New Benchmarks?

December 31, 2002

Does the USGS continue to set benchmarks, or are they "all done"? Do they ever go out and replace them? If we find one missing or damaged, do they repair/replace them? Anyone know what/where the newest benchmark is?

---Mike

December 31, 2002

There are two federal government agencies that set a lot of bench marks. The U.S. Geological Survey (USGS) and the U.S. Coast and Geodetic Survey (USC&GS). Sometime around 1970 the name of the USC&GS was changed to the National Geodetic Survey (NGS).

It is my understanding that the bench marks in Groundspeak’s database came from NGS.

New marks are still being set by USGS and NGS, but not very many.

The USGS Mapping Division set most of its marks to provide control on the ground for map making. This was from the era when most maps were made by surveyors on the ground.

http://www.photolib.noaa.gov/historic/c&gs/theb1749.htm

The drawing board is called a plane table. The instrument that the man is looking through is called an alidade. With GPS and other modern map making methods the ground control is no longer needed. USGS still makes maps, but they no longer set permanent bench marks in the process. The Water Resources Division of USGS still sets bronze disks near its stream gages.

http://www.state.nj.us/drbc/gage/gageshp.htm

NGS operates and maintains a network of Continuously Operating Base Stations (CORS). See link for details.

http://www.ngs.noaa.gov/CORS/

Base stations like these are the wave of the future.

NGS also maintains a network of traditional survey marks on the ground called the Federal Base Net (FBN). If an FBN station is destroyed NGS will reset it or set a new replacement mark in the area. Here is the FBN home page…

http://www.ngs.noaa.gov/PROJECTS/FBN/

If you look at some of the maps you can see that the FBN stations are spaced about 100km apart.

When NGS is in an area working on the FBN, local surveyors, state government, and local government have the opportunity to work with NGS to set new bench marks. These points are called the Cooperative Base Net (CBN).

The combined FBN/CBN points are also collectively called a High Accuracy Reference Network (HARN).

January 1, 2003

Many state agencies are ading to the NGS database. New York State has added several GPS set points that became part of HARN. I have found several of them and the coordinates were usesful in testing my GPS

1.5k · January 1, 2003

About the only leveling NGS is doing now is for special projects. My former employeer (retired from MDOT) is doing leveling for NGS.

I think they (NGS) only have 1 or 2 leveling crews left. They were in my area in 1996 leveling to harbors of refuge and the US Coast Guard CORS site, see Portage A, S 346. I talked with the recon team and provide some info to then to locate some control. It was a 2 man team with a 4X4 utility truck, a permanent NGS tech and college intern. The leveling party had a 4X4 suburban and 2 motorbikes for the rodman. 2 NGS techs and 2 college interns. The rodman used the motor bikes to move about and the instrument man road on the running board of the truck. They cover a lot of ground in one day leveling. They needed 3 existing BM's to start the leveling from o each line they set here in 4 different locations around Lake Superior.

[This message was edited by elcamino on January 01, 2003 at 05:24 PM.]