Abstract: A platform borne sonar system for the detection of targets includes a transmitting projector suspended beneath the water surface from a platform for generating a virtual parametric acoustic array in a water column, forming a beam of acoustic energy. The beam is scannable in azimuth to steer the direct beam in particular directions. A plurality of detectors are arranged to receive the acoustic energy scattered or reflected from any submerged objects present in said direct beam, wherein one or more of the detectors are located the of said direct beam for bistatic reception of the beam reflected off the target. A detector may be suspended beneath the projector for monostatic reception. The direct beam may be scannable in elevation. The direct beam may be narrower vertically than horizontally.

Abstract: A sonar system for use in a water body includes a projector on the bottom of a water body for generating and transmitting a direct beam of acoustic energy. A receiving array is immersed in the water body outside the direct beam for detecting reflections from an target in the direct beam. The receiving array may be a horizontal or vertical linear array of hydrophones in the water body. The array of hydrophones may have output signals coupled to an A/D convertor and a multiplexor for digitizing and multiplexing the signals to prepare for transmission and analysis of the signals. A pair of separated projectors on the bottom of the water body may generate parametric acoustic arrays for transmitting direct beams of acoustic energy through the water body towards each other. A receiving array immersed in the water body outside the direct beams detect any reflections from an object in the acoustic beams.

Abstract: Method and apparatus for changing the bit rate of a digitized analog signal stream from a first bit rate to a second bit rate. A first sequence generator provides a digital predictor sequence clocked at the first bit rate. A combiner has an output providing a combined digital stream at the first bit rate, combining the digital predictor sequence at the first bit rate and the digital analog signal stream at the first bit rate. An adaptive processor has its input coupled to at the output of the signal combiner. The adaptive processor has variable weights which are responsive to an error signal, an output providing a processed combined digital stream having a bit rate responsive to the weights, and an error signal input port. A second sequence generator provides the same digital predictor sequence, but clocked at the second bit rate.

Abstract: A system for secure communication between transmitting and receiving devices in a laser communications system using pulse position modulation, has a transmitter means to modulate and a receiver means to demodulate a transmission utilizing a protocol in which a number N (N.gtoreq.1) of optical pulses represents each symbol to be transmitted. A transmission is initiated with a trigger event. Thereafter, a multi-pulse synchronization signal is transmitted as the first symbol of each transmission, the first pulse of said synchronization symbol being transmitted within a first time frame after said trigger. A buffer in said receiver receives and stores the first of said N frames of said synchronization symbol. Each subsequently received frame of said N frames of said synchronization symbol is added to data previously stored in said buffer. A frame template is calculated from the stored pulse data of said first N pulses in said buffer and from said synchronization symbol protocol.

Abstract: A container providing environmental protection to electronic equipment includes a four sided frame, a front cover, and a rear cover. An exhaust fan is mounted on the rear cover and an air filter is mounted on said front cover to allow air to flow through the container. A viewing port is mounted on the front cover. A first door covers the viewing port. An access port on the front cover for allowing manual access to the electronic equipment. A set of elastic flaps is mounted on the cover covering the access port. A second door covers the access port.

Abstract: A narrow passband, reflective optical filter at a wavelength L, has a container filled with a pressurized gas, the pressurized gas having a ground state transition corresponding to the wavelength L and transparent to all other wavelengths. The container has at least one optically transparent major planar surface serving as the face thereof, whereby incoming broadband light is absorbed by the gas, except at its resonance wavelength L, which is specularly reflected. The optically transparent face of the container optionally has a broadband anti-reflective coating to improve its out-of-band rejection of unwanted wavelengths of the light signal.

Abstract: Spectrally pure optical radiation (SPOR) such as laser radiation is effectively distinguished from broadband optical radiation such as sunlight and herein called radiation of unknown spectral purity (RUSP) by apparatus including an etalon, which apparatus determines balance or unbalance between the respective portions of a signal incident on the etalon that are reflected by and transmitted through the etalon. Unbalance between the two signal portions indicates the presence of SPOR. The intensities of the reflected and transmitted radiation are compared and a determination of inequality or unbalance indicates SPOR whereas equality or balance indicates spectrally impure radiation. Measurement of the sum of the intensities of the reflected and transmitted radiation also provides an estimate of the angle of incidence of RUSP on the etalon.

