March 29, 2024
BANGOR DAILY NEWS (BANGOR, MAINE

Surveyors use GPS to rechart Epping Baseline

On Oct. 19, 1991, the Maine Society of Land Surveyors did a series of Global Positioning System (GPS) observations in Washington County. More than 40 people and every static GPS receiver in Maine were involved in a network of observations that included two points that form what is known as the “Epping Baseline.”

The Epping Baseline was established in 1857 by the U.S. Coast Survey as part of a triangulation network created for coastal mapping. The baseline was one of six precisely measured baselines used in that network and is the only one surviving today.

The Epping Baseline consists of two monuments set 5.4 miles apart with a road connecting them. The west base monument was carved into a granite ledge and has a copper bolt at its center. The east base monument consists of a subsurface mark, over which rests a large granite block with a copper bolt in the center. White Italian marble markers (1.6 feet square and 3.3 feet high) were originally placed over each monument.

The baseline was measured in July and August 1857, using the “Bache-Wurdemann Compensation Base Apparatus.” This was a matched set of brass and iron bars designed so that the opposing ends of the bars would remain a constant distance apart. They were enclosed in a double tin case that was about a foot in diameter and 6 meters in length.

Two sets of bars were leap-frogged 1,453 times along the baseline road, which was constructed specifically for this purpose. Professor Alexander Dallas Bache, superintendent of the Coast Survey, was the chief observer.

In 1858, Bache returned to Maine to make triangulation observations. While at Station Humpback (on what is known as Lead Mountain), he was joined by Jefferson Davis, later the only president of the Confederacy.

The GPS observations made by the Maine Society of Land Surveyors last Oct. 19 were the first complete measurement of the Epping Baseline since the original 1857 measurement. What had required several weeks to do in 1857 took only hours in 1991. Initial results look very promising, with the 1857 and 1991 measurements agreeing very closely.

The volunteers who participated in the GPS observations included practicing and retired land surveyors and surveying engineering students from the University of Maine. The nine receivers were provided by the James W. Sewall Co., Almer Huntley Jr. Associates, the UM Surveying Engineering Department, and the Maine Surveyors’ Service.

Among the people involved in the project were employees from Almer Huntley Jr. Associates in Machias and the James W. Sewall Co. in Old Town.

Information provided by Harold Nelson and Stevenson Sheppard.


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