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OCR for page 60
4
TECHNOLOGY AND DATA ACQUISITION
A large body of information is needed for planning efficient use and management of the EEZ
seabed. Many data needs cut across individual uses. For example:
· oceanographic and meteorological data for real-time forecasts to improve operations and
public safety;
· - data on sediment characteristics, including shear strength and permeability, compressibility,
and geochemistry;
· information and knowledge of seafloor geologic processes, including landsliding, turbidity
currents, faulting, erosion and scour, volcanism, and sediment transport and deposition; and
· information related to specific and multiple uses of the seafloor, including the need for
improved environmental quality monitoring of seafloor uses and their effects.
Obtaining this data in a marine environment frequently requires complex and expensive
technologies and techniques specially designed for ocean use. This chapter presents assessments of
the current status and future requirements of technologies and techniques used to gather
information about the EEZ, including surveying and mapping technologies, geotechnical data
collection activities, and environmental monitoring. A final section of this chapter discusses
approaches to managing the large amounts of data that are likely to result from increased research
and development efforts. In addition to present and emerging technologies and techniques, technical
and nontechnical constraints that may limit technology development and deployment are examined.
SURVEYING AND MAPPING
There are four basic types of surveying and bottom mapping required to support development
and protection of the EEZ seabed; these are water depth (bathymetric), seafloor imagery (mostly
acoustic, some photographic), subbottom profiling, and direct sampling of seafloor surface and
subsurface sediment characteristics. 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.
60
OCR for page 61
61
Background
Surveying and mapping of seafloor characteristics provide fundamental and essential data and
information for resource development and environmental protection. The seafloor can be mapped
using a wide variety of tools and techninllP.c fit rliff~.re.nt `~l~c earl ~rr~lrari-` anA for Aif{-r=~t
purposes.
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^~;~nna~ssance surveys provide a oroac overview or regional geology, large-scale variations in
seafloor morphology, rock or sediment type, and features resulting from long-term evolution of
continental and island margins. Higher resolution mapping (with higher positioning accuracy) is
required for task-specific or site-specific surveys. 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) for engineering design, construction, or
installation of seafloor structures; and seafloor process mapping (movements of the seafloor and its
overlying sediments) for environmental monitoring and research purposes.
The state of knowledge and map coverage of EEZ regions on the continental shelf reflect the
extent to which existing techniques have been applied in response to the needs of shallow-water
users. However, most of the EEZ is beyond the continental shelf, in water deeper than 300 m, on
the continental slope and rise. Use of these areas for resource extraction (particularly oil and gas)
and activities such as telecommunications or military installations is increasing, and these areas are
likely to become the principal location of development in the near future. This frontier region
poses considerable challenges to survey methodology and practice. Although regional reconnaissance
surveys are in progress, resource distribution and bottom conditions of the deepwater EEZ areas are
generally poorly documented.
Mapping Technologies
Most seabed mapping is done by acoustic techniques, essentially by underwater remote sensing.
Sound beams are bounced off the seafloor, or through the seafloor sediments, and their return time
or return phase angle is measured. The resolution (fineness of detail) of different seabed mapping
y~ ups use By Mu. - an'ge is lncreasea as sound frequency IS decreased. Lower
frequencies, 3.5 kHz or lower, are required to penetrate sediments (subbottom profilers); medium
frequencies, 12 kHz or higher, are required to avoid sediment penetration, thus accurately measuring
the water depth (bathymetry) to the seafloor, or water/sediment boundary. In simple terms, the
resolution of acoustic mapping data is generally increased by widening the frequency band width of
the sound source, narrowing the width of the sound beams, reducing the width of the sound swath,
reducing the survey ship speed, or reducing the system's altitude above the seafloor. The survey
resolution is increased by reducing the distance between tracklines. or hv imnrovino the. ~rrilr-~-4r~1 of
the navigation/positioning system.
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Seabed mapping technologies described below include bathymetric survey systems, side-scan
sonar systems, swath imaging and bathymetric (combined) systems, subbottom profiling systems, and
direct sampling technologies. Because accurate positions of all mapping data are necessary for the
data to be useful, navigation/positioning systems are also discussed in this section. Capabilities of
some commonly used acoustic mapping tools are described in more detail in McQuillin and Ardus,
1977; McClelland Engineers, 1982; Trabant, 1982; Kosalos, 1984; Prior and Doyle, 1984; Tyce, 1986;
Davis et al., 1986; and Prior et al., 1988.
Bathymet~y, the measure of ocean water depth, was the first bottom mapping technique to be
developed. Originally, a lead weight was lowered on a line to give depths at individual locations.
The development of sonar during World War I led to a new technique for measuring water depth.
Single sonars mounted on a ship's hull measure travel time for sound to bounce off the seafloor and
OCR for page 62
62
return to the ship. Depths are measured along a trackline directly under the ship, parallel tracklines
are surveyed, and the area between tracks is interpolated and contoured into a low-resolution
bathymetric map.
Higher-resolution bathymetric data are derived from ~multibeam" or Swath bathymetry systems.
An array of transducers on the ship's hull forms multiple acoustic beams, which completely ensonify
a wide swath on either side of the ship (Figure 4-1~. Parallel tracklines provide 100 percent
coverage of a survey area, so all areas between tracks are measured rather than interpolated. An
additional increase in accuracy is provided because adjacent measurements within each swath are
keyed to the same ship position. The first multibeam system was developed for the U.S. Navy in
the mid 1960s. The first commercial multibeam (Sea Beam) was marketed in 1975; almost 20 are
now operating worldwide. Bathymetric systems provide accurate water depth, and an accurate map
of seafloor topography, but do not provide data on sediment type or thickness or show very small
geologic features or objects on the bottom.
