2. Page 1ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 ASAR On-board Instrument  Instrument Stability and Status  Instrument Adjustments  Tracking Changes of Beam Patterns  Beam Pattern Maintenance Ramon Torres ENVISAT Programme ESA – ESTEC Noordwijk, The Netherlands

3. Page 2ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Instrument Stability  Relies on the RF Subsystem internal control and the temperature compensation scheme implemented in the Antenna Sub-arrays (Before use of the Internal Calibration correction)  ASAR Instrument has proven to be very stable in short and long term  Short term as demonstrated by the internal calibration pulses viewed through time  Long term as demonstrated by the use of the Module Stepping calibration mode

4. Page 3ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Reminder: ASAR Antenna  Major element in the ASAR end-to-end product quality  Active antenna with 320 individual subarrays  T/R module: Transmit/Receive in H and V polarisation  5 panels  4 tiles  16 subarrays  Control and operations at tile level  Temperature compensation scheme based on individual sub-array on-ground characterisation  Radar mode timing  Pattern definition at row level  8 Stripmap beams  5 ScanSAR beams

5. Page 4ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Antenna Temperature  Initial temperatures were lower than predicted  Increased operations from May 3 achieved realistic temperature conditions:  0  -6  for HR only  4  -10  for full  Low temperatures corresponding to instrument switchoffs

6. Page 5ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Short Term Stability – Internal Calibration Tx Main Rx Main Radiating Row T/R Module (1 of 32x10) Signal BFN Cal BFN Tx Aux Rx Aux Cal  Variations in Tx signal and Rx conditions during acquisition  Analysis of the internal calibration pulses  P1  Tx  P2  Rx  P3  RF s/s P2 P3 P1

7. Page 6ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Short term Stability  Instrument variations are taken into account by the ASAR internal calibration, nevertheless:  RF s/s conversion levels are extremely stable (P3 pulse July 21-August 9)  Variations of Tx and Rx characteristics due to temperature at antenna level are well handled by the temperature compensation scheme (P1 and P2 pulses for row 18, July 21-August 9) 

8. Page 7ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Long Term Stability  Long-term (along the instrument lifetime): Sub-array T/R module failures, drifts and degradation  ASAR monitors T/R modules for failures or drifts for eventual correction  Use of Module Stepping Mode:  Sampling all 320 T/R modules sequentially in less than 1 s (Tx/Rx Gain/Phase) anywhere in the orbit  Comparison with reference measurement  Statistical analysis of variations

9. Page 8ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Long Term Stability - Module Stepping Mode  Individual T/R Modules  Tx and Rx  H and V  Gain and Phase Tx Main Rx Main Signal BFN Cal BFN Tx Aux Rx Aux Cal T/R Module Radiating Row TxRx

10. Page 9ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping - Last Results - TxH <> ± 1.5 dB <> ± 3.0 dB <> ± 10.0 dB >< ± 10.0 dB <> ± 5.65º <> ± 11.2º <> ± 22.5º >< ± 22.5º 

11. Page 10ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping - Last Results - RxH <> ± 1.5 dB <> ± 3.0 dB <> ± 10.0 dB >< ± 10.0 dB <> ± 5.65º <> ± 11.2º <> ± 22.5º >< ± 22.5º

12. Page 11ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping - Last Results - TxV <> ± 1.5 dB <> ± 3.0 dB <> ± 10.0 dB >< ± 10.0 dB <> ± 5.65º <> ± 11.2º <> ± 22.5º >< ± 22.5º 

13. Page 12ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping - Last Results - RxV <> ± 1.5 dB <> ± 3.0 dB <> ± 10.0 dB >< ± 10.0 dB <> ± 5.65º <> ± 11.2º <> ± 22.5º >< ± 22.5º

14. Page 13ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Long-term Stability Tx HRx HTx VRx V Gain  0.25 dB0.40 dB0.30 dB0.49 dB Phase  2.9º3.4º3.2º3.4º  Analysis on the T/R modules from Sep/02 to Nov/24  Close to the LSB step both for gain and phase  Tx / Rx difference from Rx gain droop not compensated in calibration modes:  0.22 dB (Rx gain droop)  0.25 dB (gain control) 

15. Page 14ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Instrument Adjustments  Early corrections:  On board beam coefficients for ScanSAR modes  Up and down converter levels  Sub-array gain and phase offsets  Timing parameters  Wave Mode exit timing  Control Software patches from operational failures  Historical Swath parameters  N-2 echo-shift  Wave mode telemetry  Alternate Polarisation mode annotation  Global Monitoring mode exit  Parameter optimisation from calibration activities:  Receiver gain adjustments  Image and WideSwath bandwidths  WideSwath timeline

