Gte Government Systems Corporation

Atlantic Richfield Company

Donald A Leonard

Harold E Sweeney

Paul J Titterton

A method and apparatus for remote detection of an oil slick at or near the surface of the water using a combination of two or more ultraviolet lasers and comparing the relative magnitude of the received Raman backscattering signal magnitudes to determine the existence of the oil slick. The use of two different laser frequencies provides for elimination of atmospheric transmission variations and wave modulation.

Technique for the remote detection of sea slicks

A technique for measuring the unknown subsurface temperature T of a bulk transparent medium such as sea water by focussing a high intensity pulsed laser beam in a first direction into the water to a predetermined depth D, producing stimulated Brillouin scattering (SBS) in a second direction opposite to the first direction and generating from the SBS stimulated Raman scattering (SRS) in the second direction, analyzing the spectra of the SRS and determining therefrom the temperature T. The depth D is is selected to insure that the entire SBS pulse is in the water.

Method of remotely measuring subsurface water temperatures by stimulated

A technique for measuring the unknown subsurface temperature T.sub.s of a bulk transparent medium such as ocean water by splitting a pulsed laser beam having a high intensity into two sub-beams, one of which is a probe beam directed into the medium. The intensity of the output beam pulses exceeds a predetermined threshold sufficient to cause stimulated Brillouin scattering within the medium and to produce therefrom a phase-conjugate beam which propagates along the path of the first sub-beam but in the opposite direction. The second sub-beam combines with the PC beam and the combined beams mix at the cathode of a photodetector thereby producing a heterodyne frequency proportional to the temperature T.sub.s. Converts the heterodyne frequency into a temperature value yields the desired unknown T.sub.s.

Remote method of measuring subsurface water temperatures

A technique for measuring the unknown subsurface temperature T.sub.s of a bulk transparent medium such as ocean water by generating a continuous (cw) laser beam and pulsed laser beam both having the same wavelength, with the intensity of the pulsed laser beam exceeding the intensity required to produce stimulated Brillouin scattering in the water. By directing the pulsed laser beam into the water, it causes a return phase-conjugate beam to emanate therefrom. The return phase-conjugate beam and the pulsed laser beam are separated, and the phase-conjugate beam and the cw beam are mixed together thereby producing a heterodyne frequency proportional to the temperature T.sub.s. By converting the heterodyne frequency into a temperature value, yields the desired unknown T.sub.s.

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.

Apparatus for measuring diffuse attenuation coefficient of sea water

A method of remotely measuring the diffuse attenuation coefficient K of ocean water from an airborne platform such as an aircraft. By directing a pulsed laser beam having a wavelength .lambda..sub.0 from the platform into the water, the beam interacts therewith to produce inelastic Brillouin backscatter signals at the wavelength .lambda..sub.1, where .lambda..sub.1 .noteq..lambda..sub.0. The desired backscatter propagate generally oppositely to the direction of propagation of the pulsed laser beam so that the backscatter can be received and collected at the platform. The upwelling optical energy includes the desired backscatter signals, which are separated out from the remainder of the upwelling optical energy. The separated backscatter signals are converted to equivalent electrical signals and periodically analyzed to generate therefrom the diffuse attenuation coefficient of the ocean water at the .lambda..sub.1 wavelength at periodic depths beneath the water surface. In another aspect of this invention both the Brillouin backscatter signals and the Raman backscatteer signals are separately filtered out to simultaneously measure the diffuse attenuation coefficient of the water at two distinct wavelengths. In another aspect of this invention the diffused attenation coefficient K is measured from a submerged platform, such as a submarine. This has the advantage of allowing deep ocean layers to be measured along with ocean water beneath the polar ice cap.

Method of remotely measuring diffuse attenuation coefficient of sea water

Apparatus for measuring the unknown subsurface temperature T.sub.s of a bulk transparent medium such as ocean water comprises a pulsed laser having a high intensity (power per unit area) output beam split into two sub-beams, one of which is a probe beam directed into the ocean water. The intensity of the output beam pulses exceeds a predetermined threshold sufficient to cause stimulated Brillouin scattering within the medium and to produce therefrom a phase-conjugate beam which propagates along the path of the first sub-beam but in the opposite direction. The second sub-beam is reflected by a mirror to and combines with the PC beam and the combined beams are mixed at the cathode of a photodetector which produces a heterodyne frequency that is proportional to the temperature T.sub.s. A frequency measuring instrument converts the heterodyne frequency into a temperature value equal to T.sub.s.

