Abstract

An innovative platform is tested to perform reflectance measurements at sea. This platform is a mini-catamaran with two hulls 1m long and set 0.7m apart, fitted with optical sensors. It can be used far away from an oceanographic ship to avoid its hull influencing the measurement. Reflectance measurements were performed with a TriOS radiance sensor placed +2cm or -2cm from the water surface and a TriOS irradiance sensor. Tests were carried out in calm seas and with cloud cover. The processing to derive marine radiances from raw measurements is detailed. When the radiance sensor is above the interface, it limits the sky reflections on the targeted surface and the radiance is identical to that deduced from measurements below the surface. When the sensor is placed at +3cm above-water or higher, glint affects the measurements. The mini-catamaran shows a good ability to measure marine reflectance with an adapted measurement protocol. Except for very turbid waters, it seems preferable to perform upwelling radiance measurements below the surface.

© 2005 Optical Society of America

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References

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Appl. Opt. (5)

Appl. Optics (2)

A. Morel, and B. Gentili, �??Diffuse reflectance of oceanic waters 2: Bi-directional aspects,�?? Appl. Optics 32, 6864-6879 (1993).
[CrossRef]

C.D. Mobley, �??Estimation of the remote-sensing reflectance from above-surface measurements,�?? Appl. Optics 38, 7442�??7455 (1999).
[CrossRef]

Bound. Layer Met. (1)

A. Morel, �??In-water and remote measurements of ocean colour,�?? Bound. Layer Met. 18, 177-201 (1980).
[CrossRef]

Coral Reefs (1)

S. Ouillon, P. Douillet, and S. Andréfouët, �??Coupling satellite data with in situ measurements and numerical modeling to study fine suspended sediment transport: a study for the lagoon of New Caledonia,�?? Coral Reefs 23, 109-122 (2004).
[CrossRef]

Deep-Sea Res. (2)

J.M Froidefond., P. Castaing, and R. Prud�??homme, �??Monitoring suspended particulate matter fluxes and patterns with the AVHRR/NOAA-11 satellite. �??Application to the Bay of Biscay,�?? Deep-Sea Res. 46, 2029-2055 (1999).
[CrossRef]

C.S. Yentsch, and D.W. Menzel, �??A method for the determination of phytoplankton chlorophyll and pheophytin by fluorescence,�?? Deep-Sea Res. 10, 221-231 (1963).

Int. J Remote Sens. (1)

S. Tassan, �??Evaluation of the potential of the Thematic Mapper for marine application,�?? Int. J Remote Sens. 8, 1455-1478 (1987).
[CrossRef]

Int. J. Remote Sens. (3)

S. Khorram, H.Cheshire, A.L. Geraci, and G. La Rosa, �??Water quality mapping of Augusta Bay, Italy from Landsat-TM data,�?? Int. J. Remote Sens. 12, 803-808 (1991).
[CrossRef]

J.M. Froidefond, S. Lavender, P. Laborde, A. Herbland, and V. Lafon, �??SeaWiFS data interpretation in a coastal area in the Bay of Biscay,�?? Int. J. Remote Sens. 23, 881-904 (2002).
[CrossRef]

S.Sathyendranath, L. Prieur, and A. Morel, �??A three model of ocean colour and its application to remote sensing of phytoplankton pigments in coastal waters,�?? Int. J. Remote Sens. 10, 1373-1394 (1989).
[CrossRef]

J. Atm. Ocean. Technol. (1)

S.B. Hooker, and A. Morel, �??Platform and Environmental effects on above-water determinations of water-leaving radiances,�?? J. Atm. Ocean. Technol. 20, 187-205 (2003).
[CrossRef]

J. Geoph. Res. (1)

J.E. O�??Reilly, S. Maritorena, G.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M. Kahru, and C. McClain, �??Ocean color algorithms for SeaWiFS,�?? J. Geoph. Res. 103, 24937-24953 (1998).
[CrossRef]

J. Opt. A: Pure Appl. Opt. (1)

T. Ohde, and H. Siegel, �??Derivation of immersion factors for the hyperspectral TriOS radiance sensor,�?? J. Opt. A: Pure Appl. Opt. 5, L12-L14 (2003).
[CrossRef]

J. Optics A: Pure Appl. Opt. (1)

D. Doxaran, R.C. Nagur Cherukuru, and S.J. Lavender, �??Estimation of surface reflection effects on upwelling radiance field measurements in turbid waters,�?? J. Optics A: Pure Appl. Opt. 6, 690-697 (2004).
[CrossRef]

J. Rech. Oceanogr. (1)

H. Etcheber, �??Comparaison de diverses méthodes d�??évaluation des teneurs en matières en suspension et en carbone organique particulaire des eaux marines du plateau continental aquitain,�?? J. Rech. Oceanogr. 6, 37-42 (1981).

