However, whilst our results suggest that using compiled bathymetry data with limited multibeam is viable as a basis for regional sediment and biotope mapping, it is not a substitute. Backscatter data and the better feature resolution provided by multibeam data remain of great value for these and other purposes.

A surrogate-based metaheuristic global search method for beam angle selection in radiation treatment planning

An important element of radiation treatment planning for cancer therapy is the selection of beam angles (out of all possible coplanar and non-coplanar angles in relation to the patient) in order to maximize the delivery of radiation to the tumor site and minimize radiation damage to nearby organs-at-risk. This category of combinatorial optimization problem is particularly difficult because direct evaluation of the quality of treatment corresponding to any proposed selection of beams requires the solution of a large-scale dose optimization problem involving many thousands of variables that represent doses delivered to volume elements (voxels) in the patient. However, if the quality of angle sets can be accurately estimated without expensive computation, a large number of angle sets can be considered, increasing the likelihood of identifying a very high quality set. Using a computationally efficient surrogate beam set evaluation procedure based on single-beam data extracted from plans employing equally-spaced beams (eplans), we have developed a global search metaheuristic process based on the nested partitions framework for this combinatorial optimization problem. The surrogate scoring mechanism allows us to assess thousands of beam set samples within a clinically acceptable time frame. Tests on difficult clinical cases demonstrate that the beam sets obtained via our method are of superior quality.

Interpretación batimétrica del área de Valparaíso: comentarios sobre el artículo de HP Vergara & R Astudillo, 'Altos estructurales costa afuera en la región de Valparaíso, Chile central'

A submarine alignment at 32o-33oS offshore within the Valparaiso Region, Chile, is composed by three peaks at 200, 733 and 880 m below sea level, which were identified by Vergara & Astudillo (2008) using a bathymetric public data base. This is composed by bathymetry which is estimated by satellite altimetry, and from ship surveys. However, after modeling recent similar data bases and also processing and modeling available multibeam bathymetry with ~100% of spatial coverage, those highs seem to be absent. The apparent creation of bathymetric artifacts would have been due to the inclusion of bad single beam data of a specific ships sounding track. The hypothesis regarding the origin of the alignment associated with the vertical displacement of a block at the outer shelf, would not be valid.

Commissioning of the ATLAS Tile Calorimeter with Single Beam and First Collisions

The ATLAS hadronic barrel calorimeter was tested using dedicated calibration systems, cosmic ray muons and single beam data prior to the start of collisions. Before collisions, in addition to the hardware maintenance, the verification of the electromagnetic energy scale set during test-beam and the read-out synchronization of the tile calorimeter were undertaken. The results obtained showed that the calorimeter was well calibrated and ready for the challenges of the LHC collisions.

The ATLAS Liquid Argon Calorimeter: Overview and Performance

The LHC is delivering collision data since November 2009 up to a 7 TeV center of mass energy world record. The ATLAS experiment has collected more than 1 nb−1 collision data until the end of April 2010. The ATLAS Liquid Argon (LAr) calorimeter system, operational since August 2006, has been carefully commissioned and checked using collision data as well as single beam data and cosmic data taken previously. This paper gives an overview of the ATLAS LAr calorimeters status and performance up to the latest 7 TeV collision data. Results on the LAr calorimeters high voltage, LAr temperature, purity and readout electronic stability as well as results on timing alignments and early collision performances are shown here. All indicates that the ATLAS LAr calorimeter system is well commissioned and shows good and promising performances for the physics at LHC era.