Side-looking (or side-scan) sonars provide acoustic images of a swath of the seafloor, showing
morphology (bottom topography), 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. A low-resolution side-scan sonar currently being used for reconnaissance
surveys of the U.S. EEZ is GLORIA (Geologic Longrange Inclined ASDIC), developed in the
United Kingdom. GLORIA is towed near the ocean surface at 10 knots with a swath width of
60 km.
There are many high-resolution side-scan sonar systems; operating characteristics of a number of
them are shown in Table 4-1. These systems typically use a side-scan sonar frequency of 30 to 100
kHz, are deep-towed from 30 to 150 m above the seafloor (some "fly automatically at a certain
height; others are controlled manually by cable length and tow speed), provide a swath of various
widths up to 5 km, and are towed across the bottom at 2 knots.
With an accuracy specification of 1 percent of water depth, SeaMARC II provides a
high-resolution system for both bathymetry and imagery. Potential additional advantages are its
ability to be towed below the water surface and moved from ship to ship.
GLORIA
SEAMARC ~ a.
SWATH MAPPING SYSTEMS
\\ "'"'a
FIGURE 4-1 Comparative swath widths of some typical swath mapping systems. SOURCE: After
Davis et al., 1986.
OCR for page 63
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64
Many deep-tow side-scan sonar systems also carry shallow-penetration subbottom profilers.
These downward-looking sonars are typically 3.5 to 7 kHz in frequency and penetrate 20-to 100 m
of sediment, depending upon sediment type. These profilers provide detailed geometry, stratigraphy,
and structure in the upper sediment layers; they may show individual sediment beds as thin as <
1 m. Sound attenuation and beam spreading in deep water will degrade data from surface ship
profilers.
These different underwater remote-sensing tools employ various sensors to detect seabed
characteristics, such as variations in acoustic reflectance and backscatter, gravity, and magnetic
properties. The differences inherent in such methods are a consequence of relationships between
range and resolution, which depend on the sensing system's properties. In common with other
forms of remote sensing, ground-truth information (from bottom samples or cores) is essential for
definitive interpretation of remotely acquired data. However, characteristics such as sediment
texture, or "hard and "soft" bottoms, can also be inferred by correlating different types of remote
data. Complementary sets of remotely acquired data from different systems conbined with direct
sampling can lead to elegant three-dimensional perspectives of seafloor phenomena. In particular,
sideways-looking (side-scan) sonar provides images of seafloor morphology, sediment distribution,
and signatures of geologic processes. Subbottom seismic profilers at various frequencies- give near-
surface sediment geometries, stratigraphy, and structure. Data from these systems is combined with
bathymetry and in situ ground-truth data. Table 4-1 reviews the principal bathymetric and seafloor
. .
Imaging sonar systems.
This area of technology development is dynamic; experimental new systems and advances in
existing ones occur with regularity. The following review is not exhaustive, but presents state-of-the-
art technology.
· Sea Beam: This multibeam bathymetry system uses sensors in the hull of the survey vessel
and has depth resolution of 1 m and accuracy between 10 m and 50 m in deep water (Circe, 1986~.
Swath widths are 0.8 times the water depth over a depth range of 100 to- 11,000 m. SeaMARC II
and Sea Beam bathymetry for the same area are depicted in Figure 4-2.
· GLORL4: This sideways-looking sonar is towed close to the survey vessel at a speed of 10
knots and has a 60-km swath. For most EEZ water depths, the actual range is 10 times the depth.
The seafloor imagery has a pixel size of 50 m. The GLORIA II system is capable of rapid, large-
area, regional coverage of large-scale features (Figure 4-3~.
Argo/Klein and SIR: Argo is a deeply towed camera system that incorporates a side-scan
sonar for high-resolution bottom images (similar to Edo 4075) over a 200-m swath at 1 knot (Tyce,
1986~. SAR is a high-frequency, high-resolution, side-scan sonar that can obtain 1.5-km swath
widths at 2 knots, but has seen only limited operational application.
· SeaMARC I: This is a deeply towed imaging system for site-specific surveys with both side-
scan (27/30 kHz) and subbottom profiler (4.5 kHz). Transmitters and sensors are contained in a
~fish" deployed 100 to 700 m above the seafloor at 2 knots. Swath widths are 1 to 5 km, and image
pixels are typically 1 x 5 m, with cross-track resolution of 0.5 to 2.5 m (Davis et al., 1986~.
SeaMARC I can simultaneously record seafloor features and subbottom sediment geometries.
· Edo 4075: This is a sideways-looking, deeply towed sonar system incorporating a 3.5- to
7.0-kHz subbottom profiler. The towfish automatically traverses bottom irregularities with the
positively buoyant vehicle held at a constant altitude of 30 to 50 m above the seafloor by a ballast
weight. Range is 200 to 400 m at 2 knots. Its high-quality images of seafloor and subbottom
topography, sediment texture, and geometry are suitable for site-specific engineering (Prior and
Doyle, 1984; Prior et al., 1988~. GLORIA II, SeaMARC I, and Edo 4075 data for the same area
are compared in Figures 4-4, 4-5, and 4-6. Although the Edo 4075 swath widths are narrow
(maximum 800 m), this system provides superior resolution.
· Scripps Deep Tow: A side-scan suIvey system capable of a wide variety of geologic,
oceanographic, and biologic missions, this system has a typical swath width of 1.5 km, tow altitude
of 150 m, and speed of 2 knots.
