Post on 22-Feb-2016
description
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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