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Full-Text Articles in Physical Sciences and Mathematics

Scientific Basis For Safely Shutting In The Macondo Well After The April 20, 2010 Deepwater Horizon Blowout, Stephen H. Hickman, Paul A. Hsieh, Walter D. Mooney, Catherine B. Enomoto, Philip H. Nelson, Larry A. Mayer, Thomas C. Weber, Kathryn Moran, P. B. Flemings, Marcia Mcnutt Dec 2012

Scientific Basis For Safely Shutting In The Macondo Well After The April 20, 2010 Deepwater Horizon Blowout, Stephen H. Hickman, Paul A. Hsieh, Walter D. Mooney, Catherine B. Enomoto, Philip H. Nelson, Larry A. Mayer, Thomas C. Weber, Kathryn Moran, P. B. Flemings, Marcia Mcnutt

Center for Coastal and Ocean Mapping

As part of the government response to the Deepwater Horizon blowout, a Well Integrity Team evaluated the geologic hazards of shutting in the Macondo Well at the seafloor and determined the conditions under which it could safely be undertaken. Of particular concern was the possibility that, under the anticipated high shut-in pressures, oil could leak out of the well casing below the seafloor. Such a leak could lead to new geologic pathways for hydrocarbon release to the Gulf of Mexico. Evaluating this hazard required analyses of 2D and 3D seismic surveys, seafloor bathymetry, sediment properties, geophysical well logs, and drilling …


Calibration Of Multibeam Echo Sounders: A Comparison Between Two Methodologies, Carlo Lanzoni, Thomas C. Weber Nov 2012

Calibration Of Multibeam Echo Sounders: A Comparison Between Two Methodologies, Carlo Lanzoni, Thomas C. Weber

Center for Coastal and Ocean Mapping

Multibeam echo sounders (MBES) are widely used in applications like seafloor imaging, fisheries, and habitat mapping. Calibration of acoustic backscatter is an important aspect of understanding and validating the performance of a MBES. Combined transmit/receive beampattern calibrations were performed on a 200 kHz Reson Seabat 7125 MBES in the acoustic tank of the University of New Hampshire utilizing two different methodologies. The first methodology employs fixed standard target spheres and a high accuracy/high resolution rotation mechanism. This method, similar to that proposed by Foote et al ["Protocols forcalibrating multibeam sonar", J. Acoust. Soc. Am. 117(4), 2005], is designed for a …


Potentially Polluting Marine Sites Geodb: An S-100 Geospatial Database As An Effective Contribution To The Protection Of The Marine Environment, Giuseppe Masetti, Brian R. Calder, Lee Alexander Nov 2012

Potentially Polluting Marine Sites Geodb: An S-100 Geospatial Database As An Effective Contribution To The Protection Of The Marine Environment, Giuseppe Masetti, Brian R. Calder, Lee Alexander

Center for Coastal and Ocean Mapping

Potentially Polluting Marine Sites (PPMS) are objects on, or areas of, the seabed that may release pollution in the future. A rationale for, and design of, a geospatial database to inventory and manipu-late PPMS is presented. Built as an S-100 Product Specification, it is specified through human-readable UML diagrams and implemented through machine-readable GML files, and includes auxiliary information such as pollution-control resources and potentially vulnerable sites in order to support analyses of the core data. The design and some aspects of implementation are presented, along with metadata requirements and structure, and a perspective on potential uses of the database.


Using A Cruise Report To Generate Xml Metadata, Briana M. Sullivan Oct 2012

Using A Cruise Report To Generate Xml Metadata, Briana M. Sullivan

Center for Coastal and Ocean Mapping

Since 2005 metadata generation at the Center for Coastal and Ocean Mapping/Joint Hydrographic Center has slowly evolved from a painful and tedious process of copying and pasting, to generate hundreds of files, to using an automated system that generates 90% of the needed metadata from the data collected on cruises. However there remained one piece missing to the automated system- the wordy part of the metadata that deals with information such as the attribute accuracy report, abstract and the process description. This information cannot be mined from the raw survey data. This paper illustrates how to generate a template from …


