What's a gravity station disk

[+dexteri]

Two years ago I found a benchmark in Great Falls Montana that had a Marker Type listed as "gravity station disk" The disk read "International Gravity Station University of Wisconsin" as was stamped "Great Falls B".

 

So what is an International Gravity Station? Didn't notice any changes in gravity in the area []

[2oldfarts (the rockhounders)]

More than you would ever want to know....

[DaveD]

Without gravity observations there would be no way that NGS (USC&GS) could provide accurate heights (bench marks) for the country. These observations are vital to the proper reduction of leveling observations. They are also an important part of the horizontal component of the reference frame as they help in the determination of what's call the Deflection of the Vertical. This allows for the accurate determination of the relations between the Earth's gravity field and the determination of coordinates on a mathematical reference surface -- the ellipsoid. NGS is currently involved in a historical undertaking to observe gravity from space platforms (GRACE, GOCE), airborne, absolute, marine and relative measurements to form the foundation for a new national vertical datum based purely on gravity data- bench marks from NGS will become a thing of the past. This effort is describe in detail on the NGS web site (http://www.ngs.noaa.gov) and search for GRAV-D (Gravity for the Redefinition of the American Vertical Datum)

[Bill93]

Don't worry-benchmarks won't be obsolete for another decade, so we have a while yet to log them.