Abstract: A method for remotely measuring an unknown temperature Ts of a transparent medium by comparison with the known temperature Tr of a transparent reference material consisting of the steps ofcombining the outputs of a continuous-wave (CW) laser and a high intensity pulsed laser to form a combined laser output beam, wherein the high intensity pulse component of the output beam exceeds the intensity required to produce stimulated Brillouin scattering (SBS) in the transparent medium;splitting the combined laser output beam into first and second sub-beams;amplifying the CW components of the first sub-beam to an intensity exceeding the intensity required to produce stimulated Brillouin scattering (SBS) in the reference material while simultaneously suppressing the pulse components in the first sub-beam;directing the first sub-beam with the amplified CW component into the reference material and thereby generating a CW phase-conjugate beam;directing the second sub-beam into the transparent medium and generating a pulse

Abstract: Apparatus for detecting sonar signals embedded in noise includes a neural network trained to detect signals in response to the slope of amplitude rank ordered noise corrected powers. A detector detects an analog waveform. Means samples and digitizes the analog waveform to obtain digital samples which in turn are passed through a cosine window. The digital samples are Fourier transformed into conjugate sets of complex numbers representing amplitude and phase. One conjugate set of the complex numbers are discarded, and the remaining complex numbers ranked according to frequency. The sum of the square of the real and imaginary component of each of the remaining complex numbers in a frequency band are provided to obtain a corresponding series of representing estimated power ranked by frequency over the band. The noise contained in subbands of the band is estimated.

Abstract: A drilling jig for holding cutting chips and other debris has two separable sections. A cylindrical body has one closed end and one open end. A circular cap is adapted to fit in or over the open end of the cylindrical body. Aligned axial holes are provided though the closed end of the cylindrical body and through the cap. An adhesive layer temporarily adheres the jig to a workpiece.

Abstract: A tracking system to enable a tracking telescope follow a light source, utilizes an atomic resonance filter positioned in close proximity to said telescope, and imaging optics positioned between the light source and the atomic resonance filter. The atomic resonance filter is positioned such that light signals from the light source pass through the imaging optics and are focused in a region within its interior. A plurality of optical sensors are positioned to detect re-emitted light signals from the atomic resonance filter. The optical sensors convert the detected re-emitted light signals to electrical signals proportional to the intensity of said re-emitted light signals. The telescope is repositioned by using these differences in electrical signals to equalize the re-emitted light signals detected by each of the optical sensors, thereby pointing the telescope directly at incoming light from the light source.

Abstract: A transition includes a sheet of dielectric material having two parallel surfaces. A tapered recess in one surface converges towards the other surface with the axis of the recess orthogonal to said surface. The dielectric material has a critical angle of reflection with respect to the axis.A RF horn is located in proximity to the surface with the recess and has an axis in common with the axis of the tapered recess. A RF lens is located between the horn and the tapered recess. The optical properties of the RF horn, RF lens, tapered recess, and dielectric material are such that all rays traced from the horn through the lens and dielectric material to the second surface have an angle with respect to said normal of the second surface greater than said critical angle. RF energy on the second surface from the center of the horn is in phase with RF energy on said second surface from the edge of said horn allowing a surface wave to be launched on the second surface.

Abstract: A foreshortened log periodic antenna comprising variously configured dipole elements and a tapered feedline is further size reduced with an improved configuration of the dipole with the lowest resonant frequency. By substantially increasing the thickness of that dipole, the overall length of the already size-reduced dipole is further decreased by 8% to 10%.

Abstract: A non-imaging optical telescope having a variable field-of-view utilizes an atomic resonance filter within its non-reflective tube. The atomic resonance filter received incoming light through the aperture of the telescope and re-emits the light to an optical sensor. The field-of-view is a function of the distance of the atomic resonance filter from the aperture. A positioning mechanism is provided to move the atomic resonance filter within the tube, thereby varying the field-of-view.

Abstract: 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.

Abstract: 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.

Abstract: An antenna includes a sheet of dielectric material having two parallel surfaces. A tapered recess in one surface converges towards the other surface with the axis of the recess orthogonal to said surface. The dielectric material has a critical angle of reflection with respect to the axis. A RF horn is located in proximity to the surface with the recess and has an axis in common with the axis of the tapered recess. A RF lens is located between the horn and the tapered recess. The optical properties of the RF horn, RF lens, tapered recess, and dielectric material are such that all rays traced from the horn through the lens and dielectric material to the second surface have an angle with respect to said normal of the second surface greater than said critical angle. RF energy on the second surface from the center of the horn is in phase with RF energy on said second surface from the edge of said horn allowing a surface wave to be launched on the second surface.

Abstract: 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.

Abstract: A method of providing secure tactical communications between a submerged submarine and an airborne platform using a pulse-modulated blue-green laser beam. During an initial acquisition mode, the airborne transceiver sends out a downlink laser beam to the ocean surface and below using a predetermined IFF code to identify the transceiver to the submarine. In the preferred embodiment the transmit optics spread the beam out into an elongated elliptically-shaped pattern to maximize coverage of the search area. When the downlink beam energy is within range of the submarine, an optical receiver on the submarine detects the beam, filters out the background light with a very narrow-band filter, and converts the light pulses to equivalent electrical pulses. A signal processor in the submarine receiver decodes the electrical pulses and verifies the IFF code to prevent the submarine from responding to a laser beam from an unfriendly source.

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.