Our Seabed Frontier Challenges and Choices (1989) / Chapter Skim
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4. Technology and Data Acquisition
4. Technology and Data Acquisition
Pages 60-97
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From page 60... ...
This section presents assessments of the current status and future requirements of seabed mapping and surveying technologies, including navigation technologies to correctly position seafloor mapping data. Included are a description of ongoing government, industry, and academic mapping programs; a discussion of mapping strategies; and an investigation of technical and nontechnical constraints that may limit technology development and optimal mapping programs.
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From page 61... ...
These are useful for precise resource assessment (Wpe, location, quality, and volume of seabed commodities) ; quantitative measurements of bottom conditions (sediment properties and geologic processes)
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From page 62... ...
, sediment type and distribution, and small geologic features showing geologic processes. Figure 4-1 shows comparative swath widths of some typical kinds of swath mapping systems.
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From page 63... ...
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From page 64... ...
For most EEZ water depths, the actual range is 10 times the depth. The seafloor imagery has a pixel size of 50 m.
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From page 65... ...
SeaMARC II is capable of large-area regional surveys with higher spatial resolution and sensitivity to bottom roughness than the GLORLA system (Davis et al., 1986~; however, relative to GLORIA, it has a significantly reduced swath width. Profiling Systems Profiling systems used to acquire information on water depth, seafloor profiles, and subsurface sediment, geometry and stratigraphy are listed in Table 4-2.
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From page 66... ...
Resolution of individual beds and strata may be less than 1 m. In deep water, beam spreading and attenuation from surface sensors reduce penetration and resolution.
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From page 67... ...
Sediment types, mineral deposits, and geotechnical properties inferred through other types of survey data are typically confirmed using direct sampling. Complementary sets of remotely
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From page 68... ...
acquired data from different systems combined with direct sampling can lead to elegant threedimensional perspectives of seafloor phenomena. Navigation/Positioning Systems The principal linkage between all survey and sampling measurements is navigation or position accuracy of the data collected.
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From page 69... ...
global land-based system, OMEGA, has been used to support open-ocean navigation, but has insufficient accuracy (1 to 4 nm) to support most EEZ surveys.
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From page 71... ...
The Navy Navigation Satellite System (NNSS) , also known as SATNAV or TRANSIT, uses doppler shift measurements from a series of polar orbiting satellites to determine ship positions.
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From page 72... ...
, also know as NAVSTAR, uses range and time determinations from several of a series of polar orbiting satellites to establish position. When the entire, "constellation" of GPS,satellites is in orbit (after 1990)
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From page 73... ...
all carry out reconnaissance surveys, basic research, and task-specific activities, but their priorities and-emphases differ. The USGS is conducting an ambitious EEZ-wide reconnaissance survey of bottom morphology using GLORIA Surveys have been completed off the Pacific, Atlantic, Gulf of Mexico, Puerto Rico and Virgin Islands coasts, and in the North Pacific off Alaska; regional atlases of GLORIA side-scan mosaics have been published for the west coast (EEZ Scan 84, Scientific Staff, 1986)
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From page 74... ...
Examples of such reconnaissance data and mapping from broadly spaced survey lines are the GLORIA II images shown in Figures 4-3 and 4-4. Figure 4-9 is a reconnaissance GLORIA II survey grid in the Gulf of Mexico, with line spacing from 26 km in deep water to 7.5 km on the upper continental slope.
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From page 75... ...
Use-specif~c resource and site evaluations and research on the continental slope and rise share the need for deep-tow high-resolution data. Data generated by such systems as SeaMARC I, High Resolution Hazard Survey End of Survey 1_ J / 1 00 M Line ,~, Upper Slope Survey 6.5 x 6.5 Km 'I /' Beginning of Survey / ~ Survey / Grid / 26 Km Hi/ / ~ , Oil and Gas Lease Block ~/ / / / FIGURE 4-9 Comparisons of survey line spacing and densities for reconnaissance versus sitespecific surveys: a GLORIA regional survey, an upper slope seismic grid, and a high-resolution deep-tow site survey for an offshore oil and gas production site.
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From page 76... ...
New bottom mapping technologies have revealed new geologic features and contexts in deepwater areas quite different from those in shelf waters. The inability to explain and characterize obseIved seafloor phenomena in use-related terms continues to pose a potential constraint to development.
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From page 78... ...
Without improved data on the mechanics of such processes, however, the interpretations of such mapped data will be severely restricted. Direct Sampling Problems Mapping based on direct sampling methods suffers from two principal disadvantages: direct sampling is time consuming and inefficient, especially in deep water; and some EEZ areas exhibit great spatial variability in features, sediments, and processes.
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From page 79... ...
Such a venture would require collaboration by government, industry, and academia to identifying technology priorities and provide sufficient funding. SEABED GEOTECHNICAL DATA Baclcground Accurate characterization of a proposed development site requires meaningful measurements of seabed and sediment properties to be made by three different methods: 1.
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From page 80... ...
Data acquisition systems are highly developed for water depths less than 300 m (Table 4-4) , whereas only moderate or little development has occurred for the Arctic or in water depths exceeding 300 m.
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From page 81... ...
Mass .- Downhole . Hydraulic Ram - Cone Penetrometer TABLE 4-4 Assessment of Capabilities for Geotechnical Data Acquisition Systems EEZ areas Systems Shallow Deep Arctic water water (< 300 m)
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From page 82... ...
