GPS Expedition Scales Mount Rainier to Measure Height

August 16, 2010

An expedition lead by land surveyors have reported the current published height of the iconic Mount Rainer, the first major peak measured via Global Positioning System (GPS) in 1988, has been re-established via updated GPS technologies as part of a multi-element observational expedition by the Land Surveyor's Association of Washington, July 21-25, 2010.

"The new elevation came in at only a few inches different than the previous observations," said Larry Signani, team geodesist for all three expeditions. "The published value will remain at 14,411 feet."

U.S. Geological Survey

According to the announcement, this means that the mountain has not shrunk nor swollen as many have speculated. The measured height was within 0.3' of the previous expeditions - not unexpected considering that the 1988, 1999 and 2010 measurements were all at the same time of year; there have been improvements in the gravity data needed to derive precise elevations from GPS observations; and the observations can now be "registered" to a statewide network of GPS "reference stations."

There were tremendous challenges on this expedition, the chief of them an unexpected storm that delayed the team at Camp Muir. In addition, a wind storm destroyed the tent of the gravity team who were travelling separately on the mountain’s west side. The team had to spend the night in a snow cave before descending; they then drove around to the main trailhead and climbed nonstop to meet the rest of the team at the summit. “This was an amazing feat of climbing," said climb leader and team trainer Bob Anderson of Star Surveying. Poor broadband connections hindered several of the observational tests, but the biggest blow to the expedition discovering that one of the only two permanent survey markers on the summit was not recoverable and that the other had been partially dislodged due to vandalism: without such monuments it would be impossible to repeat observations on the summit.

"We pounded the mark back in as best we could and completed the observations," reported climb team member Mike Lynch of Seattle Public Utilities. The disturbance of the monument could account for much of the 0.3' difference in subsequently observed heights. (Willful desecration of a survey marker is a gross misdemeanor under Washington state law).

For the measurement, the team of nine surveyors carried GPS units that weighed two pounds and were able to use more than 45 satellites for tracking. That contrasts sharply to both prior measurement events: In 1988, the team included more than 140 volunteers using some of the first portable GPS units that weighed over 65 pounds each and had only four GPS satellites visible; and in the 1999 re-measurement, the team consisted of 40 volunteers with 10 pound GPS units and only a dozen satellites available for tracking.

Volunteers from the Land Surveyors Association of Washington (www.lsaw.org) trained for many months in both climb conditioning and in the respective technologies utilized. Provisioning and sponsorship was through association chapter donations, with climb gear in part donated by Columbia Sportswear. State-of-the-art high-precision GPS equipment was provided by Trimble (www.trimble.com), who was also the technology partner for the two previous expeditions.

Along with GPS and meteorological equipment, the team used sensitive gravity meters provided by, and with technical assistance from, the University of Washington and the United States Geological Survey (USGS). The team gathered gravity measurements at various key locations on the mountain; this data will be added to public domain scientific databases. Gravity data is valuable for studies of potential volcanic hazards, like gauging the depth, density and material types that the mountain might release as a "Lahar"-type mudslide as part of an eruption event. Land surveyors are also key users of gravity-based data products; the field of physical geodesy has advanced to the point where whole countries are adopting "gravity-centric" datums that provide a more precise and consistent measure of elevation above sea level for improved floodplain determinations, irrigation and environmental stewardship. These datums are made possible in part by coupling high-precision GPS and gravity observations, particularly in challenging locations, such as this expedition.

The team reported they tested new high-precision GPS techniques and methods utilizing the Washington State Reference Network or WSRN (www.wsrn.org), a cooperative public/private array of 100 GPS continuously operating ground stations covering the entire state. These stations process together and can provide "correctors" deliverable via mobile internet for surveyors, precision agriculture, public safety, structural monitoring (like on Howard Hansen dam), machine-guided heavy construction and environmental mapping, all in real time. "Most folks are familiar with the plus or minus 20 feet that their car GPS can provide," says WSRN Administrator Gavin Schrock. "Network GPS can instantaneously provide precisions the size of a dime".