Hi Add to that the fact that not everybody is moving at an inch per year. Around here the magic number is in the 1.5 to 2 mm per year range. It’s enough to be worth correcting survey results vs benchmarks every few years. It’s not enough to get into an L1 timing system any time soon ….
Bob > On May 25, 2015, at 1:29 PM, Tom Van Baak <[email protected]> wrote: > > Attila, > > Timing people account for everything that's important. A continental drift of > an inch per year acts like a slow phase change over time, which by > definition, is a frequency offset. So an inch per year is at most 1/12 * 1e-9 > / (365*86400) or 3e-18. For the current precision with which UTC/TAI is > calculated this is too small to worry about. > > The other way to think of the frequency offset is simply the ratio of > speed-of-continent vs. speed-of-light. A continent is slow, about 1e-9 m/s > and light is fast, 3e8 m/s. This ratio is about 3e-18. > > Note that an inch-per-year is about a nanometer-per-second. I'm also told > fingernails grow about an inch a year. How's that for a rule of thumb > (literally). > > There's a nice (1 inch) 25 mm per year interactive drift map here: > http://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity-Viewer.html > > The nice thing about GPS, unlike other time transfer methods, is that can > handle the case of a moving antenna. As the antenna moves so does the time. > This is why GPS timing receivers work (almost as well) on top of your car as > on top of your house. Just think of continental drift as a slow moving car. > > /tvb > > See also: > http://www.iris.edu/hq/files/programs/education_and_outreach/aotm/14/1.GPS_Background.pdf > http://www.unavco.org/education/resources/educational-resources/tutorial/how-quickly-are-we-moving-gps-tutorial.pdf > > > ----- Original Message ----- > From: "Attila Kinali" <[email protected]> > > I am not sure whether anyone accounts for continental drift in timing > applications. I would guess that at least people in VLBI have to. > Given that most GNSS high precision time transfer is used rather locally > (a couple of 100km) and that few people are running it for more than > a couple of months without recalibrating the system, i'd say that the > drift rates (which are between 2.5cm(Arctic) and 15cm(Chile) per year) > do not induce much error/jitter. > > Attila Kinali > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