Modular Autonomous Biosampler (Mab)- A Prototype System For Distinct Biological Size-Class Sampling And Preservation, Arthur Trembanis, Craig Cary, Val E. Schmidt, Don Clarke, Tristan Crees, Eric Jackson Oct 2012

Modular Autonomous Biosampler (Mab)- A Prototype System For Distinct Biological Size-Class Sampling And Preservation, Arthur Trembanis, Craig Cary, Val E. Schmidt, Don Clarke, Tristan Crees, Eric Jackson

Center for Coastal and Ocean Mapping

Presently, there is a community wide deficiency in our ability to collect and preserve multiple size-class biologic samples across a broad spectrum of oceanographic platforms (e.g. AUVs, ROVs, and Ocean Observing System Nodes). This is particularly surprising in comparison to the level of instrumentation that now exists for acquiring physical and geophysical data (e.g. side-scan sonar, current profiles etc.), from these same platforms. We present our effort to develop a low-cost, high sample capacity modular,autonomous biological sampling device (MAB). The unit is designed for filtering and preserving 3 distinct biological size-classes (including bacteria), and is deployable in any aquatic setting …


Measurement Of Micro-Bathymetry With A Gopro Underwater Stereo Camera Pair, Val E. Schmidt, Yuri Rzhanov Oct 2012

Measurement Of Micro-Bathymetry With A Gopro Underwater Stereo Camera Pair, Val E. Schmidt, Yuri Rzhanov

Center for Coastal and Ocean Mapping

A GO-PRO underwater stereo camera kit has been used to measure the 3D topography (bathymetry) of a patch of seafloor producing a point cloud with a spatial data density of 15 measurements per 3 mm grid square and an standard deviation of less than 1 cm A GO-PRO camera is a fixed focus, 11 megapixel, still-frame (or 1080p high-definition video) camera, whose small form-factor and water-proof housing has made it popular with sports enthusiasts. A stereo camera kit is available providing a waterproof housing (to 61 m / 200 ft) for a pair of cameras. Measures of seafloor micro-bathymetrycapable of …


Chum: Chart Update Mashup, Briana M. Sullivan Oct 2012

Chum: Chart Update Mashup, Briana M. Sullivan

Center for Coastal and Ocean Mapping

The Chart Update Mash up (ChUM™) consists of various APIs/Technologies that when brought together allow for intuitive georeferenced visualization of the Critical Chart Updates published by the Office of Coast Survey (OCS). Each component of ChUM™ will be described in this paper with an explanation of how each piece works together to form ChUM™. Figure 1 shows the basic building blocks that make up ChUM™. At the base of the structure (in blue) is the data that OCS disseminates to the public via its website/web-services: Raster Nautical Charts, the CRIT data (critical corrections to the chart), and the Coast Pilot. …


U.S. Law Of The Sea Cruise To Map And Sample The Us Arctic Ocean Margin, Larry A. Mayer, Andy Armstrong Sep 2012

U.S. Law Of The Sea Cruise To Map And Sample The Us Arctic Ocean Margin, Larry A. Mayer, Andy Armstrong

Center for Coastal and Ocean Mapping

U.S. Law of the Sea cruise to map and sample the US Arctic Ocean margin

CRUISE HEALY 1202

August 25 to September 27, 2012

Barrow, AK to Dutch Harbor, AK


Sediment Mixing In The Tropical Pacific And Radiolarian Stratigraphy, Ted C. Moore Jr, Larry A. Mayer, Mitchell Lyle Aug 2012

Sediment Mixing In The Tropical Pacific And Radiolarian Stratigraphy, Ted C. Moore Jr, Larry A. Mayer, Mitchell Lyle

Center for Coastal and Ocean Mapping

The reworking of older radiolarian microfossils into near-surface sediments of the tropical Pacific has long been the source of confusion for the development of radiolarian stratigraphy and of puzzlement over the mechanism(s) that could effect such pervasive reworking. Widespread dissolution “pits” in the sediments of the tropical Pacific are believed to be associated with hydrothermal circulation cells in the older oceanic crust and are here linked to processes which expose older sections and inject older non-carbonate material into near-bottom waters. Discharging waters of these circulation cells tend to dissolve carbonate in near-surface sediments; thus, only the non-carbonate material (including radiolarians) …


R/V Kilo Moana Multibeam Echosounder System Review, Jonathan Beaudoin Jul 2012

R/V Kilo Moana Multibeam Echosounder System Review, Jonathan Beaudoin

Center for Coastal and Ocean Mapping

No abstract provided.


