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Wissam Chehade , Anna Serdyuchenko , Victor Gorshelev , John P. Burrows, Mark Weber

Har monisation of GO M E, SCIAMACHY, GOME-2 Ozone and N itrogen D i oxide C ross- section s HARMONICS i Re-analysis of SCIAMACHY and GOME-2 ozone flight model data and retrieval tests: Final Results I. Ozone II. Nitrogen Dioxide. Wissam Chehade , Anna Serdyuchenko , Victor Gorshelev ,

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Wissam Chehade , Anna Serdyuchenko , Victor Gorshelev , John P. Burrows, Mark Weber

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  1. HarmonisationofGOME, SCIAMACHY,GOME-2Ozone and Nitrogen DioxideCross-sectionsHARMONICSi Re-analysis of SCIAMACHY and GOME-2 ozone flight model data and retrieval tests: Final Results I. OzoneII. Nitrogen Dioxide WissamChehade, Anna Serdyuchenko, Victor Gorshelev, John P. Burrows, Mark Weber 08. 05. 2012 ESA, ESRIN Frascati

  2. I. Re-analysis of SCIAMACHY and GOME-2 ozone flight model data. • Whyre-analysisisneeded? • Re-analysisofsatellite FM cross-sections(WP 100). • Concatenation, Gluing • Absolute Scaling • ComparisontoLiterature Data. • OzoneRetrieval Tests (WP 300).

  3. Ozone is the most important trace gas. • plays a unique role in the chemistry and dynamics of the stratosphere (UV protection) • and the troposphere (air pollution, climate gas). • Global and long term monitoring is achieved using atmospheric remote sensing. • Accurate absorption cross-sections spectra are needed. • Laboratory absorption cross section spectra (Flight Model FM) for O3 @ 203K, 223K, • 243K, 273K, and 293K were measured. • Advantages of satellite FMs: • The use of FM cross-section in the trace gas retrievals generally lead to smaller fit • residuals in the satellite retrievals. • The a-priori knowledge of the slit function is not even required

  4. Using SCIAMACHY ozone FM cross-sections in the SCIAMACHY WFDOAS retrieval • resulted in systematic differences of about 3-5% in the retrieved total ozone column • from the 325-335 nm spectral range when compared to collocated GOME. • [Eskes et al., 2005] • GOME2 total O3 retrieval (using GOME-2 FM3) resulted in overestimation of 8%. • [Weber et al., 2011] • Harmonisation of O3 FM cross-sections from GOME-2 and SCIAMACHY for a • consistent retrieval.

  5. Re-analysis of satellite FM cross-sections (WP 100) • Concatenation, Gluing • Absolute Scaling

  6. The basic principle used for the absorption measurements is the Lambert-Beer- • Law. • Iabs(λ) = I0 (λ) · e−σ(λ)·ρ·l • CATGAS measurementsweredoneusingozonatorand a continuousflowof O2/O3 mixture • O3 concentration (ρ) andpathlength (l) wereunkown. • OD (λ) = (I0 (λ) /Iabs(λ) ) = σ(λ).ρ.l • rawdataavailable, Iabs, Ioareavailable

  7. Severalmeasurementswerecarried out for different O3 concentrationsandpathlengths („mixtures“) to cover large dynamicalrange (7 order ofmagnitude)  requiresconcatenation (scalingandgluing).

  8. GOME-2 FM3 • A starting spectrum is selected (mixture 3). • Optimal optical density 0.1 < O.D. < 1.0 • Select the overlap region between the neighboring mixtures. • A scaling factor is calculated. • Limitations : No scaling across channel borders.

  9. GOME-2 FM3 All temperaturedataarethennormalizedtounitareaunderthecurve (preserves relative temperaturedependence)

  10. Reference data : BDM & Bass Paur • convolved with the wavelength dependent GOME-2 instrumental slit function. • The scaling factor is calculated using a least square approach at each of the selected wavelengths between the optical densities and the available reference cross-sections at temperatures close to those used in the CATGAS campaign. • A single scaling factor scales all spectra at once and preserves the temperature dependence.

  11. GOME-2 Revised FM3

  12. SCIAMACHY FM • Reference data (Bass Paur) convolved to FM resolution (310-335 nm) band are used to find a single scaling factor for each temperature

  13. SCIAMACHY Revised FM

  14. Improvements in there-analysis (WP 100) • Whatarethechangesw.r.t. earlieranalysis (Bogumil, Gür et al.)? • optimising overlapregionswith wider wavelengthrangesanddifferent rawdataforconcatenation (GOME-2) • uselinear fitting(twoparameters) ratherthanratios (oneparameter) toconcatenate/scale OD spectra (GOME-2) • Different rawdataandspectralrangesforconcatenation(SCIAMACHY) • useconvolvedreferencedata (BDM, Bass Paur) for absolute scaling

  15. Comparison to Literature Data

  16. Comparison at Hg and He-Ne laser lines at room temperature

  17. Direct comparisons by non-linear least square fit in DOAS window The revised data and the high spectral resolution data convoluted with each spectrometer slit function are compared with a non-linear least square fitting program using five parameters: • a linear wavelength shift to correct for the differences in the spectral calibrations (1 parameter). • a scaling coefficient to adjust the amplitude of the cross-sections (1 parameter). • a third order baseline (cubic) polynomial (3 parameters). Comparison of GOME-2 FM3 with literature using a non-linear least square fitting program. Comparison of the new SCIAMACHY FM with literature using a non-linear least square fitting program.

