Surveying on the Icefield
The goal of surveying on the Juneau Icefield is to determine glacier movement and track surface elevation changes. Historically, this was accomplished using standard survey gear such as theodolites and EDMs. GPS equipment was used for the first time in 1992 and, due to the great advantage it offers, has now replaced the older theodolite gear and methods. Here you'll find photos showing the activities of the survey program.

This is how it was done in the old days (1988). It used to be that we could survey only when the weather was nice (tough life, eh?). But now with GPS, we're able to survey when it's raining, blowing, snowing, and cold (isn't technology supposed to make things easier?).

A typical movement profile is composed of a line of stakes placed from one side of a glacier to the other. This profile is on the Northwest Branch of the Taku Glacier. The flags, made of garbage bags stapled to 1" x 2" wooden stakes, are placed, in this photo, at an interval of 317 meters. The average daily movement of the glacier at this profile is 6 cm.

Benchmarks are extremely important in glacier surveying. They serve as a known reference point for determining how an unknown point on the glacier is moving. These benchmarks are cemented in holes that are drilled into solid bedrock.

And this is how the holes are drilled. A special steel rock drill is literally hammered into the rock, creating a 3/4" diameter hole. The brass benchmark is then cemented into the hole. In hard granodiorite, it takes about 3-4 hours to drill a hole 2" deep. It helps to have several people who can take turns hammering!

After the benchmark is cemented in place it must be surveyed to determine its exact position. To do this, a GPS receiver is centered over the benchmark. Satellite signals are then collected for several hours. The data, when combined with the data from a GPS receiver positioned over a known benchmark, then gives the position of the new benchmark within the International Terrestrial Reference Frame.

In order to determine glacier movement to within a few centimeters, a GPS receiver must be set up at a benchmark. This base station then serves as a reference in determining the position of a second receiver that is placed at each of the flags of a movement profile. This photo shows the base station set up over a benchmark on a nunatak. The Taku Glacier is in the background.

After setting up the reference receiver, the survey can commence. In the photo above, we've just placed the reference receiver and are heading down from the nunatak to begin the survey.

While the reference receiver is operating back at the benchmark, the roving receiver is placed at each flag of the movement profile. This photo shows the rover set up and collecting data at one of the flags, which has been removed, and the GPS antenna put in its place.

Here's a closer view of the roving receiver in operation.

The reference and roving receivers collect signals from multiple GPS satellites. Here, the roving receiver is currently tracking and receiving the signals from five different satellites.

You've heard the saying, "Hurry up and wait." Well, that definitely applies to GPS surveying when doing a rapid-static survey as we're doing here. The receiver is placed at each flag for 15 minutes, during which time it takes a reading every 15 seconds. Then, we hurry to the next flag so that we can wait again.

Here's another example of "hurry up and wait." Before the use of GPS equipment, surveying was accomplished with theodolites and EDMs. This required clear visibility from the benchmark to the flags in order to perform a survey. While fog often limited visibility, it was common to head out in a total whiteout in the hope that the fog would clear by the time we arrived at the survey site. More often than not though, we would simply end up waiting on a nunatak all day for the weather to clear, only to return to camp with no survey data. Here, you see our makeshift rain shelter where we're waiting for the weather to clear enough to do the survey.

Here's another view of our rain shelter later in the day bathed in a small patch of sunshine. Although the weather was starting to look promising, it soon closed in again. Result: no surveying this day!

While we can use oversnow vehicles for much of the survey work, some areas require leaving the vehicle behind and proceeding on foot. This is particularly true near the edges of the glaciers, where often extensive marginal crevasse zones require close scrutiny for safe travel.

And in some areas, such as in the Gilkey Trench shown here, vehicle support cannot be used at all. In such cases, everything we need, including survey stakes, has to be carried down on our backs. This photo was taken in 1990. During the summer of 1998, the lower third of the icefall in the background broke loose, exposing the bedrock underneath it. By the summer of 2000, the icefall was completely detached from the Gilkey Glacier.

Here, a GPS survey is being conducted at the base of the Vaughan Lewis Icefall to determine surface velocities, elevations, and strain rates. The movement here was measured at 39 cm/day.

Most surveys on the Juneau Icefield are done to determine surface movement and elevation changes. Periodically, we also survey the terminus of the advancing Taku Glacier to determine its rate of advance. Here, across the Taku River from the glacier, a helicopter ferries people and equipment to a reference point.

Before GPS totally replaced traditional surveying methods, theodolites and EDMs were the tools of choice. Here, a member of the survey team sets up the equipment in preparation for surveying the terminus of the Taku Glacier, which is seen in the background.

While most glacier surveying involves the use of a stationary benchmark on a nunatak, sometimes the requirements of a survey project dictate setting up directly on the glacier surface. One such survey is shown above. The objective here was to determine the strain rate across a triangular area of the glacier. This allows us to calculate how one part of the glacier is moving in relation to other parts.

While one team member takes angle and distance observations from one point of the strain triangle, another person sets up the target at one of the other points of the triangle. Prisms mounted on the tripod reflect the infrared beam from the EDM back to the observation point, thereby giving the distance between the observing and target points.

When doing theodolite surveys, it was imperative that we take advantage of every clear day. On this particular cloudless day, surveying was going full bore. The theodolite on the right was employed for surface movement surveys of the Gilkey Glacier, while at the same time the phototheodolite on the left was being used for a photogrammetric survey of the Vaughan Lewis Icefall in the background. The umbrella was used to shade the instruments from the distorting effects of solar radiation.

Unlike the days when we used to perform surveys on skis, we now rely on the rapid transportation available by oversnow vehicles. When establishing the survey flags for the first survey of the summer, the driver uses a handheld GPS to navigate to within 3 meters of the spot where the flag is to be located. The person riding in the sled then uses high precision real-time differential GPS to find the exact spot to within 10-50 centimeters. The survey flag is then placed and surveyed.

Most movement profiles on the Juneau Icefield are transverse profiles; they extend from one side of a glacier to the other. This provides data on the cross-glacier movement profile, but it does not show how the movement of the glacier varies along its longitudinal centerline. This photo shows the survey of a longitudinal profile on the Taku/Matthes/Llewellyn Glaciers. This profile follows the centerline of the glaciers, with survey points spaced at 500 meter intervals. This gives a very detailed view of the spatial variation of surface velocity, elevation, and gradient.