On Importance Of Acoustic Backscatter Corrections For Texture-Based Seafloor Characterization, E Fakiris, Yuri Rzhanov, D Zoura Jul 2012

On Importance Of Acoustic Backscatter Corrections For Texture-Based Seafloor Characterization, E Fakiris, Yuri Rzhanov, D Zoura

Center for Coastal and Ocean Mapping

Seafloor segmentation and characterization based on local textural properties of acoustic backscatter has been a subject of research since 1980s due to the highly textured appearance of sonar images. The approach consists of subdivision of sonar image in a set of patches of certain size and calculation of a vector of features reflecting the patch texture. Advance of multibeam echosounders (MBES) allowed application of texture-based techniques to real geographical space, and predicted boundaries between acoustic facies became experimentally verifiable. However, acoustic return from uncalibrated MBES produces artifacts in backscatter mosaics, which in turn affects accuracy of delineation. Development of Geocoder …


The International Bathymetric Chart Of The Arctic Ocean (Ibcao) Version 3.0, Martin Jakobsson, Larry A. Mayer, Bernard Coakley, Julian A. Dowdeswell, Steve Forbes, Boris Fridman, Hanne Hodnesdal, Riko Noormets, Richard Pedersen, Michele Rebesco, Hans Werner Schenke, Yulia Zarayskaya, Daniela Accettella, Andy Armstrong, Robert M. Anderson, Paul Beinhoff, Angelo Camerlenghi, Ian Church, Margo Edwards, James V. Gardner, John K. Hall, Benjamin Hell, Ole Hestvik, Yngve Krisoffersen, Christian Marcussen, Rezwen Mohammad, David Mosher, Son V. Nghiem, Maria Teresa Pedrosa, Paola G. Travaglini, Pauline Weatherall Jun 2012

The International Bathymetric Chart Of The Arctic Ocean (Ibcao) Version 3.0, Martin Jakobsson, Larry A. Mayer, Bernard Coakley, Julian A. Dowdeswell, Steve Forbes, Boris Fridman, Hanne Hodnesdal, Riko Noormets, Richard Pedersen, Michele Rebesco, Hans Werner Schenke, Yulia Zarayskaya, Daniela Accettella, Andy Armstrong, Robert M. Anderson, Paul Beinhoff, Angelo Camerlenghi, Ian Church, Margo Edwards, James V. Gardner, John K. Hall, Benjamin Hell, Ole Hestvik, Yngve Krisoffersen, Christian Marcussen, Rezwen Mohammad, David Mosher, Son V. Nghiem, Maria Teresa Pedrosa, Paola G. Travaglini, Pauline Weatherall

Center for Coastal and Ocean Mapping

[1] The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum-Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved …


Light Field And Water Clarity Simulation Of Natural Environments In Laboratory Conditions, Shachak Pe'eri, Glenn T. Shwaery Jun 2012

Light Field And Water Clarity Simulation Of Natural Environments In Laboratory Conditions, Shachak Pe'eri, Glenn T. Shwaery

Center for Coastal and Ocean Mapping

Simulation of natural oceanic conditions in a laboratory setting is a challenging task, especially when that environment can be miles away. We present an attempt to replicate the solar radiation expected at different latitudes with varying water clarity conditions up to 30 m in depth using a 2.5 m deep engineering tank at the University of New Hampshire. The goals of the study were: 1) to configure an underwater light source that produced an irradiance spectrum similar to natural daylight with the sun at zenith and at 60° under clear atmospheric conditions, and 2) to monitor water clarity as a …


Linking Goniometer Measurements To Hyperspectral And Multi-Sensor Imagery For Retrieval Of Beach Properties And Coastal Characterization, Charles M. Bachmann, Deric Gray, Andrei Abelev, William D. Philpot, Marcos J. Montes, Robert A. Fusina, Joseph Musser, Rong-Rong Li, Michael Vermillion, Geoffrey Smith, Daniel Korwan, Charlotte Snow, David W. Miller, Joan Gardner, Matt Sletten, Georgi Georgiev, Barry Truitt, Marcus Kilmon, Jon Sellars, Jason Woolard, Christopher Parrish, A. Schwarzschild May 2012

