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ENVISAT symposium, Montreux, Suisse, April 23-27, 2007 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 1: Laboratoire d’Océanographie de Villefranche, Villefranche sur mer, France 2: NASA / GSFC, Greenbelt, MD, USA 3: ACRI-st, Sophia Antipolis, France

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

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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. - PowerPoint PPT Presentation

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Page 1: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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, France2: NASA / GSFC, Greenbelt, MD, USA3: ACRI-st, Sophia Antipolis, France

Page 2: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

A reminder about BOUSSOLE

- 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...).

Motivation, objectives: establishing a long-term time series of optical properties (IOPs and AOPs), with two parallel objectives:

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

Page 3: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

The BOUSSOLE sitein the Ligurian Sea (northwestern Mediterranean)

Page 4: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Water at BOUSSOLE are permanently Case 1 waters

Buoy data

Morel & Maritorena, 2001Upper limit for Case 1 waters

Page 5: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

The range of bio-optical properties at BOUSSOLE is representative of global Case 1 waters

Thick line : BOUSSOLEThin line and thin dotted line : SeaWiFS global or Med Sea onlyGray : NOMAD

Page 6: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Range of variability in optical properties:“A field look”

Chl ~ 0.05 mg m-3 (march 2006)

Chl ~ 3 mg m-3 (April 2006)

-35 meters

-4 meters

Page 7: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Feb March Apr May Jun Jul Sept Oct Nov Dec

2001

2002

2003

2004 SeaWiFS/SIMBIOS « diagnostic data sets »

Range of variability in optical properties:“The satellite view”

Page 8: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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

Page 9: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

The BOUSSOLE buoy, some pictures

Page 10: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Buoy data are in agreement with more“classical data”, i.e., profiling radiometer’s data

Slope is 1r2 is 0.98

Bias is 8 10-4

Page 11: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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

Page 12: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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, s<70°, v<60°, clear sky

- Spatial homogeneity is checked

Page 13: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

3-year time series of w

MERIS

SeaWiFS

MODIS-A

Field data (10am – 2pm, clear sky)

Page 14: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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

Page 15: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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

Band per band

MERIS SeaWiFS MODIS

Page 16: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

N Number of points

r Mean ratio, defined as

Ni

1i i

i

y

x

N

1

RPD Average relative (signed) percent difference (%), defined as

Ni

1i i

ii

y

)yx(

N

1100

|RPD| Average relative (unsigned) percent difference (%), defined as

Ni

1i i

ii

y

yx

N

1100

r2, m and y Coefficient of determination, slope and intercept of the linear fit

RMSE Root mean square error (or root means square of differences), defined as

Ni

1i

2ii )yx(

N

1

Note the Chl data are log-transformed before computing r2, m, y and RMSE.

Statistics

Page 17: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Table 1. Match-up statistics for MERIS

l N RPD |RPD| r2m y RMSE

412 19 1.59 59.1 61.7 0.20 0.91 0.00790 0.00893443 66 1.25 24.9 30.9 0.30 0.63 0.00830 0.00492490 69 1.14 13.9 17.9 0.38 0.64 0.00650 0.00273

nLw 510 69 1.21 21.2 23.3 0.21 0.54 0.00630 0.00254560 66 1.22 22.1 25.1 0.34 0.62 0.00300 0.00153665 69 1.67 66.6 75.7 0.05 0.55 0.00070 0.00057681 70 1.59 59.4 64.2 0.29 0.50 0.00080 0.00058

all 428 1.36 36.0 40.7 0.86 1.11 0.00070 0.00316Chl 31 1.17 17.0 46.0 0.78 0.56 -0.60804 0.60432

15 1.09 9.3 41.7 0.87 0.58 -0.48613 0.61219Kd 234 1.00 -0.3 28.2 0.51 0.41 0.02649 0.02212

67 0.89 -10.6 20.4 0.66 0.51 0.02090 0.01745

For Chl and Kd, the first line reports statistics for all possible correspondances between field data and satellite observations

and the second line reports statistics for the set of points that have successfully passed the matchup criteria

Table 2. Match-up statistics for SeaWiFS

l N RPD |RPD| r2m y RMSE

412 79 0.90 -9.7 23.3 0.41 0.79 0.00160 0.00492443 212 0.99 -1.0 16.4 0.41 0.68 0.00470 0.00333490 215 0.97 -2.9 12.7 0.37 0.63 0.00490 0.00227

nLw 510 215 0.92 -7.9 14.9 0.15 0.41 0.00550 0.00204555 215 0.88 -11.7 19.4 0.15 0.42 0.00260 0.00147670 199 0.76 -24.2 50.1 0.02 0.25 0.00030 0.00035

all 1135 0.91 -9.4 22.4 0.87 0.92 0.00010 0.00244Chl 55 1.39 38.9 61.1 0.68 0.61 -0.41214 0.60522

44 1.69 68.5 84.9 0.51 0.45 -0.66199 0.68610Kd 330 1.05 4.5 34.1 0.35 0.45 0.02678 0.02561

240 1.07 6.7 35.2 0.28 0.29 0.03180 0.02387

Table 3. Match-up statistics for MODIS-A

l N RPD |RPD| r2m y RMSE

412 87 0.88 -11.8 24.2 0.55 0.85 0.00050 0.00437443 182 0.97 -3.0 16.8 0.57 0.73 0.00350 0.00320488 188 0.97 -2.9 11.9 0.54 0.70 0.00370 0.00211

nLw 551 188 0.93 -6.6 16.6 0.38 0.59 0.00190 0.00122667 177 0.78 -21.5 42.5 0.05 0.25 0.00030 0.00031

all 822 0.91 -8.7 21.9 0.89 0.91 0.00030 0.00238Chl 58 1.20 19.6 50.2 0.72 0.62 -0.49363 0.61499

31 1.21 20.7 40.9 0.82 0.77 -0.24622 0.42352Kd 344 1.09 9.1 33.0 0.44 0.50 0.02685 0.02344

187 1.08 8.1 35.5 0.31 0.34 0.03143 0.02307

r

r

r

Matchup statistics, using data from Sept 2003 to Sept 2006

Page 18: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Kd(490) time series

MERIS

SeaWiFS

MODIS-A

Field data

Page 19: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Kd(490) matchups

Page 20: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Chlorophyll time series

MERIS

SeaWiFS

MODIS-A

Field data

Page 21: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Chlorophyll matchups

Page 22: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

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?

Page 23: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

BOUSSOLE web site and data basehttp://www.obs-vlfr.fr/Boussole

Page 24: A Multi-Sensor (MERIS - SeaWiFS - MODIS)  Ocean Colour Satellite Matchup Analysis

ENVISAT symposium, Montreux, Suisse, April 23-27, 2007

Thank you for your attention