.
OCR for page 65
65
FIGURE 4-2 SeaMARC II
bathymetry (50-m contour
intervals and Sea Beam
bathymetry (20-m contour
interval) for the same
area are compared.
SOURCE: Davis et al., 1986.
· EG&G 990: This is a high-resolution, deeply towed, 1-km swath system with cross-track
resolution of 1.3 m and alongtrack of 2 m, at 100 m above the seafloor. Maximum operational
depth is 6 km; tow speed is 2 knots. Operational effectiveness in deepwater high-relief areas is
reduced by the need to tow the sensor close to the seafloor, with towf~sh altitude controlled only by
cable length and ship's speed.
· SeaMARC II: This sideways-looking sonar is towed close to a survey vessel and
simultaneously records seafloor imagery and swath bathymetry (Figure 4-3~. It is capable of ranges
of 1 to 10 km at tow speeds of ~ to 10 knots. Its imagery is composed of 1,024 equidimensional
pixels over a range of 5 km per side, with a horizontal resolution of about 5 m. The swath
bathymetry has a depth resolution of 20 to 50 m. 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.
OCR for page 66
FIGURE 4-3 GLORLA imagery and SeaMARC II imagery for the same area. The images have
reversed polarity (the SeaMARC II image shows steeper areas as dark, the GLORIA image shows
them as light). Tracklines in the SeaMARC II imagery are approximately 10 km apart.
· Water-Depth Echosounders: For deepwater surveys, narrow-beam systems are required to
minimize off-line echoes, and calibration for actual water column velocity variations is necessary to
determine absolute depth (e.g., Prior et al., 1988~.
· Subbottom Profilers: Profiling systems operating between 3.5 and 7.0 kHz can penetrate up
to 30 to 50 m in soft sediments. However, penetration and resolution depend on geologic
conditions and are highly variable. They are usually much less in sandy, cemented, or gassy
sediments. 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. Figure 4-7
compares a surface-towed, 3.5-kHz profile with data from a deeply towed system 30 m above the
seafloor (Prior et al., 1988~.
· Medium-Penetration Profilers: Various medium-penetration, medium-resolution systems are
used to provide details of sediment stratigraphy to 900 to 1,000 m below the seafloor (e.g.,
Minisparker, water gun, or minisleeve exploder). Actual penetration and resolution are affected by
geologic conditions and the type, frequency, and power of the sound source. Data recording may be
OCR for page 67
67
~ L
1-
) ~
l
. GLORIA
. _
. .. - ~
__1
_·~;
FIGURE 4-4 GLORIA imagery of part of the Gulf of Mexico. The same channel feature is
further illustrated in Figures 4-3 and 4-6.
single- or multichannel; the latter allows post-cruise processing to enhance usefulness of the profile
data. Figure 4-8 illustrates information acquired by both 3.5-kHz subbottom profiling and
multichannel data for the same area. Because of the apparent differences in penetration and
resolution of the two types of data, both types of data are usually acquired simultaneously.
Interpretation of near-surface geologic conditions is based on both 3.5-kHz and medium-penetration
profiles.
Direct Sampling
Seabed sediments and rocks can be retrieved using sediment grabs and dredges for surface
materials, and boring, coring, probing, or drilling for subsurface samples. Characteristics of the
retrieved materials and data from in situ measurements can then be mapped. Spatial integrity of the
maps is directly related to sampling density, because of seafloor and subsurface variability between
sampling sites. Sediment types, mineral deposits, and geotechnical properties inferred through other
types of survey data are typically confirmed using direct sampling. Complementary sets of remotely
OCR for page 68
.. ..: ~
::::::::::: :::::::::: ::::::::: ::::::: ::::: ::::::::: :::::: ::::::::: ::::::: ·::::::::::: :::::::::::::::::::::::::::::: :::::::::::::::::::
SEAMAR I 5~ SW=H
............... ,,,.,. , , ,~., ~,. ..... ... .... ....... ......... ... ..... ..... ......................... ...
KHZ
FIGURE 4-5 SeaMARC I imagery of the same channel showed by GLORIA data in Figure 4-2.
Contrasting scales and resolutions (5-km swath, 1-km swath) are given. The 4.5-kHz subbottom
profile accompanies the 1-km swath. SOURCE: Kastens and Shor, 1985.
acquired data from different systems combined with direct sampling can lead to elegant three-
dimensional 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. Historically, the accuracy of navigation systems has lagged the
accuracy of survey and sampling systems, which has served as motivation for development of better
navigation capabilities. Navigation systems can be characterized by the location of the reference
systems:
land-based systems,
ship-based systems,
seafloor-based systems, and
satellite-based systems.
Land-based navigation systems have long been standard for survey operations conducted within
range of shore stations. The permanent coastal navigation system, Loran C, has excellent
repeatibility (return to same spot, but not necessarily know where it is) of 15 m, and sufficient range
(300 nm) for EEZ surveys, but has insufficient accuracy (0.25 nm) to support many survey needs. A
OCR for page 69
3~5 KHZ
..
UPPER
Fll
-
EDO 4075 400M
FIGURE 4-6 Edo 4075 imagery (3.5-kHz subbottom profile and 100-kHz side scan) for a portion
of the channel shown in Figures 4-4 and 4-5. SOURCE: Prior et al., 1988.
