ssag data and algorithm subgroup, 10-11 february 2004, brussels summary of data product and...
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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
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
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)
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
SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
Various correction factors for SCIAMACHY reflectance
(work by Juan Acarreta)
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
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.
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)
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)
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)
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.
TOSOMI 0.32 example
www.temis.nl
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
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.
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)
SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
RESERVE SHEETS
SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
CLOUDS 885
SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
MIXED 442
SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
SAHARA 885
Typical fit R(MERIS) vs. R(SCIA) at 665 nm
SSAG Data and Algorithm Subgroup, 10-11 February 2004, Brussels
SCIAMACHY O2 A-bandmeasurement vs. FRESCO model
for Sahara and high cloud
TOSOMI 0.31: SZA dependence, SH