Date: Tue, 19 Nov 2002 10:48:33 -0800 From: Pascal Willis To: Nikita Zelensky Cc: jean-paul.berthias@cnes.fr, ries@csr.utexas.edu, bjh@cobra.jpl.nasa.gov, Yoaz.Bar-Sever@jpl.nasa.gov, sluthcke@xyz.gsfc.nasa.gov, krchoi@csr.utexas.edu, feissel@ensg.ign.fr Subject: JASON DORIS phase center and SAA effect 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