[time-nuts] Steve's new QTH...
tholmes at woh.rr.com
Tue Sep 7 19:26:31 UTC 2010
Maybe they were actually interested in the humidity as a source of phase
distortion or attenuation?
Maybe they wanted to prove that the temperature did not cause a problem?
Or maybe just a government paid-for helicopter ride.
Tom Holmes, N8ZM
Tipp City, OH
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Hal Murray
> Sent: Tuesday, September 07, 2010 2:57 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Steve's new QTH...
> > Many years ago I ran into a combined group on Mt. Wilson, our local
> > broadcast farm in the mountains, from Cal Tech and MIT that was
> > the movement between Southern California mountains using lazers. While
> > this was scientifically fascinating, it gave me the willies.
> I'm in Silicon Valley. There is a big USGS group here.
> They used to have a laser setup between Black Mountain and Mt Diablo which
> are on opposite sides of the fault, roughly 50 miles apart. They used to
> a helicopter along the beam, measuring the temperature so they could get a
> more accurate answer.
> Fault motion is ballpark of 1 inch per year, the same as your fingernails
> grow. So they would want to measure the distance to a (small) fraction of
> I did a quick search, but I didn't find the speed of light as a function
> temperature. 50 miles is 3E6 inches so 1 PPM would be a big deal.
> I think they do it with GPS now.
> These are my opinions, not necessarily my employer's. I hate spam.
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