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Date: Thu, 09 Nov 2006 22:00:51 +0000
Subject: Using ITRF2005 in multitechnique POD solutions
From: "Frank G. Lemoine" <flemoine@puuoo.gsfc.nasa.gov>
To: <ids.analysis.forum@cls.fr>
Message-ID: <C1795593.7AC8%flemoine@puuoo.gsfc.nasa.gov>
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Dear Colleagues,

 I forward below a brief interchange between JP Berthias and J Ries on
 how to use ITRF2005 for multitechnique POD solutions, and invite
 analysis forum users to respond. This issue obviously affects
 ENVISAT as well as TP and Jason.

 There are two issues: (1) Because of the difference in scale of
 SLR in ITRF2005, how should the SLR+DORIS+GPS ITRF2005 solutions
 be applied for POD on Jason-1 (and Topex and ENVISAT)?  (2) How do
 we handle the  stations not in ITRF2005 for both DORIS and SLR,
 which we have previously included in our POD solutions?

 FGL-

------ Forwarded Message
From: "John C. Ries" <ries@csr.utexas.edu>
Date: Thu, 9 Nov 2006 00:57:35 -0600
To: jean-paul.berthias@cnes.fr, Franck Lemoine
<Frank.Lemoine@gsfc.nasa.gov>, Bruce J Haines <bjh@cobra.jpl.nasa.gov>,
wib@cobra.jpl.nasa.gov
Cc: Houry Sabine <Sabine.Houry@cnes.fr>, Cerri Luca
<Luca.Cerri@EXCHANGE.CST.CNES.FR>, "Scott B. Luthcke"
<sluthcke@xyz.gsfc.nasa.gov>
Subject: Re: ITRF2005 and next OSTS meeting

At 2:02 PM +0100 11/8/06, Jean-Paul Berthias wrote:
>Dear colleagues,
>
>It would be helpful to start preparing the next OSTS meeting by
>computing orbits using ITRF 2005. However we are currently unable to
>do so because we do not have yet a scaled version of ITRF2005 for
>SLR (and maybe DORIS) and ITRF2005 based GPS orbits. Do you know
>when these inputs should become available ? Are we likely to obtain
>these inputs before the end of the year ? Who is supposed to provide
>the scaled ITRF ?

The final ITRF2005 is available, and an appropriate SLR solution can
be obtained by simply scaling the SLR coordinates down by about 1
ppb. The "SLR-only" solution for ITRF2005 is very likely to be
nothing more than this; we are considering not applying the apparent
scale-rate since the uncertainty is nearly as large as the rate
itself. If this is the case, then the only difference is simply using
the SLR scale rather than the VLBI scale.

My own results suggest the scale change should also be applied to
DORIS, but the impact on the orbit is negligible. I would propose it
simply so that SLR and DORIS can remain consistent, since we will
need to fill in DPOD2005 for sites that are not in ITRF2005. Failure
to scale both the same could lead to some funny business when using
local ties. Of course, this is true for ties to GPS, so it's not at
all clear just how we will handle this.

------ End of Forwarded Message


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