Emerging Survey Technologies for Alaska’s Coastal Zone
Robert J. Pawlowski1, Paul D. Brooks2, & John L. Oswald3
Abstract
The coast of Alaska has received major attention for mapping during the last decade.
Increased efforts to promote safe navigation through improved nautical charts; map
coastal habitats for endangered species and essential fish habitats; land new seabed
fiber optic cable systems; and develop port, harbor, and resource extraction
infrastructure are all requiring improved cartographic products. Alaska’s vastness
and remoteness are depending on traditional, new, and emerging technologies to
gather the surveying data upon which such projects depend. Horizontal and vertical
control has improved through the use of GPS technologies, methodologies, and
algorithms. Tidal zoning transfers this control to offshore waters and remote coastal
areas, establishing datums for both mean lower low water and mean high water, as
required by NOAA and USGS respectively. From this common point, technologies
are profiling the land or seabed to comparable degrees of precision and cartographic
definition. Photogrammetric technologies, including the use of Side Looking
Aperture Radar (SLAR), coupled with interferometry, are defining coastal uplands to
new levels of precision, regardless of land cover. Air and space borne Synthetic
Aperture Radar is defining coastal lands and land-ocean processes, and river and sea
ice parameters, allowing meter resolution that can be tide coordinated regardless of
cloud cover. Light Direction and Ranging (Lidar), in an airborne configuration, is
bridging the land sea interface, allowing airborne measurement of uplands, shoreline,
and nearshore bathymetry at new levels of efficiency. The swath of land and near
shore imaging couples with multi-beam echo sounder systems (MBES) producing
accurate 3 dimensional cartographic products portraying the coastal bathymetry and
extending off the continental shelf. Together, mapping accuracies are being obtained
to the submeter level via remote sensing tools.
1
Alaska Program Manager, Thales GeoSolutions (Pacific), Inc., 911 W. 8 th Avenue, Suite 208,
Anchorage, AK 99501; phone 907-258-1799; Bob.Pawlowski@thales-geosolutions.com
2
Governmental Affairs, AeroMap U.S., 2014 Merrill Field Drive, Anchorage, AK 99501; phone 907272-4495; pbrooks@aeromap.com
3
Hydrographic Consultant, John Oswald Consulting, 139 E. 51 st Avenue, Anchorage, AK 99503;
phone 907-273-1815; joswald@lcmf.com
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Coastal Surveying and Mapping
Results from Regional forums, including the Marine Transportation System
Northwest Regional Dialog, the ASCE TCCRE Marine Transportation and Coastal
Infrastructure breakout session, and the UAA Cold Regions Ports and Engineering
Conference have identified the need for Alaska coastal baseline data as priorities for
coastal morphology, geotechnical characterization, and erosion/accretion rates.
Interest has increased recently for use of sophisticated mapping technologies for
essential fish habitat, as demonstrated by contract surveys in summer 2001. The need
for coastal baseline data dovetails with efforts by federal agencies in improving the
mapping of Alaska’s coastal areas. Growing interests in state of the art survey
imagery for fisheries and coastal zone management, meteorology, oceanography, and
international boundaries enables technology development and use. (Monahan, 2001).
NOAA and the Department of Interior agencies employ both public and
private assets for state of the art shipborne multi-beam echosounder and airborne lidar
survey technology and dovetail with airborne photogrammetry and satellite imagery
in the coastal zone. Survey data is collected to IHO Order 1 surveys (IHO, 1988) and
to NOAA specifications (NOAA, 2000) or adjusted to DOI National Map Accuracy
Standards. Tide stations provide data for a common datum through tidal measurement
and zoning. Airborne and spaceborne instruments provide improved determination of
shorelines and shoreline features along the southern Alaska peninsula, where
synthetic aperture radar enabled tide-coordinated shoreline with cloud cover (Tuell,
1998). Recent compiling of various sources of data by NOAA was able to provide
verifiable shoreline for surveys in Aialik Bay, Harris Bay, and the Northwestern Fiord
in Kenai Fiords National Park and the southern Alaska Peninsula. MBES surveys,
supported with psuedo-sidescan imagery was collected hydrographic survey data at
each location. In addition to MBES, Lidar imagery has been collected on the
southern Alaska Peninsula, with additional reconnaissance at the Pribilof Islands.
