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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Summary of data product and algorithm development at KNMI
Ronald van der A, Juan Acarreta, Folkert Boersma,
Henk Eskes, Martin de Graaf, Piet Stammes, Gijs Tilstra
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Calibration and retrieval algorithm development
Polarisation-correction In-flight radiometric calibration PMD imaging tool (by Martin de Graaf) on SCIAVALIG
website www.sciamachy-validation.org, >Tools LIDORT model extension to near-IR (Rob Spurr, Roeland van
Oss, and Albert Goede) Absorbing aerosol index Cloud phase index Total ozone Tropospheric NO2
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Determining U from Q based on Rayleigh single scattering theory
The approximation () = ss so
U() = Q () tan 2 ss
is accurate for all POLDER wavelengths (443, 670, 865 nm) and scene types to an accuracy of 0.003 in U (1).
The PMD-45 measurement by SCIAMACHY – which is currently uncertain – is therefore not needed.
The assumption () = ss is now used in the new 0-1 processor.
(work by Gijs Tilstra)
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
In-flight radiometric calibration - reflectance correction
UV: Comparison of SCIAMACHY with DAK over cloudfree Sahara. VIS/near-IR: Comparison of SCIAMACHY with MERIS over large parts of
orbits 2509 and 2510. Preliminary SCIAMACHY reflectance correction table (error ±0.05):
wavelength (nm) correction factor
320 1.28
390 1.14
442 1.14
510 1.14
665 1.18
708 1.20
885 1.25
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Various correction factors for SCIAMACHY reflectance
(work by Juan Acarreta)
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Parabola fit of reflectance correction factor: f() = a0 + a1/( - 0) + a2/( - 0)2
0=240 nm, a0=1.3002, a1=-54.057, a2=4210.6
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Interpretation
The reflectance correction factor resembles the spectral behaviour of the inverse BSDF of a diffuser:
Correction() 1/BSDF().
(see e.g. spectral behaviour of GOME-2 diffusers).
If the correction factor has to correct for the effect of a diffuser, either internal or external to SCIAMACHY during OPTEC, then the correction factor is expected to be a continuous and spectrally smooth function in the range 300-1000 nm.
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Absorbing Aerosol Index algorithm applied to GOME, validated with EP/TOMS
Necessary for SCIAMACHYis improved radiometric calibration!
(work by Martin de Graaf)
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Cloud phase algorithm for SCIAMACHY using the spectral slope at 1.67 micron
(work by Juan Acarreta)
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Cloud phase index validation
Cloud phase Index: CPI= 100 x (R(1.70) – R(1.64))/R(1.64)CPI = 0-20: clear scenes + water clouds CPI > 20: ice cloudsValidated with MODIS cirrus reflectance.
(work by Juan Acarreta)
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Total ozone column from TOSOMI
• Based on the OMI-DOAS operational algorithm (Pepijn Veefkind)• Implementations for GOME (TOGOMI - Pieter Valks)
and Sciamachy (TOSOMI - Henk Eskes and Ronald van der A)
Innovations compared to GOME Fast Delivery, vs 3:• New treatment of Raman scattering (Johan de Haan)• Empirical air-mass factor approach• TOMS v8 ozone profile data base• AMF computed with DAK (spherical corrections, polarization)
Now also forecasted ozone fields up to one week ahead.
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TOSOMI 0.32 example
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www.temis.nl
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
SCIAMACHY total ozone from TEMISwas part of the Envisat News item on behalf of the 10,000-th orbit on 28 January ’04
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Validation TOSOMI
Comparison with assimilation and Brewers:
• good comparisons Brewer / Dobson • no obvious seasonality
• small rms• improvements at high SZA, snow (Raman)
... despite problems Sciamachy calibration (level-1b).
Validation with data assimilation has been important in the development of the retrieval code.
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Tropospheric NO2
Assimilation of NO2 slant column in a CTM model, and derivation of tropospheric column from the model.
For more results on global and regional tropospheric NO2, seethe TEMIS website:
www.temis.nl
(work by Folkert Boersma)
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
RESERVE SHEETS
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
CLOUDS 885
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
MIXED 442
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
SAHARA 885
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Typical fit R(MERIS) vs. R(SCIA) at 665 nm
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SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
SCIAMACHY O2 A-bandmeasurement vs. FRESCO model
for Sahara and high cloud
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TOSOMI 0.31: SZA dependence, SH