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. Differential OMEGA (setting up a
well-located, shore-based reference/retransmitting station) can reduce errors to 0.5 rim at 200-nm
range, still insufficient for many survey purposes. For accurate nearshore surveys, temporary
installations are generally used. These employ user-passive hyperbolic radio transmission systems
(Argo, Sylidis), or user-active radar transponder ranging systems (Falcon, Miniranger, Hi-FL~). These
systems have accuracies on the order of 1 m, but require careful surveying of the base station
locations, and have ranges of only 50 to 100 nm.
Ship-based systems generally determine range and bearing to stationary acoustic beacons,
benchmarks or structures on the seafloor, or aboard moving vehicles. Ship position is the reference
point from which all other positions are measured. These systems are called "short baseline" if they
use the time of arrival of the beacon's signal at sensors widely spaced over the ship's hull for
positioning. They are called "ultra-short baseline" if they use the phase difference of the beacon's
signal at a closely spaced array of sensors. The accuracy -of these systems is a function of both the
accuracy of the underwater acoustic transmission and reception, and of the ship's position
determined through other means.
Seafloor-based navigation systems generally consist of acoustic transponders, either on the
seafloor or tethered some distance above. While limited in range by acoustic propagation to tens of
kilometers, triangulation in range from bottom transponders produces navigation accuracy ranging
from 1 m for near-bottom receivers to 50 m for surface receivers (such as ships). Systems are being
OCR for page 70
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Centrifuge model testing is a developing technology with universal application to seabed
engineering problems. Acceleration applied to physical models can be used to induce conditions
that accelerate various processes and simulate natural events. Centrifuge testing has been conducted
to solve many offshore problems involving quasistatic cyclic loading conditions (Rowe et al., 1976;
Craig and Al-Saoudi, 1981; Rowe, 1983~. The theoretical principles of operation of the centrifuge
have been described by Schofield (1980~. This equipment provides the capability to test platform
models with diameters up to 100 m, piles with diameters of 2 m, and caissons with diameters up to
12 m. Its key benefit is the economy for experimentally checking models described by complicated
analytical procedures. Increased use of centrifuge modeling is expected to enhance the
understanding of the mechanism of foundation behavior and to provide direct design parameters for
performance predictions.
Technology Limitations/Needs
The technology for acquiring samples, performing laboratory tests, and obtaining in situ and
experimental geotechnical data is technically mature for water depths to 300 m within the
continental shelf areas (see Zuidberg et al., 1986; Briand and Meyer, 1983~. Development activities
in the Arctic and off the continental shelf in depths exceeding 300 m will depend not only on
advances in technology but on the availability of research vessels. For example, a dynamically
positioned drill ship is necessary to acquire geoscience data in water depths greater than 300 m
when seafloor penetrations greater than 10 m are required. However, there are only two of these
specialized vessels capable of working in these extreme water depths, and both are foreign-flagged
and stationed in the North Sea. Use of these vessels in U.S. EEZ waters will require costly
mobilization, which restricts their use except for the most extensive developments, such as site
investigations for oil and gas production facilities. The drill ships operated under the Deep Sea
Drilling Program (DSDP) and the Ocean Drilling Program (ODP) operate under international
scientific agreements and are not available for use for national resource assessment purposes. The
restricted availability of these vessels has limited major research programs to quantifying near-
seafloor characteristics.
The limited availability and high cost of geotechnical research drill ships could be mitigated by
development of a rapidly transportable seafloor deployment system (Figure 4-133 that could be
operated from a surface vessel, an ROV, a manned submersible, or a submarine (Young et al.,
1988b). The system needs to be compact, possess onboard memory, and be capable of thrusting
geotechnical probes and samplers to relatively deep penetrations (as much as 100 m) below the
seafloor. If operated from an ROV, it should be capable of being deployed from a small supply or
oceanographic vessel without fixed mooring. The various development applications within the EEZ
may impose exceptional requirements on the capabilities of the device as presented in Table 4-8.
In situ probes and sensors have been developed and used extensively over the past decade to
acquire geotechnical data. In situ and laboratory test results have been used successfully in water
depths to 300 m; however, stress relief and soil degassing will intensify in samples obtained from
deeper water, which will complicate data interpretation. Additional improvements in in situ data
interpretation will be needed to confirm the reasonableness of the data for design purposes. 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. For example, the location of measurement sensors and test
speed are known to influence pore pressure measurements, which could complicate data
interpretation for design purposes.
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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)
Rapid, area, region deployments
Consideration, concentration,
chemical characteristics
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89
Summary
The capability to acquire geotechnical data by sampling and by in situ, laboratory, and
experimental testing has improved greatly over the past decade, and this technology is relatively
highly developed for shallow-water areas (less than 300 m). Advancing to deeper water and the
Arctic will depend on further development of improved sampling and in situ testing equipment
capable of determining sediment properties in difficult offshore environments. It will also require
improved experimental testing methods capable of measuring seabed properties and behavior in a
more controlled manner. Compact deployment systems are needed that can operate rapidly and
automatically to measure engineering properties or sample seabed sediments. As activities expand
into EEZ frontier areas, new geologic models will be required to characterize sediment properties
and behavior in engineering terms. New interaction problems between sediments and foundation
elements arising from innovative structures, such as tension leg platforms, will require development
and verification of analytical models and field monitoring of the structures.
New and improved data acquisition systems will allow accurate and meaningful data to be
collected that better describe engineering properties and geologic conditions that could strongly
influence the design, location, construction, operation, and maintenance of engineering projects
planned for the EEZ. However, their development will require a thorough technical evaluation.
Future proposals for technology development by government and industry must consider priorities
and objectives for various data acquisition systems because of their complexity, cost, and time
frames.
