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ASAR On-board Instrument

This document discusses the stability of the ASAR instrument and the adjustments made to maintain beam patterns. It covers topics such as temperature compensation, internal calibration, module stepping mode, and long-term stability.

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ASAR On-board Instrument

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  1. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  2. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  3. 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 Reminder: ASAR Antenna • 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  4. 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 Antenna Temperature ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

  6. 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) ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  7. 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 Long Term Stability ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

  9. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  10. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  11. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  12. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  13. 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)  Long-term Stability ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  14. Instrument Adjustments • Control Software patches from operational failures • Historical Swath parameters • N-2 echo-shift • Wave mode telemetry • Alternate Polarisation mode annotation • Global Monitoring mode exit • 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 • Parameter optimisation from calibration activities: • Receiver gain adjustments • Image and WideSwath bandwidths • WideSwath timeline ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  15. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  16. 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: ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  17. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  18. 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) ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  19. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  20. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  21. 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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

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

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