Subject: Re: [ids.analysis.forum] Scaling of DORIS solution in ITRF 2005
From: "John C. Ries" <[email-masked]>
To: [email-masked], [email-masked]
Date: Wed, 15 Nov 2006 10:57:04 -0600

At 12:24 PM +0100 11/15/06, Jean-Paul Berthias wrote:
>Dear colleagues,
>
>As you probably know from previous Emails we intend to use a scaled 
>version of the ITRF2005 SLR solution as a reference for altimetry 
>missions (Jason, Topex, Envisat). This raises a question for DORIS: 
>should we scale the ITRF2005 solution in the same way as for SLR or 
>should we use the ITRF2005 DORIS solution as is ?
>
>I personally do not favor a scaling of the DORIS solution for 
>operational reasons: when new beacons are installed (and this 
>happens regularly with DORIS) the only coordinates that are 
>available for a long time are derived from GPS positioning. If we 
>scale ITRF2005, we will not know what to do to these coordinates, 
>scale them or not. If we use ITRF2005 as is for DORIS, we can 
>legitimately use ITRF2005 GPS based coordinates to fill in for new 
>stations. BUt this is not a very strong argument.
>
>I would like to hear your comments on this issue. Please let me know 
>if you have run tests with ITRF2005, with and without scaling (the 
>scaling we intend to apply to SLR is -1 ppb) and what your results 
>are.
>

Hi Everyone,

Some of you have seen my tests, and there is no question that the 1 
ppb scale offset in ITRF2005 for the SLR coordinates is necessary for 
the best results. This is clear in the LAGEOS results but also for 
Jason-1 orbit fits. There was a slight benefit for the DORIS 
residuals (in my orbit fits) to also be scaled the same, but the 
impact on the orbit was negligible.

Since it is more likely that any future DORIS site will be tied to a 
GPS position estimate, it seems reasonable to retain the ITRF2005 
scale for DORIS. There is no ideal solution; this would keep things 
less complicated. Hopefully, we'll sort this scale issue out before 
the next TRF solution. A good way to look at this is that we have 
achieved a level of accuracy where 1 ppb inconsistencies are apparent.

Best regards,
John

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