EEZ SEABED MONITORING
The seabed of the U.S. EEZ is almost as varied as the seabed of the entire ocean, and the
environmental consequences of expanded activities in this region will be difficult to predict in
advance. Environmental monitoring provides a basis on which such predictions can be made, but
past EEZ monitoring has had mixed results. During the 1970s, $27 million was spent on
background studies for environmental impact statements for OCS oil and gas (MMS, 1973-79~.
However, the biological data were collected over such a large area that the impact of subsequent
operations on local organisms and environments was difficult to assess. A more focused and useful
effort conducted on Georges Bank in the late 1970s occupied monitoring stations at various
distances from drilling vessels during all drilling phases. The effects of drilling muds on sediments
were well documented, biological impacts were easier to ascertain, and the observed changes
provided criteria for modifying discharge requirements in future drilling operations (NRC, 1978~.
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); and
· monitor to assess compliance with water or sediment quality regulations and environmental
use-permit requirements (compliance monitoring).
Based on these past efforts and evaluations, this report will focus on three types of monitoring.
1. Reference monitoring establishes transects or sites that can be occupied for years, collecting
measurements that yield general baseline reference data for time-series considerations. These data
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may or may not be linked to a specific process or activity and will aim to provide critical insights
about the variability of the seabed environment.
2. Process-onented monitoring is conducted where important near-bottom processes can be
easily studied to understand and predict their interaction with EEZ uses.
3. Use-related monitoring is the measuring of parameters to assist a proposed or ongoing
seabed use and evaluate its impact.
Reference Monitoring
Interpreting information gathered during EEZ surveys or studies of basic processes often suffers
from insufficient knowledge of the long-term environmental context. Natural temporal and spatial
variations in physical, chemical, and biological properties must be understood in order to realistically
interpret any observed changes. Proper design of use-related monitoring programs requires such
long-term knowledge.
One approach to reference monitoring is to designate specific long-term benthic reference sites
or transects in the EEZ. How many of them should be designated, how they should be selected,
and where they should be located will depend on their purpose and on available personnel and
resources. It is not physically or fiscally possible to continually monitor large areas or an extremely
large number of smaller areas. Criteria and considerations necessary for selecting specific reference
sites are examined in depth in the report of a National Academy of Sciences panel (NRC, 1984~.
Because the U.S. EEZ is so vast and monitoring time-scales can range from minutes to decades,
selecting reference locations may depend on considerations such as those that follow.
.
Me number of locations needs to be large enough to cover several characteristic types of
seabed environment and small enough to permit the intense sampling required to detect higher
frequency events.
· Locations could be similar in concept to the Long-Term Ecological Reference (LTER) sites
on land (Callahan, 1984~. They could be placed either in typical seabed regions to optimize their
basic research value or in areas where future seabed uses are anticipated to permit acquisition of
truly long-term baseline information.
· Reference locations may also be selected in areas designated as preservation areas.
Achieving a consensus on selection criteria will require considerable input from the scientific
community, environmental groups, and potential seabed users, and will depend on the projected
resources for long-term sampling and monitoring.
Sampling strategies at the reference sites may follow two major phases:
1. initial high-frequency sampling to establish the characteristic scales of temporal and spatial
variations, and
2. long-term sampling programmed to maximize information return and performed at optimal
frequencies based on phase 1 results.
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. Basic
measurements include water transport (currents, turbulence), water properties (salinity, temperature,
suspended particle concentrations, nutrients, and dissolved oxygen, etc.), biological diversity and
abundance, and sediment properties. Utilizing the latest monitoring technologies will increase cost
effectiveness: for example, measurement of current patterns by acoustic tomography (Munk and
Worcester, 1988) and measurement of sediment credibility by instrumented flumes. Although very
little reference-site monitoring is being done now, the next ten years should see increased activity.
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By then, appropriate techniques should have been perfected to such a degree that reference
monitoring could remain at a steady level into the future.
An aspect of reference monitoring that may indicate pollutant levels near the seabed and
provide early warnings of environmental degradation uses "sentinels organisms along with
measurements of sediments. Such early warnings can be followed by detailed specific investigations.
The sentinel approach is analogous to NOAA's National Status and Trends (NS&T) Program in
coastal and estuarine environments (NOAA, 1984~. (NS&T also includes a specimen bank so
substances that may be designated pollutants in the future may be evaluated in previous
environments.) 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. If a consensus could be reached, however, an EEZ NS&T program could be
pursued for 10 or even 25 years, with organisms and pollutants updated as necessary.
Process-Oriented Monitoring
The objective of process-oriented monitoring is to acquire detailed knowledge of natural
processes that have intense effects on specific seafloor areas and that cannot be adequately studied
with reference monitoring. The two monitoring approaches may overlap to some degree if
important processes happen to occur in reference areas. As interest in various processes wanes or
waxes, some process-oriented monitoring sites will be abandoned and new ones chosen, thus making
process-oriented monitoring inherently shorter-term than reference monitoring.
Typical processes that have been studied include the following.
.
Shifts in major ocean currents that impinge on the bottom, such as those examined in the
mid-Atlantic region (Lee et al., 1981, 1982~. Their study focused on physical and chemical changes
associated with the Gulf Stream moving onto the U.S. continental shelf, but did not include
consequences to benthic organisms.
· Grounding of sea ice and its impact on sediment properties and seabed communities off
Alaska has been investigated by the Navy and by oil and gas industries (AO GA, 1978), but
techniques for observing it directly are not well developed, and many questions remain (NRC, 1985~.
