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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes First verification of SCIAMACHY’s polarisation measurements Gijs Tilstra,

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Presentation on theme: "SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes First verification of SCIAMACHY’s polarisation measurements Gijs Tilstra,"— Presentation transcript:

1 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

2 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.

3 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.

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

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

6 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.

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

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

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

10 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 ?)

11 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.

12 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.

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

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

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

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

17 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.

18 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.

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


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