Validation of SCIAMACHY polarisation using POLDER as a reference bonus: reflectance validation

1
Validation of SCIAMACHY polarisation using POLDER
as a reference(bonus reflectance validation)
Tiger Team Meeting 23, SRON, 23 May 2006
2
POLDER

• imager
• CCD detector matrix
• bandfilter carousel
• wide FOV lens
• resolution 6 7 km2
• polarisation at 443,
• 670, and 865 nm
• well-calibrated

443, 443, 490, 565, 670, 763, 765, 865, 910 nm
3
Intercomparison SCIAMACHY versus POLDER? look
for collocated data (position, time) with
identical viewing geometry

• POLDER image (reflectance _at_ 670 nm) previous
  images
• POLDER viewing angles (in green). In black
  SCIAMACHY nadir pixels of 1.0 s IT
• POLDER viewing angles for data where the viewing
  geometry is similar to SCIAMACHYs
• For the same measurement data again the
  reflectance _at_ 670 nm. In white SCIAMACHY nadir
  pixels of 0.25 s IT
• Data can be compared

4
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
5
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
6
Reflectance comparison with other sources
? 1020 error in radiometric calibration.
7
Results (polarisation)
(SCIAMACHY s/w version 5.01)

• 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

water land
? IT 0.25 s
8
PMD 4 simple check

• zero-point problem
• unphysical values

? IT 0.25 s
9
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

10
EXTRA SLIDES PMD 4 versus single scattering
value Q/I and U/I
IT 0.25 s
IT 1.00 s