[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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