Re: [LEAPSECS] UT1 confidence

From: Warner Losh <imp_at_BSDIMP.COM>
Date: Wed, 17 Jan 2007 12:31:14 -0700 (MST)

> In message <20070117122430.GA23443_at_fysh.org>, Zefram writes:
> >IERS Bulletin A gives an expression for the uncertainty of its UT1-UTC
> >data predictions:
> >
> > S t = 0.00025 (MJD-today)**0.75
> >
> >where "today" is the MJD of the bulletin's publication. The Bulletin
> >only predicts a year ahead. Applying that formula gives an uncertainty
> >a year ahead of 21 ms.
>
> The question is what domain of validity the above formula has ?
>
> In the builletin they only apply it up to 40d.

In addition, since the drift is a higher order polynomial (13th order
I recall hearing), a simple linear formula (or close approximation) is
likely only going to fit the curve near the prediction date with wider
variances the further one gets from today.

It has been remarked that the current state of the art is that 100ms
accuracy can be predicted about a year in advance only and that the
models are constantly undergoing refinement. It has been estimated
that IERS could issue leap seconds, with today's technology, about 3-5
years out and still be in a 95% or 99% band of certainty that the 0.9s
margin is maintained. However, I can't find papers that show these
models or point to any better data than hearsay...

Warner
Received on Wed Jan 17 2007 - 11:35:03 PST