[time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference
bg at lysator.liu.se
bg at lysator.liu.se
Sun Dec 10 19:12:57 EST 2017
Citerar Mark Sims <holrum at hotmail.com>:
> In the standards definitions that include "at sea level", the
> question these days is "which sea level?". As ocean temperature
> changes sea level will change (except maybe in Washington DC). Will
> the standards be amended to include something like "at sea level in
> 1990" or will the value being defined drift around with the changing
> sea level?
From the current Swedish vertical datum.
(http://www.lantmateriet.se/globalassets/kartor-och-geografisk-information/gps-och-matning/geodesi/rapporter_publikationer/rapporter/lmv-rapport_2007_4.pdf)
"This realisation was made using the Normaal Amsterdams Peil (NAP)
as zero level
in the traditional European way. [...] It has for instance been
questioned whether NAP is the most suitable way to fix the
zero level. Is it not better to wait for a so-called World Height
System (WHS), which is fixed using GPS and a global geoid model of cm
accuracy?"
Has the World Height System been agreed/released?
http://www.euref.eu/documentation/Tutorial2015/t-04-02-Ihde.pdf
Picture showing reference origin for vertical datums in Europe.
https://en.wikipedia.org/wiki/File:Vertical_references_in_Europe.svg
--
Björn
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