Apparatus for measuring diffuse attenuation coefficient of sea water

Abstract

Apparatus is disclosed for remotely measuring the diffuse attenuation coefficient K of ocean water from a platform such as an aircraft flying over the ocean. A pulsed laser beam is directed as a probe beam from the aircraft into the water to produce therein Brillouin backscattering signals which emanate back up through the water to the aircraft. An optical receiver in the aircraft receives and processes those backscattered signals. A very narrow optical bandpass filter passes the Brillouin signals to a photodetector, a digitizer and a data processor, the latter being programmed to compute the diffuse attenuation coefficient at predetermined depths and at the Brillouin wavelength. Measurements of the diffuse attenuation coefficient at various depths is accomplished by sampling and digitizing the Brillouin signals at predetermined intervals, each interval corresponding to a depth beneath the surface of the water. A preferred embodiment of the invention features similar apparatus having two signal-processing channels for simultaneously deriving the diffuse attenuation coefficient at two wavelengths by analyzing the upwelling Brillouin (blue) and Raman (green) backscatter generated by the probe beam. An alternate embodiment of the invention features apparatus for measuring the diffuse attenuation coefficient K of ocean water from a submerged submarine.