Remote subsurface water temperature measuring apparatus with Brillouin

Apparatus is disclosed for remotely sensing the unknown subsurface temperature T.sub.s of a bulk transparent medium, such as ocean water, using a cw laser beam and a pulsed laser beam. In one embodiment the cw output of a continuous laser is split into two sub-beams. An optical amplifier periodically amplifies the first such sub-beam thereby generating an intense pulsed laser beam having a plurality of pulses with the same wavelength as the cw laser beam. The intensity level of the pulses is sufficient to produce stimulated Brillouin scattering when focussed into the ocean water. The pulsed laser beam is directed into the water thereby generating an intense return phase-conjugate beam propagating along the path of the pulsed laser beam but in the opposite direction thereto. The phase-conjugate beam and the second sub-beam are mixed at the cathode of a photodetector to produce a heterodyne frequency proportional to the temperature T.sub.s. A frequency measuring instrument converts the heterodyne frequency into a temperature value equal to T.sub.s. Since the cw beam in always present at the photodetector for mixing with the return phase-conjugate pulses, the path lengths of the cw laser beam and the pulsed laser beam may be unequal.

The etendue (throughput or area-solid angle product) of a high resolution interferometer is maintained at a substantially high level by use of a transparent chamber defined by a highly reflective internal surface, the chamber being located at the input to the interferometer. The chamber has an input aperture to admit light into the chamber and an output aperture or exit opening to pass light to the interferometer. By integrating the input light through multiple reflections thereof within the chamber until it exits to the interferometer, the etendue of the latter is substantially enhanced.

High resolution interferometer with high etendue

Subsurface waves in an ocean are created by the turbulence in a submarine's wake. These waves can be remotely detected by a search submarine by monitoring subsurface water temperatures using a laser. A pulsed laser beam is directed into the water to at least the depth of the thermocline and an analysis is made of the resultant Brillouin and Rayleigh backscatter components. Wavelength shifted Brillouin scatter is mixed with the unshifted Rayleigh scatter in a self-heterodyne manner for each volume element of illuminated water, and the frequency of the heterodyne signal is measured and converted into equivalent temperature values. This produces the desired temperature-depth profile of the water enabling detection of the first submarine by tracking the internal waves at or near the ocean thermocline.

Method of remotely detecting submarines using a laser

The subsurface temperature of a body of water such as an ocean is measured remotely by directing a laser beam deeply into the water and analyzing the resultant Brillouin and Rayleigh backscatter components. Wavelength shifted Brillouin scatter is mixed with the unshifted Rayleigh scatter in a self-heterodyne manner for each volume element of illuminated water and the frequency of the heterodyne signal is measured. This produces the desired temperature-depth profile of the water.

Apparatus for and method of remotely sensing sub-surface water

Subsurface waves in a body of water such as an ocean caused by a submarine are remotely nonacoustically detected by monitoring subsurface water temperatures using a laser. A pulsed laser beam is directed into the water to at least the depth of the thermocline and an analysis is made of the resultant Brillouin and Rayleigh backscatter components. Wavelength shifted Brillouin scatter is mixed with the unshifted Rayleigh scatter in a self-heterodyne manner for each volume element of illuminated water, and the frequency of the heterodyne signal is measured and converted into temperature. This produces the desired temperature-depth profile of the water enabling detection of internal waves generated by submarines.

A system for rapidly scanning a remote field of regard with transmitter laser beams comprises an optical system having a focal plane, a plurality of lasers capable of being sequentially fired, and a like number of optical fibers coupled at one end to the respective laser outputs. The opposite fiber ends lie in the focal plane of the optical system and are aligned in the direction of the height of the field of regard. The beams move rapidly across the width of the field of regard simultaneously with sequential operation of the lasers, thus illuminating the entire area of interest in a minimum of time.

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Cupertino, CA, United States of America

Donald A Leonard