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ENVISAT Calibration Review DORIS and Orbit Validation Team Work

ENVISAT Calibration Review DORIS and Orbit Validation Team Work. Introduction (P. Vincent, CNES) DORIS Instrument & System Checkout - DIODE real time orbits (B. Bonhoure, CNES) Global OVT results (P. Vincent, CNES) POD processing at ESOC (M. Otten, ESOC)

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ENVISAT Calibration Review DORIS and Orbit Validation Team Work

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  1. ENVISAT Calibration Review DORIS and Orbit Validation Team Work • Introduction (P. Vincent, CNES) • DORIS Instrument & System Checkout - DIODE real time orbits (B. Bonhoure, CNES) • Global OVT results (P. Vincent, CNES) • POD processing at ESOC (M. Otten, ESOC) • Conclusion and Summary (B. Duesmann, ESTEC)

  2. Global Orbit Validation Team work results from: * contributions from the CNES POD team in charge of the operational Precise Orbit Determination for ENVISAT * contributions from the other various experts groups in Europe and in the US, thus benefiting from a synergy with Jason-1 Global OVT work

  3. One major limit of the Precise Orbit Validation exercise by the OVT lies in the percentage of data coming from the PDS to the CNES SSALTO (see next slide) * DORIS data volume coming to SSALTO is enough to perform « Preliminary evaluations » of the MOE / POE quality * « Final Performance » figures to be consolidated in december 2002 once all data acquired are available Present limits of the OVT exercise

  4. * When in nominal conditions, daily MOEs with DORIS are regularly produced: Altimetry IGDRs processing is now fed with the daily MOE * Doppler residuals are of the order of 0.55mm/s, which is compliant with what is observed for other comparable missions (like the SPOT missions) * Accuracy of the radial component presently estimated at the level of 5 cm rms: * previous figure assessed using laser data and computing laser-only orbits. 1. Daily MOE main results from CNES POD Team

  5. Previous slide shows that radial Overlaps are of the order of 3 cm but can be larger up to 6 to 8 cm These figures have to analyzed carefully on a case by case basis as overlaps may occur within periods of large DORIS data gaps or within maneuver periods! Detailed analysis to be continued. About MOE Radial Overlaps

  6. Mixed « DORIS + laser » POE have been generated for several orbital arcs: * Last 7-day arc of ENVISAT cycle 6 * All arcs of cycle 7 * First arc of cycle 8 All DORIS doppler data available, all auxiliary information, and all orbit ephemeris made available to the OVT 2. POE main results from the Operational CNES POD team

  7. POE preliminary Assessment

  8. Estimated POE accuracy is of the order of 3 to 4 cm for the radial component POE Figure to be kept in mind

  9. DEOS/ Delft made a careful analysis of the ENVISAT laser tracking (see next slides): * Density of laser observation * Using the DEOS/Delft POE orbits computed from DORIS and laser data, laser residuals were analyzed as an external index of orbit quality About laser tracking

  10. About SLR Tracking (From DEOS/Delft)

  11. SLR coverage: 3 % DORIS coverage: 31% (not representative of normal situation) 2002/04/24 00:00 2002/05/01 00:00

  12. Preliminary comparisons with DEOS and GFZ POEs

  13. 1. One example of worst case: the Mid-July orbit arc * RMS differences between DEOS and CNES orbits of the order of 7 cm in the radial direction * RMS differences between DEOS and CNES orbits of the order of 90 cm in the along-track direction Explainations: combination of : * a sudden increase in solar activity, * gaps in the DORIS tracking, * and differences in SLR editing at DEOS and CNES Recent comparison figures from DEOS (1)

  14. 2. Example of Best case: Arc from July 12 to July 15 * Mean difference DEOS -CNES better than 0.5 cm in the radial direction * RMS differences of the order of 1.5 to 2.5 cm * Very good 3D consistency at the level of 4.5 to 6.0 cm RMS! Recent comparison figures from DEOS (2)

  15. Present figures that may be agreed: * MOE: radial: better than 5 cm * « not tuned » POE: radial: better than 3 to 4 cm * Preliminary assessment within the OVT: * Very good agreement with DEOS, GFZ and ESOC POD orbits in terms of rms (see next presentation about the ESOC POD work) Still some work to be done for the final assessment and the provision of « Final Performance » figures OVT overall conclusion (1)

  16. Laser data coverage somewhat poor  Then, laser–only ephemeris are of low quality… However, DORIS/Laser mixing produces good-quality orbits. Altimeter crossovers needed to provide external validations OVT overall conclusion (2)

  17. Present limitations of the computations : Final tuning (dynamical parameterization) tested from CYCLE 8 only (large data gaps too frequent before) : * 6H Drag coefficients * Pressure Radiation coefficient heavily constrained * Empirical (1Cy/rev) Hill Acceleration adjusted every Day Seems to be OK, but needs to be tested on further arcs OVT overall conclusion (3)

  18. Will the Satellite Model be revisited ? Final selection for the gravity field, tide model to be done Content of attitude quaternion files remains unclear Nominal law is therefore used only at the present time. Measured quaternions might be of interest Attitude behaviour around manoeuvers would still be appreciated (at least when is YSM nominal law irrelevant around the manoeuver) OVT overall conclusion (4)

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