1. 1 Improving SO 2 AMFs: Comparison of different approaches P. Hedelt, P. Valks, D. Loyola Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) Institut für Methodik der Fernerkundung Abteilung Atmosphärenprozesooren First German S5P Verification Meeting, Bremen 28-29. November 2013

2. Overview Prototype Algorithm: Fitting windows: 312-326nm 325-335nm (VCD>40 DU) 360-390nm (VCD>250DU) Single Wavelength AMF Verification Algorithm: Fitting windows 312-324nm 326.5-335nm (VCD>40 DU) AMF: Different Approaches The SO 2 amount and plume height is unknown at the time of the measurement Direct fitting computational too expensive 2

3. Current aproach: Classical DOAS approach Current GOME-2 SO 2 approach DOAS fit of measured spectra  SO 2 SCD Single-wavelength AMF Viewing & surface/cloud conditions Fixed SO 2 profile (Gaussian at 2.5, 6 and 15km) SO 2 VCD assumed for AMF: Standard fitting window: 3 DU VCDs underestimated > 25 DU! VCD=SCD/AMF Approach independent of measured SO 2 SCD 3

4. Current aproach: Classical DOAS approach Current GOME-2 SO 2 approach DOAS fit of measured spectra  SO 2 SCD Single-wavelength AMF Viewing & surface/cloud conditions Fixed SO 2 profile (Gaussian at 2.5, 6 and 15km) SO 2 VCD assumed for AMF: Standard fitting window: 3 DU VCDs underestimated > 25 DU! Alternative fitting window (>40 DU): 100 DU Currently under investigation VCD=SCD/AMF Approach independent of measured SO 2 SCD 4

5. Improved approach: Iterative AMF approach Approach based on GOME-2 O 3 retrieval DOAS fit of measured spectra  SO 2 SCD Single-wavelength AMF Viewing & surface/cloud conditions Fixed SO 2 profile (Gaussian at 2.5, 6 and 15km) Calculation of AMF in iterative way Determine VCD from initial (arbitrary) AMF Calculate new AMF Iterate until VCD converges VCD = SCD/AMF AMF (partly) depends on measured SO 2 SCD 5

6. Improved approach: Empirical DOAS approach Approach based on OMI O 3 retrieval DOAS fit of measured spectra  SO 2 SCD Creation of simulated spectra (312-335nm) Viewing & surface/cloud conditions Fixed SO 2 profile (2,5km FWHM Gaussian at 2.5, 6 and 15km) Assuming set of SO 2 VCDs DOAS fit of simulated spectra  SCDs for assumed VCDs Interpolation of measured SCD on retrieved SCD grid  SO 2 VCD VCD depends on measured SCD Errors in DOAS fit cancel out 6

7. Examples Kasatochi 08-08-2008 7

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10. Examples Kasatochi 09-08-2008 10

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12. Examples Grimsvötn 23-05-2011 12

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14. Current Status Classical DOAS approach (GOME-2) LUT ready for Standard fitting window S5P LUT can be created very fast Iterative AMF approach AMFs are currently calculated on-line AMF LUTs for different VCDs can be created fast Empirical DOAS (GOME-2) Spectra have been computed from 312-335nm VCD LUT for different fitting windows is ready LUT interpolation under construction Currently tests are performed S5P spectra generation take about 1 month 14

15. Physical parameters of LUTs Parameter# grid pointsGrid values SZA130 - 90° VZA70 - 60° RAA100 - 180° Albedo100.0 - 1.0 Pressure51021.63 - 372.42 mbar O 3 VCD7225 – 525 DU Plume height32.5, 6, 15 km AMF wavelength (Classical approach & Iterative AMF) 2315,327 nm SO 2 VCD grid (Empirical DOAS & Iterative AMF) 100 - 500 DU 15

16. Summary & Conclusion Current approach AMF independent of measured SO 2 SCD VCDs are under/overestimated Iterative AMF approach AMF is fitted in iterative way AMF partly dependent on measured SCD Better VCDs Empirical DOAS approach DOAS fit of both measured an simulated spectra AMF (or VCD) depends on measured SCD DOAS errors potentially cancel out Results close to direct fitting results 16

17. Thank you for your attention! 17

18. Summary Classical DOAS approach: Single-wavelength AMF for viewing & surface conditions (315 / 327nm) Independent of measured SO 2 SCD Underestimates high SO 2 VCDs Iterative AMF approach Single-wavelength AMF for viewing & surface conditions (315 / 327nm) Iterative AMF fitting AMF (partly) depends on SCD Empirical DOAS approach DOAS retrieval of simulated spectra on pre-defined VCD grid Interpolation of measured SCD on grid of simulated SCDs Dependent on measured SO 2 SCD Errors in DOAS fit cancel out 18