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<DIV dir=ltr><FONT face=Arial color=#000000 size=2>I agree with Tom about GPS. Over the past decade both GPS's delivered prediction of UTC(USNO) and GPS time have been getting closer and closer to UTC(USNO), modulo 1 second and as measured by the RMS. That is mostly due to improved GPS clocks, but tighter steering was implemented about ten years ago, and other algorithm improvements have also been made. GPS III's times will adhere even closer to UTC(USNO) - because clocks, algorithms, and official specs are being improved.</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>While I can't speak for the USNO's sister-institution, I do remember the paper referenced below. It was presented at a PTTI meeting by someone who at that time was an employee of NIST and this must be why they include it in their reprint library. I am quite sure that it does not now represent nor ever has represented any official position of NIST in any way. However, USNO did at one time host a web page that included UTC(tvb)! </FONT></DIV></DIV>
<DIV dir=ltr><BR><FONT face=Tahoma size=2><STRONG>From:</STRONG> Tom Van Baak<BR><B>Sent:</B> Sat 1/3/2009 5:36 AM<BR><B>To:</B> Leap Second Discussion List<BR><B>Subject:</B> Re: [LEAPSECS] temporal turf wars<BR></FONT><BR></DIV>
<DIV><PRE style="WORD-WRAP: break-word">> An interesting NIST document from 2000 gives insight into the turf wars
> about precision time scales.
>
> http://tf.nist.gov/general/pdf/1429.pdf
>
> The document makes it clear that GPS time was never designed to follow
> UTC(USNO) (and by implication, TAI).
I think you're misreading that sentence. GPS is in fact steered to
the USNO MC which is steered to UTC. But I think the steering
parameters are quite different between the two though. I also
suspect there have been improvements in the past ten years.
Demetrios can explain more, if needed.
> The document also clarifies the distinction between (raw) GPS time and
> GPS time corrected by the offset given in subframe 4 page 18.
The GPS ICD 200 describes the A0 and A1 correction. I believe
most (all?) GPS timing receiver implement the correction. Steve, you'd
have fun with a GPS timing receiver like a Thunderbolt or an M12;
all those subframe parameters can be dumped over the serial port
and played with.
> The document also coins the term UTC(GPS) with very interesting
> footnotes disclaiming the validity of the use of such a term.
I doubt Al coined that term; I recall seeing it long before. But like
the editor implies, people realized it was not a valid term and so
you rarely see it any more. Maybe marketing people still use it.
I remember being gently corrected by the BIPM and I stopped
using it myself. I think UTC(tvb) is ok, though ;-)
/tvb
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