On 2/19/14 10:24 AM, Brooke Clarke wrote:
Hi:
This means that the concrete piers where many Cesium clocks and GPS reference stations are located are bobbing up and down as if they were on a ocean, although only tens of inches.
My GPS friends comment when you start getting to sub-meter precision for non-differential measurements, there's a whole lot of effects that start getting in the way. ionosphere, multipath, solid earth tides, etc. They're all in the "centimeters but not meters" bucket.
I think there was an earlier post saying this puts a limit (E-16?) on the ultimate quality of a clock because of it's movement. I wonder if NIST has one of the GWR gravitymeters on a pier and uses that to discipline their fountain clocks for the elevation change of the pier or if that's done for the GPS reference antennas?
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