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Preliminary validation of the first SCIAMACHY CH 4 and CO measurements

Preliminary validation of the first SCIAMACHY CH 4 and CO measurements. Authors: A.G. Straume, I. Aben (PI), A.N. Maurellis, H. Schrijver (SRON), M. Krol (IMAU), H. Eskes, J.F. Meirink, M. van Weele (KNMI), J. Gille (NCAR). COMETH, AOID241.

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Preliminary validation of the first SCIAMACHY CH 4 and CO measurements

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  1. Preliminary validation of the first SCIAMACHY CH4 and CO measurements Authors: A.G. Straume, I. Aben (PI), A.N. Maurellis, H. Schrijver (SRON), M. Krol (IMAU), H. Eskes, J.F. Meirink, M. van Weele (KNMI), J. Gille (NCAR)

  2. COMETH, AOID241 • Comparison of the operational CO and CH4 products (Poper) with an SRON retrieved product • Comparison with measurements by the MOPITT instrument (cooperation with NCAR) • Comparison of Poper with calculations by the chemical transport model TM5 (cooperation with IMAU) • Will use data assimilation for extended validation and analysis (cooperation with KNMI)

  3. Status of the SCIAMACHY near-infrared channels • The SCIAMACHY instrument is stable. Only anomaly: • Ice build-up in NIR channels 7 and 8. The influence of the ice is relatively smooth. Main effect: reduced Signal-to-Noise ratio. Problem solver: frequent decontamination. • Updates needed with respect to the on-ground calibration: • Dead and bad pixel mask • Wavelength calibration of channel 8 • Change in frequency of updating calibration annotation data due to the ice buildup: • Channel 7 and 8 dark current must be updated (at least) once pr day • In verification orbits 2509 and 2510 (SW v. 4.00) the above mentioned updates to the L1b product were implemented

  4. BIAS retrieved CH4 columns (two micro windows), orbits 2509-2510 23 August Micro window 1 (SW v. 4.0) Micro window 2 (SW v. 4.0)

  5. BIAS CH4 columns compared to simulation by a chemical transport model (resolution 2.52.5) orbits 2509-2510 23 August SW v. 4.0

  6. BIAS CO columns (left) compared to MOPITT beta data (right) orbits 2509-2510 23 August SW v 4.0

  7. 4,0 3,6 3,2 2,8 2,4 2,0 1,6 PMD measurements Average surface elevation [m] 1,2 0,8 0,4 0 Methane columns [1019 cm-2] SRON retrieved CH4 columns, orbits 2337-2338 11 August

  8. # comparisons: 681 BIAS: 24% RMSD: 26% Correlation: 0.4 (99% significant) SRON retrieved CH4 columns v.s. topography (left), v.s. simulation by a chemical transport model with resolution 2.52.5 (right) Non-clouded pixels only. NB! The SCIAMACHY CH4 columns are here NOT binned to the model resolution, i.e. an artificially large spread (bias) is seen Non-clouded pixels only and error bars representing the measurement error

  9. SRON retrieved CO compared with CO from MOPITT (beta data), orbits 2337-2338 The CO signal is still below the systematic residuals and the instrument noise, giving erroneously low or 0 column values

  10. CONCLUSIONS • The BIAS product is not correct (suspects: calibration, L1-2 processor, ...) • The SRON retrieved CH4 product looks promising and shows physically consistent variations. Still bias of ~15% (too low) probably related to still unresolved calibration issues • The CO signal is still below the systematic residuals and the instrument noise. A comparison with MOPITT data shows that it is ~50% too low • Still unresolved calibration issues, channel 8: variations with time in the dark current signal, pixel-to-pixel gain (PPG), ...

  11. Figure: Courtesy of Louisa Emmonds, NCAR

  12. BIAS_2 retrieved CH4 columns and SRON PMD image, orbits 2509-2510 23 August SW v 4.0

  13. SRON retrieved CH4 and CH4 error v.s. albedo, orbits 2337-2338 11 August Cloud-free pixels only Cloud-free pixels only

  14. Cloud-free CH4 columns compared with model (including measurement errors) and CH4 errors v.s. albedo Non-clouded pixels only. NB! The SCIAMACHY CH4 columns are here NOT binned to the model resolution, i.e. an artificially large spread (bias) is seen

  15. SCIAMACHY channel 8 residuals Residuals between the measured and a modelled spectrum for different albedos: Black and red: residuals during high albedo cases (desert). Blue: residuals during a low albedo case (boulders).

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