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SCIAMACHY has 7 broadband polarisation monitoring devices (PMDs): Central wavelengths:

First verification of SCIAMACHY’s polarisation measurements Gijs Tilstra, Martin de Graaf, Piet Stammes KNMI, De Bilt, The Netherlands. SCIAMACHY has 7 broadband polarisation monitoring devices (PMDs): Central wavelengths: 340, 485, 650, 850, 1560, 2320 nm (Q), 850 nm (U) Purpose:

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SCIAMACHY has 7 broadband polarisation monitoring devices (PMDs): Central wavelengths:

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  1. First verification of SCIAMACHY’s polarisation measurementsGijs Tilstra, Martin de Graaf, Piet StammesKNMI, De Bilt, The Netherlands

  2. SCIAMACHY has 7 broadband polarisation monitoring devices (PMDs): Central wavelengths: 340, 485, 650, 850, 1560, 2320 nm (Q), 850 nm (U) Purpose: 1. Polarisation-correction: correct radiance I for instrumental sensitivity to Q and U polarisation. 2. Imaging of Earth scenes: PMDs have higher spatial resolution (30x7.5 km2) than the spectral channels; useful for cloud detection.

  3. Verification of fractional polarisationQ/I for orbit 2209 (2 Aug. 2002) – nadir states Blue=West pixels Black=East pixels Model value data (l < 300 nm): Conclusion: OK.

  4. PMD 1 (lc = 340 nm): Conclusions: - Resembles model values. - Zero’s occur.

  5. PMD 2 (lc = 485 nm):

  6. PMD 3 (lc = 650 nm): Conclusions: - A “hole” appears without any values. - “Mirroring” of Q/I between 0-30 N.

  7. PMD 4 (lc = 840 nm):

  8. PMD 5 (lc = 1560 nm): Conclusions: - Q/I is around 0.5. - Many zero’s.

  9. PMD 6 (lc = 2320 nm):

  10. Verification of U; model value U/Q (l < 300 nm) vs. tan 2ss for00 pixels Conclusion: U is switching sign (due to wrong use of -0 ?)

  11. Verification of U; PMD values Measured U/Q vs. tan 2ss for00 points Conclusions: - U is switching sign like the model value.

  12. Use of PMDs for imaging nadir states • PMD2= “Blue”, PMD3=“Red”, PMD4=“Green”. • 4x32 = 128 PMD pixels in swath of 960 km. • Pixel size: 30 km along track x 7.5 km across track. • Pixel stretching needed to fill gaps between consecutive forward scans. • Geolocation for individual PMD pixels is not given, but has to be calculated by interpolation. • - Signals are normalized to maximum per state.

  13. Global overview of nadir states on 2 Aug. 2002

  14. Netherlands/Germany/Belgium

  15. MODIS image of 2 Aug. 2002, 10:30 UTC

  16. Corsica (non-stretched pixels)

  17. Conclusions • Problems with nadir polarisation Q/I and U/I from the PMDs, due to: • probably wrong usage of (relative) azimuth • errors in processing of PMD signals into polarisation data Q/I and U/I. • 2. Problem: overlap polarisation is exactly zero everywhere.

  18. Conclusions (cont’d) 3. The following data seem to be OK: - date/time, lat/lon, solar zenith angle, viewing zenith angle, viewing azimuth, solar azimuth. 4. From PMD images we may conclude: - The signals of PMD 2, 3, and 4 seem to be OK. - The nadir lat/lon coordinates are accurate to at least a few km.

  19. Corsica (stretched pixels)

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