An Optimal Estimation An Optimal Estimation Approach to AIRS CO Approach to AIRS CO Retrievals Retrievals Stuart MacCallum Stuart MacCallum Chris Merchant Chris Merchant School of Geosciences School of Geosciences The University of Edinburgh The University of Edinburgh s.maccallum@ed.ac.uk
Retrieval Method Retrieval Method Maximum a-posteriori (MAP) 1 Gauss-Newton iterative scheme � 1 ( ) T T ˆ ( ( ) ) x x S K KS K S y y K x x = + + � + � a a a l l a � x a = a-priori estimate of CO profile (US Standard profile) S a = a-priori covariance matrix (Modelled CO) K = CO Jacobians (From forward model, RTTOV) S ε = error covariance matrix (Measurement errors) y = observed radiances (Radiances observed by AIRS) x l = linearisation profile (Most recent estimation of CO in the iterative scheme) y l = simulated radiances for (Modelled radiances for our most linearisation profile recent estimate of CO) 1. Rodgers, C.D., Inverse Methods for Atmospheric Sounding, 2000.
Components of the Retrieval Method Components of the Retrieval Method Forward Model – – RTTOV RTTOV Forward Model NWP SAF NWP SAF Comparable with RFM Comparable with RFM http://www.metoffice.gov.uk/ http://www.metoffice.gov.uk/ research/interproj/nwpsaf/ research/interproj/nwpsaf/ Prior covariance, S Prior covariance, S a a STOCHEM + manual adjustment STOCHEM + manual adjustment Prior CO, x x a Prior CO, a AFGL US standard AFGL US standard AIRS level 2 products AIRS level 2 products Cloud cleared radiances Cloud cleared radiances ~50 channels ~50 channels 4.67 4.67 µ µm - CO fundamental m - CO fundamental T, H T, H 2 2 O, T O, T surf surf , , ε ε Errors contribute to Errors contribute to S ε Averaging kernels Averaging kernels Peak around 500 hPa Peak around 500 hPa ~1 degree of freedom ~1 degree of freedom
Validation Data Validation Data Coincidence criteria Coincidence criteria Sources Sources ± 6 hours ± 6 hours NOAA NOAA – – CMDL CMDL ± 1° Latitude/longitude ± 1° Latitude/longitude http://www.cmdl.noaa.gov/ http://www.cmdl.noaa.gov/ 6 sites 6 sites Sept 02 Sept 02 – – Dec 04 Dec 04 FAAM FAAM – – EAQUATE EAQUATE http://www.faam.ac.uk/ http://www.faam.ac.uk/ UK Met Office and NERC UK Met Office and NERC Sept 2004 Sept 2004 NASA NASA – – AVE AVE http://www.espo.nasa.gov/ http://www.espo.nasa.gov/ 3 missions 3 missions Jan 04, Oct/Nov 04, Jun Jan 04, Oct/Nov 04, Jun 05 05
Profile Retrievals Profile Retrievals Black Black – – x x a Retrievals on 9 levels Retrievals on 9 levels a Green Green - - SNM SNM x a = AFGL US Standard x a = AFGL US Standard Red Red - - Aircraft Aircraft x x smooth = = x x a + + A A ( ( x x m – – x x a ) smooth a m a ) Orange -Smoothed Aircraft Orange -Smoothed Aircraft x x m = aircraft CO m = aircraft CO Dark Blue – – AIRS AIRS Dark Blue Light Blue – – Smoothed AIRS Smoothed AIRS Light Blue
CO on Levels – – Aircraft Aircraft vs vs SNM SNM CO on Levels SNM vs Aircraft (smoothed) SNM vs Aircraft (smoothed) Larger errors at levels towards Larger errors at levels towards top and bottom of atmosphere top and bottom of atmosphere % a-priori < 50% % a-priori < 50% Fewer pixels with Fewer pixels with Negative bias Negative bias % a-priori < 0.5 % a-priori < 0.5 Good Correlation Good Correlation Larger contribution from x x a at Larger contribution from a at these levels these levels
CO on Levels – – AIRS AIRS vs vs SNM SNM CO on Levels SNM vs AIRS (smoothed) SNM vs AIRS (smoothed) Same behaviour as Aircraft vs Same behaviour as Aircraft vs % a-priori < 50% % a-priori < 50% SNM at top and bottom of SNM at top and bottom of High correlation High correlation atmosphere atmosphere Negative bias Negative bias
Total Common Column CO – – No smoothing No smoothing Total Common Column CO All data included (any % priori) All data included (any % priori) Aircraft Aircraft vs vs AIRS AIRS Aircraft vs vs SNM SNM Aircraft Good correlation Good correlation Good correlation Good correlation Better with high CO values Better with high CO values Problems with high CO values Problems with high CO values
Total Common Column CO – – No smoothing No smoothing Total Common Column CO All data included (any % priori) All data included (any % priori) AIRS AIRS vs vs SNM SNM Aircraft vs vs SNM SNM Aircraft Excellent correlation Excellent correlation Good correlation Good correlation Similar at high CO values Similar at high CO values Problems with high CO values Problems with high CO values
Total Common Column CO - Smoothed Total Common Column CO - Smoothed Smoothed AIRS vs vs SNM SNM Smoothed AIRS % a-priori < 50% % a-priori < 50% Excellent correlation Excellent correlation Problems with high CO values Problems with high CO values Aircraft vs Aircraft vs SNM SNM Excellent correlation Excellent correlation Still problems with high CO Still problems with high CO values values
Total Column CO – – All levels All levels Total Column CO All levels (not just in common with aircraft) All levels (not just in common with aircraft) % a-priori < 50% % a-priori < 50% High Correlation High Correlation
Validation Study - Conclusions Validation Study - Conclusions Total Column CO Total Column CO Good correlation between SNM and Aircraft Good correlation between SNM and Aircraft Comparable to AIRS product Comparable to AIRS product Good correlation with AIRS product for full column Good correlation with AIRS product for full column Negative bias in SNM relative to AIRS Negative bias in SNM relative to AIRS CO Profiles CO Profiles Good correlation on mid-troposphere levels but not so good at Good correlation on mid-troposphere levels but not so good at top and bottom top and bottom Heavy reliance on prior at top and bottom of the profile Heavy reliance on prior at top and bottom of the profile Larger errors at these levels Larger errors at these levels
Retrievals for 30 th th Aug 2004 Aug 2004 Retrievals for 30 http://mopitt.eos.ucar.edu/mopitt/data/plots/mapsv3.html http://rapidfire.sci.gsfc.nasa.gov
Total Column CO – – Region 1 Region 1 Total Column CO SNM AIRS
Total Column CO – – Region 1 Region 1 Total Column CO SNM AIRS QF < 2 All All QF < 2
Total Column CO - Region 2 Total Column CO - Region 2 SNM AIRS
Total Column CO - Region 3 Total Column CO - Region 3 SNM AIRS
Total Column CO - Region 3 Total Column CO - Region 3
Total Column CO - Region 4 Total Column CO - Region 4 SNM AIRS
Total Column CO - Region 4 Total Column CO - Region 4
Total Column CO - Region 5 Total Column CO - Region 5 SNM AIRS
Region 1 – – Profile Levels Profile Levels Region 1 SNM 950 750 550 350 150 AIRS
Region 1 – – Profile Level Errors Profile Level Errors Region 1 SNM 950 750 550 350 150 AIRS
Region 4 – – Profile Levels Profile Levels Region 4 SNM AIRS
Region 4 – – All data All data vs vs a-priori < 0.5 a-priori < 0.5 Region 4
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