1. Page 1ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Systematic Product Analysis Christopher Buck ENVISAT Programme ESA/ESTEC

2. Page 2ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Purpose  ASAR generates typically ~100 products per day  Each contains vital information on the health of the instrument, level settings, processing problems etc  Systematic product analysis is required to monitor the instrument and product status, providing inputs to the instrument and processor operation and flagging any problems in a timely fashion

3. Page 3ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Product Types Ingested for Analysis  Module Stepping Mode: ASA_MS__0*  Image Mode Medium Resolution ASA_IMM_1*  Wave Spectra ASA_WVS_1*  Wave Image ASA_WVI_1*  Global Monitoring ASA_GM1_1*  Alternating Polarization Medium Resolution ASA_APM_1*

4. Page 4ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping Mode Analysis  Source packet chirps read in  Compressed with ideal chirp  Gain and phase of each module determined  Transmit and Receive  Horizontal and Vertical Polarization  Time stamped  Entered into Database

5. Page 5ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping Mode Database 320 H or V ASA_MS__0*.N1 A1-E4 1-16

6. Page 6ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping Mode Analysis  Provides:  Instant health check of all modules tx/rx, H/V, Gain/Phase  History of tx/rx, Gain/Phase for each module and each polarization  Phase and amplitude errors as input into antenna pattern analysis

7. Page 7ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping Mode Health Check < 1 LSB error > 1 LSB error > 2 LSB error > 3 LSB error

8. Page 8ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 External Characterisation Antenna B/F Test Results Antenna Gain Test Results Beam Antenna Gain Beam Radiation Pattern Module Stepping Antenna B/F Near-field data Transponder Internal Calibration Rain Forest Pattern and Gain Calibration Embedded Row Test Results Beam Coefficients Doppler Spectrum

9. Page 9ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Module Stepping Mode History  Long-term comparison against pre-launch reference data set shows trends in module behaviour

10. Page 10ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Antenna Stability - Tx  = 0.25dB

11. Page 11ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Antenna Stability - Rx  = 0.4dB

12. Page 12ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Internal Calibration ASAR is equipped with an automatic temperature compensation scheme to compensate for phase/gain drifts at T/R module level Direct monitoring of any residual gain drifts for later correction Continuous measurements even during data acquisition Tx Main Rx Main Radiating Row T/R Module (1 of 32x10) Signal BFN P2 P1A P3 P1 Cal BFN Tx Aux Rx Aux Cal P1 Use of special calibration signals (cal pulses) and additional hardware (cal network)

13. Page 13ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Image Product Analysis  Product header parameters systematically extracted from ASAR products and entered into database for subsequent analysis  Parameters extracted are:  Internal calibration pulses (P1, P1a, P2 and P3) for each of the 32 rows  Product quality parameters (3dB IRF width, sidelobe level, ISLR, peak location, chirp power and scaling factor)  Doppler

14. Page 14ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Image Product Database   32

15. Page 15ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 dummy Interface  Implemented in IDL  Backed by MySQL Database

16. Page 16ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Product Analysis  Confirmation of correct functioning of internal calibration  Generation of INS files with computed default calibration pulse values  Provides overview of main quality parameters  Confirmation of correct pointing and correct Doppler estimation

17. Page 17ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Calibration Pulse Analysis - Wave

18. Page 18ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Calibration Pulse Analysis Wave P2 Spurious results, if ignored, can lead to problems in processed imagery

19. Page 19ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Calibration Pulses - APM

20. Page 20ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Doppler Analysis  In white, 27000 Doppler estimates from Wave Mode Data  In red, the predicted Doppler calculated from orbit parameters

21. Page 21ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Doppler Estimation

22. Page 22ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Doppler Bias Subtracting the predicted Doppler from that estimated from the image data shows a bias of –54Hz

23. Page 23ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Doppler Analysis – Effect of Relief Doppler prediction based on WGS84 hence high altitude of Greenland results in an offset

24. Page 24ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Internal Calibration Occasional spurious results Fall outside threshold limits and are replaced by the nominal values in the processor Wide Swath, SS5, HH

25. Page 25ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 White: PF-ASAR Red: In-house code Calibration Pulse Phase Unwrapping  PF-ASAR currently has a problem when unwrapping the phase of the calibration pulse  This introduces noise in the elevation gain factor calculation  In-house code unwraps correctly and will soon be implemented in PF- ASAR

26. Page 26ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Corrupted Wave Pulses  Normal wave pulses have blocks of 108 samples of constant amplitude  Occasional corrupted wave pulses display irregular amplitude 1 st ten source packets plotted

27. Page 27ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Corrupted Wave Pulses 2  Corrupted pulses change the elevation gain  Problem is not restricted to the northern hemisphere  Not deterministic meaning that if it were dependent on the timing then it would always appear in the same SWST segment

28. Page 28ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Corrupted Cal Pulses in Wide Swath  P2 calibration pulse in wide swath mode is corrupted for sub-swaths 4 and 5 SS1SS2SS3SS4SS5

29. Page 29ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Gain Droop Compensation  P2 gain droop compensation is incorrect when the calibration sequence changes (cal order 0 or 1) in Wide Swath mode  Lower curve is from PF-ASAR with droop compensation using pre-launch characterization data  Upper curve is in- house code and no compensation

30. Page 30ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Conclusions  Systematic product analysis proving to be extremely useful for:  Troubleshooting  Health checking  Consistency checking  Updating processor parameters  So far over 2500 products ingested  949 IMM  1346 WVS  213 WSM  57 APM

31. Page 31ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Conclusions 2  Antenna in great shape, very good stability  0.25dB tx, 0.4dB rx  Doppler tracking error ~50Hz consistent with 10-15 mdegrees of mispointing  Problem with noisy calibration pulse gains identified due to phase unwrapping - solution ready  Problem with P2 gain droop compensation identified – solution at hand

32. Page 32ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 Conclusions 3  Ongoing problems requiring further analysis:  Occasional corrupted Wave pulses  Corrupted cal pulses in Wide Swath Mode  Further problems with the internal calibration are just starting to be addressed in AP and GM modes