Subject: JASON DORIS phase center and SAA effect
From: Pascal Willis <[email-masked]>
To: Nikita Zelensky <[email-masked]>
Cc: [email-masked], [email-masked], [email-masked], [email-masked], [email-masked], [email-masked], [email-masked]
Date: Tue, 19 Nov 2002 10:48:33 -0800

Hi Nikita,

following your latest message, I have done some new computations 
because your results looked quite different for the Z-axis.

The difference between your results and mine is that you use all 
DORIS/JASON data. In my case, I do not use DORIS/JASON data for 
stations that are in the SAA region, for reasons explained before.

When I only take the remaining (good) data I estimate an additional 
R_OFF offset of about -10 cm. When I use all the DORIS data the 
estimated value is closer to -3 cm (close to what you found). I did 
it for several days and I should know soon if it is the case with the 
complete first 20 cycles.

I now wonder if there is some 'calibration' of the data by CNES using 
all stations (and in particular the Kourou station). Could some 
pseudo-ranges errors in Kourou bias the long-term satellite frequency 
drift that is used to provide data in TAI?

My present conclusion is that when someone uses all DORIS/JASON data 
the R_OFF value is almost compatible with the specification and the 
estimated orbit is close to GPS solutions (what you found). If 
someone (like me) uses only the stations outside the SAA it seems 
that the DORIS orbits are shifted by a fair amount in radial (2-3 cm) 
or he needs to estimate a phase center offset that is big (-10 cm) 
and not physical.

Best regards
Pascal