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Polarization correction based on ray tracing simulations: Effects on L2 data, day 2002 226

Polarization correction based on ray tracing simulations: Effects on L2 data, day 2002 226. Presentation to CalVal group by Gerhard Meister, December 2005 Data analysis by Ewa Kwiatkowska. Raytracing simulation:. Created by Nordine Souaidia (UM, Ken Voss) with ZEMAX

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Polarization correction based on ray tracing simulations: Effects on L2 data, day 2002 226

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  1. Polarization correction based on ray tracing simulations: Effects on L2 data, day 2002 226 Presentation to CalVal group by Gerhard Meister, December 2005 Data analysis by Ewa Kwiatkowska

  2. Raytracing simulation: • Created by Nordine Souaidia (UM, Ken Voss) with ZEMAX • Based on measured reflectances/ transmittances of MODIS components (piece parts) • Available per detector • No 4-cycle contamination in bands 13-15

  3. Difference in polarization sensitivity between ray- tracing and prelaunch results

  4. Maximum difference in polarization sensitivity between detectors from raytracing results

  5. Degree of Polarization versus scan angle

  6. nLw L2 MODIS/L3 SeaWiFS versus scan angle(red: all bands with polarization sensitivityfrom raytracing analysis; black: operational)

  7. nLw L2 MODIS/L3 SeaWiFS versus scan angle (red: NIR bands with operational polarization sensitivity, other bands raytracing)

  8. nLw L2 MODIS/L3 SeaWiFS detector-to-detector variation (red: all bands with polarization sensitivityfrom raytracing analysis)

  9. nLw L2 MODIS/L3 SeaWiFS detector-to-detector variation (red: prelaunch measurements, without selection of best detectors or view angles)

  10. nLw L2 MODIS/L3 SeaWiFS versus scan angle (red: prelaunch measurements, without selection of best detectors or view angles)

  11. Further refinement of analysis: • Polarization correction polcor can increase or decrease TOA radiance, depends on the polarization state of the TOA radiance • If polcor<1 and polcor>1 occur equally often, net effect may be zero • => evaluate data separately for each case

  12. TOA detector residuals (preliminary)

  13. Summary • Polarization sensitivity from raytracing significantly increases detector variation for highly polarized pixels, it slightly improves scan dependence versus SeaWiFS L3 • Prelaunch sensitivity from prelaunch measurements without selection process improves detector variation for 412nm, worsens it for 488nm-551nm • TOA residuals for bands 15 and 16 show artifacts that prevent polarization analysis

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