However, risk to personnel has limited the use of manned submersibles under ice, and this limitation will continue to be a constraint in the future. DRILLING RIG SELF-CONTAINED UNIT FIGURE 4-12 Deployment systems used for sampling, in situ, and experimental testing.
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From page 83... ...
Technological advances in vehicle navigation, command and control, power and propulsion, acoustic and optic sensors, robotics, and support and handling systems have allowed ROVs to be built that can operate in water depths up to 3,500 m from a multitude of support platforms in the open ocean. An ROV can be supported, powered, and controlled from a surface vessel; the system has proven it can support acquisition of samples, in situ measurements, and visual observations of the seabed.
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From page 84... ...
Although both types have traditionally been limited to water depths up to 1,200 m with vessels installed with a permanent drilling or portable rig, the Ocean Drilling Program (ODP) has demonstrated through its international program that the advanced piston corer has the capability to acquire downhole samples in water depths up to 6,000 m using the ODP highly specialized, deepwater drilling vessel (Peterson, 1984~.
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From page 85... ...
Most laboratory tests are performed onshore, so sample packing, transporting, and storing are critical to minimize moisture loss or physical disturbance (Young et al., 1983~. During the past five to ten years,
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From page 86... ...
The high costs of performing full-scale tests in deep water and the Arctic precludes their use, and use of experimental model testing to improve understanding of seafloor responses to various foundation loadings has increased in the last decade. Plate load tests using the Seacalf jacking system to load a seafloor plate have been used in the North Sea to determine soil stiffness and seafloor bearing capacity (Andresen et al., 1979~.
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From page 87... ...
The capability to measure true, in situ ambient pore pressure to determine the existence of hydraulic gradients in various geological environments will also require special attention in the future, because knowledge of in situ ambient pore pressures will provide a better understanding of altered pore pressures induced in samples obtained from extreme water depths (Denk et al., 1981~. Samplers and in situ testing probes and sensors feature a number of different designs, and standardization of test procedures will be needed in the future.
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From page 88... ...
88 Handling / Frame ~ Hoisting / // System Electromechanical Umbilical ~ ; 1 Tethered Seafloor Plafform Geotechnical Probe FIGURE 4-13 Rapidly transportable deployment systems. SOURCE: Young et aL, 1988b TABLE 4-8 Exceptional Testing Requirements for Various EEZ Development Applications Development application Exceptional requirements Oil and gas Waste disposal Military Piplines and cables Minerals and mining Large penetrations beneath seabed Wide variety of tests Site variability definition Chemical and thermal characteristics Permeability and absorbent characteristics Rapid deployment Acoustic characteristics Bottom signatures Rapid, route deployments Thermal characteristics (Arctic)
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From page 89... ...
Several possibilities for structuring an EEZ monitoring program have been suggested (Segar, 19~) monitor to verify or refine models of the transport, fate, and impact of materials; monitor to determine if the response of specific indicator organisms to pollutant levels is sufficient to trigger remedial action; · establish background levels of critical substances prior to using a particular area and then monitor to evaluate temporal and spatial changes (trend assessment monitoring)
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From page 90... ...
Protocols for seabed and near-bottom reference sampling will depend on the phenomena being studied and the terrain. Complex seabed terrain with large relief will a Anon be a candidate for higher density sampling than low-relief seabed or gradually changing water depths.
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From page 91... ...
An ~EEZ-NS&~ program would not necessarily be linked to a specific seabed use or to reference-site monitoring. Because of EEZ water depths and seafloor environment diversity, choosing sentinel organisms and sediment analysis methods might be more difficult than in the NS&T program.
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From page 92... ...
focuses on how and over what time scales organism-sediment interactions may be affected by changes in particulate material composition or character on the seabed, and on the feedback of monitoring data to modify a permitted dumping protocol (Figure 4-14~. To restrict scattering, particulate wastes dumped at sea are typically placed in long-term repositories in areas thought to be quiescent.
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From page 93... ...
However, greater water depth and more varied terrain will require modification of the monitoring decision protocol. For example, wastes dumped into deeper waters will be more dispersed and diluted than in shallow water, so more sensitive surveying and sedimentary analysis techniques will be required.
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From page 94... ...
The accessibility of Navy monitoring data of disposed equipment is better. For example, as part of the CHASE (Cut Holes And Sink 'Em)
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From page 95... ...
Reaching compromises between optimum sampling schemes, available technologies, and funding resources will probably be among the thorniest issues to be faced by EEZ monitoring programs.
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From page 96... ...
, and · rapid acquisition of data from monitoring buoys using satellites. Nontechnical Problem Resolution The principal nontechnical constraints to EEZ monitoring are monitoring priorities, designation of monitoring organizations, determination of monitoring frequency and duration, quality control, protocol for monitoring data release, and adequate funding.
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From page 97... ...
An EEZ GIS could combine data on water depth, bottom gradients and roughness, sediment types and thicknesses, seafloor biology, and bottom processes with precise locations of sample sites, monitoring sites, boreholes, and survey lines. Additional data would include past, present, and anticipated manmade features, such as wrecks, dumpsites, cables, pipelines, abandoned wells, and bottom structures.
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