Recovering stations a family activity


Over time, some of the marks located flush with the ground can become buried. This one, EF1666 beside Highway 195 in front of the Double Springs Elementary School, had to be uncovered. It was monumented in 1989.

WINSTON COUNTY - Instead of making a long trip during this pandemic we’re in, why not take your family on a historically fun activity and never leave the area? It can be done by a hobby called benchmarking, where the use of a smart phone and GPS locating can help find triangulation stations and survey marks. Who knows. You may be the first to visit one of the stations since it was placed, or monumented. It is similar to geocaching in where an object is hidden, the latitude and longitude is given and someone tries to find the object. The same principle applies to benchmarking.
Survey marks from the National Geodetic Survey, part of the National Oceanic and Atmospheric Administration, are located throughout the country, yet they are not widely known about. They are spread through Winston County as well. Did you know they were there? Chances are you did not. What are the marks used for? What are they? How do you find them?
The survey marks are generally small round disks, 3.5 inches in diameter and are set in a block of concrete flush with the ground. A carsonite witness post is found by some of the newer ones to help mark its location. A year is almost always stamped on the disks and have been in the ground for decades.
There are more than 100 stations in Winston County, and they date back as far as 1929 and as late as 1994.
These marks help surveyors and the NGS in keeping “horizontal control” through North America. With two marks, triangulation and trigonometry can be used to measure direction, distance and elevation. This helps locate boundaries and monuments  while helping map makers understand the volume and area of the earth. Those listed as triangulation stations will have a triangle stamped on the disk.
Another useful example is the horizontal change during the 1964 earthquake at Prince William Sound near Alaska. Measurements before and after the earthquake showed a change of more than 15 meters both horizontally and vertically each way over several hundred square kilometers.
“The establishment of the triangulation stations (horizontal survey control monuments) was originally a method of extending the U.S. national datums and providing a way of access to them,” Denis Riordan, regional geodetic advisor of NOAA, explained. “The first U.S. national datum was the North American Datum of 1927 (NAD27), which was updated with a new datum in 1983 (NAD83). These stations were established through angle measurements between stations, that could then be used to establish positions on new marks. Most of the triangulation marks established up to the last of them in the early 1980s were miles apart and required multiple ‘sets’ of angles to be taken to reduce the errors that could be a part of the instruments and methods of measurements. Along with the station there was also an ‘azimuth’ mark that was normally about a quarter of a mile away and would allow a user to set up their instrument over the station, sight in the azimuth mark and then begin a horizontal traverse with known angles relative to the national datum.”

 


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