· Mass wasting of sediment near the shelf break, at the head of submarine canyons, or in
other EEZ areas has been studied for many years (see Chapters 2 and 3) and very likely will be
continued and expanded.
Parameters to be measured and monitoring frequency (from minutes to years) and duration will
vary by process and proposed use. Important parameters include temperature, salinity, geotechnical
properties, near-bottom turbidity, dissolved substances (nutrients, oxygen, and trace metals), current
speeds and directions, and pollutants in both the seabed and the adjacent water column.
The need for process-oriented monitoring will increase in the next 25 years as EEZ uses
increase. Two uses of the seafloor near the shelf break expected to expand in the next 10 years-oil
and gas production and undersea submarine surveillance will require better ways to predict physical
and chemical consequences of shelf-break erosion or sediment loss. The effects of these processes
will need to be studied well in advance of installation of bottom-tethered equipment because of the
large variety of potential sites and length of time over which predictions must be made.
Use-Related Monitoring
Use-related monitoring ensures that seabed installations function properly and determines
whether remedial action is necessary if a particular EEZ use (waste disposal or mineral exploration,
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for example) poses hazards to human health, living marine resources, or overall quality of the
marine environment. Monitoring for use-related impact is the most common form of monitoring
conducted today, particularly trend assessment and compliance monitoring.
Waste Disposal
A conceptual model setting the framework for waste-related environmental impact monitoring
and its associated decision-making process proposed by an NRC panel on particulate wastes (NRC,
1989) 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. To confirm the suitability of potential waste sites, a
monitoring program normally includes short- (days) and long-term (seasons to years) measurements
of water flow and circulation.
In the initial stages of dumping, short-term baseline monitoring of the water and the physical
and biological characteristics of the sediments around dumpsites may be advisable. A technique that
may prove useful is the technology of remotely sensing the seafloor using optical data on the upper
sediment. Its appeal is the ability to survey large areas (i.e., square kilometers) of the seabed in
only a few days (Rhoads and Germano, 1986~. Remote sensing technology is particularly effective
for evaluating the depth to which dissolved oxygen penetrates the sediment, which is critical to the
mobility of both contaminants and benthic organisms. Because of speed and low cost, some
improved version of this technology will probably be employed to survey areas around dumpsites and
PARTICUlATE WASTES I
Dumping Protocol 6' CHANGE
, . .
1 ! 1
LOSS TO WATER COLUMN
LONG-TERM QUIESCENT REPOSITORY
1
1 1
Benthic Processes
a. Physical -- currents, tides,
turbulence, etc.
b. Biological -- bioturbation, respiration
colonization, population
development, etc.
FINAL CONDITION
a. Contaminants dispersed
or sequestered?
b. Benthic populations
healthy or unhealthy?
Physical Monitoring
Quick Bio-monitoring
(e.g., REMOTS)
Chemical Monitoring
(Sediments, indicator species, etc)
Long-term Population Monitoring
(REMOTS, BRAT, histopathology,
benthic species distribution
and chemical composition)
FIGURE 4-14 A monitoring decision model for waste dumping in the EEZ.
.
'Short-term Monitoring - ~ TECHNICAL
DECISION
MATRIX
r
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determine which ones need more detailed, longer-term studies. Remote sensing technology is
limited to providing a quick scan of a vertical section and does not produce information about
complex benthic interrelationships.
Long-term monitoring (Figure 4-14) will also involve a more complete benthic evolution of
sediment and fish or benthic animals living in (infauna) or on (epifauna) the sediments at sites
likely to be affected by dumping (Rhoads and Germano, 1986~. This longer-term monitoring will
also include histopathologic studies of collected organs and tissues of animals, which are the easiest
and most effective way to assess their physiological condition or "healths (Yevich and Barszc, 1983~.
The single most important consequence of waste-disposal monitoring should be a rapid
response to detected changes. Dumpsite monitoring data fed into a Technical Decision Matrix at
several stages of dumping (Figure 4-14) can indicate unacceptable environmental departures from
previously established limits. In such a situation, a speedy regulatory decision to modify the
dumping protocol will minimize damage to the biological community at the site.
Some projections can be made about waste disposal monitoring over the next ten years. For
dredged material disposal, the Army Corps of Engineers has designed a project using a more
elaborate version of Figure 4-14 to anticipate the impact of dredged material deposited in New
England coastal waters (NRC, 1989; Fredette et al., 1986~. A similar approach may be increasingly
employed to follow and manage dredged material dumping in the EEZ, and could also be applied to
fly ash and incineration ashes. 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. This problem was highlighted by the difficulty of
finding dumping residues at deepwater dumpsite 106 off the east coast (O'Connor et al., 1983~.
Further, management decisions may have to be made on the basis of fewer samples, because of the
difficulty and greater costs of deepwater sampling.
Over the next ten years disposal of ~packaged" wastes (i.e., ash and sludge blocks or
containerized nuclear wastes) is anticipated (Manheim and Vine, 1987~. Packaging of incineration
ash and hazardous waste in stabilized blocks may require special monitoring strategies that will differ
from those discussed above because interactions between the benthos and the package itself will
have to be considered (Roethel et al., 1986; Shieh et al., 1989; Manheim and Vine, 1987~. These
interactions will be important to predicting package lifetimes and waste release rates. Packages may
attract or repel species, thus different indicator organisms may be needed and sampling strategies
may require sampling near the packages without disturbing them.
