Date: Fri, 8 Nov 2002 15:14:19 +0100 (Paris, Madrid) From: Martine Feissel-Vernier To: Henno.Boomkamp@esa.int Cc: Jean-Paul Berthias , jries@csr.utexas.edu, Markus.Rothacher@bv.tu-muenchen.de, John.Dow@esa.int, Jean-Jacques Valette , Laurent Soudarin , Pascal Willis , feissel@ensg.ign.fr Subject: Re: proposed JASON campaign Dear colleague I have a few short comments on your plan. - Proposed statistics (2B, p.2). Statistics in the three directions would be more informative than 3D statistics (if I did not misunderstand your wording). - 2C, p. 2: you could use version numbers as part of the filenames. - It seems to me that having a number of solutions obtained by three techniques allows you to go a little further in the comparison statistics. You could estimate the variances of the individual solutions (all techniques), and the covariances between solutions from the same technique, by the "three-corner hat technique", i.e. a least square inversion of equations of the type "variance(A-B)=variance(A)+variance(B)+covariance(A,B)" where variance (A-B) is derived from the orbit differences analysis, and covariance(A,B) is assumed to be zero if solutions A and B are obtained by different techniques. The latter hypothesis may be not rigorously verified (common modelling error effetcs may exist), but that's life... What do you expect to be the timetable of the project? I am glad to see the progress in the JASON orbit comparison campaign. We view the consideration of DORIS in the game as extremely important. As you know, we would like to develop orbit comparisons in the framework of the future IDS. We are sure to learn much from your analysis campaign. With my best wishes. Martine Feissel-Vernier Analysis coordinator, DORIS Pilot Experiment -- Martine Feissel-Vernier Internet: feissel@ensg.ign.fr Observatoire de Paris and Institut Geographique National Telephone: 33 (0) 1 64 15 32 83 ENSG/LAREG Fax: 33 (0) 1 64 15 32 53 8 Av. Blaise Pascal, Champs sur Marne 77455 Marne la Vallee Cedex 2, France --