From jean-paul.berthias@cnes.fr Fri Jun 18 08:32:46 2004 Date: Mon, 29 Mar 2004 18:48:25 +0200 From: Jean-Paul Berthias To: "John C. Ries" Cc: Jean-Michel Lemoine , Pascal Willis , Laurent Soudarin , Gilles Tavernier , Jean-Jacques Valette , Jean-Pierre Granier , Martine Feissel-Vernier Subject: Re: Participation in the IDS-GRACE Campaign Hi John, If I am not mistaken, there is one key element of the various works on the SAA effect that you are not taking into account. It is the fact that TOPEX and Jason fly close enough to see the DORIS beacons at roughly the same time, so that you can compare their on-board clocks. If you assume that the TOPEX clock is well modeled -- which in a sense is similar to saying that you assume that TOPEX gives you good results in positioning -- you observe the Jason clock, and you can try to model it. You could do it in your solutions if in addition to fixing the station locations you would fix the beacons frequency offsets to the values derived from your TOPEX runs. This observation of the behavoir of the Jason clock, and the model derived from it, are global, that is they work "everywhere". As long as TOPEX works well, its DORIS data can be used to refine the model. With enough observation time, trends could emerge as to how this model relates to the underlying physics. Whether these models can be trusted enough to correct Jason data on the long term when TOPEX is gone remains to be seen. I am not very hopeful, but who knows ... Best regards, Jean-Paul