Oil and Gas
Monitoring associated with oil and gas exploration and production has two purposes: to
guarantee stability of pipelines and platforms, and to ascertain and minimize environmental damage
during drilling and production. Stability assurance requires pre-use, site-specific information on
subsea and seafloor charcteristics, and historical data on winds, waves, and currents. Process
monitoring will determine the magnitude and velocity of the seafloor sediment movement and
seismic surveys of active surface faults (e.g., the Santa Barbara Channel), will estimate potential
effects of fault motion on structures, and will determine if fault motion is influenced by production
operations.
Exploration and drilling in the deeper water and the arctic EEZ will probably increase most
rapidly over the short term (ten years). In deeper waters, monitoring will have to be modified to
cope with the rigors of greater depths. This may result in reliance on remotely operated vehicles
and sampling systems. In the Arctic, ice floe movements, seasonal ice presence, and marine animal
migration and life cycle patterns need to be predicted both regionally and at specific exploration and
production sites. Tracking ice by satellites using microwave radiation in synthetic aperture radar
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(SAR) may become important because of SAR's ability to penetrate cloud cover. SAR's large
power requirements are a problem that will have to be overcome, however.
It should be noted that there is no procedure presently set up to follow the long-term effects-of
a large oil spill that happens to reach the EEZ seabed.
Minerals
Monitoring needs of EEZ seabed mining are difficult to forecast. If sand and gravel mining in
waters increases and moves to deeper deposits, pre-use and use-related monitoring would be
indicated (U.S. Bureau of Mines, 1987~. For any mining activity, impacts on benthic communities at
the mine site and surrounding areas large enough to evaluate far-field effects that need to be
assessed include recolonization rates, metabolic energy fluxes, sensitivity to sedimentation, and other
ecosystem relationships. Mining of iron-manganese crusts could cause serious environmental
impacts, but few studies of undersea mining impacts on surrounding environments have been done
(Manheim, 1986~. Research for environmental impact analysis (fates and effects of suspended
sediments in surface water and composition and dynamics of benthic ecosystems, for example) needs
to keep pace with the schedule of commercial development.
Military
Use-related monitoring of military activities in the EEZ seabed occupies a curious position
because so much data is and probably will remain classified. Weather-related data are not generally
available to other EEZ users, and other data (e.g., from the Fleet Numerical Weather Facility) may
have only limited availability due to the Navy's need to keep sampling locations secret. Naval test
ranges are used thoughout the EEZ, but it is not clear if there will be environmental investigations
related to this use. Recent changes in policy have opened up much of the bathymetry to the public
domain. The accessibility of Navy monitoring data of disposed equipment is better. For example,
as part of the CHASE (Cut Holes And Sink 'Em) scuttling operations, environmental evaluations
were performed to assess impacts, and the data are generally available. Navy monitoring of disposal
of surplus or outdated equipment and supplies will probably continue over the next 25 years, and
data will likely be available.
Monitoring Needs
Pollutant Detection
Detecting sewage sludge in sediments at deepwater dumpsites (such as Site 106 off the New
York Bight), may be extremely difficult because the presence of existing nonsludge sediment and the
feeding and movement of seabed organisms lower the sludge content of the sediments (O'Connor et
al., 1983~. The sediment analysis may not accurately reflect the extent of the environmental
damage. Also, the coarse-grained sediments in the shelf-edge portions of the EEZ are more
difficult to analyze than the finer-grained coastal and estuarine sediments analyzed under NOAA's
NS&T program, since pollutants are primarily associated with clays. In these situations sediment
traps might be used to collect sinking particles and estimate the rain of pollutants to the seabed.
There are problems with sediment traps (e.g., the hydrodynamics of particles), however, and research
on trapping techniques is still required (NRC, 1984~.
Which pollutants should be measured in EEZ monitoring has not been addressed either. The
organic and trace-metal pollutants monitored under the NS&T program (NOAA, 1984) might be
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adopted for the entire seabed region of the EEZ, with some adjustments made for substances to be
measured and tissues to be analyzed.
Biological Assessments
Choosing sentinel or indicator organisms may be more difficult in the EEZ than in coastal
waters. Benthic life in the EEZ differs from that of coastal waters. For example, increasing depth
works against the presence of large multicellular plants (macroalgae) on the seabed because
overlying water absorbs too much light. Also, assessing species populations over the larger areas
and great variety of benthic environments in the EEZ will be a lengthy process using conventional
techniques, such as taking core or sediment samples, sorting animals into size fractions with sieves,
and identifying and determining their condition. This work is expensive and takes days to weeks to
do for a single site. A well-conceived monitoring program will have to consider many sites spread
over a large area, some of which will be reoccupied continuously. Demand for data will require
continued development of remote sensors of physical, biological, and chemical conditions on the
EEZ seabed.
Sampling Strategies
Determining sampling frequencies and technologies to define a given phenomenon are difficult
because time and space capabilities of sampling devices or platforms have to be matched to the
domain of the phenomenon being studied (Figure 4-15~. For example, a single ship cannot
determine synoptic spatial distribution of phenomena that recur every few days because it cannot
return to a given location in an area that may cover hundreds or thousands of square kilometers.
Sampling frequency is also affected by costs, since the magnitude of sampling needed may be
financially prohibitive even though the technology exists to do it. 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.
lo7
oh
~ 1 o6
Al
O.