  18. Temperature parameterizations and smoothness comparisons The temperature parameterization is used in the total ozone retrieval together with temperature climatology to express the change of ozone absorption with altitude.

  19. Temperature smoothness

  20. OzoneRetrieval Tests (WP 300)

  21. Ozone Retrieval Tests (WP 300) • The total ozone column is retrieved using the Weighting Function Differential Optical Absorption Spectroscopy (WFDOAS) method (Coldwey-Egbers et al., 2005, Weber et al., 2005) (325-335 nm). • A wavelength dependent weighting function of ozone and temperature that describes the relative radiance change due to a vertical profile change. • The temperature parameterization is used in the radiation transfer code together with temperature climatology to express the change of ozone absorption with altitude.

  22. The cross-section shifts are tested . The optimum applied shift improves the fit residual RMS. -0.038 nm 0.018 nm The optimum applied shifts are in good agreement to the values found in previous tests.

  23. The total ozone values retrieved are roughly within +0.5% to the values retrieved currently. • The fit residuals (RMS) are improved

  24. The total ozone values retrieved are roughly within +1% to the values retrieved currently. • The fit residuals (RMS) are the same

  25. Retrieval tests using the new ozone cross-section data • The new experimental cross-section data are tested in total ozone retrieval of GOME-2 and SCIAMACHY. • The data have to be convolved to GOME-2 and SCIAMACHY slit function. -0.007 nm 0.007 nm

  26. The total ozone columns retrieved from GOME-2 and SCIAMACHY satellites are in good agreement with the amounts retrieved by the current data, +1% and +2% respectively. • fit residuals (RMS) for GOME-2 and SCIA similar to satellite FM.

  27. II. Re-analysis of SCIAMACHY and GOME-2 NO2 flight model data. • Is there-analysisneeded? • ComparisontoLiterature Data. • NO2 Retrieval Tests (WP 300).

  28. Nitrogen dioxide (NO2) is an important trace gas in the Earth’s atmosphere. • In the stratosphere, it is involved in ozone chemistry as a catalyst for ozone destruction and also in the formation of halogen reservoirs such as chlorine nitrate. • In the troposphere, nitrogen oxides (NOx = NO + NO2) are key ingredients for ozone formation. • Long term measurements of NO2 total column, tropospheric column and its stratospheric profile provide unique information about the changes in tropospheric pollution around the globe and the state of the stratosphere. • Nadir measurements from GOME, SCIAMACHY and GOME-2 have been used in many studies on tropospheric NO2 burdens, the importance of different NOx emissions sources (by industry and traffic) and their change over time.

  29. The NO2 absorption cross-section data is not the significant error source for the total vertical column retrieval when the data retrieved from GOME-2 and SCIAMACHY compared with GOME. • The usage of the same settings as applied to data from the predecessor instrument is essential to obtain a high degree of consistency among them. • [Richter et al., 2005, 2011] • The setting should provide the best differential NO2 signal. • The least interference of other absorbers in the retrieval spectral window (DOAS). • Geophysical parameters (common solar spectrum, field of view, spatial resolution). • Moreover, the instruments have overpass time that differ by about 30 minutes which can make a difference in the stratospheric and tropospheric NO2 due to daytime variations.

  30. Comparison to Literature Data and Retrieval Tests Nitrogen dioxide is retrieved in the UV/visible region using the strong differential absorption structures of the NO2 molecule (DOAS fitting technique). The NO2 absorption cross-section measured at 223K is used in the retrieval in the 425-450 nm DOAS region. Good consistency between GOME-2 and SCIAMACHY is also achieved by using a larger fitting window (425-497 nm) [Richter et al. 2011]

  31. The NO2 reference data is compared to Vandaele et al. reference data convolved with the GOME-2 slit function in a non-linear least square fitting program in the two retrieving windows. Excellent agreement (scaling differences are below 0.5%)

  32. Both data were tested in the vertical NO2 column retrieval using a stratospheric air mass factor on one day of GOME-2 data . The differences between the columns are hardly noticed.

  33. higher values (1 – 2 %) retrieved in regions of good NO2 fit. • slightly higher values (2 – 4 %) over the tropics where the absorption is small and the signal is noisier

  34. The usage of GOME-2 cross-section data produces slightly better fit residuals (up to 5%) mainly in the region where the NO2 absorption is large

  35. Summary • The O3 revised data are in good agreement with the literature data. • correct temperature dependence • in the DOAS region (better than 3%) • An improvement in the retrieved total ozone column. • GOME-2: +0.5% difference to WFDOAS standard • SCIAMACHY: +1% difference to WFDOAS standard • Retrievaltestfor IUP Bremen cross-sections • GOME-2: +1% • SCIAMACHY : +2% • revised versions of GOME-2 FM3 and SCIAMACHY FM data and IUP experimental ozone cross-sections are ready for use.

  36. The NO2 data are in good agreement with the literature data in the DOAS region (better than 0.5%) • The retrieved vertical column is within few percents (1-4%) compared to column retrieved with Vandaele data. • The fit residuals (RMS) are up to 5% better when GOME-2 data is used • The NO2 absorption cross-section’s quality is good enough to be used in the retrieval and no re-analysis was required.

  37. Thank you for your attention !

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