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