Diapositive 1

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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 dOcéanographie de Villefranche,
Villefranche sur mer, France 2 NASA / GSFC,
Greenbelt, MD, USA 3 ACRI-st, Sophia Antipolis,
France
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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
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The BOUSSOLE site in the Ligurian Sea
(northwestern Mediterranean)
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Water at BOUSSOLE are permanently Case 1 waters
Morel Maritorena, 2001 Upper limit for Case 1
waters
Buoy data
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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
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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)
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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 
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The BOUSSOLE buoy transparent-to-swell taut
mooring
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The BOUSSOLE buoy, some pictures
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Buoy data are in agreement with more classical
data, i.e., profiling radiometers data
Slope is 1 r2 is 0.98 Bias is 8 10-4
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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
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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,
qslt70, qvlt60, clear sky - Spatial homogeneity
is checked
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3-year time series of rw
MERIS SeaWiFS MODIS-A Field data (10am 2pm,
clear sky)
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Full matchup set, using data from Sept 2003 to
Sept 2006
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Full matchup set, using data from Sept 2003 to
Sept 2006 Band per band
MERIS
SeaWiFS
MODIS
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Statistics
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Matchup statistics, using data from Sept 2003 to
Sept 2006
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Kd(490) time series
MERIS SeaWiFS MODIS-A Field data
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Kd(490) matchups
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Chlorophyll time series
MERIS SeaWiFS MODIS-A Field data
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Chlorophyll matchups
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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?
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BOUSSOLE web site and data base http//www.obs-vlf
r.fr/Boussole
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Thank you for your attention