Abstract: An acoustic wave device with a bent section is disclosed. The acoustic wave device includes a piezoelectric layer and an interdigital transducer electrode on the piezoelectric layer. The bent section is arranged to create a curvature in a waveguide of the acoustic wave device to suppress a transverse spurious mode of the acoustic wave device.

Abstract: A method for using Synthetic Aperture Radar (SAR) to perform a maneuver in a land vehicle is provided. The method includes: receiving digitized radar return data from a radar transmission from a SAR onboard the vehicle; accumulating a plurality of frames of the digitized radar return data; applying a RADON transform to the accumulated plurality of frames of the digitized radar return data and odometry data from the vehicle to generate transformed frames of data for each three-dimensional point, wherein the RADON transform is configured to perform coherent integration for each three-dimensional point, project a radar trajectory onto each three-dimensional point, and project Doppler information onto each three-dimensional point; generating a two-dimensional map of an area covered by the radar transmission from the SAR based on the transformed frames of data for each three-dimensional point; and performing a maneuver with the land vehicle by applying the generated two-dimensional map.

Abstract: Systems and methods for suppressing noise and detecting voice input in a multi-channel audio signal captured by a plurality of microphones include (i) capturing a first audio signal via a first microphone and a second audio signal via a second microphone, wherein the first and second audio signals respectively comprises first and second noise content from a noise source; (ii) identifying the first noise content in the first audio signal; (iii) using the identified first noise content to determine an estimated noise content captured by the plurality of microphones; (iv) using the estimated noise content to suppress the first and second noise content in the first and second audio signals; (v) combining the suppressed first and second audio signals into a third audio signal; and (vi) determining that the third audio signal includes a voice input comprising a wake word.

Abstract: In one aspect, a playback deice is configured to identify in an audio stream, via a second wake-word engine, a false wake word for a first wake-word engine that is configured to receive as input sound data based on sound detected by a microphone. The first and second wake-word engines are configured according to different sensitivity levels for false positives of a particular wake word. Based on identifying the false wake word, the playback device is configured to (i) deactivate the first wake-word engine and (ii) cause at least one network microphone device to deactivate a wake-word engine for a particular amount of time. While the first wake-word engine is deactivated, the playback device is configured to cause at least one speaker to output audio based on the audio stream. After a predetermined amount of time has elapsed, the playback device is configured to reactivate the first wake-word engine.

Abstract: A survey system and method to improve one or more of survey quality, efficiency, and utility for example by utilizing a vessel mounted MBES and a selected survey plan to check sound speed(s) via eliciting echoes from reflectors in colocated groups of reflectors using multi-perspective ensonification.

Abstract: A sonar assembly is provided including at least one transducer configured to transmit one or more sonar beams into an underwater environment, a gyroscope configured to measure angular velocity associated with the at least one transducer, a processor, and a memory. The memory including computer program code configured to, when executed on the processor, cause the processor to determine orientation data associated with the at least one transducer based on the angular velocity measured by the gyroscope, determine if the orientation data corresponds to the at least one transducer being in a desired orientation, and cause an alert in response to the at least one transducer not being in the desired orientation.

Abstract: A survey system including a multibeam echo sounder having a projector array and a hydrophone array in a Mills Cross arrangement uses a multi-component message to ensonify one or more fans to estimate a Doppler velocity.

Abstract: An acoustic wave device with a bent section is disclosed. The acoustic wave device includes a piezoelectric layer and an interdigital transducer electrode on the piezoelectric layer. The bent section is arranged to create a curvature in a waveguide of the acoustic wave device to suppress a transverse spurious mode of the acoustic wave device.

Abstract: A survey system including a multibeam echo sounder having a projector array and a hydrophone array in a Mills Cross arrangement uses a multicomponent message to ensonify one or more fans to estimate a Doppler velocity.

