1. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Thomas J. Kleespies NOAA/NESDIS Camp Springs MD USA

2. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Motivation Informal comparisons with R. Saunders of OPTRAN with RTTOV suggested that –1) OPTRAN performed better with water vapor –2) RTTOV performed better with mixed gases It seems obvious that an attempt should be made to merge the two

3. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Problems with Earlier Comparisons Used different line by line Used different dependent atmospheres Used different number of levels No serious independent comparison for OPTRAN This work corrects most of these deficiencies

4. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds RTTOV Review Performs regression on fixed pressure levels Optical depth is the predictand

5. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds RTTOV PRFINOPDEP PRFTAU RTTAU RTINT RTTOV Calls PRFIN to unpack state vector Calls OPDEP to compute optical depths Calls RTTAU to compute transmittances Calls RTINT to compute radiances and brightness temperatures PRFIN Unpacks input state vector Calls PRFTAU to compute predictors PRFTAU Computes predictors RTINT Integrates the radiative transfer equation to produce radiances and brightness temperatures OPDEP Computes optical depth RTTAU Computes transmittances RTTOV

6. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds OPTRAN Review Regression is performed on levels of absorber amount Predictand is absorption coefficient, easily combined with absorber amount to give optical depth

7. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Transmittance Driver. Set up coefficients on first invocation. Compute absorber profile. Call OPTRAN_SPECIES to compute optical depths. Compute transmittances from optical depths. Find levels in absorber space that bracket input profile. Call GET_PREDICTORS_ALL to compute predictors. Compute absorption coefficients in absorber space. Interpolate absorption coefficients to pressure space. Compute optical depth in pressure space. Compute predictors in absorber space. OPTRAN2 OPTRAN_SPECIES GET_PREDICTORS_ALL OPTRAN2 Double Interpolation (Original OPTRAN)

8. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Transmittance Driver. Set up coefficients on first invocation. Compute absorber profile. Call OPTRAN_SPECIES to compute optical depths. Compute transmittances from optical depths. Find levels in absorber space that bracket input profile. Call GET_PREDICTORS_ALL to compute predictors on pressure levels. Compute absorption coefficients by interpolating regression coefficients from absorber space to pressure space. Compute optical depth in pressure space. Compute predictors in pressure space. OPTRAN1 OPTRAN_SPECIES GET_PREDICTORS_ALL OPTRAN1 Single Interpolation

9. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds SAF-NWP Objective Merge OPTRAN into the RTTOV 6.7 framework Permit switching of individual absorbers between OPTRAN and RTTOV Permit switching off individual absorbers Perform a ‘clean test’ comparison

10. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds RTTOV Calls PRFIN to unpack state vector Calls OPDEP to compute optical depths Calls RTTAU to compute transmittances Calls RTINT to compute radiances and brightness temperatures PRFIN Unpacks input state vector Computes absorber profile (vice OPTRANS) Calls PRFTAU to compute predictors PRFTAU Computes predictors. Find levels in absorber space that bracket input profile (vice OPTRANS_SPECIES). Calls GET_PREDICTORS_ALL. RTINT Integrates the radiative transfer equation to produce radiances and brightness temperatures OPDEP Computes optical depth Calls OPTRANS_SPECIES RTTAU Computes transmittances OPTRAN1-RTTOV Code is switchable between OPTRAN and RTTOV for each absorbing species: UMG, H2O, O3 RTTOV PRFINOPDEP PRFTAU RTTAU RTINT GET_PREDICTORS_ALL OPTRAN_SPECIES

11. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds “If you’ve made up your mind to test a theory, or you want to explain some idea, you should always decide to publish it whichever way it comes out. If we only publish results of a certain kind, we can make the argument look good. We must publish both kinds of results.” Richard Feynman

12. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

13. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

14. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds What happened to ozone??

15. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

16. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

17. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds K code

18. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Brute Force

19. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Brute Force

20. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Status RTTOV/OPTRAN1 with TL,AD,K done RTTOV/OPTRAN2 only forward model Nagging question of OPTRAN1/2 ozone H 2 O Jacobians incorrect

21. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Is this a clean comparison? NWP models have to interpolate to RTTOV model levels NWP models do not have to interpolate to OPTRAN levels, this is done internally. These comparisons to LBL data on RTTOV levels give a bit in favor to RTTOV. A clean test would compare the two within the context of NWP analysis, or independent profiles with arbitrary pressure levels.

22. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Summary OPTRAN H2O combined with to RTTOV UMG&O3 improves overall performance for most channels. This may be a moot point given the results of Matricardi et al.

23. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds Acknowledgements This work was sponsored by the SAF-NWP, The Metoffice, Bracknell UK. Appreciation to Roger Saunders and others who made my visit a memorable experience.

24. ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds