Next message: Alexandre Eremenko: "Re: SNO sextants"
On Wednesday, November 10, 2004 9:16 AM
Trevor J. Kenchington asked:
> Could you add one further detail: How does "GPS time" relate to UTC
> and/or the various grades of UT?
GPS time is the number of seconds since 06-Jan-1980 00:00:00.0 UTC, and is
steered to an accuracy of better than 1 microsecond. It is encoded in the
GPS NAV message as the number of weeks since 06-Jan-1980 and the number of
seconds since the start of the week. As such, it does not include leap
seconds, so a naive reading of GPS time would be fast of UTC today (13 or 14
seconds, I believe, for the number of leap seconds since 06-Jan-1980).
However, elsewhere in the GPS messages it gives the correction, so receivers
can display UTC or UTC-derived zone time.
Interestingly, on 22-Aug-1999, the 10-bit week number field wrapped around
from 1023 to 0, causing some early GPS receivers to lose track of the date.
The US Naval Observatory's GPS page at http://tycho.usno.navy.mil/gps.html
has some info.
-- Peter
