Control on the Edge
October 1, 2009
How do you build an airport for a small island characterized by rugged terrain? For the city of Akutan on Akutan Island in the eastern Aleutian Islands of Alaska, it was a challenging question. The mountainous island, which lies 35 miles east of Unalaska and 766 air miles southwest of Anchorage, is home to the largest seafood production facility in North America. The city occupies 14 square miles of the 129-square-mile island. Although fewer than 800 people live in Akutan year-round, seasonal employment in the commercial fish-processing industry often doubles the island’s population. Yet access to the island is difficult. Most transportation is by boat or seaplane, neither of which is reliable given the frequently rough sea conditions. Additionally, the amphibious plane that serves Akutan out of Unalaska--a 1940s-era Grumman Goose that is the only aircraft capable of handling the wave conditions in Akutan Bay--is nearing the end of its useful life. Without the Grumman Goose, Akutan will no longer be accessible by air.
When officials with the Alaska Department of Transportation & Public Facilities (DOT&PF) began studying the problem several years ago, they decided that a land-based airport was imperative to improving the mobility of people and goods in the region and ensuring continued direct-flight access to the island. Since Akutan was not a viable location for an airport, officials turned to the neighboring island of Akun. Although it is just 12 miles long, Akun Island is unpopulated and features a 1-mile strip of lowland--enough space to accommodate the 4,500-foot paved runway, taxiway, apron, and snow removal equipment and sand storage buildings that would comprise the airport. A hovercraft and barge system would be developed to transport people and freight across the Akun Strait to Akutan. It was the ideal solution. The only remaining challenge was overcoming the remote location, extreme weather and rocky terrain of Akun Island.
DOT&PF officials selected HDR Alaska Inc. as the design-build consultant for the project. HDR, in turn, contracted USKH Inc., an Anchorage-based multidisciplinary firm, to handle the survey work. USKH was already familiar with the region: In 2001 and 2003, the firm had performed photo control and profiling surveys on Akutan Island under contract with HDR, and in 2005, USKH crews conducted limited control and profiling surveys on Akun Island. “We learned from our previous survey jobs that this location presented many physical and logistical challenges,” says Jake Gerondale, PLS, USKH project manager. “These factors, combined with a fast turnaround time and an extensive uplands topographic survey area, created a daunting project. But,” he says with a laugh, “we are Alaska surveyors--this is what we do.”
Planning the ExpeditionUSKH was tasked with establishing an extensive control network for the airport and conducting bathymetric surveys around the two islands to assist in the selection and design of the landing sites for the hovercraft and barge. Crews would also need to conduct uplands topographic surveys for the proposed runway, access road, and infrastructure for the barge landing site on an area that totaled approximately 1,100 acres while locating and recovering all of the Public Land Survey System monuments in the area for use in right-of-way mapping and acquisition. It was an ambitious project, and the crews had no time to waste: All of the work had to be completed within a three-month time frame.
“The conditions on the Aleutian Islands can be some of the most unforgiving and difficult conditions in the world,” Gerondale says. “Just getting personnel and survey gear to the jobsite alone was a challenge. We had to collaborate closely with HDR Inc. and DOT&PF to determine which methods to use and figure out the travel and lodging logistics.”
The team knew that such an extensive survey would require a combination of GNSS and leveling as well as specialized equipment like hydrographic gear and tide gauges. For the land-based surveys, USKH decided to rely primarily on Trimble R8 Model 2 receivers with integrated antennas and Bluetooth technology. The equipment’s lack of cables was a key factor in this decision. “Our crews had learned on previous projects that the native Arctic foxes are particularly fond of chewing on bright yellow GPS cables,” Gerondale explains. Additionally, the equipment’s higher efficiency meant fewer and lighter batteries, and the light weight and compact size meant that more ground could be covered in a day with less fatigue.
For the hydrographic work, USKH chose the Ross Surveyor Model 960 integrated echo sounder because it records a digital trace that would be easier to transfer back to the Anchorage office via electronic file on a CD instead of a thermal paper trace. It also has an integrated computer in a weatherproof case, which would lend itself well to temporary installation on an open survey vessel.
Before heading out, surveyors searched the recorder’s office, BLM, NOAA and other public records for any details and historical documentation that would aid their work. However, except for the PLSS plats and field notes, little outside information existed on the small, remote island. Fortunately, the crews had access to internal interferometric synthetic aperture radar (IfSAR) digital terrain models (DTMs) of Akun Island from the 2005 project. “The single most important piece of information we had was our prior knowledge of the site,” Gerondale explains. “That information helped us to perform this project in the most efficient way possible.”
