Photons emitted by a narrow laser beam are followed through multiple scattering events in the ocean until registered by a detector at the source position. A realistic ocean model is used which takes account not only of molecular scattering (Rayleigh) and absorption, but also scattering and absorption by the hydrosols (Mie). The single scattering function for the hydrosols is calculated from Mie theory assuming a relative index of refraction of 1.15 and a size distribution with a modal radius of 3 μ. Targets with various surface albedos (A) are introduced at various distances from the source. The three-dimensional path of the photons is followed by a Monte Carlo technique. When A ≥ 0.02 the returned flux per unit photon path length from the targets is greater than the background from the laser beam for any target distance. The returned flux is plotted as a function of the photon path length. In practice the detection distance is limited by the lowest flux that can be detected and the background of natural light. Inhomogeneities in the optical properties of the ocean can also be measured in this way.
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