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Enhancements in ERS-1 & ERS-2 Altimetry: Addressing Instrumental Errors and Gyroscope Status

The ERS-1 and ERS-2 missions have implemented significant improvements in altimetric range correction, effectively removing anomalies and jumps in data. Operational as of December 15, 2000, the new formats and IF filter shapes are designed to enhance data accuracy. Gyroscope status and performance continue to be critical, with ongoing work to characterize IF filter evolution and potential backup modes for satellite control. The integration of these features aims to sustain mission performance and ensure data validity for future analyses.

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Enhancements in ERS-1 & ERS-2 Altimetry: Addressing Instrumental Errors and Gyroscope Status

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  1. ERS RA Instrumental Errors • New ERS-1 & ERS-2 SPTR2000 altimetric range correction => Real improvement in the removal of the jumps associated with anomalies => New format as described in the TN ERE-TN-ADQ-GSO-6001 => Operationally available as from December 15, 2000 from the new under-construction PCS Web Site pcswww.esrin.esa.it/ra • Ultra Stable Oscillator Frequency Drift => Available now at pcswww.esrin.esa.it/ra • I/F Filter Shape => Not applied to the URA FD and WAP data product => On-ground characterized IF filter shape applied to the OPR Envisat RA-2&MWR CCVT Meeting, ESRIN, December 14, 2000

  2. ERS RA Instrumental Errors • I/F Filter Shape (cnt’d) => preliminary simulations showed an impact on the data (Ref CLS doc): - few tenths of dB on the Sigma0 - few cm on the altimetric range => processings have been performed at F-PAF using different IF filters for both ERS-1 and ERS-2. (14 orbits processed, 1 day) Differences in range (mm) between operational and current IF filters (preliminary results) ERS-1 ERS-2 Envisat RA-2&MWR CCVT Meeting, ESRIN, December 14, 2000

  3. ERS RA Instrumental Errors • I/F Filter Shape (cnt’d) => The ERS OPR data should clearly be processed with the current IF filter. Do we change it for the Envisat Commissioning Phase ? => Work on-going to characterize the IF filter evolution along the ERS-1 and ERS-2 missions and to propose a output correction file. • Off-nadir pointing => Gyroscopes status: - Piloting today with gyro #1, which has very little random noise - Gyro #6 as back-up for piloting, Gyro #4 kept for the safe mode - Gyro #3 (noisy) for CAM - Gyro #2 and #5 non operational Envisat RA-2&MWR CCVT Meeting, ESRIN, December 14, 2000

  4. ERS RA Instrumental Errors => Gyroscopes status (cnt’d) - If Gyro #1 fails today, ERS would go to CAM. - If subsequently Gyro #6 fails, ERS would go to Safe mode. • In order to avoid this, ERS could go to “extra-back-up-mode”, a new mode currently being developed by Matra for 8 December (delivery). • The plan is to upload and commission this software before Christmas (to be confirmed). • This mode permits only satellite control. No requirement on attitude stability has been made. Nevertheless some instruments may be operated in this mode. • Zero gyro mode attitude software under development. Delivery not before October 2000. Envisat RA-2&MWR CCVT Meeting, ESRIN, December 14, 2000

  5. ERS RA Instrumental Errors => ERS Gyroscopes strategy - Pilot ERS-2 as long as possible with the Gyros #1 and #6 - Attitude currently monitored at ESRIN/PCS from data analysis (SAR, RA) and still shows to be < 0.1 deg - The PTF attitude information is not recoverable from the PTF data => the attitude error can’t be properly characterized => no mispointing correction available - A mispointing threshold shall be defined (for the RA-2&MWR CCVT exercise), over which the ERS data will be considered as invalid. - If these 2 gyros are declared non operational before the delivery of the gyro-less attitude software, the ERS RA mission could be suspended. Envisat RA-2&MWR CCVT Meeting, ESRIN, December 14, 2000

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