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SCIAMACHY v6.02 reflectance and the resulting Absorbing Aerosol Index

SCIAMACHY v6.02 reflectance and the resulting Absorbing Aerosol Index. L.G. Tilstra 1,2 , M. de Graaf 2 , I. Aben 1 , P. Stammes 2 1 SRON; 2 KNMI. Outline. Absorbing Aerosol Index (AAI) and the residue Reflectance: version 6.02 versus version 5.04 Effects of degradation in the AAI / residue

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SCIAMACHY v6.02 reflectance and the resulting Absorbing Aerosol Index

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  1. SCIAMACHY v6.02 reflectance and the resulting Absorbing Aerosol Index L.G. Tilstra1,2, M. de Graaf2, I. Aben1, P. Stammes2 1SRON; 2KNMI

  2. Outline • Absorbing Aerosol Index (AAI) and the residue • Reflectance: version 6.02 versus version 5.04 • Effects of degradation in the AAI / residue • Conclusions All results shown apply to the scientific product (SC-AAI).

  3. Absorbing Aerosol Index (AAI) and the residue • Definition of the residue: • where the surface albedo A for the simulations is such that: • no clouds, no absorbing aerosols : r < 0 • clouds, no absorbing aerosols : r < 0 • absorbing aerosols, no clouds : r > 0 • B. Definition of the AAI: • AAI = residue > 0 (where residue < 0 the AAI is not defined)

  4. AAI in 2004:(monthly mean)Normal distribution of UV-absorbing aerosols. Similar to observations by TOMS. AAI in 2006:(monthly mean)Degradation of the opticsleads to anomalously highvalues of the residue / AAI.

  5. SCIAMACHY & GOME AAI data are available on the TEMIS website http://www.temis.nl Available data: GOME SCIA : 1995–2000 : 2002–2006

  6. (2) Reflectance: version 6.02 vs 5.04 6.02/5.04 Correction factor from comparison with: × = DAK + = MERIS O = POLDER

  7. (3) Degradation of the residue Global monthly means: Global monthly average of residue should be ~constant and should lie between -2 and -1

  8. Degradation of the reflectance: “Light Path Monitoring” results from Stefan Noël(for the wavelengths 340 and 380 nm relevant to the AAI) c380 c340

  9. Effect of instrument degradation (c340 ; c380) on residue/AAI: • Trend in residue can be explained by degradation as found from “Light Path Monitoring” results. • Residue/AAI is very sensitive to (absolute) reflectance calibration. • Degradation correction is really important for the AAI. • Residue is recording its own degradation correction

  10. Conclusions: • Absolute calibration of the reflectance has improved with v6.02, but the calibration problem is still not solved • AAI and residue are very sensitive to the radiometric calibration and therefore suited for monitoring degradation of the optics • Effects of degradation in the residue/AAI are found, and can be explained by degradation from “Light Path Monitoring” results. • A proper degradation correction is essential for the AAI.

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