New measurements of the intensity and geometrical structure of the upwelling and downwelling underwater light fields (radiance distributions) David Antoine 1 , Edouard Leymarie 1 , André Morel 1 , Amel Houyou 1,2 , Stéphane Victori 2 , Didier Crozel 2 , and Bertrand Fougnie 3
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New measurements of the intensity and geometrical structure of the upwelling and downwelling underwater light fields
David Antoine1, Edouard Leymarie1, André Morel1, Amel Houyou1,2, Stéphane Victori2, Didier Crozel2, and Bertrand Fougnie3
1Laboratoire d’Océanographie de Villefranche (CNRS-LOV), Villefranche surmer, France,
2CIMEL Electronique, Paris, France,
3 Centre National d’EtudesSpatiales (CNES), Toulouse, France
What do we call the “radiance distribution”?
Why measuring L()?
Two main objectives:
Better characterization / understanding of L(). The vertical structure of the underwater light field is important for biology (photosynthesis) and physics (heating rate).
1 - L() determines the distribution of radiances escaping the ocean, i.e., the water-leaving radiances (Lw) that we measure from space with so-called “ocean color” remote sensing satellites.
It is, therefore, necessary to know L() (at least L(u)) in order to know how Lw’s are distributed over space (normalization of observations taken under various sun elevations and different view angles; data merging)
Well characterized for open ocean waters (at least just beneath the sea surface); totally undocumented for coastal turbid waters
2 - An accurate knowledge of depth changes of L() within the water column in principle gives access to all optical properties (through inversion procedures); this would be a sort of “generic” or “universal” measurement.
What was done before?
What was done before?
Unidirectional photometer with elevation scanning
Radiances distribution in Lake Pend’Oreille
Redrawn from the data published by Tyler, 1960
The Sea, Vol 1., M. N. Hill Ed., (1962)
Previous developments, cont’d
Upwelling radiances downwelling radiances
(Med. Sea 1972)
Smith R.C., R.W. Austin, and J.E. Tyler, 1970.
An oceanographic radiance distribution camera system, Applied Optics 9(9), 2015-2022
(Vis. Lab at Scripps)
Optical Aspects of Oceanography, N.G. Jerlov, (1974)
Previous (and current) developments, cont’d
Our new development
Our new development:
The “CE-600” radiance camera system
406 438 494510560 628
Bandpass filters (on a filter wheel)
CMOS (Altasens HD3560).
Auxiliary sensors (tilt, compass, pressure, internal temp)
Data transfer (fiber optics) & commands
Container rated to 200 m depth
Radiometric characterization / calibration
Full radiance distributions: L(, z)
High values near the direction of the sun
have been divided by 1000 (in order to use one single color scale for the entire plot)
l=494 nm, clear waters (Chl~0.1 mg m-3), sun zenith angle ~65° in air (Arctic)
Validation against more classical in-water radiometers
Tentative inversion of L() in terms of
optical properties: method
Starting from L(, z):
Gershun (1939) equation; Preisendorfer (1976)
Zaneveld, R.J.V., 1989, An asymptotic closure theory for irradiance in the sea and its inversion to obtain the inherent optical properties, Limnology and Oceanography19, 1442-1452.
Tentative inversion of L(): results
l=494 nm, clear waters (Kd~0.1 m-1), qs in air ~ 65° (Arctic)
Conclusions / perspectives
Improved design for the 2-camera profiling system
for your attention