These surveys join with photogrammetric surveys to depict coastal features.
Tidal Measurement, Datums, and Zoning
Tidal datums are vertical reference surfaces used for a variety of coastal zone studies.
Tide data and the associated reference levels are an integral part of all hydrographic
surveying, as well as for determination of the offshore and onshore marine
boundaries, and many other GIS related activities in the coastal zone. No
hydrographic survey has meaning unless the soundings are corrected to a common
datum. The Mean Lower Low Water (MLLW) datum is the reference for sounding
data in the United Sates, while other tidal and geodetic datums are generally used for
data above MLLW.
In Alaska, the importance of tidal datums reached it zenith in the Dinkum
Sands dispute. Dinkum Sands is a low lying gravel feature in the Beaufort Sea, just
offshore from Prudhoe Bay. Offshore oil leasing was conducted in this area in 1978
but the federal and state governments disputed ownership of the tracts. Part of the
dispute concerned whether the Dinkum Sands was indeed an island and above a
specific tidal datum. Because the financial stake of the parties was so great (original
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lease was $450 million), the case was eventually heard by a Special Master (of the
Supreme Court). The U.S. Supreme Court decided the case in 1997 (Reed, 2000),
and highlighted the importance of tidal datum data in establishing mean high water
and accurate shoreline maps. This case brought to attention the poor distribution of
accurate tidal datums and acceptable modern shoreline mapping.
NOAA, National Ocean Service (NOS) has been the primary authority in the
United States concerning the tidal datums. This organization maintains a network of
175 operation tide stations in the United States. In Alaska, NOS maintains and
operated 16 tide-gauging sites. In addition NOS, has occupied nearly 900 gauging
sites throughout Alaska, primarily in support of hydrographic surveying for
production of nautical charts. Due to the age and quality of the data, stability of
bench marks, and vertical crustal motion NOS only publishes about 110 tidal datums
in Alaska, from Prudhoe Bay to Adak to the Tongass Narrow. There are huge linear
gaps in these published datums in western and northern Alaska. From Sand Point
west and north, only 6 additional published datums are available over more than 3600
miles of coastline, spanning 700 miles between the datum between Dutch Harbor and
Nome. NOS maintains data and information at http://co-ops.nos.noaa.gov, which
includes tidal benchmark sheets (descriptions and elevations); accepted tidal datums;
observed and archived tidal data at operation sites; tidal predictions; and publications.
NOAA and contractors add perhaps a dozen new stations per year in Alaska.
Typically, a tide station supporting hydrographic surveying consists of one or more
tide gauges mounted on shore attached to sensors that are anchored below the lowest
tides. The gauges are electronic and typically interfaced to a satellite telemetry
system, with near real time access to the data via the internet. Five bench marks are
established to physically preserve the tidal elevations once the data is analyzed. The
data is downloaded via the web, at a central processing facility. During hydro
operations, the gauges are visited 1-3 times per week to ensure proper operation.
For new sites in Alaska, the tidal datum is computed using 7 to 30 days (or
more) of data using the accepted NOAA method of Simultaneous Comparisons. Data
from an operation NOAA gauge is used as the “base” or control site, and the new data
is mathematically related to this know datum. For re-occupations of existing sites,
the surveyor just needs to establish suitable equipment, and recover the bench marks;
no comparisons with a control station are then needed.
Tidal zoning is a concept of predicting the time offsets and height differences
in a limited project area. Theoretically a tide datum is only adequate in the immediate
vicinity of the tide gauge. For practical purposes the surveyor desires to establish as
few gauging sites that will be practical and meet project standards. For data points
between tide gauging sites a zoning scheme can be made using new and/or historic
data. Conventional techniques rely on linear interpolation to define the geometry of
the zoning cells. Figure 1 shows a recent project in upper Cook Inlet using a
combination of linear interpolation (for the co-range lines) and a wave travel speed
formula for the co-phase lines. NOS is also examining more robust methods for
zoning using harmonics (TCARI) and GPS, while others are trying to adapt numerical
analysis techniques.