Abstract: An ultrasound inspection apparatus of the present invention includes: a probe provided with a plurality of elements; a transmitter configured to transmit the ultrasonic beam to an inspection object using the probe; a receiver configured to receive an ultrasonic echo signal from the inspection object; a sound velocity determiner configured to determine a sound velocity value inside the inspection object; and an element data processing section configured to generate a piece of second element data from at least two pieces of first element data using the sound velocity value, the piece of second element data corresponding to any of the at least two pieces of first element data, the sound velocity determiner being configured to obtain an optimum sound velocity value by optimizing the sound velocity value which is used when the piece of second element data is created in the element data processing section.

Abstract: The invention provides an analysis system for Doppler ultrasound image includes: a capture device, a processing device, and an output device. The capture device obtains a plurality of Doppler ultrasound images. The processing device arranges the color value in each pixel of the images based on the time domain, and obtains a reference sequence through a referencing method, furthermore performs a clustering method to obtain a plurality of correlation coefficient values, then uses a clustering and noise reducing method to classify into a primary pulsatile signal, a secondary pulsatile signal, and a noise signal, finally annotates the primary pulsatile signal, a secondary pulsatile signal, and a noise signal with different color values, respectively. The output device displays a plurality of visualized pulsatile ultrasound images for visualization.

Abstract: Systems and methods for detecting and estimating parameters for a phase-modulated signal in a continuous manner with near-optimal performance. The methods generate these estimates using streaming (or on-the-fly) calculations and so are suitable for hardware-based implementation. These estimates can be used as part of standard pulse descriptor words for radar and other pulsed or continuous signals that are reported by an electronic warfare receiver to a processing and display system. Also, the methods can be computed using sub-sampling methods in order to reduce overall computations.

Abstract: Methods, apparatuses, and computer program products are provided for producing a 3D image of an underwater environment. 2D sonar return data that defines an angle and distance value may be taken from a theoretical 2D slice of the underwater environment. Multiple sets of 2D sonar return data are taken from corresponding 2D slices of the underwater environment during travel. The multiple sets of 2D sonar return data can be inputted into a 3D point cloud/matrix based on the distance value and angle and the corresponding 2D slice associated with each sonar return. The 3D point cloud/matrix can then be processed to determine a cluster of sonar returns that correspond to the bottom surface. Additional filtering may be performed and the bottom surface can be reconstructed to form a 3D image for display to a user.

Abstract: The systems and methods described herein relate to an improved stretchable hose apparatus which enables the transmission of high-throughput signals along several conductors within a conductor cable. In particular, the stretchable hose enables consistent high speed communications and high power transmission between a buoyant object and an optional underwater device in all weather conditions by permitting compression of the conductor cable in a first range of hose extensions and limiting elastic elongation of the conductor cable in a second greater range up to full hose extension.

Abstract: A carrying device for a side-scan sonar, including a suspension rod, a hanging rack, and a flange. The side-scan sonar is in fixed connection to the lower part of the hanging rack. The suspension rod includes a suspension unit, a universal joint, and a tension rod. The flange is disposed below the lower part of the tension rod. The hanging rack includes a Z-shaped main cross beam. Two U-shaped hooks are disposed at two ends of the Z-shaped main cross beam for supporting the side-scan sonar. A vertical drag hook is disposed in the inner side of each of the two U-shaped hooks for hanging the side-scan sonar. The flange is fixed in the center of the Z-shaped main cross beam.

Abstract: Sonar devices for detecting underwater objects are provided whereby a set of angled ultrasound transducers are employed to sense ultrasound signals from a plurality of different spatial regions. The angled ultrasound transducers may include a first pair of side-viewing ultrasound transducers and a second pair of ultrasound transducers configured for interrogating forward and reverse directions. The ultrasound signals from the set of angled ultrasound transducers may be processed to identify the presence of underwater objects in each spatial region, and the resulting identified underwater objects may be displayed, on a per-region basis, on a user interface. The ultrasound signals may additionally or alternatively be processed to generate a topographical model of the bed surface, and to generate a topographical surface image based on the three-dimensional topographical model. The topographical surface image may be displayed as a fly-over animation.

