Subject: [ids.analysis.forum] Redelivery of 1998 SPOT4 DORIS files
From: "Cerri Luca" <[email-masked]>
To: <[email-masked]>
Cc: "Ferrage Pascale" <[email-masked]>, "Houry Sabine" <[email-masked]>
Date: Fri, 11 Dec 2009 19:55:36 +0100

Dear DORIS analysts,

As most of you certainly know, SPOT4 DORIS files up to arc number 31 
(before year 1999) contain an erroneous phase center correction, 
as reported by Willis et al. in the reference below.
This was due to a software error in the position of the DORIS antenna 
reference point with respect to the spacecraft center of mass. 

This error equally affects the 2GHz and the 400Mhz propagation
distances, 
and therefore has no impact on the ionospheric correction. 
However, it has an impact on the tropospheric correction as the
estimated
tropospheric bias partially compensates for error in the phase center
position.
I will assume that the tropospheric correction in the DORIS file is
generally 
not used by analysis centers. Errors in the tropospheric correction
field will
be ignored.
The above considerations also imply that the error in the phase center
positions only affects users that are not computing their own phase
center
correction.

For these users, I have replaced the phase center correction field of
existing DORIS file with the correct value.

Everything is looking good to me, but I join three sample files to this
message 
which you might want to test before official redelivery to CDDIS and IGN
data servers.
Thank you in advance for letting me know of any problem that you might 
encounter.

Best regards 
and have a nice time at AGU meeting for those who attend it !

Luca 

References:
P. Willis, J.-P. Berthias , Y.E. Bar-Sever. 2006. Systematic errors in
the Z-geocenter 
derived using satellite tracking data: a case study from SPOT-4 DORIS
data in 1998, 
J. Geod  79: 567-572 
__________________________________
Luca CERRI
Centre National d'Etudes Spatiales
DCT\SB\OR
18, av Edouard Belin
31401  Toulouse Cedex 09 - FRANCE
tel.   +33 (0)5 61283549
fax    +33 (0)5 61281855
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email  [email-masked]