1. Page 1 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-MTR: A 2-Dimensional Multi Target Retrieval System for MIPAS/ENVISAT Observations M. Carlotti, E. Papandrea, M. Prevedelli, M. Ridolfi DCFI, Bologna University, Bologna, Italy B.M. Dinelli, L. Magnani ISAC-CNR, Bologna, Italy A. Dudhia AOPP, Oxford University, Oxford, UK

2. Page 2 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 A new retrieval system for MIPAS measurements has been developed in the frame of ESA contract No. 16700/02/I-LG by: The new system (named GEO-MTR) will be distributed by ESA as an open source code. DCFIAOPPLPPM Science [&] Technology The system is designed for “nominal” and “special” observation modes

3. Page 3 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Features of the ESA Level-2 processor F Retrieval from narrow-band spectral intervals (MicroWindows); F Global-fit of one limb-scan at a time; F Atmosphere assumed horizontally homogeneous; F Sequential retrieval of the target species: pT (pointing), H 2 O, O 3, HNO 3, CH 4, N 2 O, and NO 2.

4. Page 4 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Assumptions of the ESA Level 2 processor (atmospheric model) F The sampled atmosphere is assumed as perfectly stratified (Horizontal Homogeneity Assumption). F In the case of “along track” measurements, because of the movement of the platform, this assumption extends to a scale of the order of 2000 km. F When pronounced horizontal gradients are present, this assumption introduces systematic errors that are difficult to assess.

5. Page 5 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 F For along track observations, the information content about a given location of the atmosphere can be gathered from all the lines of sight that cross that location; F The loop of cross-talk between nearby sequences closes when the starting sequence is reached again at the end of the orbit (North Pole); F The information is fully exploited by merging in a simultaneous fit the observations of an entire orbit. GEO-FIT rationale

6. Page 6 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 A 2-Dimensional discretization of the atmosphere must be operated

7. Page 7 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-FIT advantages F Enables to model the horizontal variability of the atmosphere F The retrieval grid is independent from the measurement grid: the horizontal resolution of the retrieved atmospheric fields can be optimized; F Enables to exploit at best the information content of along- track measurements;

8. Page 8 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Assumptions of the ESA Level 2 processor (retrieval strategy) F The analysed MicroWindows usually contain transitions of several gases that generate composite spectral features. F Individual targets are sequentially retrieved. F The uncertainty on the VMR of non-retrieved (interfering) species acts as a systematic error source of the retrieval. F To minimize these errors, the following items were optimised: 1. the sequence of the retrievals; 2. the selection of the analysed MWs. Nevertheless, in most cases, these errors are not negligible.

9. Page 9 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Multi Target Retrieval (MTR) rationale F The simultaneous retrieval of target quantities that are correlated eliminates the systematic error propagation due to “interfering” species. F The uncertainty on the initial guess of the quantities that are simultaneously retrieved does not act as a source of systematic error;

10. Page 10 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 MTR – advantages F No systematic error propagation due to “interfering” species; F The error due to the cross-talk between different target quantities is properly represented in the covariance matrix of the retrieved parameters; F The selection of MicroWindows is no longer dominated by the need to reduce the interferences among target species; F The information on pressure and temperature can be gathered from the spectral features of all target species (not only from CO 2 lines, as in the ESA's Level 2 processor).

11. Page 11 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-MTR functionalities (1/2) Main functionalities of the new retrieval system are: 1. Geofit analysis (2-Dimensional) of a full orbit; 2. Orbit-segments analysis (2-Dimensional); 3. Single-sequence analysis. 4. MTR analysis of: u p,T + n VMRs (with n=1,2,…) u p,T u n VMRs F Any combination of MTR with 1, 2, or 3 can be selected.

12. Page 12 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-MTR functionalities (2/2) F Sequential retrievals can be obtained by running the analysis system in sequence through a UNIX script; F Any combination of MTR and sequential retrievals can be used; F Operates 2-D analyses on all the backward looking observation- modes; F Cross-track observations can be analyzed with the Single-scan option. Not suitable for daytime Upper Atmosphere observations (NLTE is not modeled)

13. Page 13 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 F P, T, H 2 O, O 3 retrieval with GEO-MTR Performance test on orbit 2081+2082 Data acquired on 24 July 2002 (1/6)

14. Page 14 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 F Dedicated MWs have been produced for GEO-MTR. F Test using pointing information and initial guess profiles obtained from ESA's Level 2 processor: Convergence is reached after 2 Gauss - Newton iterations:  2 - test 4.95  1.78  1.70 F Test using Level-1b pointing information and climatological profiles for the initial guess: Convergence is reached after 3 Gauss - Newton iterations:  2 - test 80.18  3.41  1.87  1.83 Performance test on orbit 2081+2082 (2/6)

15. Page 15 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Performance test on orbit 2081+2082 (3/6) Temperature North Pole South PoleEquator

16. Page 16 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Performance test on orbit 2081+2082 (4/6) Pressure

17. Page 17 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Performance test on orbit 2081+2082 (5/6) Water vapour

18. Page 18 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Performance test on orbit 2081+2082 (6/6) Ozone

19. Page 19 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-MTR vs ESA Level 2 (1/3) Temperature ESD GEO - MTRESA Level 2

20. Page 20 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-MTR vs ESA Level 2 (2/3) Water vapour ESD GEO - MTRESA Level 2

21. Page 21 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 GEO-MTR vs ESA Level 2 (3/3) Ozone ESD GEO - MTRESA Level 2

22. Page 22 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 NOMINAL #6673 (10 Jun 2003) 75 Scans 17 Sweeps / scan (68-6 km) S2 #6687 (11 Jun 2003) 89 Scans 14 Sweeps /scan (40-5 km) Test on special mode S2 vs NOMINAL mode (1/5)

23. Page 23 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Test on special mode S2 vs NOMINAL mode (2/5) #6673 Nominal Mode#6687 Special Mode (S2) Temperature

24. Page 24 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Test on special mode S2 vs NOMINAL mode (3/5) #6673 Nominal Mode#6687 Special Mode (S2) Temperature

25. Page 25 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Test on special mode S2 vs NOMINAL mode (4/5) #6673 Nominal Mode#6687 Special Mode (S2) Temperature

26. Page 26 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Test on special mode S2 vs NOMINAL mode (5/5) Temperature ESD #6673 Nominal Mode#6687 Special Mode (S2)

27. Page 27 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Computing Performance on composite orbit 2081+2082 MTR retrieval of P, T, H 2 O, O 3 followed by sequential retrieval of HNO 3, CH 4, N 2 O, NO 2 F Time required for the retrieval on the full orbit: u 105 min on a single CPU Pentium IV (2.8 GHz) u 17 min on a cluster of 8 CPU Pentium IV (2.8 GHz) F Memory (RAM) required: u 1.05 Gb with static allocation u 600 Mb with dynamic allocation (FORTRAN 90)

28. Page 28 ENVISAT Symposium – Salzburg - Austria 6-10 September 2004 Conclusions F A new retrieval system has been developed for MIPAS observations F The system operates 2D analyses in Multi Target mode F The accuracy on nominal mode is better than that of the ESA Level 2 F A validation-tests program is in progress F Computing requirements are reasonable; F Can perform real time processing of MIPAS observations; F The code will be distributed by ESA as open source (no profit!).