Hal... 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 EM79 > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@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 measuring > > 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 fly > 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 > that. > > I did a quick search, but I didn't find the speed of light as a function of > 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. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.