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A Multi-Sensor (MERIS - SeaWiFS - MODIS) Ocean Colour Satellite Matchup Analysis

A Multi-Sensor (MERIS - SeaWiFS - MODIS) Ocean Colour Satellite Matchup Analysis in the Mediterranean Sea (BOUSSOLE Project) David Antoine 1 , Fabrizio D'Ortenzio 1 , Stanford B Hooker 2 , Guislain Bécu 1,3 , Bernard Gentili 1 , Dominique Tailliez 1 , Alec J. Scott 1.

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A Multi-Sensor (MERIS - SeaWiFS - MODIS) Ocean Colour Satellite Matchup Analysis

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  1. A Multi-Sensor (MERIS - SeaWiFS - MODIS) Ocean Colour Satellite Matchup Analysis in the Mediterranean Sea (BOUSSOLE Project) David Antoine1, Fabrizio D'Ortenzio1, Stanford B Hooker2, Guislain Bécu1,3, Bernard Gentili1, Dominique Tailliez1, Alec J. Scott1 1: Laboratoire d’Océanographie de Villefranche, Villefranche sur mer, France 2: NASA / GSFC, Greenbelt, MD, USA 3: ACRI-st, Sophia Antipolis, France

  2. A reminder about BOUSSOLE Motivation, objectives: establishing a long-term time series of optical properties (IOPs and AOPs), with two parallel objectives: - Scientific objective: IOPs et AOPs documentation and understanding (bio-optics research), short-time changes... - Operational objective: vicarious radiometric calibration of ocean color satellite observations, and validation of the Level-2 geophysical products derived from these observations (e.g., chlorophyll, reflectances...). Strategy: combination of 3 elements: - A Deep-sea mooring, for continuous collection of data at the surface - Monthly cruises for the buoy servicing and the collection of data complementary to the buoy data - An AERONET coastal station, to provide the necessary aerosol parameters

  3. The BOUSSOLE site in the Ligurian Sea (northwestern Mediterranean)

  4. Water at BOUSSOLE are permanently Case 1 waters Morel & Maritorena, 2001 Upper limit for Case 1 waters Buoy data

  5. The range of bio-optical properties at BOUSSOLE is representative of global Case 1 waters Thick line : BOUSSOLE Thin line and thin dotted line : SeaWiFS global or Med Sea only Gray : NOMAD

  6. Range of variability in optical properties: “A field look” -4 meters Chl ~ 3 mg m-3 (April 2006) -35 meters Chl ~ 0.05 mg m-3 (march 2006)

  7. Range of variability in optical properties: “The satellite view” Feb March Apr May Jun Jul Sept Oct Nov Dec 2001 2002 2003 2004 SeaWiFS/SIMBIOS « diagnostic data sets »

  8. The BOUSSOLE buoy “transparent-to-swell” taut mooring

  9. The BOUSSOLE buoy, some pictures

  10. Buoy data are in agreement with more “classical data”, i.e., profiling radiometer’s data Slope is 1 r2 is 0.98 Bias is 8 10-4

  11. Status of deployments - 3 ½ years of deployment, with a quasi permanent data collection - Bi-monthly servicing since July of 2007 - One system lost in Feb 2007 (likely a ship collision) – immediately replaced by the companion system  only 2 weeks of interruption - Next rotation is scheduled Sept 2007 - Evolution towards hyper-spectral measurements will start in fall of 2007. Nominal set of data is however preserved for continuity

  12. Matchup procedures Essentially follows: Bailey S.W., and P.J. Werdell, 2006: A multi-sensor approach for the on-orbit validation of ocean color satellite data products. Remote Sens. Environ., 102, 12-23. - MERIS: level-2 RR, last reprocessing - SeaWiFS: level-2 Merged Local Area Coverage (MLAC; until Dec. 2004) or Global Area Coverage (GAC; 2005-2006) data from reprocessing 5 (completed March 18, 2005) - MODIS-A: level-2 GAC data from reprocessing 1 (completed in February 2005) - 5x5 pixel box - Flags: glint, clouds, haze, qs<70°, qv<60°, clear sky - Spatial homogeneity is checked

  13. 3-year time series of rw MERIS SeaWiFS MODIS-A Field data (10am – 2pm, clear sky)

  14. Full matchup set, using data from Sept 2003 to Sept 2006

  15. MERIS SeaWiFS MODIS Full matchup set, using data from Sept 2003 to Sept 2006 Band per band

  16. Statistics

  17. Matchup statistics, using data from Sept 2003 to Sept 2006

  18. Kd(490) time series MERIS SeaWiFS MODIS-A Field data

  19. Kd(490) matchups

  20. Chlorophyll time series MERIS SeaWiFS MODIS-A Field data

  21. Chlorophyll matchups

  22. Conclusions - The requirements in terms of accuracy of the atmospheric correction are only met at 443 and 490 nm by the SeaWiFS and MODIS-A products. - The MERIS products never meet the requirements. - The water-leaving radiance reflectances provided by the three sensors at 412 nm are severely affected by atmospheric correction errors. - The uncertainty is significantly reduced for the “blue-to-green” reflectance ratio. - These results and the matchup statistics are in agreement with the results obtained by two other similar efforts carried out at a coastal site [Zibordi et al., 2006] and globally [Bailey and Werdell, 2006]. Questions: - Atmospheric corrections are still an issue. Are they however considered as the unique source of these uncertainties? - Should we move to a vicarious calibration of MERIS?

  23. BOUSSOLE web site and data base http://www.obs-vlfr.fr/Boussole

  24. Thank you for your attention

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