Page 1 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann

Page 2 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann F Main mission of DORIS, Doppler ORbitography Integrated by Satellite, is to provide to various users satellite Ephemerides F Integrated real-time 3D navigator on-board, one block time/position/velocity/quality every 10 seconds F DORIS Doppler data are processed off-line for precise orbits F Real-time time-tagging is done on-board on BCP2/4 pulses DORIS Mission

Page 3 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann Instrument Performances F DORIS Doppler data residuals against MOE orbit are mm/s F Navigator accuracy is : u cm radial RMS u Less than 1 meter 3D RMS F Performances are better than specifications (10 m RMS per axis) F DORIS Datation Accuracy is OK (on BCP2 pulse following a BCP4), u accuracy better than 15 microseconds, comparison of navigator orbit with ground orbits (MOE, POE including laser data), one microsecond error means 7mm along-track

Page 4 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann F Functioning and Performances of the DORIS instrument are fully nominal F Operations of DORIS are routine F DORIS Performances are better than specifications DORIS Conclusions

Page 5 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann F Global Orbit Validation Team work results from: u contributions from the CNES POD team in charge of the operational Precise Orbit Determination for ENVISAT u contributions from the other experts groups in Europe and in the US, benefiting from a synergy with Jason-1 Global OVT work

Page 6 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann F Mixed « DORIS + laser » POE have been generated for several orbital arcs: u Last 7-day arc of ENVISAT cycle 6 u All arcs of cycle 7 u First arc of cycle 8 F All available DORIS doppler data, all auxiliary information, and all orbit ephemeris made available to the OVT F Estimated POE accuracy is of the order of 3 to 4 cm for the radial component POE results from CNES POD team

Page 7 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann F One example of worst case: the Mid-July orbit arc u RMS differences between DEOS and CNES orbits 7 cm in the radial direction 90 cm in the along-track direction u Explainations: combination of : * a sudden increase in solar activity, * gaps in the DORIS tracking, * and differences in SLR editing at DEOS and CNES F Example of Best case: Arc from July 12 to July 15 u Mean difference DEOS -CNES better than 0.5 cm in radial direction u RMS differences of the order of 1.5 to 2.5 cm u Very good 3D consistency at the level of 4.5 to 6.0 cm RMS Recent comparison figures from DEOS

Page 8 ENVISAT Calibration Review, ESTEC 9-13 Sept 2002, DORIS & ORBIT, Berthyl Duesmann F Present figures that may be agreed: u MOE: radial: better than 5 cm u « not tuned » POE: radial: better than 3 to 4 cm u Very good agreement with DEOS, GFZ and ESOC OVT overall conclusion