sciamachy calibration review, estec, 11 september 2002 tilstra, de graaf, stammes first verification...
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![Page 1: SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes First verification of SCIAMACHY’s polarisation measurements Gijs Tilstra,](https://reader035.vdocuments.net/reader035/viewer/2022062511/551b1d1d55034607418b58e9/html5/thumbnails/1.jpg)
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
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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 km2) than the spectral channels; useful for cloud detection.
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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.
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
PMD 1 (c = 340 nm):
Conclusions:
- Resembles model
values.
- Zero’s occur.
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
PMD 2 (c = 485 nm):
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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.
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
PMD 4 (c = 840 nm):
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
PMD 5 (c = 1560 nm):
Conclusions:
- Q/I is around 0.5.
- Many zero’s.
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
PMD 6 (c = 2320 nm):
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
Verification of U; model value
U/Q ( < 300 nm)
vs. tan 2ss
for 00 pixels
Conclusion:
U is switching sign
(due to wrong use
of -0 ?)
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
Verification of U; PMD values
Measured U/Q
vs. tan 2ss
for 00 points
Conclusions:
- U is switching sign
like the model value.
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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.
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
Global overview of nadir states on 2 Aug. 2002
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
Netherlands/Germany/Belgium
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
MODIS image of 2 Aug. 2002, 10:30 UTC
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
Corsica (non-stretched pixels)
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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.
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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.
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SCIAMACHY Calibration Review, ESTEC, 11 September 2002 Tilstra, De Graaf, Stammes
Corsica (stretched pixels)