Hi Mike,
> the system needs an estimate of current UT1
Can you give some references to your observation? I don't recall seeing
UT1 mentioned in the first couple of decades of GPS documentation. The
system runs on GPS time, the WGS84 coordinate system, broadcast
ephemeris including SV clock corrections. Where does UT1 appear in those?
> That estimate is applied internally so the end user does not need to
know the details
Right, the user is shielded from many details. But I didn't think even
GPS receivers had knowledge of UT1, nor the satellites themselves. So
where in "the system" does UT1 apply?
Thanks,
/tvb
On 12/28/2023 1:23 AM, Mike Hapgood - STFC UKRI via LEAPSECS wrote:
Jim outlines a calculation I've done many times. But there's a similar
calculation for GNSS systems (GPS, Galileo, Beidou, etc). If you want
to use GNSS to determine positions on Earth's surface to accuracy of a
few metres, the system needs an estimate of current UT1 accurate at
least to a few milliseconds. That estimate is applied internally so
the end user does not need to know the details, just as that user does
not need to know about the relativistic clock corrections or
corrections for ionospheric signal delay that also underpin safe use
of GPS. But the bottom line is that knowledge of UT1 (i.e. the spin
phase of the Earth) is essential for GNSS - and many other space systems.
Mike
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