Message-Id: <200501241452.j0OEqWK13459@cnes.fr>
Date: Mon, 24 Jan 2005 15:52:26 +0100
From: Jean-Paul Berthias <jean-paul.berthias@cnes.fr>
Reply-To: jean-paul.berthias@cnes.fr
Organization: Centre National d'Etudes Spatiales
MIME-Version: 1.0
To: ids.analysis.forum@cls.fr
Subject: Re: [ids.analysis.forum] anomalous TZ geocenter value from
    DORIS/SPOT4 data in 1998
References: <p0611040bbe16d0905f94@[128.149.70.153]>
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Dear colleagues,

In the mail in reference Pascal Willis showed that his results are coherent with
an error in the cross-track position of the phase center for SPOT 4.

Looking back at the old processing system we found that the old software (which
was in operations until the end of 1998) used different values for the phase
center location than the current software; old and new values differ by 13.2 cm
cross-track and 1.7 cm radial. This confirms what Pascal sees. We have no
explanation for these differences.

Cycle 29 was certainly reprocessed with the new software for a reason or
another.

Even though the orbits produced by CNES during that period are inpacted by this
error, this has only very minimal inpact on the delivery data. Only the phase
ecnter correction term is truly wrong. Those of you who recompute the center of
phase correction using the satellite description available at the IDS should not
see any problem. For others, we will look into regenerating either the whole
data files or the center of phase corrections.

Best regards,
Jean-Paul

Jean-Paul Berthias
CNES - DCT/SB/DA
tel: 33 (0) 561283236