Status report: Level 2 project Bruno Carli IFAC - CNR (Italy)

1. Status report: Level 2 project Bruno Carli IFAC - CNR (Italy)

2. Contributing Institutes • IFAC-CNR - Italy • University of Bologna - Italy • ISAC-CNR - Italy • IMK - Germany • University of Oxford - U.K. • University of Leicester - U.K. • LPPM - France • Instituto de Astrofisica de Andalucia - Spain

3. Contents • Introduction • - Operations of Level 2 • - Level 2 approach • - Level 2 Commissioning Phase objectives • Preliminary L2 Commissioning Phase activities • - Baseline verifications • - Tuning • - Preliminary L2 performances • Evolution of algorithm baseline • Conclusions

4. Introduction Operations of Level 2 Level 2 Calibrated and geolocated spectra Retrieved profiles • Retrieved vertical profiles of : • altitude correction and temperature (p,T retrieval) • VMR of minor constituent (H2O, O3, HNO3, CH4, N2O and NO2)

5. Introduction Level 2 approach • Use of micro-windows

6. Introduction Level 2 approach • Use of micro-windows • Use of non-linear least-square fit

7. Introduction Level 2 approach • Use of micro-windows • Use of non-linear least-square fit • Global fit of • limb scanning sequence

8. Introduction Level 2 approach • Use of micro-windows • Use of non-linear least-square fit • Global fit of • limb scanning sequence • Sequential fit of species

9. Introduction Level 2 approach • Use of micro-windows • Use of non-linear least-square fit • Global fit of • limb scanning sequence • Sequential fit of species • Near real time operation

10. Introduction Objectives of Level 2 Commissioning Phase • To verify assumptions of algorithm baseline • To Tune processor set-up parameters for robustness, accuracy and time efficiency • To assess performances • To consider and test options for evolution of the algorithm baseline

11. Level 2 Activities Diagnostics and baseline verifications • Intensity calibration

12. Level 2 Activities Diagnostics and baseline verifications • Intensity calibration • Frequency calibration

13. Level 2 Activities Diagnostics and baseline verifications • Intensity calibration • Frequency calibration • ILS calibration

14. Height correction vs horizontal gradient Correlation coefficient = - 0.0196 Probability for Delta(z) e gradT to be uncorrelated = 58 % Level 2 Activities Diagnostics and baseline verifications • Intensity calibration • Frequency calibration • ILS calibration • Assumption of vertical profile

15. Retrieval with engineering LOS information Level 2 Activities Diagnostics and baseline verifications • Intensity calibration • Frequency calibration • ILS calibration • Assumption of vertical profile • Use of LOS info

16. Level 2 Activities Diagnostics and baseline verifications • Intensity calibration • Frequency calibration • ILS calibration • Assumption of vertical profile • Use of LOS info • Altitude independent instrument offset

17. Level 2 Activities Diagnostics and baseline verifications • Intensity calibration • Frequency calibration • ILS calibration • Assumption of vertical profile • Use of LOS info • Altitude independent instrument offset • Local Thermal Equilibrium

18. Level 2 Activities Difference between temperature retrieved with and without LTE assumption

19. Level 2 Activities Tuning • Performed the tuning of • convergence criteria • Marquardt parameters • Altitude range of fitted continuum • FOV modelling

20. The time for the full analysis (62 available scans of the 75 made in one orbit) is less than one hour on a COMPAQ ES45 Server with 2 CPU at 1000 MHz. Preliminary L2 Performances Performances of orbit #504 retrievals

21. Preliminary L2 Performances Results of orbit #504 retrievals Temperature [K] Altitude [km] Orbital coordinate [deg]

22. VMR (ppmv) Water vapour Ozone N2O Altitude [km] CH4 HNO3 NO2 Orbital coordinate [deg] Preliminary L2 Performances Results of orbit #504 retrievals

23. Temperature profile error budget Preliminary L2 Performances Error budget

24. Preliminary L2 Performances Averaging Kernels The Averaging Kernels are tabulated in the case of the nominal measurement scenarios for a set of latitude ranges and seasons.

25. Evolution of algorithm baseline Implemented in prototype • The delay of Envisat launch was used to implement in prototype some options that were identified as possible critical points: • handle sweeps at low altitudes & low latitudes by constraining correction of profile in pT • handling of single microwindow OM in the case of regularisation • recursive pT & H2O retrievals • cloud detection and filtering of L1B input during L2 pre-processing

26. Evolution of algorithm baseline Cloud top height

27. Evolution of algorithm baseline Implemented in scientific code • Some changes are implemented in the scientific code in order to assess their relevance : • use of a tunable scaling factor for the definition of the unknown of the continuum • correction of negative VMR profile points • modification in the numerical correction of the singularity at tangent point • extension of minimum retrieval altitude from 12 to 6 km

28. Evolution of algorithm baseline Extension of retrieval to 6 km altitude

29. Evolution of algorithm baseline Possible future changes for scientific code • As a result of ACVT activities other changes may be considered for the scientific code, e.g. : • check that a consistent definition of continuum parameters is used in the case of retrieval range defined by cloud detection • linear vs polynomial interpolation for FOV convolution • improved modelling of troposphere for extension of retrieval to 6 km • additional outputs ( continuum profiles, cloud indices, initial guess profile, product confidence data)

30. Conclusions (1/2) • Results are based on preliminary analysis • Some improvement of intensity calibration. Level 2 is affected by intensity calibration errors and cannot easily detect them. • A frequency calibration much better than requirements is possible. Level 2 is little affected by frequency calibration errors and can accurately detect them. • A very small bias is observed in ILS determination • Good agreement between calibration diagnostics of Level 1 and Level 2.

31. Conclusions (2/2) • Assumptions made in code development are verified with real data (small and altitude independent instrument offset, use of LOS information and hydrostatic equilibrium, LTE) • A small number of iterations is sufficient to reach convergence • Our error budget is slightly overestimated • Retrieval is robust • Details are being considered for baseline changes.