Message-Id: <6.2.1.2.2.20061117175415.027671a8@pop.cls.fr>
Date: Fri, 17 Nov 2006 18:20:11 +0100
To: Jean-Paul Berthias <jean-paul.berthias@cnes.fr>, ids.analysis.forum@cls.fr
From: Jean-Jacques Valette <valette@cls.fr>
Subject: Re: [ids.analysis.forum] Scaling of DORIS solution in ITRF 2005
In-Reply-To: <200611151125.kAFBP2q01543@cnes.fr>
References: <200611151125.kAFBP2q01543@cnes.fr>
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Dear Jean-Paul and dear colleagues,

To complete your point on operational consideration and new DORIS stations 
it seems interesting to add a comparison between the scaling (+ scaling 
derive?) of ITRF2005 and the differences between ITRF2005/IDS and 
ITRF2005/IGS stations velocities.

For Toulouse (TOUL & TLSA), the difference is 1.1 mm/yr in amplitude that 
is to say about 7 mm since 2000. For Easter Island (ISPA-EISL & EASA) it is 
about 3 mm/yr or nearly 2 cm since 2000. Those stations have a long 
standing operation and we can expect a difference probably higher with 
recent stations. The order of magnitude of such station coordinate errors 
(mainly horizontal) is at least similar and probably higher than the one 
resulting from the scaling.

Another approach of the investigation you request for could be the final 
altimeter user approach. Why not making some CAL/VAL cy tests at epochs 
separated by 6 months but over a 10 years period? Would those tests 
significant enough to evaluate improvements on geographically correlated 
errors, and long terms derives? Would it be relevant, profitable and 
reasonnable effort?

JJacques

Le 12:24 15/11/2006, vous avez écrit:
>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.
>
>Thank you for your help,
>Jean-Paul
>
>
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