Feature: Mapping Alaska's Biorka Island
Professional Surveyor Magazine - September 2003
Robert 'Chic' Chichester, LS
Alaska is considered to be America's last great frontier for a good reason. From its northern Arctic tundra, to massive mountain ranges, temperate rainforests, and volcanic islands in the south, most of the state is wilderness. Across its vast area, roads are few and far between. Just getting from one point to another can be the most interesting part of the visit.
Needless to say, I was more than a little intrigued when we got a request this past March to bid a job in Alaska. The client, a prominent defense contractor for the U.S. government, needed approximately one square mile of ground surveyed on a small island somewhere near Sitka. The client needed sub-centimeter precision and they were on a very short fuse; we had only days to respond.
Being a small firm, we can usually accommodate a client's need for fast turnaround. Aside from the time required for travel to and from the site, we estimated the entire job could be completed in a day, but threw an extra travel day in to handle any surprises. As an early adopter of GPS equipment, my firm is well-versed in high-precision work. Since dual-frequency GPS was first introduced in a handheld version for geodetic surveying by Allen Osborne Associates, I've found it to be an essential technology when precision and speed are required. Up to that point, Alaska was the only state where I hadn't used my Rascal GPS equipment.
Just one week after submitting the bid, we were awarded the contract. My party chief, Dan Griggs, and I would travel to Alaska in two weeks. All things considered, I was excited and a bit apprehensive about the job, especially as the details of our travel arrangements began to materialize.
During preparations, our main questions centered on the weather and what clothes we should bring. Would it be warm or cold? Would we have to deal with precipitation? With no airstrip on the island, people and supplies come and go by sea, so a small boat would be the final leg of our journey, and neither of us really knew what to expect.
After some calls and a bit of research, the picture about weather and the island's terrain started to come a bit more into focus. Sitka is situated on a protected bay on the Pacific coast, smack dab in the middle of Alaska's southeast panhandle. The entire region is mostly made up of massive ice fields, glacier-scoured peaks, steep valleys, and iceberg-strewn fjords (See map page 10).
Fortunately, in the spring, the low-lying coastal areas enjoy relatively mild weather, with limited precipitation and daytime temperatures that range from the mid-40s to 60s. We figured we would only need a day on the island to complete the work, so we booked overnight accommodations in Sitka. In the end, we still probably packed more clothes than we really needed.
Deciding on our choice of equipment would be simple. Over the years, much of my work has required air travel, so knowing exactly how much gear two men can comfortably carry and still get a job finished easily has become second nature. Three Rascal 8 GPS units, a total station, a tripod, two bipods, and a couple of radios would be all we'd need to get the job done. The Rascal surveying system supports real-time survey calculations, but we knew that this project would require differential GPS, and so we would perform static GPS sessions and bring a lightweight laptop computer for post-processing back in our room in Sitka. We figured that we could always go back out to the island the next day if something went awry.
The area near our destination includes limited habitable areas, which break up the steep and inhospitable terrain. In the 500-mile Southeast Alaska panhandle, there are more than a thousand named islands, and numerous unnamed islets and reefs. Spruce, hemlock, and cedar cover the shorelines, valleys, and mountainsides up to the permanent tree lines that ring the snow- and ice-covered peaks. Wildlife in the area is abundant.
The Expedition Begins
Sitka has quite a bit of history. Serving as the Russian capital of Alaska through the better part of the first half of the 1800s, the town was later the site of the U.S. territorial capital until the end of 1906, when it was moved north to Juneau. Although it was once the center of a vast fur-trapping empire, the area's economy is now based primarily on fishing and tourism.
We left Denver on a chilly April morning. Three flights and 12 hours later, we arrived in Sitka in the late afternoon, with temperatures hovering in the balmy 50s. Early the next morning we would be boarding a small boat for Biorka Island, our final destination.
Most communities in Southeast Alaska are accessible only by plane or boat, making travel somewhat time-consuming. The state's primary air carrier, Alaska Airlines, carries passengers, cargo, and mail, and each stop requires extra time for unloading and loading. Much of the cargo consisted of fish that was headed to markets around the world. Our long layover in Seattle didn't help matters either. With the much-anticipated boat ride scheduled for early the next morning, we had only enough time to check into our hotel rooms, grab a meal, and prepare for a watery trip in the morning before hitting the sack.
The following morning, we awoke to the splendor of Sitka, the only city in Southeast Alaska that actually fronts the Pacific Ocean. They say that on a clear day, Sitka rivals Juneau for the sheer beauty of its surroundings. Arriving at the harbor, we met our client's representatives and boarded our floating taxi, cramming the six of us into its enclosed cabin. Our equipment went into large plastic bins on the deck. "Sorry gents, but they haven't paved the road recently," joked the captain as we motored out of the harbor and into the choppy waters of the bay.
