Adjacency effects on water surfaces: primary scattering approximation and sensitivity study.

The making of atmospheric corrections is a critical task in the interpretation of ocean color imagery. In coastal areas, a fraction of the light reflected by the land reaches a sensor. Modeling the reduction of image contrast when the atmospheric turbidity increases, the so-called adjacency effect, requires large amounts of computing time. To model this effect we developed a simple approach based on the primary scattering approximation for both nadir and off-nadir views. A sensitivity study indicates that the decisive criterion for measurement accuracy for aerosols is their vertical distribution. As this distribution cannot generally be determined from space, it is not possible to include a suitable correction of the adjacency effects on satellite imagery. Conversely, we propose a simple correction for molecular scattering based on the isotropic approximation. We also address the problem of reduction of the coupling between the Fresnel reflection and the atmosphere for observations of coastal water. We study the influence of the adjacency effects on determination of the abundance of chlorophyll in water by combining use of the red and the infrared bands for aerosol remote sensing and the blue/green-ratio technique for retrieval of these data.