Controlling the WildWith the background information and DTMs in hand, the USKH survey crews traveled to Dutch Harbor in Unalaska, Alaska, in July 2008. There they chartered the Grumman Goose to transport them and their gear to Akutan Island. From Akutan, the surveyors had to rent a boat and cross the Akun Strait to Akun Island. It was an arduous and sometimes treacherous journey. “Just getting from Dutch Harbor to Akutan could take anywhere from two to seven days depending on the weather conditions,” Gerondale says. Crossing the Akun Strait to reach Akun Island was also difficult. “The extreme tidal influences in the area can cause significant wave action, even without the help of the 50-plus mph wind that frequently visits the area,” Gerondale explains. “There were multiple days where our survey crews could not work because it was too dangerous to cross.”
Once on the island, the crews’ first task was to establish an extensive control network, which included setting primary and secondary airport control stations in accordance with NGS and Federal Aviation Administration standards. Due to the unique tidal influences of the area, crews set two bubbler tide gauges (Design Analysis Associates/YSI H350XL/H355) to establish the mean lower low water elevation as the basis of the vertical control for the project. “The orifice location needed to be very stable and stay well below the water column, which presented a problem at the aptly named Surf Beach,” Gerondale explains. “Our solution was to venture out at extreme low tide with chest waders and drive a 6-foot rebar into the sand well below the waterline to support the orifice.”
When weather and water conditions permitted, the crews worked 10 to 12 hours per day, seven days a week, walking countless miles on the steep, rocky terrain of the island. Using four Trimble R8 Model 2 GNSS receivers and two Trimble 5700 GPS receivers, crews logged static GPS data for eight or more hours during three sessions at the primary and secondary airport control stations. They conducted subsequent four-hour-plus sessions at 15 secondary control points at three locations on Akun Island and at the hovercraft storage facility and seaplane base on Akutan Island. They logged additional fast-static sessions to tie cadastral corners with at least two baselines and to determine the loop closure to each measured point.
Using a Leica NA2 automatic level, the surveyors also performed third-order differential leveling on the island between secondary control and connected to the primary and secondary airport control stations. Numerous temporary bench marks were loop-connected to secondary control; these were used at various tide and water-level observation stations.
For the bathymetric surveys around both islands, the USKH surveyors developed a plan that would ensure a quality product for design of the hovercraft landing sites and related infrastructure. The team converted their rented boat into a survey vessel by installing an adjustable steel rigging they fabricated for this purpose. Relying on RTK for navigation and tide measurement, the surveyors used a side-mounted 200 kHz three-degree shallow water transducer connected to a Ross Surveyor Model 960 echo sounder to collect bathymetry at three locations on Akun Island and at the hovercraft storage facility and seaplane base on Akutan Island. To compensate for the heave- and roll-induced vertical movement of the transducer, they used the Trimble R8 system in low-latency mode at 10 Hz. The crews used HYPACK 2008 software with GPS time syncing to collect the sounding data. Quality-control procedures included a frequent schedule of bar, navigation, and water-level checks as well as several latency test lines to ensure that the GPS time syncing was working properly.
Extensive RTK topographic surveying was performed in the areas of Akun Island surrounding the proposed access road and runway alignments and within selected areas to provide ground truth for the DTM derived from the 2005 IfSAR. Uplands topography was also gathered at all five bathymetric locations. To assess RTK topographic quality, several base stations were set up and periodically used consecutively at the same point to perform system checks. “I was able to rely on the technical experience of my staff and their experience working on remote jobsites--especially in this area--to ensure that we were able to overcome the technical and logistical challenges of this project,” Gerondale says.
Mapping the WildernessCollecting the data was one challenge; processing and transferring them to USKH’s Anchorage office for additional post processing proved equally demanding. The only reliable means of transferring data from and to Akutan was mailing CDs. But mail in Akutan is also weather-dependent. “If the Grumman Goose doesn’t fly, mail doesn’t get delivered,” Gerondale says with a laugh. “We knew this, and we planned accordingly.”
As the static observations were processed, work didn’t always go as planned. “Loop closure errors for several combinations of baselines between the two islands were higher than expected in the vertical component, so many attempts at cleaning and adjusting baseline processing settings were made,” Gerondale says.
The leveling observations, including differences in elevation and number of turns between control points, were keyed into Excel spreadsheets and entered into StarNet for a least squares adjustment. Comparisons between uncalibrated GEOID06 orthometric heights and leveling results at static control points and temporary bench marks observed with RTK on Akun Island revealed a trend indicating a slope north of approximately -45 ppm. The team decided to apply this slope to all GPS observation on Akun Island to best match leveling results.
