On Feb 15, 2011, at 2:31 PM, Warner Losh wrote:
> On 02/15/2011 09:12, Rob Seaman wrote:
>> So, what is the state of the art for long term predictions of UT1? Could
>> the algorithms used by the EOP PCC teams simply be run on the historical
>> Bulletin B numbers to find out?
>
> At the Torin conference they had a sliding scale for confidence in UT1
> predictions, and it was very non-linear. I don't have the reference handy,
> but it went something like:
>
> 10 days a few microseconds
> 100 days a few milliseconds
> 1000 days a second or two
>
> which fits with other statements that said operationally, they can model the
> earth well enough to predict leap seconds about 2-3 years into the future
> with a 98% confidence level to conform with the DUT1 .9s requirement.
So in 2003, they estimated that UT1 could be predicted no better than 1s over
1000 days. c. 2008 they actually performed the exercise and found that UT1
could be predicted more than an order of magnitude better than this over 500
days. This raises the ante over what can actually be achieved and what the
necessary DUT1 tolerance trade-offs might have to be.
The original November 1999 McCarthy & Kelpczynski GPS World article that
started this all off:
http://gauss.gge.unb.ca/papers.pdf/gpsworld.november99.pdf
outlined five separate options for the "continued maintenance of UTC".
Wouldn't it be good to examine one of the other four options using actual
scientific methods?
Operationally the IERS is using older procedures that are likely significantly
more simplistic algorithmically than the recent EOP PCC while also being
entangled with other parts of the workflow. For instance, how much evolution
in the UT1 prediction operations has occurred since 1990:
http://www.springerlink.com/content/x272116284525311/
Also, it is a different exercise to predict UT1 separately from all the other
Earth orientation parameters, if all you need to constrain is the former.
> Looking at the Bulletin B's might not give a long enough time horizon. Those
> only predict out 30 days or so.
Correct me if I'm wrong: Bulletin A are the predictions (using methods
presumably less advanced than the EOP PCC). Bulletin B are the final observed
parameters. My point is that whatever the necessary input data (including such
things as atmospheric angular momentum models), the new-and-improved
predictions can be compared against the archival data. The data challenge (at
least for this purpose) doesn't have to be conducted in real time.
> IERS provides historical aggregated earth orientation data that can be used
> to see how well predictions match actual data over any given time horizon.
Precisely.
> There's enough grunt work here that you might be able to publish a paper on
> this. :)
They are publishing papers. The question is whether the papers resulting from
efforts like:
http://www.springerlink.com/content/g216411573882755/
and
http://maia.usno.navy.mil/eopcppp/eopcppp.html
can be turned into improved workflows for predicting UT1 as input to a new
extended scheduling paradigm.
Apparently the lion share of the effort on EOP predictions is invested in the
short term numbers for real time operations. Meanwhile, the 500 day UT1
predictions from EOP PCC appear remarkably good. What improvements can be
realized on the long term side of operations? Is the epoch during which the
EOP PCC was conducted representative of the results that can be expected?
Rob
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