Sitka Sound provides an interesting array of wildlife, including a myriad of sea birds, sea otters, and sea lions. Of particular interest was a group of bald eagles catching herring right out of the water in mid-flight, very close to our boat. It is remarkable how much larger and majestic these birds appear when you encounter them up close in the wild.
After a jarring one-and-a-half hour boat ride, we landed at Biorka Island. The island is lower in elevation than most of the surrounding islands, with an area of a little less than three square miles, and a maximum elevation of approximately 300 feet. It is basically the last rock before the Pacific Ocean, receiving approximately 80 inches of rainfall per year.
Amid the island's scattered trees and brush the ground is mostly wet, consisting of soft, spongy, moss-covered earth and marshland. A couple of vertical bench marks, radio towers, cabins, and a Coast Guard observation station are among the few features noted on topographic maps of the area. Most of these had changed or disappeared since the map was made in 1951. Symonds Bay, the island's primary landing area, is a protected cove on the north shore that includes a permanent dock. The few permanent residents—maintenance and security personnel—live in small cabins nearby. After a quick greeting at the dock by one of the residents we were given the use of the island's only SUV and simple directions.
Finding the Mark
Back in Denver, we had determined that the best starting point for the survey would be the "Biorka" Triangulation Station, set sometime in the middle of the last century. The station coordinates were adjusted by GPS in 1986, but the area's weather and lush vegetation could make finding the point a bit of a challenge. Also, the ground on the island was very wet, with numerous ponds and puddles. Even the rocks were covered with a thick moss. If locating the triangulation station proved impossible, our fallback would be the Coast Guard Continuously Operating Reference Station (CORS), a site that had been fixed more recently, but that provides horizontal data only. The nearest alternative vertical bench mark was back in Sitka.
After an hour of poking, prodding, and kicking the ground, our search paid off. Since the ground is so soft, the brass triangulation station marker had originally been placed on the top of a three-inch steel pipe driven into the ground. As reported in the NGS Datasheet description, the brass cap was missing, possibly chiseled off as a souvenir by someone wandering around the island. The top of the pipe stem had been marked with an "X" and became a point of reference.
We needed to fix the location of three points on the island, all within an area of about a square mile. Two of the points were situated so that GPS units could be located directly above them, and were located with ease.
The third was positioned close to a metal radio tower. In order to avoid GPS multipath effects (signal reflections from metal objects that can interfere with accuracy), we employed differential GPS—a process that uses two GPS units simultaneously.
To perform differential GPS, you place one GPS unit on the known control point, while the second unit is on the unknown point. We found several marker pins (rebar with a stamped aluminum cap) from a previous survey, but had no data on their locations, so Biorka triangulation station served as our known control point.
Since we took three GPS units, we could find the coordinates of two unknown points simultaneously. If not for airline baggage restrictions and the difficulty of hauling equipment through airports, we might have taken more than three GPS units with us. (We actually have five, and often take all of them with us when traveling by car, depending on the job.)
So, using our three units, we set two control points about 150 feet from the tower. We then used these points as a baseline to turn to the point near the tower using the total station and conventional surveying techniques.
We enjoyed excellent GPS satellite coverage at our location. All of our GPS sessions were well over-determined, acquiring eight satellites at each point. Given our unique location, we opted to err on the side of caution and run the survey data on each point three times to minimize the possibility of error. Even so, after less than six hours on the island, we were finished with the physical survey.
GPS technology is a powerful surveying tool for our business. When combined with NGS control point information relatively available through the Internet, in addition to modern mapping programs, we can easily go into unfamiliar areas and perform surveys in a relatively short period of time.
Nearing the End
With some time to kill before meeting our boat back at the dock, we took the chance to take in a bit more of Biorka Island. Probably because of its strategic location at the southern entrance to Sitka Sound, the island has served a number of government and civilian purposes over the years. The remnants of decaying World War II gun emplacements are scattered about the island. After our exploration, we soon found ourselves back at the dock, loading onto the boat.
The ride back to Sitka was just as interesting as the trip out. We took a short detour to watch a group of sea lions frolicking around a rock. Later, the boat's propeller got snagged on a crab trap buoy line and Dan helped the captain to free it.
Although the surveying that day required only a moderate amount of hiking, the two boat trips had added their physical toll. By the time we arrived back in Sitka, fatigue had set in. Fortunately, the only work left was back in the hotel room, where the binary data collected by the Rascal handhelds would be downloaded into the laptop and then processed. The post-processing was performed using Allen Osborne's TurboSurvey software, which features an intuitive graphical user interface that is very simple-to-use. It even enables you to download, manipulate, and process CORS/IGS data with ease.
An hour later, I had completed the data processing and verified that our survey was successful. All I wanted now was a hot meal and some shut-eye before the long trip home to Colorado. I'll remember this trip for a long time—it ranks right up there as one of the most unique and enjoyable survey projects I've ever performed.
Robert "Chic" Chichester is president of Contract Surveyors Ltd., a GPS surveying firm in Denver, Colorado that he established more than 25 years ago.
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