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Abstract

Direct fitting of NO 2 from GOME-1, GOME-2, SCIAMACHY, and OMI K. Chance 1 , T.P. Kurosu 1 , R.V. Martin 1,2 , T. Beck 3 , and S. Kondragunta 3 1 CfA-SAO 2 Dalhousie U. 3 NOAA/NESDIS. Abstract.

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Abstract

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  1. Direct fitting of NO2 from GOME-1, GOME-2, SCIAMACHY, and OMIK. Chance1, T.P. Kurosu1, R.V. Martin1,2, T. Beck3, and S. Kondragunta31CfA-SAO 2Dalhousie U. 3NOAA/NESDIS

  2. Abstract We have implemented direct fitting of radiance spectra from the GOME-1, SCIAMACHY, OMI, and GOME-2 satellite spectrometers. We are attempting to analyze the spectra from these instruments in as identical a fashion as possible, with the most complete treatment of underlying algorithm physics, in order to separate instrumental, algorithmic, and temporal differences in satellite measurements. Initial efforts concentrate on NO2 slant column measurements.

  3. OMI NO2 Tropospheric Column NO2(Sector Method) July 2005 Total Column NO2(geometric AMF) July 2005 Cloud screening: cloud fraction ≤ 20%

  4. OMI NO2

  5. OMI NO2

  6. Limb-nadir matching: orbits 2509-2510 Largest value over Athens, Greece: 5.41015 cm-2 vertical column density

  7. GOME/SCIAMACHY/OMI/GOME-2

  8. Best fitting 210-4 FS

  9. Algorithm Overview • Requires precise (dynamic) wavelength (and often slit function) calibration, Ring effect correction, undersampling correction, and proper choices of reference spectra (HITRAN!) • Best trace gas column fitting results come from directfitting of radiances, (except for OE: tropospheric ozone and SO2)

  10. Algorithm Overview • Slant column abundances from direct fitting of radiances by nonlinear least-squares fitting: - Simple Ring effect formulation (no induced Fraunhofer structure or induced wavelength mismatch) - No distortion of measured data (no high-pass filtering) • Correction for: - Wavelength calibration - Instrument transfer (slit) function - Ring effect - Spectral undersampling (GOME-n, SCIA, OMI, OMPS do not Nyquist sample the spectra) • Division by air-mass factor (AMF) using LIDORT radiative transfer model and GEOS-CHEM 3-D tropospheric chemistry and transport model to determine vertical column abundances - Tropospheric residuals may require further adjustment (e.g., for NO2) • Ozone profiles: Direct fitting for profile using optimal estimation

  11. Fitting approach: Nonlinear least-squares fitting of radiances with lots of optimization Radiance R is fitted directly (“BOAS fitting”) as: N.B. ! Other approaches: Division by I0 Further manipulation, for Beer’s law fitting gives: But note: It is NOT a linear fitting problem! “DOAS” fitting adds high-pass filtering (“H”) to give:

  12. “Kurucz” sun  NO2 Reference spectra for determination of NO2 from SCIAMACHY Ring O3 O2-O2 H2O H2O Ring Undersampling

  13. High resolution solar reference spectrum

  14. Top-of-atmosphere solar spectral irradiance The high resolution solar spectral irradiance is critical in analyzing atmospheric trace gases: • Solar lines are source of accurate wavelength calibration (0.0003-0.0004 nm for GOME!) – Our method now used operationally on GOME, SCIAMACHY, OMI, and OMPS • Determination of the Ring effect • Improved knowledge of instrument slit functions • Partial correction for spectral undersampling • Photochemistry of Schumann-Runge system A space-based determination would be an ideal support mission for 12+ international atmospheric missions! • Range: 240-1000+ nm • FWHM: 0.01 nm or better • Ideal FTS Space Shuttle experiment Canadian experiment

  15. Ring effect calculation Multiple-scattering versions and molecular interference by successive orders of absorption implemented *K. Chance and R.J.D. Spurr, Ring effect studies: Rayleigh scattering, including molecular parameters for rotational Raman scattering, and the Fraunhofer spectrum, Appl. Opt. 36, 5224-5230, 1997. (www.cfa.harvard.edu/atmosphere/) New, improved, version now available! Better absolute accuracy Less gas interference Better sampling Ask me for details

  16. Examples from March 12, 2007

  17. Conclusions and Future Directions • Correction of SCIAMACHY L1b difficulties • Improved OMI stripe correction • Improved vertical column determination • Validation to separate temporal from instrument differences

  18. The End!

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