Message-ID: <455C36AB.1040302@esgt.cnam.fr>
Date: Thu, 16 Nov 2006 11:00:11 +0100
From: laurent morel <laurent.morel@esgt.cnam.fr>
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To: ids.analysis.forum@cls.fr
Subject: Re: [ids.analysis.forum] Scaling of DORIS solution in ITRF 2005
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Dear colleagues,

I want to mention that I did the study during my Phd and an ASR article
has been published (Morel and Willis, Terrestrial reference frame 
effects on global sea level rise determination from T/P altimetric data, 
ASR 36 (2005) 358-368, doi:10.1016/j.asr.2004.05.113).
It has been shown that a scale factor had no impact on the orbit (even 
for a 10 ppb value), the perturbation due to the scale factor on 
stations is absorbed by residuals and tropospheric parameter estimation. 
Only a TZ shift create larger periodic orbital errors and disturb the 
mean sea level estimation.

best regards

MOREL Laurent


John C. Ries wrote:

>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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