Systematic Product Analysis of ASAR within the ENVISAT Programme

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

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

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

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

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

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

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

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

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

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

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

12. P3 P2 Tx Aux P1A P1 P1 P1 Cal BFN Cal Rx Aux 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 T/R Module (1 of 32x10) Radiating Row Signal BFN Tx Main Rx Main • Use of special calibration signals (cal pulses) and additional hardware (cal network) ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

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

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

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

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

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

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

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

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

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

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

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

25. 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 White: PF-ASAR Red: In-house code ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

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

28. Corrupted Cal Pulses in Wide Swath • P2 calibration pulse in wide swath mode is corrupted for sub-swaths 4 and 5 SS1 SS2 SS3 SS4 SS5 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

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

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

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