Linking Goniometer Measurements To Hyperspectral And Multi-Sensor Imagery For Retrieval Of Beach Properties And Coastal Characterization, Charles M. Bachmann, Deric Gray, Andrei Abelev, William D. Philpot, Marcos J. Montes, Robert A. Fusina, Joseph Musser, Rong-Rong Li, Michael Vermillion, Geoffrey Smith, Daniel Korwan, Charlotte Snow, David W. Miller, Joan Gardner, Matt Sletten, Georgi Georgiev, Barry Truitt, Marcus Kilmon, Jon Sellars, Jason Woolard, Christopher Parrish, A. Schwarzschild

Center for Coastal and Ocean Mapping

In June 2011, a multi-sensor airborne remote sensing campaign was flown at the Virginia Coast Reserve Long Term Ecological Research site with coordinated ground and water calibration and validation (cal/val) measurements. Remote sensing imagery acquired during the ten day exercise included hyperspectral imagery (CASI-1500), topographic LiDAR, and thermal infra-red imagery, all simultaneously from the same aircraft. Airborne synthetic aperture radar (SAR) data acquisition for a smaller subset of sites occurred in September 2011 (VCR'11). Focus areas for VCR'11 were properties of beaches and tidal flats and barrier island vegetation and, in the water column, shallow water bathymetry. On land, cal/val …


Develping A Methodology For The Mapping And Characterization Of The Nigerian Coastline Using Remote Sensing, Olumide Fadahunsi, Shachak Pe'eri, Lee Alexander, Christopher Parrish May 2012

Develping A Methodology For The Mapping And Characterization Of The Nigerian Coastline Using Remote Sensing, Olumide Fadahunsi, Shachak Pe'eri, Lee Alexander, Christopher Parrish

Center for Coastal and Ocean Mapping

Coastline delineation is important in maritime boundary determination, as well as for analyzing coastline change rates due to coastal erosion, sea level change, storms, and other causes. Coastline change rate estimates depend on the uncertainty of the current and historical coastlines used in the analysis, which, in turn, depend on the surveying technologies and techniques that were originally used. Current techniques for coastline mapping include photogrammetric delineation using tide-coordinated aerial imagery. However, in many developing countries, the charted coastlines may have been inadequately and inconsistently mapped largely due to inadequate resources. This paper describes the use of an automated technique …


Development Of A Geo-Spatial Analysis Methodology For Assessing The Adequacy Of Hydrographic Surveying And Nautical Charts, Chukwuma Azuike, Shachak Pe'eri, Lee Alexander, Christopher Parrish, Andy Armstrong May 2012

Development Of A Geo-Spatial Analysis Methodology For Assessing The Adequacy Of Hydrographic Surveying And Nautical Charts, Chukwuma Azuike, Shachak Pe'eri, Lee Alexander, Christopher Parrish, Andy Armstrong

Center for Coastal and Ocean Mapping

IHO Publication C-55 (Status of Hydrographic Surveying and Nautical Charting Worldwide) contains information about the progress of hydrographic surveying and nautical charting for a country with navigable waters under its jurisdiction. Listed primarily as percent coverage, it is difficult to use this information to determine: 1) if the current level of surveying or charting is adequate or in need of action, or 2) can be used to compare different locations. An analysis and assessment methodology has been developed to assess the adequacy hydrographic surveying and nautical charting coverage. Indications of chart adequacy and completeness as depicted on current charts or …


Developing A Gis-Database And Risk Index For Potentially Polluting Marine Sites, Giuseppe Masetti, Brian R. Calder, Lee Alexander May 2012

Developing A Gis-Database And Risk Index For Potentially Polluting Marine Sites, Giuseppe Masetti, Brian R. Calder, Lee Alexander

