Intercomparison: SCIAMACHY versus POLDER look for collocated data (position, time) with identical viewing geometry a.POLDER image (reflectance @ 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 reflectance @ 670 nm. In white: SCIAMACHY nadir pixels of 0.25 s IT Data can be compared
Reflectance: spectral averaging --- IT = 0.25 s --- IT = 1.00 s transform SCIAMACHY reflectance into 9 broadband values for comparison with POLDER broadband reflectance measurements
Results for the reflectance: (SCIAMACHY s/w version 5.01) × = cloudy + = cloud-free Cloudy data are less reliable; fit results for cloud- free data Slope ≠1 (known) calibration problem of 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, bad correlation 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 IT = 0.25 s
PMD 4: simple check IT = 0.25 s - zero-point problem - “unphysical” values
Conclusions radiometric calibration SCIAMACHY contains errors reflectance 10-20% too low in visible wavelength range for the first time successful polarisation intercomparison polarisation errors for PMD 2 and 3 polarisation retrieval of PMD 4 is in a very bad shape
EXTRA SLIDES: PMD 4 versus single scattering value: Q/I and U/I IT = 0.25 s IT = 1.00 s