A
Al 104
-
C' 1 03
of:
~2
to 10
1o1
- (a) Be
r
~ 1 ~ 1
10 2 1o~1 1 10 102 103
TIME DAYS
n ZOOPLANKTON
- (b)
I
1 1
1 1
AIRCRAFT
~1 1
1 1
1 1
~1
BALOONS /
SATELLITES
WHIPS
~ 1 ~
~ ~ ,
/ I I Be
1 ~11 ~ 1
-2 10 1 1 10 1o2 103
TIME DAYS
Figure 4-15 (a) Time and space domains of circulation events, habitat variance, and biological
abundance in relation to (b) duration and scale of sampling platforms. SOURCE: After Walsh,
1988.
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Frontier Environment Considerations
Monitoring instrumentation needs for the EEZ are those needed to adapt to deeper water and
arctic environments. Instruments left for longer exposure times (due to sampling frequency
requirements or longer distances) and in deeper water may face problems of fouling, stability, and
calibration of physical and chemical sensors. In the Arctic, technology improvements are needed to
follow ice movements and study ice gouging in detail (NRC, 1985~. SAR power and data storage
requirements of synthetic aperture radar are too great, and the minimum sizes of ice floes detectable
by other remote techniques are too large.
Technology Advances
include
Advances in measurement technologies that will improve monitoring over the coming years
· acoustic tomography to obtain large-scale pictures of water-mass movements in short time
periods (Munk and Worcester, 1988),
· lasers to study movement of suspended particles (Carder et al., 1982),
· instrument packages with oxygen microelectrodes to investigate sediment chemistry on
millimeter scales (Revsbeck et al., 1986), 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. Information sharing among EEZ
seabed users will be a problem because there is no central repository for monitoring data that can
provide timely access for users (see "Data Managements for a more complete discussion). Given the
many and varied U.S. monitoring efforts, a single project will probably not obtain all the data that
will ultimately be needed. Especially important are data taken simultaneously from many locations,
which are vital to devising computer models that can predict actual events as closely as possible to
real time frames. Delays in data delivery will make short-term predicting (hours to days) after a
monitored event extremely difficult.
Another data-sharing problem is the classified or proprietary nature of Department of Defense
(DOD) and industry monitoring data. For example, DOD may choose to classify bathymetry data in
areas that are also important for such uses as deciphering the shape of terrain around waste-disposal
sites. Mechanisms to speed review and release of such data would be useful.
Summary
Monitoring will provide vital data on natural variability and baseline information about benthic
processes that affect areas of proposed or ongoing EEZ use. Linking use monitoring data to
regulatory decisions will allow rapid response to hazardous situations. The magnitude of the EEZ
area, variety of benthic environments, and greater depths will affect what is selected for monitoring,
how much it will cost, how long it will take, and what kind of technology is needed. Accomplishing
EEZ monitoring will require planning and commitment of resources adequate to the task. Without
them, data quality and quantity could be inadequate for making sound decisions regarding permitted
uses, perhaps ultimately leading to inadvertent and unacceptable environmental damage.
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DATA MANAGEMENT
As development of the EEZ progresses, enormous amounts of data will be collected by
government agencies, industry, and academia using the technologies described in this chapter.
Already very large data sets exist or are being developed, including bathymetry, seafloor imagery,
subsurface seismic profiles, bottom samples, and cores, together with oceanographic and biological
data for the seafloor and benthic boundary layer. These data are widely dispersed and exist in
different formats and archiving styles, a situation that lends itself to a distributed network rather
than a centralized system. Much of the data gathered by government agencies are archived at
NOAA's National Geophysical Data Center and are publicly available. By comparison, seismic data,
particularly multichannel exploration profiles, are collected by industrial groups and are proprietary.
Various projects, including CONMAP (USGS) and the Strategic Assessment Atlas Project are
compiling inventories of EEZ data. Industry consortia projects frequently combine and phase data
for mutually agreed tasks for particular EEZ areas, but there are no shared data inventories.
Management objectives for rapidly expanding the EEZ data base are the efficient use of
available data and the reduction of unnecessary duplication by facilitating data accessibility and
exchange. While EEZ data sets are large and will expand dramatically in the future, data
management hardware is not a problem. The computer industry is aggressively competing to
develop more capable components and systems for data handling, manipulation, transmission, and
storage. Nonhardware problems do exist, however, including appropriate management systems and
diversity in hardware, software, networks, and user operation conditions. Various data management
options need to be examined within an actual, defined framework of what data exists, what will be
acquired, and how available they are. Compiling a basic inventory of industry, government, and
academia data collections, formats, styles, quality, and availability is the logical next step.
Geographical information systems (GIS) are effective data storage and retrieval tools in which
geographic location and areal distributions are important attributes. 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.
Data that might be contributed to an EEZ management system come in a variety of forms, so
any system will face the special challenges of not only locating and cataloging data, but describing
specific formats and providing instruction as well. Thus establishing standard formats and guidelines
for directories, catalogs, and networks is an essential preliminary task for achieving effective data
management.
Another important problem is the diversity of existing computer facilities and networks. Since
this situation is unlikely to change, there is a need to link various existing computer networks. Such
development requires leadership, which could be provided by a committee of EEZ data system
participants, a U.S. government interagency group, or an academic or industrial systems organization.
Security of data will require careful attention, especially in an open, highly distributed, data
management system. There are three main aspects to securing data: control of access, control of
expenditure of resources, and damage to data sets and other resources.
Government leadership will be vital for establishing a comprehensive data management system
and implementing standards to facilitate the easy exchange of data, while at the same time
maintaining the appropriate level of security. The most important function of such a system is to
provide coordination and management of a widely dispersed database. Users must be able to access
information about data, i.e., what data are available and how to obtain them.
Representative terms from entire chapter:
sediment properties
