RTTOV-7: A satellite radiance simulator for the new millennium

1. R Saunders, M Matricardi, P Brunel S English and G Deblonde RTTOV-7: A satellite radiance simulator for the new millennium What is RTTOV Latest developments from RTTOV-6 to 7 Validation results for RTTOV-7 How to get it

2. Acknowledgements NWP Satellite Application Facility A Collard, P Rayer, S English, E Carroll/F Smith M Matricardi, F Chevallier, G Kelly, Erik Andersson, D Salmond P Brunel G Deblonde, V Sherlock, T Kleespies EUMETSAT for partial funding

3. Other RTTOV related talks/posters • M Matricardi New transmittance predictors/AIRS • F Chevallier Diverse profile datasets • V SherlockGastropod for AIRS simulations • T KleespiesInclusion of OPTRAN in RTTOV

4. Fast Model Approaches (profile TOA radiances) • Linear regression (profile  optical depth) • On fixed pressure levels • On fixed absorber overburden layers (OPTRAN) • Physical method • Look up tables • Neural nets

5. History of RTTOV • RTTOV-3 released in 1993 by ECMWF Eyre, (1991) • 40 levels mixed gases, 15 levels H2O • Based on 32 NESDIS profile dataset and ITPP TOVSRAD • RTTOV-5released in 1999 Saunders et al (1999) • 43 levels for mixed gases, H2O and O3. • Based on 43 TIGR profile dataset and GENLN2/MPM-89/92 • FASTEM • RTTOV-6 released in Apr 2000 SAF report • RTTOV-7 released Feb 2002 SAF report

6. RTTOV-6 model • Statistical regression of layer optical depths with profile variables on fixed pressure levels for mixed gases, water vapour and ozone • IR optical depths based on GENLN2, HITRAN-96/CKD2.1 in range 500 - 3000 cm-1 • MW optical depths based on MPM 89/92 Line by Line models • 43 diverse TIGR profile dataset used to compute coeffs for model (dependent set)

7. RTTOV-6 model (cont) • Includes fast surface emissivity models (ISEM for IR and FASTEM for MW) at least over water, more work needed over land • Includes simplistic treatment of cloud • Code written in F77 & F90 and available through SAF (RTTOV-6 has > 40 users worldwide including major NWP centres) • Variety of different sensors supported (next slide)

8. Recent RTTOV developments • Improved water vapour and ozone optical depth predictors (ECMWF) • Multi-layer clouds, more realistic emissivities and random overlap assumption have been added for both IR and MW External routines(ECMWF) • Update of microwave sea surface emissivity model FASTEM to FASTEM-2 (METO/MSC) • Inclusion of cosmic background radiation (MSC) • Addition of high spectral resolution sounders (ECMWF) and SSMI(S) (MSC/METO) • Code rewritten in standard F90,vectorised and made threadsafe (MeteoFrance/ECMWF) • Separate coefficient files for each sensor (MeteoFrance) • New web site (METO)

9. Satellite sensors supported by RTTOV-6/7 Chan # Sensor Italics RTTOV-7 only

10. How to validate RTTOV? • Use an independent set of profiles (e.g. ECMWF diverse 117 profile set) but with same LbL model computed transmittances • Gives estimate of inherent model accuracy of trasmittances and TOA radiances • Fast model comparisons (e.g. Garand et al 2001, Gastropod) of radiances and jacobians • Gives performance of model compared to others • Line-by-line model comparisons (e.g. ISSWG LIE) • Gives estimate of underlying LbL model accuracy • Comparisons with real satellite data using NWP fields

11. Validation of AMSU-B transmittances Dashed RTTOV-6; solid RTTOV-7

12. Dependent vs independent statistics HIRS 1-20 AMSU 21-40

13. Validation of radiances HIRS HIRS 1-20 AMSU 21-40

14. Validation of jacobians AMSU 21-40 HIRS 1-20

15. Garand fast model intercomparison for HIRS channels RTTOV 5 and 6

16. SSMI(S) Filters

17. SSMIS brightness temps

18. Validation of jacobians

19. NWP O-B scan angle stats RTTOV-7 RTTOV-5

20. Validation of HBHT RTTOV-5 Model background error as HIRS-12 radiance RTTOV-7

21. New water vapour spectroscopy Using Toth revision of the water vapour spectroscopy, resulted in a better agreement between observations and simulations

22. Summary • RTTOV-7 now available with improved water vapour and ozone simulation for both IR and MW channels • Smoother jacobians better assimilation • More realistic cloudy radiances can be computed using RTTOVCLD routines • Improved simulation of MW surface emissivity • AIRS/SSMIS/FY radiance simulation included

23. Future plans  RTTOV-8 • Improve interface with NWP model levels • Update LbL dependent transmittances with latest spectroscopy • Optimise predictors (number, robustness) • Improve fast land surface emissivity models and extend range of ISEM-6 • Add solar reflection • Include precipitation in state vector for microwave • Add more variable gases (e.g. CH4, N2O, CO2) • Add IASI simulation capability

24. RTTOV-7 Distribution http://www.metoffice.com/research/interproj/nwpsaf/rtm/ • Requests: email rttov.nwpsaf@metoffice.com or fax request to me on +44-1344-854026 • I will reply with a 2 page licence form to sign which you then fax to number above • RTTOV-7 code is then distributed via ECMWF data services: data.services@ecmwf.int on requested format/medium • Two formats: • Compressed unix tar file of F90 code+files • CDROM of F90 code+files • Media: ftp transfer or CDROM • Documentation + updates available from NWP-SAF web page above. • RTTOV-6 is also available (e.g. for F77 users) • Please give feedback on any bugs by email to: rttov.nwpsaf@metoffice.com

25. RTTOV-7 Documentation/Updates http://www.metoffice.com/research/interproj/nwpsaf/rtm/ • Users guide (overview, installation, testing, interfaces) • Science and validation plan (overview of new science and links to papers/reports giving more details, validation results documented here). • Technical report (details of software architecture, file formats and interfaces) • SAF reports on RTTOV (access from web page) • Bugs and fixes (alerts on RTTOV email list, details on web page)