SCIAMACHY v6.02 reflectance and the resulting Absorbing Aerosol Index L.G. Tilstra1,2, M. de Graaf2, I. Aben1, P. Stammes2 1SRON; 2KNMI
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).
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)
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.
SCIAMACHY & GOME AAI data are available on the TEMIS website http://www.temis.nl Available data: GOME SCIA : 1995–2000 : 2002–2006
(2) Reflectance: version 6.02 vs 5.04 6.02/5.04 Correction factor from comparison with: × = DAK + = MERIS O = POLDER
(3) Degradation of the residue Global monthly means: Global monthly average of residue should be ~constant and should lie between -2 and -1
Degradation of the reflectance: “Light Path Monitoring” results from Stefan Noël(for the wavelengths 340 and 380 nm relevant to the AAI) c380 c340
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
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.