From: "John C. Ries" <[email-masked]>
To: [email-masked]
Cc: Jean-Michel Lemoine <[email-masked]>, Pascal Willis <[email-masked]>, Laurent Soudarin <[email-masked]>, Gilles Tavernier <[email-masked]>, Jean-Jacques Valette <[email-masked]>, Jean-Pierre Granier <[email-masked]>, Martine Feissel-Vernier <[email-masked]>
Date: Mon, 29 Mar 2004 13:47:28 -0600

Hi everyone,
 
 In preparation for the upcoming meeting, and to stimulate discussion,
 I had a thought or two about any attempt to model or repair the
 Jason-1 DORIS data for the SAA effect. First, the frequency
 acceleration in the SAA might be modelable but this model must
 presuppose that the mean frequency drift that would be present
 without the SAA is somehow known. This isn't possible, and can only
 be inferred by assuming the DORIS stations heights are already
 correct. Thus SAA data cannot be used for station positioning.
 Second, the non-SAA data have been corrupted due to the mechanism
 Pascal pointed out...all the SAA data have an erroneous drift model
 applied. The drift model is correct as an average across the network
 but it is incorrect (and growing) for the non-SAA stations. This is
 easily seen as the non-SAA stations appear to be moving in height in
 the opposite direction of the SAA stations. There is, of course, the
 issue of the data escaping the CNES editing.
 
 In short, I don't see how any Jason-1 data can be used for
 positioning, neither SAA with a model or non-SAA data. The 'correct'
 frequency drift model can never be known. I can estimate the
 'correct' frequency drift for the non-SAA stations in the POD
 process, but it can be recovered only because I fix the stations.
 
 It may be possible to parameterize the data well enough to keep it in
 the POD process, and recover at least the along-track time-bias
 information that is Doppler's main strength.
 
 See ya,
 JR