Proceedings PaperPredicting Intensity Of Optical Signals Passing Through Substantial Water-Air Paths
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Experiments have been performed which measure the intensity of an optical signal which originates from a "collimated" underwater light source. A narrow beam (5°) light source was submerged at varying depths up to 16 attenuation lengths (alpha = 2.4 m-1) and pointed in a vertical direction. An optical detector was flown through the beam at altitudes to 3000 feet and pointed downward at the underwater source. The signal intensity measured through a vertical path is found to be in good agreement with the following expression: P e -kD 2 Signal Intensity = o watts/meter (at Airborne Receiver) ir(A tan 0s )2where: k = Diffuse attenuation coefficient (meters) s = Scattering coefficient (meters- 1) D = Water path length (meters) A = Air path length (meters) Po = Transmitter power (watts) Os = Half beamwidth (function of s) The data was obtained under conditions of a calm sea such that wave contributions to spreading appear negligible. Methods are discussed of predicting 0(s) from easily measured parameters.