Abstract: System and methods for compensating a depth signal for a depth finder of a boat. In one embodiment, a compensation system is implemented between the depth finder and a transducer mounted on the boat. The compensation system receives a depth signal (i.e., a plurality of electrical impulses) from the transducer that directs sound waves toward the bottom of a body of water. The compensation system also monitors a change in elevation of the transducer, such as due to waves rocking the boat. The compensation system then compensates the depth signal based on the change in elevation, and provides the compensated depth signal to the depth finder.

Abstract: The systems and methods described herein relate to a device which enables oceanographic surface buoy mooring systems to detect and monitor underwater noise at most sea state and weather conditions. In particular, the systems and methods described herein provide mooring systems that can support a hydrophone or other underwater listening devices connected to a surface buoy located at a deep sea position. As will be more fully described below, the mooring includes an expandable tether cable/hose that reduces noise generated underwater when the buoy moves in response to wave and weather.

Abstract: The systems and methods described herein relate to a device which enables oceanographic surface buoy mooring systems to detect and monitor underwater noise at most sea state and weather conditions. In particular, the systems and methods described herein provide mooring systems that can support a hydrophone or other underwater listening devices connected to a surface buoy located at a deep sea position. As will be more fully described below, the mooring includes an expandable tether cable/hose that reduces noise generated underwater when the buoy moves in response to wave and weather.

Abstract: A system for an adaptable aperture planar array for maintaining source resolution is provided. The system includes a first nested array defining a first aperture responsive to a first range of frequencies. The first aperture is sized based on an angle between the array and the source, and includes a first subset of sensor elements. The system includes a second nested array defining a second aperture responsive to a second range of frequencies that is less than the first range of frequencies. The second aperture is sized based on the angle between the array and the source, and includes a second subset of sensor elements. The first aperture and second aperture change in size as the angle changes, which results in a change in the sensor elements within the first subset and the second subset to maintain the source resolution for the array.

Abstract: A system and method for forming acoustic beams is disclosed. One embodiment is an acoustic system configured to generate a plurality of beams non-orthogonal to a transducer array simultaneously with a vertical acoustic beam orthogonal to the array. The acoustic system includes a plurality of transducer elements arranged to form a two-dimensional array and electrically connected into rows in a first dimension and columns in a second dimension.

Abstract: The invention concerns a method for reproducing spatial impression of existing spaces in multichannel or binaural listening. It consists of following steps/phases: a) Recording of sound or impulse response of a room using multiple microphones, b) Time- and frequency-dependent processing of impulse responses or recorded sound, c) Processing of sound to multichannel loudspeaker setup in order to reproduce spatial properties of sound as they were in recording room, and (alternative to c), d) Processing of impulse response to multichannel loudspeaker setup, and convolution between rendered responses and an arbitrary monophonic sound signal to introduce the spatial properties of the measurement room to the multichannel reproduction of the arbitrary sound signal, and is applied in sound studio technology, audio broadcasting, and in audio reproduction.

Abstract: This invention concerns the field of passive sonar systems simultaneously processing several linear antennas. This invention includes a method to eliminate ghost sources for a passive sonar having at least two linear antennas A and B, the method including: An initial acquisition step during which the signal received is measured at different moments ti, and for each antenna, the Doppler frequency f of the signal received is determined, as well as the potential values of the azimuth ? of the source; A second step of determining the potential values of the source performed by use of the measured azimuth ? frequency f values; A third step of eliminating ambiguity and rejecting ghost sources during which it is determined, for which of the potential sources, the speed and frequency values will satisfy, for each moment ti, the measurement equations linking the frequency of the signal received to the frequency f0 emitted by the source, at the source speed and position.

