****************************************************************************** DORISMail 06-Jun-2005 10:10:39 Message No 0383 ****************************************************************************** Author: Martine Feissel-Vernier Subject: Report of the 2003 IDS Analysis campaign (fwd) Dear colleagues The report on the 2003 IDS Analysis Campaign, "Impact of the GRACE graviy fields models on IDS products", by M. Feissel-Vernier, J.-J. Valette, K. Le Bail and L. Soudarin is available at http://lareg.ensg.ign.fr/IDS/events/2003_camp_report.pdf The initial aim of this analysis campaign was to evaluate the impact of the advent of Earth gravity field models derived from the GRACE mission on DORIS-derived positioning and terrestrial reference frame. Thanks to the availability of daily orbital reference comparisons, the study could be extended to orbital references through their origin and scale. In addition, the availability of four long time series from three Analysis Centers made it possible to evaluate the analyst related differences. The major anomalies in the measured motion of the TRF origin are discrepant amplitudes of the annual components in Tz between Analysis Centers (10 mm) and with respect to the geophysical expectation (5-15 mm). The interannual TRF origin motion differences between solutions reach up to 3 mm, maybe related to the gravity field model in one case. The TRF scale differences between Analysis Centers have a complex signature, including drifts (0.6 ppb/year), biases (6 ppb), interannual (0.3 ppb) and annual (0.5 ppb) components. These are probably due to differences in modelling stil to be understood. The study of the influence of the gravity field on the orbital reference frame was studied on three-month time span with results. The short term sensitivity to the change in gravity field is at the level of 4 mm on the origin and 0.2 ppb in scale. The medium term variations reach 10 mm/90d and 0.4 ppb/90d. The spectral investigation of the signal leads to a global white noise diagnostic, ruling out the presence of significant perturbations at long periods with respect to the 90-day data span. Parallel comparisons of terrestrial and orbital reference frame effects, based on various gravity field models show modest medium term differences in the frame origins (2 mm/90d in Tx, Ty, and 4-8 mm/90d in Tz) and quite large effects in scale (3 ppb/90d). More details at http://lareg.ensg.ign.fr/IDS/events/2003_camp_report.pdf Best regards. Martine Feissel-Vernier IDS Analysis Coordinator -- Martine Feissel-Vernier Observatoire de Paris and Institut Geographique National Telephone: 33 (0) 1 64 15 32 83 DT/LAREG Fax: 33 (0) 1 64 15 32 53 8 Av. Blaise Pascal, Champs sur Marne 77455 Marne la Vallee Cedex 2, France -- Please do not reply directly to this message, but send comments and suggestions to IDS.central.bureau@cls.fr