Center for Coastal and Ocean Mapping

The increasing availability of geospatial marine data provides an opportunity for hydrographic offices to contribute to the identification of “Potentially Polluting Marine Sites” (PPMS). These include shipwrecks, oil rigs, pipelines, and dumping areas. To adequately assess the environmental risk of these sites, relevant information must be collected and converted into a multi-scale geodatabase suitable for site inventory and geo-spatial analysis. In addition, a Risk Index – representing an assessment of the magnitude of risk associated with any site – can be derived to determine the potential impacts of these PPMS. However, the successful collection and integration of PPMS information requires …


Usage Of Videomosaic For Computer Aided Analysis Of North Sea Hard Bottom Underwater Video For Baseline Study Of Offshore Windmill Park, Aleksej Shashkov, Thomas Dahlgren, Marie-Lise Schlappy, Yuri Rzhanov May 2012

Usage Of Videomosaic For Computer Aided Analysis Of North Sea Hard Bottom Underwater Video For Baseline Study Of Offshore Windmill Park, Aleksej Shashkov, Thomas Dahlgren, Marie-Lise Schlappy, Yuri Rzhanov

Center for Coastal and Ocean Mapping

Windmill park on the open North Sea coast at Hävsul area in Norway is one of the first in the world to be build on such extreme high-energy coast. To determine possible environmental impact of this project, baseline study was performed in 2010-2011. Two areas, impacted (area where windmill park is planned to be build) and reference were chosen. For hard bottoms work class ROV was used to take underwater video, as no traditional sampling methods are suitable for such environment and depths. The system was equipped with powerful (400 Watt) xenon lights, USBL navigation and HDTV color camera. For …


Establishing A Multibeam Sonar Evaluation Test Bed Near Sidney, British Columbia, Rob Hare, Clay Whittaker, J.E. Hughes Clarke, Jonathan Beaudoin May 2012

Establishing A Multibeam Sonar Evaluation Test Bed Near Sidney, British Columbia, Rob Hare, Clay Whittaker, J.E. Hughes Clarke, Jonathan Beaudoin

Center for Coastal and Ocean Mapping

The Canadian Hydrographic Service (CHS), Naval Oceanographic Office (NAVOCEANO) and the Ocean Mapping Group of the University of New Brunswick (OMG) collaborated on establishing a multibeam sonar test bed in the vicinity of the Institute of Ocean Sciences in Sidney, British Columbia Canada. This paper describes the purpose of the sonar evaluation test bed, the trials and tribulations of two foreign governments collaborating on projects of mutual interest, the evaluation areas and their characteristics for sonar testing, and sample results of sonar evaluations using this test bed. Some target detection comparisons of several systems over a range of artificial sonar …


Beyond The Chart: The Use Of Satellite Remote Sensing For Assessing The Adequacy And Completeness Information, Shachak Pe'eri, Chukwuma Azuike, Lee Alexander, Christopher Parrish, Andy Armstrong May 2012

Beyond The Chart: The Use Of Satellite Remote Sensing For Assessing The Adequacy And Completeness Information, Shachak Pe'eri, Chukwuma Azuike, Lee Alexander, Christopher Parrish, Andy Armstrong

Center for Coastal and Ocean Mapping

Chart adequacy and completeness information consists of the symbols, abbreviations and warnings used to inform mariners of the level of confidence that should be given to data on a nautical chart. This information is derived both from the nautical chart and sailing directions. However, analysis based solely on these datasets is limited without access to the sources (e.g., smooth sheets). Publically-available, multi-spectral satellite imagery and published algorithms can be used to derive estimates of the relative bathymetry in shallow, clear waters. In this study, we evaluate the potential of these methods for supplementing the procedure to assess the adequacy of …


The Impact Of Sea State Condition On Airborne Lidar Bathymetry Measurements, Torbjorn Karlsson, Andreas Axelsson, Shachak Pe'eri May 2012

The Impact Of Sea State Condition On Airborne Lidar Bathymetry Measurements, Torbjorn Karlsson, Andreas Axelsson, Shachak Pe'eri

Center for Coastal and Ocean Mapping

Due to a large number of available Airborne Lidar Bathymetry (ALB) survey datasets and scheduled future surveys, there is a growing need from coastal mapping communities to estimate the accuracy of ALB as a function of the survey system and environmental conditions. Knowledge of ALB accuracy can also be used to evaluate the quality of products derived from ALB surveying. This paper presents theoretical and experimental results focused on the relationship between sea surface conditions and the accuracy of ALB measurements. The simulated environmental conditions were defined according to the typical conditions under which successful ALB surveys can be conducted. …


