SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes First verification of SCIAMACHY’s polarisation measurements Gijs Tilstra, Martin de Graaf, Piet Stammes KNMI, De Bilt, The Netherlands

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes 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 km 2 ) than the spectral channels; useful for cloud detection.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Verification of fractional polarisation Q/I for orbit 2209 (2 Aug. 2002) – nadir states Blue=West pixels Black=East pixels Model value data ( < 300 nm): Conclusion: OK.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes PMD 1 ( c = 340 nm): Conclusions: - Resembles model values. - Zero’s occur.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes PMD 2 ( c = 485 nm):

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes PMD 3 ( c = 650 nm): Conclusions: - A “hole” appears without any values. - “Mirroring” of Q/I between 0-30 N.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes PMD 4 ( c = 840 nm):

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes PMD 5 ( c = 1560 nm): Conclusions: - Q/I is around Many zero’s.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes PMD 6 ( c = 2320 nm):

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Verification of U; model value U/Q ( < 300 nm) vs. tan 2  ss for  0 0 pixels Conclusion: U is switching sign (due to wrong use of  -  0 ?)

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Verification of U; PMD values Measured U/Q vs. tan 2  ss for  0 0 points Conclusions: - U is switching sign like the model value.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes 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.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Global overview of nadir states on 2 Aug. 2002

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Netherlands/Germany/Belgium

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes MODIS image of 2 Aug. 2002, 10:30 UTC

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Corsica (non-stretched pixels)

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Conclusions 1.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.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes 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.

SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes Corsica (stretched pixels)