Abstract: A method of automatically performing a patch test for a sonar system is disclosed, where data from a plurality of overlapping 3D sonar scans of a surface as the platform is moved are used to compensate for biases in mounting the sonar system on the platform.

Abstract: A method of automatically performing a patch test for a sonar system is disclosed, where data from a plurality of overlapping 3D sonar scans of a surface as the platform is moved are used to compensate for biases in mounting the sonar system on the platform.

Abstract: A method and system for synthetic aperture sonar provide improved position estimates of a receive array as in moves through a body of water.

Abstract: The present information comprises the stages of: applying frequency analysis to positional information on a platform, generating virtual positional information on the platform based on a frequency analysis result; extracting a signal based on the generated virtual positional information; and performing a synthetic aperture processing based on the extracted signal, and in this manner, even if the positional information lacking in precision and inaccurate is used, the shake compensation of the platform in the synthetic aperture processing system can be effectively performed.

Abstract: In an underwater acoustic bearing sensor, the vector sensor, heading sensor, and pitch and roll sensor are held in a common mounting ring to ensure that their coordinate systems are collinear. The vector sensor includes x, y, and z accelerometers mounted in the ring and a hydrophone that can be mounted independently.

Abstract: A quantitative echo sounder includes delay circuits, phase correction circuits, an incidence angle calculator and a directivity correction unit. The delay circuits adjust transmission start timing or phases of acoustic waves radiated by individual vibrating elements based on pitch and roll angles measured by a motion sensing device so that the direction of an acoustic axis of a transmitting beam matches a sounding direction. The phase correction circuits adjust phases of received echo signals based on the pitch and roll angles so that the direction of an acoustic axis of a receiving beam matches the sounding direction. The incidence angle calculator calculates echo signal incidence angle with respect to the sounding direction from phase differences among receiving beam signals obtained by four vibrating element groups. The directivity correction unit corrects a measured target strength by using the echo signal incidence angle calculated by the incidence angle calculator.

Abstract: The disclosure relates to a signal processing method for a towed linear antenna, notably to resolve right-left ambiguity, said antenna comprising a set of hydrophone multiplets each with n?3 hydrophones spread over a straight section of the longitudinal axis of said antenna, wherein the roll angle of each multiplet relative to the vertical is measured, the signals of said hydrophones and said roll angles are used to synthesize p?3 linear sub-antennas, then M azimuth channels are formed with each sub-antenna and 2 adaptive right-left channels are formed from said p sub-antennas for each direction corresponding to each azimuth channel. The invention resolves right-left ambiguity with optimal performance in detection and for long antennas.

Abstract: A synthetic aperture side looking sonar system which includes an array of active elements, which provide output signals in response to acoustic reflections received from a target area, during travel over the target area. The array has a first section of elements, the output signals of which are used to obtain target information. The array additionally has a second section, including space apart transducers, the output signals of which are used exclusively to determine yaw and sway of the system, as it travels over the target area. Signal processing circuitry, using displaced phase center principles, is provided, and is responsive to the element output signals to derive yaw and sway correction signals for synthetic aperture beam formation.

Abstract: The disclosure relates to a signal processing method for a towed linear antenna, notably to resolve right-left ambiguity, said antenna comprising a set of hydrophone multiplets each with n≧3 hydrophones spread over a straight section of the longitudinal axis of said antenna, wherein the roll angle of each multiplet relative to the vertical is measured, the signals of said hydrophones and said roll angles are used to synthesize p≧3 linear sub-antennas, then M azimuth channels are formed with each sub-antenna and 2 adaptive right-left channels are formed from said p sub-antennas for each direction corresponding to each azimuth channel. The invention resolves right-left ambiguity with optimal performance in detection and for long antennas.

Abstract: A free-floating altitude stabilized system is provided. Independently energizable wire coils are linearly aligned with one another in a vertical direction on a buoyant body. An induced magnetic field is generated by any of the wire coils that are energized. A float housing a magnet is coupled to the body in such a way that it is capable of independent movement relative thereto. A control system energizes a selected one or more of the wire coils in such a way the magnet's magnetic field and wire coil's induced magnetic field react with one another to generate movement of the float vertically in a direction that is the same as a vertical component of wave motion.