Seafloor Characterization For Trawlability Using The Simrad Me70 Multibeam Echosounder In The Gulf Of Alaska, Jodi L. Pirtle, Thomas C. Weber, Chris Rooper, Christopher D. Wilson, Brian R. Calder May 2012

Seafloor Characterization For Trawlability Using The Simrad Me70 Multibeam Echosounder In The Gulf Of Alaska, Jodi L. Pirtle, Thomas C. Weber, Chris Rooper, Christopher D. Wilson, Brian R. Calder

Center for Coastal and Ocean Mapping

No abstract provided.


Extracting More Data From Lidar In Forested Areas By Analyzing Waveform Shape, Thomas Adams, Peter Beets, Christopher Parrish Mar 2012

Extracting More Data From Lidar In Forested Areas By Analyzing Waveform Shape, Thomas Adams, Peter Beets, Christopher Parrish

Center for Coastal and Ocean Mapping

Light Detection And Ranging (LiDAR) in forested areas is used for constructing Digital Terrain Models (DTMs), estimating biomass carbon and timber volume and estimating foliage distribution as an indicator of tree growth and health. All of these purposes are hindered by the inability to distinguish the source of returns as foliage, stems, understorey and the ground except by their relative positions. The ability to separate these returns would improve all analyses significantly. Furthermore, waveform metrics providing information on foliage density could improve forest health and growth estimates. In this study, the potential to use waveform LiDAR was investigated. Aerial waveform …


Hydrographic Data Processing On A Robust, Network-Coupled Parallel Cluster, Rohit Venugopal, Brian R. Calder Feb 2012

Hydrographic Data Processing On A Robust, Network-Coupled Parallel Cluster, Rohit Venugopal, Brian R. Calder

Center for Coastal and Ocean Mapping

Increasing data volumes and adoption of computer-assisted hydrographic data processing algorithms necessitate higher data processing rates if gains in efficiency achieved in the last decade are to be maintained and enhanced. Recent advances in desktop computer architectures have made multi-core and multi-processor systems readily available, and some advances have been made in implementing multi-threaded versions of common hydrographic data processing algorithms. In many cases, however, although the algorithms might be ideal for parallel implementation (so called ‘embarrassingly parallel’ tasks), limitations in memory, disc and network bandwidth within a single system can have significant limitations on the scalability of these solutions. …


Use (And Potential Abuse) Of Uncertainty In Hydrography, Brian R. Calder Feb 2012

Use (And Potential Abuse) Of Uncertainty In Hydrography, Brian R. Calder

Center for Coastal and Ocean Mapping

The evaluation and use of uncertainty as a component of hydrographic data processing systems has grown considerably in the last decade. Uncertainty models for sounding data are now common, and progress has been made in developing models, methods and implementations for preserving this uncertainty in intermediate hydrographic data products. Less progress has been made in dealing with expressing the uncertainty in hydrographic data products to the user, however, which we contend should be our ultimate aim.

We draw here a distinction between the uncertainty assessed for observed sounding (and auxiliary) data and uncertainty as expressed to the user, and observe …


Designing A Better Weather Display, Colin Ware, Matthew D. Plumlee Jan 2012

Designing A Better Weather Display, Colin Ware, Matthew D. Plumlee

Center for Coastal and Ocean Mapping

The variables most commonly displayed on weather maps are atmospheric pressure, wind speed and direction, and surface temperature. But they are usually shown separately, not together on a single map. As a design exercise, we set the goal of finding out if it is possible to show all three variables (two 2D scalar fields and a 2D vector field) simultaneously such that values can be accurately read using keys for all variables, a reasonable level of detail is shown, and important meteorological features stand out clearly. Our solution involves employing three perceptual "channels", a color channel, a texture channel, and …


Submarine Landslides On The Upper Southeast Australian Passive Continental Margin – Preliminary Findings, S L. Clarke, T Hubble, D Airey, Phyllis Yu, R Boyd, J Keene, N Exon, James V. Gardner Jan 2012