Several agencies and countries are beginning to implement GPS for use as a
“tide gauge”. The GPS is mounted on the hydrographic vessel, and phase data
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processed in the Real Time Kinematic (RTK) mode or post processed relative to a
known elevation. This holds great promise, as the tidal corrector is then observed
exactly where needed and not at a shore based tide gauge and then zoned. NOAA
recently funded a Small Business Innovative Research grant to adapt GPS in an
offshore buoy measuring water levels. One hurdle to the GPS approach is that the
fundamental GPS height system (ellipsoidal heights) is different than the tidal datums
that are required for most marine work. The relationship between MLLW and
ellipsoidal height system is poorly known, in Alaska. As the GPS technology
matures more coastal “tide” applications will become commonplace.
Figure 1. Tidal zoning model for upper Cook Inlet. The N-S lines represent co-range
lines while the NW-SE lines represent co-phase lines. Each diamond shaped cell
represents a tidal zone with associated time and height offsets to an operating gauge.
Multibeam Echosounder Surveying
MBES is the technological advance from the coupling of single beam echosounder
systems and side-scan sonar systems. Controlled by GPS and reduced through heavemotion compensation, MBES enables an accurate swath of the seabed acoustically.
However, MBES provides better coverage over the individual systems in that it
enables faster data collection rates and overcomes the limits in the area of coverage,
as was observed in the data collection in upper Cook Inlet. In previous surveys, tidal
currents in excess of 5 knots were routinely encountered and cause difficulties in
maintaining data collection speed and side scan sonar towfish depth and position.
4
MBES enabled a more accurate survey of the area, with high resolution of migratory
features like sand waves, ridges, as well as boulder fields and pipelines.
MBES provides a complete survey of the ocean bottom from a motorized
vessel versus towed vehicle. Collecting a maximum of 101 beams over 150o swath,
an acoustic portrayal of the seafloor is collected. Providing for overlap in accordance
with IHO and NOAA standards, a complete acoustic survey of the ocean floor is
obtained. Sounding volumes, in excess of 3.2 billlion per 150 square nautical miles
are amassed, prior to reduction to a level adequate for accurate digital terrain
modeling. This enables resolution of seabed features at the sub-meter level coverage.
Figure 2. MBES survey of pilot shipping corridors in upper Cook Inlet, as completed
for NOAA, 1999.
Figure 2. depicts a survey of Cook Inlet, as produced from high density
MBES data collected by the Reson 8111 system, on contract for the NOAA. The
survey provides an acoustic portrayal of seabed structures that previously could only
be portrayed by side scan sonar imagery. MBES allows the complete understanding
of the 3 dimensional features that form the seabed structure. Rocky outcroppings,
depositional areas between structures, sand waves, and varying substrate types can be
identified. In the case of Cook Inlet, previous unmapped areas of migratory sand
waves were identified. Similarly, the extent of boulder fields and glacial erratics
could be clearly charted. This presentation also shows the value of combining digital
terrain models with the nautical chart in discerning bathymetric detail versus charted
soundings, shadings, and contours.
5
MBES Psuedo-sidescan and Backscatter Imagery
To address fishery habitat questions, a better understanding of sediment types is
required. The capability to utilize sound attenuation in determining marine sediment
types has been noted for years with the relationship of grain size, porosity, and
attenuation defined by Hamilton (1972). Modern multi-beam technology creates
psuedo-sidescan imagery through the interpretation of the intensity of sound
backscatter. In surveys conducted during 2001, backscatter data was collected with a
Reson 8111 aboard R/V Davidson. The Reson 8111 multibeam sonar produces
backscatter records along with range and angle packets used for bathymetry. The
8111 can generate backscatter data, which can be collected on a beam-by-beam basis.
