[time-nuts] The GPS velocity of light versus neutrinos

Hal Murray hmurray at megapathdsl.net
Mon Nov 21 21:06:47 UTC 2011


> Has anyone measured the speed of light with GPS clocks in the same way that
> neutrinos are measured - say between mountain tops? 

I'm pretty sure that won't work very well.  The problem is that air isn't 
vacuum.  The index of refraction changes slightly with temperature.

The subtle changes in the index of refraction are what causes mirages.


The San Andreas fault (and friends) runs right down the middle of Silicon 
Valley.  The USGS has a big research group here.  There are two convenient 
mountains.

They used to do laser ranging between the mountain tops to track the fault 
motions.  In order to get good data, they had to run a helicopter along the 
beam to measure the air temperature.  (Maybe they also measured other things 
like humidity.  ??)  I don't remember where I heard that story.  It was a 
long time ago.

These days, the USGS uses GPS.  They don't need mountain tops.  It's not 
uncommon to see them slightly off a highway.

Maybe I'll remember to ask more at their next open house.

For anybody in the area...  The next open house in Menlo Park is May 19+20, 
2012.
  http://openhouse.wr.usgs.gov/2012/index.html
They have them every 3 years.  Kids welcome.  I always have fun.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.






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