Submarine Landslides On The Upper Southeast Australian Passive Continental Margin – Preliminary Findings, S L. Clarke, T Hubble, D Airey, Phyllis Yu, R Boyd, J Keene, N Exon, James V. Gardner

Center for Coastal and Ocean Mapping

The southeast Australian passive continental margin is narrow, steep and sediment-deficient, and characterized by relatively low rates of modern sedimentation. Upper slope (<1200m) sediments comprise mixtures of calcareous and terrigenous sand and mud. Three of twelve sediment cores recovered from geologically-recent, submarine landslides located offshore New South Wales/Queensland (NSW/QLD) are interpreted to have sampled failure surfaces at depths of between 85 cm and 220 cm below the present-day seabed. Differences in sediment physical properties are recorded above and below the three slide-plane boundaries. Sediment taken directly above the inferred submarine landslide failure surfaces and presumed to be post-landslide, returned radiocarbon ages of 15.8 ka, 20.7 ka and 20.1 ka. The last two ages correspond to adjacent slide features, which are inferred to be consistent with their being triggered by a single event such as an earthquake. Slope stability models based on classical soil mechanics and measured sediment shearstrengths indicate that the upper slope sediments should be stable. However, multibeam sonar data reveal that many upper slope landslides occur across the margin and that submarine landsliding is a common process. We infer from these results that: a) an unidentified mechanism regularly acts to reduce the shear resistance of these sediments to the very low values required to enable slope failure, and/or b) the margin experiences seismic events that act to destabilise the slope sediments.


Evaluation Of Rockfish Abundance In Untrawlable Habitat: Combining Acoustic And Complementary Sampling Tools, Darin Jones, Christopher D. Wilson, Alex De Robertis, Chris Rooper, Thomas C. Weber, John L. Butler Jan 2012

Evaluation Of Rockfish Abundance In Untrawlable Habitat: Combining Acoustic And Complementary Sampling Tools, Darin Jones, Christopher D. Wilson, Alex De Robertis, Chris Rooper, Thomas C. Weber, John L. Butler

Center for Coastal and Ocean Mapping

—Rockfishes (Sebastes spp.) are an important component of North Pacific marine ecosystems and commercial fisheries. Because the rocky, high-relief substrate that rockfishes often inhabit is inaccessible to standard survey trawls, population abundance assessments for many rockfish species are difficult. As part of a large study to classify substrate and compare complementary sampling tools, we investigated the feasibility of using an acoustic survey in conjunction with a lowered stereo-video camera, a remotely operated vehicle, and a modified bottom trawl to estimate rockfish biomass in untrawlable habitat. The Snakehead Bank south of Kodiak Island, Alaska, was surveyed repeatedly over 4 days and …


Mapping Gas Seeps With The Deepwater Multibeam Echosounder On Okeanos Explorer, Thomas C. Weber, Larry A. Mayer, Jonathan Beaudoin, Kevin W. Jerram, Mashkoor A. Malik, Bill Shedd, Glen Rice Jan 2012

Mapping Gas Seeps With The Deepwater Multibeam Echosounder On Okeanos Explorer, Thomas C. Weber, Larry A. Mayer, Jonathan Beaudoin, Kevin W. Jerram, Mashkoor A. Malik, Bill Shedd, Glen Rice

Center for Coastal and Ocean Mapping

No abstract provided.


Acoustic Sensing Of Gas Seeps In The Deep Ocean With Split-Beam Echosounders, Thomas C. Weber, Kevin W. Jerram, Larry A. Mayer Jan 2012

Acoustic Sensing Of Gas Seeps In The Deep Ocean With Split-Beam Echosounders, Thomas C. Weber, Kevin W. Jerram, Larry A. Mayer

Center for Coastal and Ocean Mapping

When in the form of free gas in the water column, methane seeps emanating from the seabed are strong acoustic targets that are often detectable from surface vessels using echo sounders.In addition to detecting that a seep is present at some location, it is also desirable to characterize the nature of the seep in terms of its morphology and flux rates. Here, we examine how much we can learn about seeps in the deep (> 1000 m) northern Gulf of Mexico using narrow-band split-beam echo sounders operating at fixed frequencies (18 kHz and 38 kHz).Methane seeps in this region are …