This backscatter from an individual beam is referred to as a snippet. While a standard
sidescan image is produced using one large beam on each side of the sonar, snippets
are produced individually from each beam in the multibeam sonar. Snippets can be
laced together, end to end, to produce a sidescan type image. The advantage in
snippets stems from a large improvement in signal to noise ratio in the image; the
result of using a focused beam, rather than a broad beam to sample the backscatter
(Lockhart, personal communication). By collecting snippet data as a part of the
multibeam survey, greater understanding of the seabed characteristics can be derived.
Figure 3. depicts a combined digital terrain model, derived from the MBES
bathymetry data overlaid with the psuedo-sidescan swaths enhanced for backscatter.
The image shows the increased distinction of seabed structure derived from the
analysis of beam-by-beam backscatter data and provides association with geologic
features. This processing enables interpretation for classifying seabed morphology
and identifying substrates associated with various habitats.
Figure 3. MBES digital terrain model with backscatter drape from Kodiak, Alaska.
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Airborne Lidar
Airborne Lidar (Light Detection and Ranging) technology is an emerging technology
that is proving itself in addressing coastal issues through Airborne Lidar Hydrography
(Barbour, 2001) and the capability for Rapid Environmental Assessment with
Airborne Lidar Bathymetry (ALB) (West et. al. 2001). ALB provides the ability to
survey in sensitive areas with minimal impact, as demonstrated by the SHOALS
system. Comparable applications have been completed during the 2001 field season
employing the Tenix Laser Airborne Depth Sounder (LADS) (Sinclair, personal
communication). Operating at 1200 feet, surveys were completed over the sensitive
nearshore areas of islands located in the Alaska Maritime Wildlife Refuge. The
Semidi Islands, along with Chankliutt, Chowiet, and Nakchamik Islands. Surveys
were completed from + 20 meters to –23 meters. Depth of survey was influenced by
water clarity, turbulence, and lack of surface obstruction, e.g. kelp. Survey data
provided cartographic information for nautical chart. However, survey also provided
nearshore information on the steepness of beach slope, breadth of intertidal and storm
impacted surf zone, and areas of runoff (through turbidity). Masking of signal
represented areas of submerged and floating aquatic vegetation and runoff associated
with turbidity plumes. Additional reconnaissance imagery provided insight into
specific engineering applications. Figure 4. shows the aerial photograph and lidar
swath of St Paul harbor, Pribilof Islands, including the entrance channel, breakwater,
and harbor basin, as completed by Tenix LADS.
Recognizing the different capabilities based on the technology involved and
the platforms flown, the application of Lidar for ALH proves to be an effective tool
for working in the nearshore zone, where bathymetric data collection is difficult
because of physical factors and environmental conflicts. Utilizing such tools in
engineering applications, particularly environmental assessment, may prove to be a
Figure 4. Aerial photograph and LADS lidar imagery from St. Paul harbor, Pribilof
Islands during August 2001. Images courtesy of Tenix LADS.
cost effective alternative for large well coordinated projects, as long as the
environmental conditions allow adequate penetration into the water column. The
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Aleutian Islands and Southeast Alaska provide just such applications. Cook Inlet, and
other glacially impacted waterways do not. Season applications may exist for the
deltas of Western and Northern Alaska, including Kotzebue Sound and Alaska’s
north slope, where periods of clear water occur during periods of decreased wind and
runoff. The application should be integrated into future decisions, based on
magnitude of the area to be surveyed, shallowness of the bathymetry, and costs for
mobilization and operations.
Aerial Photography and Airborne Positioning (GPS)
Aerial photography and remote sensing have been employed for assessing completion
of integrated airborne and ground-based GPS surveying for many years (Figure 5.).
Data collected is developed into photo laboratory reproductions, image analysis and
GIS services, cartography, digital image processing and mapping, and software
development.
In planning aerial photography missions, remotely sensed satellite imagery is
utilized in real time to dispatch flight crews to optimized acquisition of imagery. The
efficient dispatch system, coupled with multiple flight crews and aircraft, provide the
best possible assurance that projects will be completed on schedule. Flying heights
are customized for each flight line, ranging from 1200 feet to 24,000 feet above mean
terrain. The versatility of equipment and staff to deal with large, multi-state projects,
or small single exposure jobs means critical details such as sun-angle, film type,
camera settings, camera exposure stations and environmental conditions, are correct
for all projects.
