On Mon, 30 Nov 2015 12:00:01 -0500, time-nuts-requ...@febo.com wrote: > Message: 2 > Date: Sun, 29 Nov 2015 08:31:18 -0800 > From: "Tom Van Baak" <t...@leapsecond.com> > To: "Discussion of precise time and frequency measurement" > <time-nuts@febo.com> > Subject: Re: [time-nuts] Einstein Special on PBS > Message-ID: <F12DE74B7F824FF8BEB815D51C1C3965@pc52> > Content-Type: text/plain; charset="utf-8" > > Hal, > > Right. The orbits are nominally circular -- but not exactly. The set > of orbital parameters cover these details. A quick google search > suggests the eccentricity for GPS is around 0.01. Still, that's > enough to cause +/- 23 ns of accumulated phase error per orbit. I'm > pretty sure the receivers take care of this math, since eccentricity > is a key part of any orbit model. I wish we could see the source code > to a GPS timing receiver. > > I'm not sure I understand your elevation question. Are you talking > about elevation as in mountain vs. sea level altitude? Or elevation > as in satellite Az/El? > > GPS satellites in view are about 20,000 km (overhead) to about 25,000 > km (horizon) away, so the signal gets to you within about 65 to 85 > ms. Whether you apply the full 4.5e-10 relativistic correction or no > correction to the SV clock at all, it makes only a 1 cm > time-of-arrival difference. That's why I said for trilateral > navigation purposes, the relativistic effects are in the noise. For > UTC time-transfer, however, an uncorrected 4.5e-10 frequency error > would continuously accumulate, giving 38 us/day phase error, the > number you often hear. > > About survey grade -- I suspect the post-processing takes into > account anything you can think of, from the shape of the antennas to > space weather to the phase of the moon (literally).
Yes, literlly: .<https://gipsy-oasis.jpl.nasa.gov/> Ten or twenty years ago, I dug deep into this stuff. Every module was somebody's PhD thesis. Joe Gwinn > > /tvb > > ----- Original Message ----- > From: "Hal Murray" <hmur...@megapathdsl.net> > To: "Discussion of precise time and frequency measurement" > <time-nuts@febo.com> > Cc: <hmur...@megapathdsl.net> > Sent: Saturday, November 28, 2015 2:37 PM > Subject: Re: [time-nuts] Einstein Special on PBS > > >> >> hol...@hotmail.com said: >>> The GPS spec implies the satellites have a fixed frequency offset to >>> compensate for relativistic effects. But do they actually >>> dynamically and/ >>> or individually adjust the frequency to adjust for orbit variations and >>> eccentricities? >> >> I think the orbits are circular so the frequency won't depend on the >> orbital >> position. >> >> The next question is does the math in the receiver have to correct for >> changes due to elevation? Does it become relevant if you are trying for >> survey grade results? >> >> -- >> These are my opinions. I hate spam. >> > > End of time-nuts Digest, Vol 136, Issue 32 > ****************************************** _______________________________________________ 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.