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Improving SO2 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, Bremen28-29. November 2013

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Overview

Prototype Algorithm: Fitting windows:

312-326nm325-335nm (VCD>40 DU) 360-390nm (VCD>250DU)

Single Wavelength AMFVerification Algorithm:

Fitting windows312-324nm326.5-335nm (VCD>40 DU)

AMF: Different ApproachesThe SO2 amount and plume height is unknown at the time of the measurement

Direct fitting computational too expensive

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Current aproach:Classical DOAS approach

Current GOME-2 SO2 approach

DOAS fit of measured spectra SO2 SCDSingle-wavelength AMF

Viewing & surface/cloud conditionsFixed SO2 profile (Gaussian at 2.5, 6 and 15km)

SO2 VCD assumed for AMF:

Standard fitting window: 3 DUVCDs underestimated > 25 DU!

VCD=SCD/AMFApproach independent of measured SO2 SCD

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Current aproach:Classical DOAS approach

Current GOME-2 SO2 approach

DOAS fit of measured spectra SO2 SCDSingle-wavelength AMF

Viewing & surface/cloud conditionsFixed SO2 profile (Gaussian at 2.5, 6 and 15km)

SO2 VCD assumed for AMF:

Standard fitting window: 3 DUVCDs underestimated > 25 DU!

Alternative fitting window (>40 DU): 100 DUCurrently under investigation

VCD=SCD/AMFApproach independent of measured SO2 SCD

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Improved approach:Iterative AMF approach

Approach based on GOME-2 O3 retrieval

DOAS fit of measured spectra SO2 SCDSingle-wavelength AMF

Viewing & surface/cloud conditionsFixed SO2 profile (Gaussian at 2.5, 6 and 15km)

Calculation of AMF in iterative wayDetermine VCD from initial (arbitrary) AMFCalculate new AMFIterate until VCD converges

VCD = SCD/AMF

AMF (partly) depends on measured SO2 SCD

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Improved approach:Empirical DOAS approach

Approach based on OMI O3 retrieval

DOAS fit of measured spectra SO2 SCDCreation of simulated spectra (312-335nm)

Viewing & surface/cloud conditionsFixed SO2 profile (2,5km FWHM Gaussian at 2.5, 6 and 15km)

Assuming set of SO2 VCDs

DOAS fit of simulated spectra SCDs for assumed VCDsInterpolation of measured SCD on retrieved SCD grid SO2 VCD

VCD depends on measured SCDErrors in DOAS fit cancel out

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ExamplesKasatochi 08-08-2008

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ExamplesKasatochi 09-08-2008

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ExamplesGrimsvötn 23-05-2011

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Current Status

Classical DOAS approach(GOME-2) LUT ready for Standard fitting windowS5P LUT can be created very fast

Iterative AMF approachAMFs are currently calculated on-lineAMF LUTs for different VCDs can be created fast

Empirical DOAS(GOME-2) Spectra have been computed from 312-335nmVCD LUT for different fitting windows is readyLUT interpolation under constructionCurrently tests are performedS5P spectra generation take about 1 month

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Physical parameters of LUTsParameter # grid points Grid values

SZA 13 0 - 90°

VZA 7 0 - 60°

RAA 10 0 - 180°

Albedo 10 0.0 - 1.0

Pressure 5 1021.63 - 372.42 mbar

O3 VCD 7 225 – 525 DU

Plume height 3 2.5, 6, 15 km

AMF wavelength(Classical approach &

Iterative AMF)2 315,327 nm

SO2 VCD grid(Empirical DOAS &

Iterative AMF)10 0 - 500 DU

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Summary & Conclusion

Current approachAMF independent of measured SO2 SCD

VCDs are under/overestimatedIterative AMF approach

AMF is fitted in iterative way AMF partly dependent on measured SCDBetter VCDs

Empirical DOAS approachDOAS fit of both measured an simulated spectraAMF (or VCD) depends on measured SCDDOAS errors potentially cancel outResults close to direct fitting results

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Thank you for your attention!

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SummaryClassical DOAS approach:

Single-wavelength AMF for viewing & surface conditions (315 / 327nm)Independent of measured SO2 SCD

Underestimates high SO2 VCDs

Iterative AMF approachSingle-wavelength AMF for viewing & surface conditions (315 / 327nm)Iterative AMF fittingAMF (partly) depends on SCD

Empirical DOAS approachDOAS retrieval of simulated spectra on pre-defined VCD gridInterpolation of measured SCD on grid of simulated SCDs Dependent on measured SO2 SCD

Errors in DOAS fit cancel out