Figure 5. Aerial photograph of Anchorage, Alaska from 1950 and 1999, showing 50
years of growth. Photographs courtesy of AeroMap Inc.
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Effective photogrammetry requires the application of precision GPS and
attitude determination of airborne platforms. By resolving combined solutions of
GPS, airborne mobile and land fixed, integrated with Inertial Measurement
instruments and software, project control design is achieved. This provides datum
resolution; accurate geodetic ground control; precise GPS positioning of aircraft and
mapping sensors; and attitude determination of aerial mapping cameras and other
airborne sensors. Present technology allows positioning airborne mapping sensors to
accuracies of 5cm, and to determine orientation angles to accuracies of 20 arc
seconds. Using the GPS/IMU solutions (Figure 6.), sub-meter accuracy can be
carried for distances up to 100 km from the GPS Base Station. Together, advanced
positioning systems greatly reduce, or sometimes eliminate, the need for ground
survey control for mapping operations.
Figure 6. Example of GPS/IMU xyz
control solutions required for attitude
adjustment during airborne data
collection.
In some cases the need for the aero-triangulation step in map production can
also be eliminated, leading to greater costs savings and accelerated schedules.
These stated accuracies are in reference to the map product ground control coordinate
system and allow the production of the highest accuracy and most cost efficient
mapping in the industry. On-going research and development programs continue to
improve accuracies and broaden applications with these airborne positioning systems
Remote Sensing and Geographic Information Systems (GIS)
The latest in airborne GPS and inertial systems are used to control both aerial
photography and remote sensing acquisitions including digital thermal multispectral,
hyperspectral, and LIDAR surveys. Once data for mapping or GIS projects are
compiled, setting up the applications, populating databases, selecting an analytical
approach, and conducting the analysis is completed. By combining GIS and remote
sensing, a wide variety of spatial relationships from simple overlay analysis to
complex network and surface models are accomplished. A recent example was
completed for Fort Knox Mine in interior Alaska. Employing the Intermap
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Technologies, Inc. STAR-3i interferometric synthetic aperture radar products, which
include high resolution DEM (0.5 – 3-meter vertical accuracy, 2.5-meter horizontal
accuracy and 5-meter posting) and Ortho-rectified Radar Imagery (ORRI), Aeromap
conducted image collection for the Fort Knox Mine in interior Alaska (Figure 7).
Figure 7. Orthorectified Radar Image of Fort Knox Mine Project. Plot scale was
1:18,000 and enlarged area at 1:5,000-scale, with absolute accuracy of 2.5 meters.
For this project data was acquired, products developed, and samples provided
of the products with the original data to Alaskan miners for their evaluation and use
as a learning and product-familiarization tool. Below are examples of products that
were produced over the Anchorage area to demonstrate the IFSAR technology and
the value-added products that can be produced to meet the high accuracy mapping
requirements of the State.
Applications of remotely sensed data are not restricted to one sensor, but build
upon the myriad of sensors available. Since the 1980’s data archives have been
privately and publicly available for satellite imagery including LandSAT, SPOT, IRS,
Figure 8. STAR-3i derived products: Topographic map with five-meter contours;
orthorectified radar image map; shaded relief with five-meter contours
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IKONOS, RADARSAT, and both ERS satellites. The data from airborne sensor
systems as well as from satellite platforms, cover the range from the ultraviolet to
infrared and thermal spectral bands. This provides the ability to depict the specific
feature of interest to the scientists or engineer, as shown in Figure 8. This has enabled
low-cost, high-resolution, multispectral solutions using SpecTerra Systems DMSV
system, the Daedalus AMS and Positive System’s ADAR sensor. Hyperspectral
services requiring a selection of more discrete, simultaneously acquired, spectral
bands are being applied. This technology is being complimented by the evolution of
laser-profiling and LIDAR survey acquisitions to develop precision digital elevation
models (DEM) upon which modern GIS systems are dependent.
