ASAR Onboard Instrument Instrument Stability and Status Instrument

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 1

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 2

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 Scan. SAR beams ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 3

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

Short Term Stability – Internal Calibration § Variations in Tx signal and Rx conditions during acquisition § Analysis of the internal calibration pulses § P 1 Tx § P 2 Rx § P 3 RF s/s T/R Module (1 of 32 x 10) P 3 Tx Aux P 2 Tx Main Radiating Row Signal BFN P 1 Rx Main Rx Aux Cal BFN Cal ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 5

Short term Stability § Instrument variations are taken into account by the ASAR internal calibration, nevertheless: § RF s/s conversion levels are extremely stable (P 3 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 (P 1 and P 2 pulses for row 18, July 21 -August 9) ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 6

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 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 7

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

Module Stepping - Last Results - Tx. H <> ± 1. 5 <> ± 3. 0 <> ± 10. 0 >< ± 10. 0 <> <> <> >< ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 ± ± d. B 5. 65º 11. 2º 22. 5º 9

Module Stepping - Last Results - Rx. H <> ± 1. 5 <> ± 3. 0 <> ± 10. 0 >< ± 10. 0 <> <> <> >< ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 ± ± d. B 5. 65º 11. 2º 22. 5º 10

Module Stepping - Last Results - Tx. V <> ± 1. 5 <> ± 3. 0 <> ± 10. 0 >< ± 10. 0 <> <> <> >< ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 ± ± d. B 5. 65º 11. 2º 22. 5º 11

Module Stepping - Last Results - Rx. V <> ± 1. 5 <> ± 3. 0 <> ± 10. 0 >< ± 10. 0 <> <> <> >< ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 ± ± d. B 5. 65º 11. 2º 22. 5º 12

Long-term Stability § 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 d. B (Rx gain droop) § 0. 25 d. B (gain control) Tx H Gain Phase Rx H Tx V Rx V 0. 25 d. B 0. 40 d. B 0. 30 d. B 0. 49 d. B 2. 9º ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 3. 4º 3. 2º 3. 4º 13

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

Adjustments: Early Corrections § Scan. SAR 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 15

Adjustments: Parameter Optimisation § Receiver Gain for all modes and beams in order to maximise the dynamic range § Image Mode Bandwidth increased to maximum 16 MHz for all beams § Wide. Swath Bandwidth increased: SS 1 SS 2 SS 3 SS 4 SS 5 7. 15 5. 33 4. 39 3. 01 2. 82 14. 75 12. 86 10. 48 9. 54 8. 78 § Wide. Swath Timeline modified by reducing the number of pulses per burst to improve azimuth ambiguities: SS 1 SS 2 SS 3 SS 4 SS 5 50 80 67 87 74 50 65 55 71 60 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 16

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 17

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 18

Synthesis of Elevation Patterns § IS 1 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 d. B § Same order as prelaunch patterns ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 19

Synthesis of Azimuth Patterns § June 2002 image mode IS 3 over Edam, Zwolle and Swifterband § Very good correlation between simulated data and transponder flyovers § Better than 2 db at the level of – 20 db ( 0. 02 db) § IS 1 synthesised from MS § Mispointing agrees with doppler ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 20

Pattern Estimation: Conclusions § Rainforest estimation: § Estimation approach based on combinations of pattern estimates in different modes (IM&WS) with a standard deviation of ~0. 1 d. B § 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. 2 d. B 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. 02 d. B and 0. 01 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 21

Antenna Elevation Pattern Maintenance Reference Module Stepping TRM Drifts TRM Failures MS Analysis Offset/K 0 Correction Antenna IMBF Test Results MS Analysis Offset/K 0 Rain Forest Far sidelobes Rainforest Patterns TRM Drifts TRM Failures (TSS Failures) MS Analysis Offset/K 0 New Coefficients Rain Forest Far sidelobes ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping Rainforest Patterns 22

Antenna Azimuth Pattern Maintenance Reference Module Stepping TRM Drifts Offset/K 0 Correction Antenna IMBF Test Results Module Stepping TRM Drifts TRM Failures (TSS Failures) Offset/K 0 MS Analysis New Coefficients Offset/K 0 MS Analysis Transponder Synthesised Patterns ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Synthesised Patterns 23