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Trace gas vertical column retrieval using channel 8 nadir measurements: First preliminary results

Trace gas vertical column retrieval using channel 8 nadir measurements: First preliminary results. M. Buchwitz IFE/IUP University of Bremen, Germany. Level 2 BIAS Products Verification Approach:. SPCVP objective: “Verify Level 2 NRT and OL nadir products” SPCVP task: “Verify BIAS MDS”

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Trace gas vertical column retrieval using channel 8 nadir measurements: First preliminary results

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  1. Trace gas vertical column retrieval usingchannel 8 nadir measurements:First preliminary results M. Buchwitz IFE/IUP University of Bremen, Germany

  2. Level 2 BIAS Products Verification Approach: • SPCVP objective: “Verify Level 2 NRT and OL nadir products” • SPCVP task: “Verify BIAS MDS” • Approach: Comparison of BIAS VCDs with VCDs derived using independent algorithms (here: WFM-DOAS) • Data used: Initial verification data products made available by ESTEC via the SPCVP data base • Focus: Orbit 2338 (11-Aug-2002) covering parts of central Europe and western Africa

  3. Status of Ch.8 Lv1 and Lv2 Nadir Data Products: • Level 1c: • Spectral and radiometric calibration still preliminary • Level 2: • Quality of BIAS products suffer from imperfect calibration • Focus of the following: First WFM-DOAS results and identification of Level 1c issues to be resolved for accurate VC retrieval

  4. Examples of WFM-DOAS Fits:

  5. WFM-DOAS Derived Methane Columns:

  6. Conclusions and Recommendations • The major NIR absorbers CH4, H2O, and CO2 have been clearly identified in the spectra • The calibration / Level 0-1 processing needs to be improved for • Accurate quantitative retrieval • Identification of minor NIR absorbers (CO, N2O) • To be improved / investigated: spectral calibration (e.g., -0.3 nm shift @ ~2365 nm); scan angle dependence of radiance; dark signal correction; SMR calibration (D1 ~ 50% too low in Ch.8); missing polarisation correction, etc. • Level 1-2 processing: Significant improvement of BIAS products required

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