Abstract: A system and method are described for locating and communicating with miners in an underground mine, in which miners carry a battery-powered signal unit with an impact actuator engagable with a wall, floor, or ceiling surface of the mine to transmit acoustic signals through the ground, and actuate controls on the unit to send a predefined message or a specific message via the impact actuator to ground-coupled acoustic receivers coupled with a base station that includes a decoder to determine the message sent by the miner and a location component to determine the miner's location based on the received signals.

Abstract: A system and method is provided for using acoustical pulses generated from an airborne laser source to locate objects under water. An array of acoustic sensors, such as passive sonobuoys at the ocean surface, is deployed in known or determinable locations by aircraft. Each area surrounded by acoustic sensors comprises a search cell, within which sonar scattering data can be used to locate objects. Following sonobuoy deployment, the aircraft uses the laser to rapidly generate many laser-acoustic pulse sources within each search cell, which in turn generate spherical acoustic pulses traveling through the water. The acoustic sensors receive the acoustic pulses, either on a direct path or on a scattered path after the pulse strikes an underwater object. The sensors record the acoustic signatures of the received pulses and transmit data of the recorded acoustic pulses to a processor such as processor on a nearby ship.

Abstract: A system and method is provided for using acoustical pulses generated from an airborne laser source to locate objects under water. An array of acoustic sensors, such as passive sonobuoys at the ocean surface, is deployed in known or determinable locations by aircraft. Each area surrounded by acoustic sensors comprises a search cell, within which sonar scattering data can be used to locate objects. Following sonobuoy deployment, the aircraft uses the laser to rapidly generate many laser-acoustic pulse sources within each search cell, which in turn generate spherical acoustic pulses traveling through the water. The acoustic sensors receive the acoustic pulses, either on a direct path or on a scattered path after the pulse strikes an underwater object. The sensors record the acoustic signatures of the received pulses and transmit data of the recorded acoustic pulses to a processor such as processor on a nearby ship.

Abstract: A direct-sequence spread-spectrum communications method of de-spreading and decoding received data transmitted through an acoustic channel. A first code match filter is applied to receive data to output a first code impulse response comprising a channel impulse response modulated by a pseudo-random number bit. A second code match filter is applied to the received data to output a second code impulse response comprising the channel impulse response modulated by a message symbol bit. The first code impulse response is correlated with the second code impulse response to output the message symbol bit modulated by the pseudo-random number bit. The pseudo-random number bit is eliminated to identify the message symbol bit, thereby decoding the message symbol bit from the received data.

Abstract: A system and method are described for locating and communicating with miners in an underground mine, in which miners carry a battery-powered signal unit with an impact actuator engagable with a wall, floor, or ceiling surface of the mine to transmit acoustic signals through the ground, and actuate controls on the unit to send a predefined message or a specific message via the impact actuator to ground-coupled acoustic receivers coupled with a base station that includes a decoder to determine the message sent by the miner and a location component to determine the miner's location based on the received signals.

Abstract: Underwater communications apparatus and methods are presented using iterative correlation-based equalization in which initial estimated symbols of a current data block are produced using a correlation-based equalizer (CBE) based at least partially on the received sound transmissions of the current data block and an estimated channel impulse response (CIR) of a previous data block, the CIR of the current data block is estimated using the initial estimated symbols, and re-estimated symbols of the current data block are produced using a CBE based on the estimated CIR, and the estimated symbol having the lowest error is selected as the received data.

Abstract: A system and method is provided for using acoustical pulses generated from an airborne laser source to locate objects under water. An array of acoustic sensors, such as passive sonobuoys at the ocean surface, is deployed in known or determinable locations by aircraft. Each area surrounded by acoustic sensors comprises a search cell, within which sonar scattering data can be used to locate objects. Following sonobuoy deployment, the aircraft uses the laser to rapidly generate many laser-acoustic pulse sources within each search cell, which in turn generate spherical acoustic pulses traveling through the water. The acoustic sensors receive the acoustic pulses, either on a direct path or on a scattered path after the pulse strikes an underwater object. The sensors record the acoustic signatures of the received pulses and transmit data of the recorded acoustic pulses to a processor such as processor on a nearby ship.

Abstract: An underwater communications system includes an antenna array, a sound transmission source for transmitting communication packets, and a receiver including a processor. The processor is programmed for receiving and detecting a Doppler-sensitive probe signal and training sequence, for estimating a channel impulse response function for correlating the received signal to yield a plurality of processed channel outputs, and for summing the channel outputs to yield a common receiver output. The common receiver output is applied to a Decision Feedback Equalizer (DFE) for adaptive correction of the inter-symbol interference and to retrieve the transmitted communication message.

Abstract: A direct-sequence spread-spectrum communications method of de-spreading and decoding received data transmitted through an acoustic channel. A first code match filter is applied to received data to output a first code impulse response comprising a channel impulse response modulated by a pseudo-random number bit. A second code match filter is applied to the received data to output a second code impulse response comprising the channel impulse response modulated by a message symbol bit. The first code impulse response is correlated with the second code impulse response to output the message symbol bit modulated by the pseudo-random number bit. The pseudo-random number bit is eliminated to identify the message symbol bit, thereby decoding the message symbol bit from the received data.

Abstract: An apparatus for processing passive acoustic signals received on a horizontal line array that were either emitted from an underwater object or echo returned from an object, is proposed to track the motion (bearing change and range change) of an object (target) relative to the receiver horizontal line array. Adaptive array processing for a moving object is biased for a moving source when the number of data samples is limited by the stationariness condition. Motion compensation can be carried out in the beam domain by beam shifting for a bearing changing object and frequency shifting for a range changing object. The method includes receiving acoustic signals from the target, determining the beam covariance matrices, determining the target bearing rate and range rate, processing the beam covariance matrices by compensating for the target motion, and producing a beam power plot versus time.

Abstract: The advanced vertical array beamformer signal processor accomplishes acoustic beamforming of an underwater vertical array used in shallow water utilizing matched beam processing to suppress generated noise and/or ship radiated noise thereby increasing the detectability of a submerged source emitting only a low noise signal. The processor exploits the difference of the signal arrival angle of both active and passive signals with that of the wind generated noise and ship radiated noise which is prominent in downward refractive sound speed profiles. After filtering the undesired noise, the processor uses the depth of the source as a clue for detection; the processor is an energy detector focused on the returns of a deep source.

Abstract: The sonar array post processor employs an adaptive processing, known as matched beam processing, in the beam domain which takes analog or digital conventional beamforming outputs from a sonar array, multiplies them by a set of adaptive weighting coefficients and produces a new set of beams. The new output beam of highest intensity yields the ideal maximum signal gain and correct target bearing. Continuous target tracking provided by the sonar array post processor in the endfire direction of a horizontal line array minimizes the towing ships maneuvers and for, a bottom mounted surveillance system, a smaller number of arrays are required.

Abstract: A method and system provide for the sensing of objects under water where the acoustic energy is suitably focused or directed so that reverberation returns are minimized. A vertical source array of adjustable acoustic sources is located in the water body, with each acoustic source producing a separate acoustic pulse or continuous wave controlled by a control device. The control device controls a phase and amplitude of the separate acoustic pulses such that a waveform (combined acoustic pulse) with selective nodes adjustable to a desired depth is emitted. A calibration device is also located at a distance from the source array for calibrating the separate acoustic pulses or continuous wave so that the source array emits a desired waveform. The calibration device includes a checking device for determining whether the emitted waveform conforms to the desired waveform and for calculating a deviation of the emitted waveform from the desired waveform.