Subject: Re: estimating DORIS pole motion rates? 1-week preliminary results
From: "Prof. Markus Rothacher" <[email-masked]>(au lieu de Laurent Soudarin <[email-masked]>)
To: [email-masked]
Date: Thu, 23 Mar 2006 11:28:31 +0100

Dear Pascal,

let me shortly add a comment to your nice tests. I think that we should
clearly make a difference between

1) a contribution to the IERS CPP or IERS long-term series

2) getting th best possible results for an individual technique

Your comparisons clearly show that the DORIS results get better, if
you do not estimate polar motion rates. Thereefore, to obtain
as good results as possible for DORIS alone, this might be the way to go.

If you think of a combination of different techniques, then the individual 
contributions are much less important than the combination
making use of the advantages of all the techniques. In the combination
the consistency is of atmost importance, however. Assuming that for DORIS 
you fix the rates, this would imply that the rate you fixed will
be included into the combination and the contributions of other techniques 
will not have the possibilizty to improve these rates any longer. Since the 
rates you use as a priori are certainly not the "truth", the polar motion 
rates and the UT1 rate should, in my opinion, be kept for the combination task.

With best regards,
                             Markus

Pascal Willis schrieb:

>dear Laurent and Frank,
>here is a discussion that Frank could initiate at the next IDS meeting in 
>Venice.
>Just to start the discussion, I recomputed the most recent week of DORIS 
>data (Jan 1 to Jan 7, 2006) in 2 different ways:
>     A) usual IGN/JPL: estimating daily pole motion + daily polar motion
>     rate + daily UTC-UT1 rate
>
>     B) usual LEGOS/CLS: estimating daily pole motion
>
>First, I don't see any change in the station coordinates results for both 
>cases. To test for any improvement, I compute RMS of comparison for all 
>stations with IGN04D02 solution (long-term solution) after a 7-parameter 
>transformation.
>             N(mm)   E(mm)   V(mm)
>     case A  18.5    21.5    12.7
>     case B  18.4    21.1    13.0
>
>However, I see some significant improvement in the polar motion itself. To 
>test for improvement, I do daily difference of polar motion at 12:00 with 
>JPL/GPS and compute a RMS of the 7 values without removing any bias. I use 
>Bulletin B as a priori in my DORIS computations:
>             XP(mas) YP(mas) sqrt((XP**2)+(YP**2))
>     case A  1.01    0.40    1.09
>     case B  0.68    0.54    0.87
>
>it also removes the asymmetry I usually see between XP and YP and that 
>Laurent does not see at all in his results. It could be related to the 
>estimation of the daily polar motion rates that are not totally observable 
>with DORIS.
>So, if we want to go from typically 1 mas polar motion results for DORIS 
>to 0.5 mas that may be an easy way to go. The other possibility is also to 
>add more smoothing to our daily results (imposing continuity or linearity 
>at day boundary).
>Is any of these choices useful and desirable?
>I am ready to stop estimating polar motion rate for DORIS, but I would 
>like to be 100% sure that nothing will be lost for IERS EOP, IERS CPP, 
>future ITRF, IDS combination,... I would also like to be sure that all IDS 
>groups will follow the same rules.
>Do you think I should do some additional tests on a longer time span to 
>get a more reliable and convincing conclusion? Then it could make sense to 
>enlarge the distribution list to the IDS Analysis Forum and ask for feed-back.
>What is your opinion?
>Thanks in advance
>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]

-- 
-------------------------------------------------------------------------
Prof. Dr. Markus Rothacher              Phone : ++49-331-288-1101
GeoForschungsZentrum Potsdam (GFZ)      Fax   : ++49-331-288-1111
Dept.1: Geodesy & Remote Sensing        E-mail: [email-masked]
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D-14473 Potsdam / Germany