Date: Sat, 19 Jun 2004 11:50:10 +1000
From: Frank.Lemoine@ga.gov.au
To: valette@cls.fr, feissel@ensg.ign.fr
Cc: Jean-Jacques.Valette@cls.fr, Ramesh.Govind@ga.gov.au,
    frank.lemoine@gsfc.nasa.gov, jean-pierre.granier@cnes.fr,
    feissel@ensg.ign.fr, Laurent.Soudarin@cls.fr
Subject: RE: More data for the IDS analysis campaign?

Jean-Jacques-
The information you cite in the link below is the information I question.
I use the 2 Ghz phase center explicitly as the coordinates for the DORIS
Antenna on Envisat (the referece point + vector gives you the z value of
-1.725 meters which I quoted).  The problem is when I apply this value on
Envisat, I obtain offsets in the scale wrt ITRF2000 of +35-40 mm. So
something on Envisat is consistently in the wrong  place. I can fax you the
plots on Monday. We empirically tried -1.69 and -1.75 m. -1.69 m moved the
scale further away (+45 to 55 mm offset); -1.75 m moved it closer to zero
(=+25 to 30 mm offset). So, it is important to verify exactly the values CNES
Uses when they compute the corrections that go on the data. The way to do
this verification is look at the programs that do the offset + attitude
correction that go on the DORIS data records, not the documentation.
What do they use?  

Second question, if I'm calculating my own correction, should I *not* use the
2 Ghz phase center? Is there something unique about DORIS on Envisat
That is unlike DORIS on topex or spot-2, where we also compute our own
Corrections and have no problems?

Another good thing to do would be to verify the attitude model for Envisat.
Could we get a set of quaternion data - even for one day. That would help
verify that I've implemented the attitude model correctly.  I have to say
though, I doubt there is a problem there. If our attitude were incorrect by a
significant amount, we would pick up something in the SLR residuals and we
Seem to fit the SLR data on ENVISAT quite well: On average 2 cm RMS.

A+,
Frank

PS- please remember to reply to flemoine@bowie.gsfc.nasa.gov (or
Frank.Lemoine@gsfc.nasa.gov) not my Geoscience Australia address.
Thanks.