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The Merger of OPTRAN and RTTOV: The Best of Both Worlds

The Merger of OPTRAN and RTTOV: The Best of Both Worlds. Thomas J. Kleespies NOAA/NESDIS Camp Springs MD USA. 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

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The Merger of OPTRAN and RTTOV: The Best of Both Worlds

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

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

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

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

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

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

  7. OPTRAN2 OPTRAN_SPECIES Transmittance Driver. Set up coefficients on first invocation. Compute absorber profile. Call OPTRAN_SPECIES to compute optical depths. Compute transmittances from optical depths. GET_PREDICTORS_ALL 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 Double Interpolation (Original OPTRAN) ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

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

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

  10. 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 RTTOV PRFIN OPDEP RTTAU RTINT PRFTAU 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. OPTRAN_SPECIES GET_PREDICTORS_ALL OPDEP Computes optical depth Calls OPTRANS_SPECIES RTTAU Computes transmittances RTINT Integrates the radiative transfer equation to produce radiances and brightness temperatures OPTRAN1-RTTOV Code is switchable between OPTRAN and RTTOV for each absorbing species: UMG, H2O, O3 ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

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

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

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

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

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

  20. Status • RTTOV/OPTRAN1 with TL,AD,K done • RTTOV/OPTRAN2 only forward model • Nagging question of OPTRAN1/2 ozone • H2O Jacobians incorrect ITSC 12 5 March 2002 The Merger of OPTRAN and RTTOV: The Best of Both Worlds

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

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

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

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

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