In-water and remote measurements of ocean color |
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| Authors: | André Morel |
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| Institution: | (1) Laboratoire de Physique et Chimie Marines, Station Marine de Villefranche-sur-mer, B.P. 8 F-06230, Villefranche-sur-mer, France |
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| Abstract: | Spectral measurements of downwelling irradiance, E
d( ), above the surface, and of upwelling irradiance just below the surface, E
u(), allow computation of spectral values of the diffuse reflectance R() = E
u()/E
d(); this yields full information about the true color and brightness of the ocean. Typical results are presented and interpreted for waters very different in turbidity and phytoplankton content. Conversely, the possibility of infering the water content from R() data at selected wavelengths is examined in terms of the respective number of equations and unknowns. The necessary use of assumptions and of empirical laws is emphasized.The magnitude of the useful signal emerging from the water, and the magnitude of the additional signals due to specular reflexion at the interface and to atmospheric scattering, are compared on the basis of spectroradiometric measurements performed within and above the sea, from different altitudes. These unwanted signals are dominant, causing a drastic change in the spectral composition of the light received by a remote sensor. The evaluation of the atmospheric effect must be very precise in order to recover the marine signal with a sufficient accuracy for a meaningful application of any kind of algorithm.This work was supported in part by the Centre National d'Exploitation des Océans (under contract CNEXO 77/1695) and in part by the Centre National de la Recherche Scientifique (RCP 247 & ERA 278). |
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