Mapping, Editing and Image Processing
Editing, Image processing, and GIS applications employ data collection technology
with DAT/EM Summit Softcopy and Analytical Stereoplotter systems. Specially
modified aero-triangulation software, designed for conventional ground control or
airborne GPS control is applied to Alaska mapping projects. With precision image
scanning and a full suite of image processing software and equipment, products
including digital orthographic imagery, color-matched digital mosaics, thematic maps
or high-resolution panchromatic and multispectral satellite imagery are derived.
These techniques are applied to image analysis and land classification or
environmental impact analysis.
Processing to produce comparable images of the seabed is completed through
a comparable specialized suite of software, tailored for resolving acoustically
collected bathymetric data. By employing WinFrog, CARIS, and TRITON-ELICS, 3
dimensional DTM’s, as well as decimated smooth sheets, contoured for depth are
produced. New processing techniques, as applied to backscatter data collected during
the psuedo-sidescan mode, is yielding geomorphology and geotechnical data. These
processing techniques are expanding the information available from specific acoustic
sampling, a limiting factor in surveying beyond the immediate coastal zone.
In the near shore zone, light, in the form of LIDAR, enables bringing
specialized image processing to the data. This processing bridges the challenges
between high speed data collection and reflectance challenges in the land-water
interface. Specialized software enables integrating LIDAR with horizontal and
vertical control to insure consistency between flight lines and accuracy in resolving
water levels with various stages of the tide.
All coastal zone data sets are controlled for both the horizontal (GPS geocorrected image) and vertical (tidal datum) control. Tidal zone models are developed
to derive correctors that may be applied to MBES, LIDAR or coastal
photogrammetry. In either case, rectifying the vertical component is essential in
providing an accurate image or DTM for use in cartographic production or GIS
interpretation. Once processed, all imagery listed above, can be moved into various
GIS applications.
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Conclusion
In conclusion, emerging technologies via airborne, spaceborne, and shipborne
platforms are providing a visual depiction of Alaska’s coastal zone never achieved.
The recent application of MBES with 100% bottom coverage yields information on
seabed that will benefit not just shippers and engineers, but environmental scientists,
fishery biologists, and geologists into the far future. Bridging the shallow coastal
zone with Lidar technology will enable cost effective data collection for coastal
geomorphology and the angle of repose, upon which decisions on coastal
management projects can be made. The juncture of airborne Lidar with aerial
photography promises improved continuity of data into the uplands, given use of
common elevations and combined technologies. Together, when referenced to
accurate horizontal and vertical datums, high resolution cartographic products are
available for engineers, scientists, and managers working in Alaska’s coastal zone.
References
Barbour, K. E. (2001). “Remote Sensing in Hydrography.” Hydro International.
5(3), 7-9.
Hamilton, E. L. (1972). “Compressional-wave attenuation in marine sediments.”
Geophysics. 37(4), 620-646.
International Hydrographic Office (IHO). (1988). IHO Standards for Hydrographic
Surveys (S-44). IHB. Monaco.
NOAA. (2002). “NOS Hydrographic Surveys Specifications and Deliverables.”
http://chartmaker.ncd.noaa.gov/hsd/specs/specs.htm
NOAA. (2002). “Center for Oceanogrpahic Operations Products and Services”
http://co-ops.nos.noaa.gov
Reed, M. W. (2000). Shore and Sea Boundaries. Volume 3. U.S. Department of
Commerce. Washington, D.C.
West, G.R., Lillycrop, W. J. and Pope, R.W. (2001). “Utilizing Airborne Lidar
Bathymetry Technology for REA.” Sea Technology. 42(6), 10-15.
West, G.R., Lillycrop, W.J. and Pope, R.W. (2001). “Keeping a Low Profile.” Hydro
International. 5(4), 28-31.
Tuell, G. H. (1998). “The Use of High Resolution Airborne Synthetic Aperture
Radar (SAR) for Shoreline Mapping.” ISPRS Commission III Symposium. ISPRS
Monahan, D., Wells, D.E., and Hughes-Clark, J. (2001).
Slantendicular Look Ahead.” Sea Technology. 42(6), 44-51.
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“Ocean Mapping: A