A Model for the Reflectance of Thin Layers, Fronts, and Internal Waves and Its Inversion

THE INTERPLAY OF physical and biogeochemical processes in the ocean can result in well-defined vertical gradients and maxima in biological properties. When these gradients and maxima exist near the sea surface, it is possible to use satellite or airborne remote sensing to infer physical structure of thin layers, fronts, and internal waves within the ocean. The necessary conditions for this application of remote sensing are tied to the Inherent Optical Properties (IOP) of the water and to the local concentration (layers) of particles within the optical viewing range of remote sensing systems. In this paper, we use a two-stream radiative transfer model to demonstrate that discrete layers of particles (usually phytoplankton) can provide sufficient remotely sensed reflectance to resolve associated subsurface physical features such as the depth of specific layers of optical materials, depth and position of frontal boundaries, and the wavelength and amplitude of nearsurface internal waves. This inversion of remotely sensed optical properties to obtain inlbrmation on physical structure depends on the association of in-water biological, optical, and physical structure (lbr specific examples, see other a~icles in this issue). To understand when the conditions are right for such a visualization of physical properties via biooptical remote sensing, we need to look at the vertical structure of the optical properties in relation to the physical properties. The IOP (Preisendorfer, 1976) govern the radiative transfer in the ocean. They are not directly dependent on the external lighting conditions. These IOP are due to particulate matter, dissolved substances, and water itself. Of these three, it is the particulate matter, primarily the