Validation of SCIAMACHY using POLDER as a reference 25 April 2006

SCIAMACHY spectrometer 240–2400 nm (resol. 0.2–1.5 nm) onboard ENVISAT (“Environmental Satellite”) launched March 1, 2002 radiance & irradiance  reflectance  ozone, NO 2, BrO, CO 2, … nadir or limb mode still severe calibration problems

POLDER imager CCD detector matrix bandfilter carousel resolution: 6 × 7 km 2 polarisation at 443, 670, and 865 nm well-calibrated 443, 443, 490, 565, 670, 763, 765, 865, 910 nm

Intercomparison: SCIAMACHY versus POLDER  look for collocated data (position, time) with identical viewing geometry a.POLDER image 670 nm) + previous images b.POLDER viewing angles (in green). In black: SCIAMACHY nadir pixels of 1.0 s IT c.POLDER viewing angles for data where the viewing geometry is similar to SCIAMACHY’s d.For the same measurement data again the 670 nm. In white: SCIAMACHY nadir pixels of 0.25 s IT

Reflectance: spectral averaging --- IT = 0.25 s --- IT = 1.00 s  transform SCIAMACHY reflectance into 9 broadband values for comparison with POLDER broadband measurements.

Results (reflectance) (SCIAMACHY s/w version 5.01) × = cloudy + = cloud-free Cloudy data are less reliable; fit results for cloud- free data. Slope ≠1  calibration problem SCIAMACHY

Reflectance: comparison with other “sources”  10–20% error in radiometric calibration…

Results (polarisation) (SCIAMACHY s/w version 5.01) × + = water × + = land PMD 2: something is wrong PMD 3: looks better, but look at the slope PMD 4: a lot of serious errors  polarisation product of bad quality  much better than version 4.01, though

Conclusions radiometric calibration SCIAMACHY contains errors reflectance 10-20% too low in visible wavelength range for the first time successful polarisation intercomparison polarisation errors PMD 2, 3, 4 (especially PMD 4)