Subject: estimating EOP rates for DORIS or not / IDS and IERS goals
From: Pascal Willis <[email-masked]>(au lieu de Laurent Soudarin <[email-masked]>)
To: [email-masked]
Date: Thu, 23 Mar 2006 11:30:09 +0100

Dear colleagues,

thanks to all those who participated in the discussion.

I reprocessed 1 year of DORIS data without estimating polar motion rates 
and I confirm the first results: EOP RMS towards JPL/GPS solution (no bias, 
no drift removed) go down to 0.2 - 0.8 mas, leading to a factor of 2 
improvement, as expected.

I also agree with Markus that if we don't estimate EOP rate, it will create 
problems when further computations are done, this is exactly why we estime 
polar motion and rate, per day, using 24 hours of data and no additional 
constrain at JPL.

    * Markus you will have to talk to the ILRS groups who decided some time 
ago not to estimate these parameters anymore.

I don't think that Analysis Centers are ready to submit 2 solutions (1 for 
IDS to show best results and 1 for IDS with complete estimation) unless one 
can be derived directly from the other (no reprocessing) adding some type 
of constrains.

It may be obvious, but people analysis these results have the possibility 
to use both polar motion and polar rate and fix the rate to an known series 
before analysis the polar motion results. This would allow distribution of 
complete SINEX results (polar motion and rate) but showing better polar 
motion results, if the technique (DORIS or SLR) does not have the data 
strength to really estimate the polar motion rate per day.

Concerning the DORIS LCA solution, none of the hypothesis that I proposed 
seem to be correct (see complete answer from Jean-Michel Lemoine). However, 
I think that connecting the EOP estimation every 6 hours and forcing some 
smoothing (imposing condition on the rate) may add some rather tight 
constrains.

    * In my opinion, if the improvement does not come from this smoothing, 
the LCA group has to explain how they can get a factor of 2 improvements 
from their last solution. Not estimating the rate would be one way (see 
above), but it is not the case. Some tests could be conducted to show if 
the constrain used by LCA is tight or not.

At least, we have something to discuss at the Venice meeting, and maybe 
also to better explain in the Position paper from Frank Lemoine, so that 
people can understand the consequences of these choices.

Best regards
Pascal
-- 
Pascal Willis
Jet Propulsion Laboratory, MS 238-646     Ph : 1-818-393-4748
4800 Oak Grove Drive                      FAX: 1-818-393-4965
Pasadena CA 91109                         Em : [email-masked]

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