[time-nuts] Valentines Day & Love Numbers
jimlux at earthlink.net
Wed Feb 19 23:33:46 EST 2014
On 2/19/14 10:24 AM, Brooke Clarke wrote:
> 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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