16. Page 15ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Adjustments: Early Corrections  ScanSAR beam coefficients wrongly burnt in the on-board EPROMs  upload of new  Up and down converter levels too low for Module Stepping mode  upload of new  Gain and phase offsets to correct on-ground deviations and post-launch drifts  upload  Timing parameters not compatible with orbit data  upload of new  Wave Mode exit timing not compatible with complete vignette termination  MPS control

17. Page 16ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Adjustments: Parameter Optimisation  Receiver Gain for all modes and beams in order to maximise the dynamic range  Image Mode Bandwidth increased to maximum 16MHz for all beams  WideSwath Bandwidth increased:  WideSwath Timeline modified by reducing the number of pulses per burst to improve azimuth ambiguities: SS1SS2SS3SS4SS5 7.155.334.393.012.82 14.7512.8610.489.548.78 SS1SS2SS3SS4SS5 5080678774 5065557160

18. Page 17ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 On-board Software Patches  Historical Swath Parameters  Switchdowns  Uploaded 02-Aug-2002. Anomaly solved!  N-2 Echo Shift  Large shifts in images  Uploaded 05-Sep-2002. Anomaly solved!  Wave Mode telemetry handling between vignettes  Switchdown  Uploaded 17-Oct-2002. Anomaly solved!  Alternate Polarisation Annotation of the SWST changes  Shift between polarisations  Uploaded 11-Nov-2002. Anomaly solved!  Global Monitoring exit  Switchdown  Uploaded completed 9 December at 18:56:16. GM operating correctly from 9 December at 19:02:30 

19. Page 18ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Tracking Beam Pattern Changes  Estimation based on Module Stepping results and the radiation model of each sub-array based on  On-ground characterised embedded row pattern for elevation  Uniform distribution for azimuth  Generation of antenna radiation patterns:  full elevation and azimuth pattern for ambiguity analysis  swath elevation pattern for tracking changes  swath azimuth pattern for Doppler estimation and descalloping  A single MS generates the full set of antenna patterns (Tx/Rx and Hpol/Vpol)

20. Page 19ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Synthesis of Elevation Patterns  IS1 Pattern:  Elevation VV  Measured Pre-launch  Estimated Rainforest  Simulated from MS  Elevation HH  Measured Pre-launch  Estimated Rainforest  Simulated from MS  Conclusion:  MS agrees with RF within ± 0.2 dB  Same order as pre- launch patterns

21. Page 20ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Synthesis of Azimuth Patterns  June 2002 image mode IS3 over Edam, Zwolle and Swifterband  Very good correlation between simulated data and transponder flyovers  Better than 2 db at the level of – 20db (  0.02db)  IS1 synthesised from MS  Mispointing agrees with doppler

22. Page 21ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Pattern Estimation: Conclusions  Rainforest estimation:  Estimation approach based on combinations of pattern estimates in different modes (IM&WS) with a standard deviation of ~0.1dB  Long process as it requires several acquisitions per beam and polarisation  Synthesis from Module Stepping results:  Very good tool to track variations of the antenna radiation patterns  From a 1-second acquisition full set of radiation patterns can be generated as frequently as needed (no orbit constraint)  Elevation patterns can be simulated with an error of 0.2dB due to limited quality of ground characterisation data  Embedded row patterns measured with only 14 tiles and insufficient control of T/R modules  Azimuth patterns and pointing can be simulated better than 0.02dB and 0.01  

23. Page 22ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Antenna Elevation Pattern Maintenance Antenna IMBF Test Results Reference Module Stepping Antenna IMBF Test Results Rainforest Patterns Module Stepping Module Stepping Module Stepping Module Stepping Offset/K0 Correction TRM Drifts TRM Failures MS Analysis Offset/K0 TRM Drifts TRM Failures Offset/K0 MS Analysis Rain Forest TRM Drifts TRM Failures Offset/K0 New Coefficients Rain Forest (TSS Failures) Rain Forest Far sidelobes MS Analysis Far sidelobes 

24. Page 23ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Antenna Azimuth Pattern Maintenance Antenna IMBF Test Results Reference Module Stepping Antenna IMBF Test Results Synthesised Patterns Module Stepping Module Stepping Module Stepping Module Stepping Offset/K0 Correction TRM Drifts TRM Failures TRM Drifts TRM Failures Offset/K0 Transponder TRM Drifts TRM Failures Transponder (TSS Failures) MS Analysis Offset/K0 MS Analysis Offset/K0 MS Analysis New Coefficients 