****************************************************************************** dorismail 25-May-2007 15:13:46 Message No 0498 ****************************************************************************** Author: "Cerri Luca" Subject: New ionospheric correction and redelivery of Jason-1 files Dear colleagues, Starting from Spot2 arc 623 Spot4 arc 374 Spot5 arc 187 Jason1 arc 196 Envisat arc 256 Doris data files will be delivered with an improved ionospheric correction that is independent from the estimated frequency bias per pass. This allows to deliver a meaningful correction even for invalidated passes, for which the frequency bias cannot be correctly identified. This improved ionospheric correction is obtained from a linear combination of phase measurements on the two frequencies (2 GHZ and 400 MHz), as it is usually done for GPS. Due to the fact that measurement noises are now combined in a different way, users will see postfit residuals increase of about 4%, which corresponds to the ratio 1/(1-g) , where g=(400MHz/2GHz)^2 . The number of valid measurements will not be impacted by this modification. The number of edited measurements will increase due to the presence of those points belonging to invalidated passes that were not included up to now. These passes can be edited either because of standard preprocessing criteria, or edited because they belong to Doris beacons in the so-called "re-start mode". In the second case the preprocessing indicator is set to 4 . This change has a negligible impact on orbit determination and positioning. In the frame of current reprocessing activities involving Jason-1 we have produced new measurements files from cycle 1 to cycle 195, that are being delivered to CDDIS and IGN servers, at the usual locations. Best regards, Luca __________________________________ Luca CERRI - CNES POD Team Centre National d'Etudes Spatiales DCT\SB\OR 18, av Edouard Belin 31401 Toulouse Cedex 09 - FRANCE tel. +33 (0)5 61283549 fax +33 (0)5 61281855 bpi 1323 email luca.cerri@cnes.fr Please do not reply directly to this message, but send comments and suggestions to IDS.central.bureau@cls.fr