The radiance N, resulting from an initially narrow collimated beam, propagating in the ocean, is investigated with the aid of the small-angle-scattering theory of electron scattering. The resulting expression for N is calculated approximately and compared both with experiments and numerical calculations. Various properties of the approximate expression for N are explored; an observer, located off the axis of the beam at an axial distance z from the source, who attempts to determine the direction to the source by seeking the maximum of N with respect to ray direction, would sight a point on the beam axis at a distance z/3 from the source.
© 1972 Optical Society of America
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