The RTK topography was processed holding static network results for RTK base station positions and control points used for the check shots fixed in 3D. A 2008 coordinate system developed by DOT&PF was used as the basis for all project RTK measurements, as well. A large number of check shots were performed to ensure good on-the-fly initialization and to rule out systematic errors. “The vast majority of RTK check shots were well under 0.10-foot in XYZ,” Gerondale says.
For the hydrographic work, latency lines evaluated in HYPACK 2008 confirmed that GPS time syncing was working well. As a result, the team decided not to apply time offsets during line editing. The HYPACK 2008 line editor was used to simultaneously view and edit the navigation route, the echogram profile and the RTK water-level profile. Each bathymetric line was carefully edited to remove kelp artifacts and to replace false readings from the water column with depths representing the bottom. Ross Playback software was used to view each raw sounding trace during HYPACK line editing and to identify and measure the bottom where an invalid depth had been recorded.
After the cleaning process, cross-line statistics were evaluated. “These statistics yielded a good bell-shaped distribution well within survey design parameters that considered the irregularity of the bottom, survey depths and three-degree beam width for the shallow water transducer,” Gerondale explains.
To process the tidal datums, USKH relied on the expertise of JOA Surveys, an Alaska-based surveying firm specializing in tides and water-level measurement. The USKH team gathered from the West Coast and Alaska Tsunami Warning Center (WC/ATWC) a full year of raw data from a radar tide gauge installed at the Akutan skiff mooring area in Akutan Harbor. They provided this data along with tide gauge data and staff observations collected on the Akun Island to the JOA Surveys team, who processed them to calculate mean low low water datums for both islands using NOAA/NOS methods.
Selected hydrographic survey points in the study areas were contoured to provide a final check on the bathymetry. RTK topography was processed using Carlson Survey 2009 Field-to-Finish in groups of approximately 3,000 points. Once complete, the separate groups of RTK points, line work and symbols were combined into one drawing file representing the topography. Triangular irregular network (TIN) borders were then created surrounding both the uplands topography and bathymetry, and continuous DTMs were generated. “We performed quite a bit of TIN editing, especially in and around drainages, to ensure the ground was modeled correctly,” Gerondale says. Deliverables were provided in AutoCAD Land Desktop 2008 drawing and surface files. USKH also provided HDR with a detailed survey report.
Despite the complex requirements of the project and the numerous challenges encountered during the fieldwork and processing, the team completed the project on time and within budget thanks to their experience, skill, collaboration and use of technology. “The extreme remoteness, weather, terrain and wildlife truly make this one of the most difficult yet interesting places in the world to work,” Gerondale says. “We wouldn’t have been able to complete this job without the dedication of our field and office staff.”
Acknowledgments: During this project, USKH survey crews lived and worked in the city of Akutan. “This project’s success can be attributed in part to our friends in Akutan who provided lodging, rentals, labor, and their expertise of the area,” Gerondale says. “The residents of Akutan were always willing to help us in whatever way they could and made us feel welcome in their community.”
Sidebar: Project SummaryKey Players
• Jake Gerondale, PLS, Project Manager
• Sam Denny, Survey Party Chief
• Dean Bergman, LSIT, Geomatics Specialist
• Jake Maxwell, Survey Technician
• Marshall Hetlet, PLS, Senior Surveyor
• Dan Androes, Survey Technician
• Tom Reber, PLS, Survey Party Chief
• Gary Runa, PLS, Survey Party Chief
• Jennifer Brownlee, Survey Technician
• Tom Copley, Survey Technician
JOA Surveys (www.joasurveys.com)
• Erik Oppegard
• John Oswald, PLS
HDR Alaska Inc. (www.hdrinc.com)
• Scott Wharton, PE, Project Manager
Alaska DOT&PF (www.dot.state.ak.us)
• Doug Campbell, LSIT
• Bob Keiner, PLS
• Matt Burkholder, PLS
• Ryan Quigley, LSIT
• Mike Miller, PLS
• Louise Hooyer, PLS
• Trimble R8 Model 2 GNSS receivers
• Trimble 5700 GPS receivers (www.trimble.com)
• Leica NA2 automatic level (www.leica-geosystems.us)
• Ross Surveyor Model 960 echo sounder (www.rosslaboratories.com)
• Design Analysis Associates/YSI H350XL/H355 bubbler tide gauges (www.waterlog.com)
• HYPACK 2008 (www.hypack.com)
• Carlson Survey 2009 (www.carlsonsw.com)
• Trimble Geomatics Office
• Trimble Business Center (www.trimble.com)
• StarNet (firstname.lastname@example.org)
• Autodesk Land Development Desktop (www.autodesk.com)