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A Multi Sensor (MERIS, SeaWiFS, MODIS-A) Ocean
Color Satellite Matchup Analysis in the
Mediterranean Sea BOUSSOLE Project
Fabrizio DOrtenzio, David Antoine, Guislain
Bécu Laboratoire dOcéanographie de Villefranche,
CNRS et Université Pierre et Marie Curie
Stanford B. Hooker NASA/GSFC, Greenbelt, MD 20771
USA
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Overview of the presentation
1. Some elements about the BOUSSOLE project 2.
Matchup Procedure and evaluation of the
results 3. Conclusions
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Description of the BOUSSOLE Project
Motivations
Establish a time series of inherent and apparent
optical properties (IOPs and AOPs).
Strategy

• Combination of 3 elements
• A deep-sea mooring, collecting data on a
  continuous basis
• Monthly cruises for collecting data that are not
  accessible to the mooring (vertical profiles,
  water sampling)
• A coastal AERONET station, providing the
  necessary information about the aerosol
  properties

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Characteristics of the buoy site physical
dynamics
BOUSSOLE
Located in the middle of the Cyclonic Circulation
of the NW Med The physical dynamic is
prevalently vertical i.e. 1-dimensional Surface
currents are generally weak Millot, 1999
Mixed-layer depth varies from 10 to 200
meters Marty et al. 2002
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Characteristics of the buoy site biological
dynamics
Biomass concentration is generally low. Intense
spring bloom is however observed. Chlorophyll
concentration varies from 0.05 to 5 mg/m3
SeaWiFS Chlorophyll Concentration
BOUSSOLE
13 April 1999
28 May1998
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Why a new mooring type?
Irradiance profilers provide highly noisy data
near the surface because of the effect of
capillary and gravity waves ? the horizontal
gradient in E or L is often an order-of-magnitude
larger than the vertical gradient (see, e.g.,
Zaneveld et al., Appl. Opt., 40(9), 2001).
Depth
Irradiance 490
The data near the surface are often unusable
whereas they are the ones that should be used
when satellite validation is concerned.
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Why a new mooring type?
The solution we have adopted Integration over
time with a sensor maintained at a fixed position
and depth

• The new type of buoy ensures
• the verticality of the instruments,
• the stability of the instruments,
• the minimisation of shading of the instruments by
  the buoy structure.

See Poster 204 of Bécu et al. for a complete
description of the BOUSSOLE programme.
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Measurement suite, instrumentation
4 meters
At 9 meters
At 4 and 9 meters

• Wetlabs C-star
• 2 ls, Hobilabs Hydroscat
• Chelsea MiniTracka
• SeaBird SBE37

7 ls Satlantic OCR-OCI 200 Series
Surface irradiance (Es) Downwelling irradiance
(Ed) Upwelling irradiance (Eu) Upwelling
radiance at nadir (Lu)
Attenuation coefficient Backscattering
coefficient Chlorophyll fluorescence Temperature,
Pressure Salinity Buoy tilt
Fully normalized reflectances ?w (defined as p
nLw/Es ) Water leaving radiances Lwn
-20 meters
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nLw Time Series
nLw670
All data collected every 15 minutes during
daylight
nLw560
One day of data collection (15-min. resolution)
nLw490
nLw490
nLw443
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nLw Time Series
nLw670
Data further filtered for 1. Excessive buoy
tilt or depth 2. Sun zenith angle gt 70
nLw560
nLw490
nLw443
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Satellite Data
SeaWiFS (2003-2004) level-2 MLAC data from
reprocessing 5 Obtained at http//oceancolor.gs
fc.nasa.gov/cgi/browse.pl?senam
AMODIS (2003-2005) level-2 data from reprocessing
1 Obtained at http//oceancolor.gsfc.nasa.gov/cg
i/browse.pl?senam
MERIS (2003-2005) level-2 1-Km reduced
resolution data processed by the MERIS prototype
version 7.4.1 (called MEGS7.4.1) Obtained at
http//merci-srv.eo.esa.int/merci/welcome.do
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The Matchup procedure
The matchup process follows four steps (Bailey
and Werdell, 2006, with additional considerations
related to the specificity of the buoy-derived
observations)
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Results MERIS

• ? Satellite Data
• , , , Buoy Data

?w560
?w490
?w443
?w443/ ?w555
Chl
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Results MODIS

• ? Satellite Data
• , , , Buoy Data

nLw551
nLw448
nLw443
nLw443/ nLw555
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Results SeaWiFS

• ? Satellite Data
• , , , Buoy Data

nLw551
nLw448
nLw443
nLw443/ nLw555
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Results All sensors, all bands
Satellite
In Situ
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Results Statistics
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Results comparison with other studies
The overall agreement between the
satellite-derived and the in situ reflectances or
radiances is similar for the three sensors, and
it is close to what has been already reported
elsewhere
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Conclusions
BOUSSOLE provides a suitable set of data to
validate Level-2 satellite Ocean Color
products. An overall agreement between the in
situ and the SeaWiFS, MODIS and MERIS
reflectances and radiances is obtained.
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Conclusions
Some specific points 1) the MERIS data products
in the red part of the spectrum (i.e., l gt 600
nm) are overestimated by a factor of two to
four 2) the MERIS data products for the blue
wavelengths appear to be overestimated 3) the
SeaWiFS and AMODIS data products exhibit a slight
tendency of underestimation in the blue
domain 4) AMODIS data for July and August 2005
appear to be underestimated but the cause of the
error is at the moment unidentified.
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Thank you for your attention