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Large scale validation of SCIAMACHY nadir reflectance

Large scale validation of SCIAMACHY nadir reflectance. Gijs van Soest * , L. Gijs Tilstra, Juan Acarreta, Piet Stammes. Outline. Reflectance validation Known issues Method and data Large data set validation New key data: an improvement?. Reflectance and irradiance validation.

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Large scale validation of SCIAMACHY nadir reflectance

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  1. Large scale validation of SCIAMACHY nadir reflectance Gijs van Soest*, L. Gijs Tilstra, Juan Acarreta, Piet Stammes SCIAMACHY validation workshop, Bremen, 6 Dec ‘04

  2. Outline • Reflectance validation • Known issues • Method and data • Large data set validation • New key data: an improvement? Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  3. Reflectance and irradiance validation Errors in reflectance cause errors in geophysical parameters retrieved from it Spot and characterize possible problems in SCIAMACHY level 1 data • Instrument, calibration data, algorithms Approach: compare measured and calibrated UV spectra with radiative transfer calculations • Single states: careful, detailed characterization • Large data sets: spot drifts, possible geographical & seasonal trends Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  4. UV reflectance spectrum Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  5. Known issues of UV reflectance • Radiometric calibration: reflectance is 20% too small • Also in other channels • Showstopper for non-DOAS retrievals (O3 profile) • Spectral feature associated with polarization • Near 350 nm: BrO and CHOH retrieval affected • Improved in recent (V5.0x) data • Spectral stray light, memory effect Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  6. Large scale validation: method & data • Comparison of SCIA nadir reflectance spectra with RTM LIDORT • Data from Sep – Dec 2003, Apr – Aug 2004, decontaminations excluded • 4 “substates” per state: East, East-C, West-C, West • Wavelength range 250 – 400 nm or 270 – 340 nm • NRT SCIA L1B data (SCI_NL__1PN*) • Processor version 4.0x in 2003, 5.0x in 2004 • L1C using SciaL1Ctool, all calibrations on Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  7. Large scale validation: method & data Inputs for RTM: • Cloud mask based on FRESCO • GOME ground albedo data base • O3 profiles • IFE limb retrieval (FTP server) • TOMS v8 climatology using TOSOMI O3 columns • Temperature and geopotential height from ECMWF • 1100 states between 09/2003 and 12/2003 • 9400 states between 04/2004 and 08/2004 Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  8. Fraunhofer lines Spread depends on polarization O3 profile Small signal: extremely sensitive to calibration east Histograms of SCIA/RTM-1 (2004) Ozone TOMS v8 climatology Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  9. 370-390 Map of <SCIA/RTM-1>: 320-340 nm Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  10. SAA Map of <SCIA/RTM-1>: 270-290 nm Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  11. gradient Problem in ozone profiles w/ IFE limb O3 profiles: 270-290 nm Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  12. ESRIN orbits Difference map 2003: 270-290 nm CHANNEL 1 DATA FROM ESRIN NRT ORBITS (SCI_NL__1PNPDE*) PRIOR TO MARCH 2004 SHOULD NOT BE USED! Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  13. Effect of decontamination: 270-290 nm decontamination: orbits 12031-12208 Signal for  < 300 nm is so small that reliable calibration is a real problem Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  14. New radiometric key data set • Based on measurements from the PI period, IFE have calculated new radiometric key data • Two sets: Spectralon and NASA sphere • Irradiance now more or less OK (w/in ± 5% from reference in UV/Vis/NIR) Assess quality of reflectance with new KD Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  15. Reflectance: comparison with MERIS old Spectral averaging of SCIA, spatial averaging of MERIS. Orbits 2509/2510 several versions of new Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  16. Reflectance: comparison with RTM DAK Sahara state from orbit 2509 KNMI polarization correction Rest as in other SCIA/RTM study Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  17. Regular key data: (SCIA/5.00) NASA sphere key data:  strong unphysical spectral features Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  18. Regular key data: (SCIA/5.00) Spectralon key data:  offset smaller, but unphysical spectral features remain Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  19. Feature Increased noise Feature in channel overlap 2509 Sahara state Channel 3 Spectralon NASA sphere V5.00 Channel 3 Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  20. Conclusion (1) Large scale comparison between SCIA and RTM suited for finding geographical/slowly varying features in data • Flexible tool, possible to include several data sources • No temporal trends found; technique may be used for degradation monitoring • Ch 1 extremely sensitive to calibration (low signal) • Don’t use ESRIN NRT Ch1 data before 03/2004!!! Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  21. Conclusion (2) New IFE Key Data investigated • Irradiance looks reasonable • Reflectance offset improved • Many spectral features introduced • Reflectance is sometimes very noisy Alternative: use current key data and correct the reflectance with a smooth function based on validation result Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  22. Characterisation of validation method <SCIA/RTM – 1> albedo orbit number Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 cloud fraction viewing angle

  23. west Histograms of SCIA/RTM-1 (2004) Ozone TOMS v8 climatology Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  24. 320-340 Map of <SCIA/RTM-1>: 370-390 nm Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  25. Feature Feature Channel 2 2509 Sahara state Channel 2 Spectralon NASA sphere V5.00 Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  26. Channel overlaps still unsolved Channel 4 Feature 2509 Sahara state Channel 4 Spectralon NASA sphere V5.00 Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  27. 2509 Sahara state Channel 5 Spectralon NASA sphere V5.00 Increased noise Channel 5 Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

  28. Increased noise + feature Increased noise + feature Channel 6 2509 Sahara state Channel 6 Spectralon NASA sphere V5.00 Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04

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