Limn. Ocean. (1)

A. Morel, and L. Prieur, �??Analysis of variations in ocean colour,�?? Limn. Ocean. 22, 709-721 (1977).
[CrossRef]

Limnol. Ocean. (2)

J.T.O. Kirk, �??Dependence of relationship between inherent and apparent optical properties of water on solar altitude,�?? Limnol. Ocean. 29, 350-356 (1984).
[CrossRef]

H.R. Gordon, �??Dependence of the diffuse reflectance of natural waters on the Sun angle,�?? Limnol. Ocean. 34, 1484-1489 (1989).
[CrossRef]

MTS journal (1)

S. Ouillon, P. Forget, J.M. Froidefond, and J.J.Naudin, �??Estimating suspended matter concentrations from SPOT data and from field measurements in the Rhône river plume,�?? MTS journal 31, 15-20 (1997).

Proc. SPIE (1)

H.R. Gordon, R.C. Smith, J.R.V. Zaneveld, �??Introduction to ocean optics,�?? in Ocean Optics VII, M.A. Blizard, ed., Proc. SPIE 489, 2-41 (1984).

Remote Sens. Envir. (1)

F. Lahet, S. Ouillon, and P. Forget, �??A three component model of ocean colour and its application in the Ebro River mouth area,�?? Remote Sens. Envir. 72, 181-190 (2000).
[CrossRef]

Other (3)

IOCCG, Remote Sensing of Ocean Colour in Coastal and Other Optically-Complex Waters (IOCCG, Darmouth, 2000).

H.R. Gordon, and A. Morel, Remote assessment of ocean color for interpretation of satellite visible imagery: a review (Springer-Verlag, Berlin, 1983).
[CrossRef]

N.G. Jerlov, Marine optics (Elsevier, Amsterdam, 1976).

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Figures (9)

Fig. 1.
Fig. 1.

Calibration radiance spectra measured using the FieldCal device.

Fig. 2.
Fig. 2.

Measurement platform fitted with TriOS irradiance and radiance sensors.

Fig. 3.
Fig. 3.

Testing device comprised of an aquarium placed on a white reflectance Spectralon® plate and in the shade to avoid major reflections on the glass tank.

Fig. 4.
Fig. 4.

Spectral radiances obtained following the schema of Fig. 3. The below-water spectrum L(λ,-1) corresponds to a non-corrected radiance.

Fig. 5.
Fig. 5.

Irradiance measured at Aiguillon under a covered sky on 17 February 2004 between 10:44 and 10:46 am and between 10:50 and 10:52 am.

Fig. 6.
Fig. 6.

Upwelling radiance measured at +2cm±1cm (17 red curves) and at -2cm±1cm (13 blue curves, uncorrected radiance) simultaneously with an irradiance measurement presented in Fig. 5. Aiguillon, 17 February 2004.

Fig. 7.
Fig. 7.

Radiance measured above-water at +3cm (7 red curves) and below the sea surface at -2cm (33 blue curves, uncorrected measurements), Teychan, 18 February 2004.

Fig. 8.
Fig. 8.

Remote-sensing reflectance calculated from irradiance and radiance shown in Fig. 5 and 6 at Aiguillon on 17 February 2004: Rrs=Lw/Ed with Lw computed from Lu(-2) in blue (measurements taken between 10:44 am and 10:46 am) and Rrs=L(+2)/Ed in red, measurements taken between 10:50 am and 10:52 am).

Fig. 9.
Fig. 9.

Remote-sensing reflectance and corresponding concentrations in Total Suspended Matter (S) and in chlorophyll-a (chl) for 7 stations in the Bay of Arcachon, 17 and 18 February 2004.

Equations (13)

Equations on this page are rendered with MathJax. Learn more.

R ( λ , z ) = Eu ( λ , z ) Ed ( λ , z )
Eu ( λ , 0 ) = Eu ( λ , z ) e [ Ku ( λ ) . z ]
R ( λ ) = f . [ b b ( λ ) ( a ( λ ) + b b ( λ ) ) ]
a ( λ ) = a w ( λ ) + a ch ( λ ) + a s ( λ ) + a y ( λ )
b b ( λ ) = b b w ( λ ) + b b ch ( λ ) + b b s ( λ )
Rrs ( λ , θ , ϕ ) = Lw ( λ , θ , ϕ , 0 + ) Ed ( λ , 0 + )
Lw ( λ ) = t n 2 * Lu ( λ , 0 )
L t ( λ , 0 + ) = L w ( λ ) + ρ L sky ( λ ) + Δ L ship ( λ )
θ water = arcsin [ ( 1 n ) * sin θ air ]
Ω IFOV = 2 π ( 1 cos θ )
Lw ( λ ) = 0.98 * L ( λ , 2 )
Rrs ( λ ) = 0.98 * L ( λ , 2 ) Ed ( λ , 0 + )
Ed ( λ , z ) = Ed ( λ , 0 ) . e [ Kd ( λ ) . z ]

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