Abstract: A free-floating altitude stabilized system is provided. Independently energizable wire coils are linearly aligned with one another in a vertical direction on a buoyant body. An induced magnetic field is generated by any of the wire coils that are energized. A float housing a magnet is coupled to the body in such a way that it is capable of independent movement relative thereto. A control system energizes a selected one or more of the wire coils in such a way the magnet's magnetic field and wire coil's induced magnetic field react with one another to generate movement of the float vertically in a direction that is the same as a vertical component of wave motion.

Abstract: In a surface acoustic wave resonator in which an interdigital transducer is formed on a piezoelectric substrate with apodization based on cross lengths of electrode fingers and the inside face of each bus bar is not parallel to a group velocity direction of a surface acoustic wave excited on the interdigital transducer, reflector electrode fingers and excitation-area electrode fingers are disposed to provide relatively shifted positioning therebetween in the group velocity direction of the surface acoustic wave or a distance between the periphery of an excitation area and the inside face of each bus bar is limited within a predetermined range.

Abstract: The depthimeter comprises a heave sensor, a mean path compensator and a combiner. The mean path compensator comprises a ranging device which measures the instantaneous distance of the vehicle from a fixed point on the vehicle to ocean surface as a function of time; a range compensator to compensate for signal dropouts in the ranging devices data, for sensor offset angle, and vehicle pitch and roll, thereby providing a signal that contains the vehicles vertical motion and the vertical motion of the sea surface. A low-pass filter within the mean path compensator eliminates the components of the resulting signal due to the motion of the sea surface and the high frequency components of the vehicle's vertical motion, thereby producing a signal that is the mean path of the vehicle, referenced to mean sea level.

Abstract: A method of correcting errors in in inertial navigation system, without imposing restrictions on the ships course, utilizing bathymetric data collected during the Ocean Survey Program (OSP). As the ship is in transit in or crosses an OSP swath, sonar transmissions commence and continue only to acquire bottom data within data areas of predetermined dimensions. Depth gates and transmission power levels are established in accordance with OSP provided bottom data and depth is determined by an autocorrelation process. A virtual linear map is established with the OSP data in the predicted locations of data collection areas. The collected data is then compared to corresponding OSP data to determine inertial navigation system corrections.

Abstract: An improved bottom cable for a seismic marine data acquisition system 10. The bottom cable 30 includes a cable section 30b having a bus 48. The cable, along with the cable section and bus, are used to electrically connect a master control unit 40 to first and second modules 32b and 32c, respectively. The bus 48 includes first and second switches 48b and 48c, respectively, located near opposite ends of the bus. In this way, if a leak R1 occurs in the bus, the first and second switches can be opened, thereby electrically isolating the bus and stopping the leak.

Abstract: An apparatus and method for beamforming for a toroidal volume search sonar. onar array vehicle motion is used to reduce reverberation by fixing beams geometrically in space to prevent beam contact, prior to a specified range, with the sea surface or sea bottom interfaces. Reverberation is further reduced by creating a composite beam from one scanned beam containing the target dominated by surface reverberation and another dominated by bottom reverberation. A correlation and averaging procedure is applied to the two scanned beams to further reduce the reverberation in the composite beam. To further reduce reverberation, the two beams selected for correlation and averaging processing are chosen such that the number of common elements associated with the two beams is a minimum within a given angular separation.

Abstract: A method for compensating for lateral distortion in a moving linear array using a frequency domain beamformer, comprising the steps of measuring the instantaneous lateral distortion of the linear array at discrete points along the array, corresponding to array element locations, calculating a shading weight for each of the discrete points along the array, corresponding to array element locations based on the instantaneous lateral distortion at each said point and calculating the compensated beam magnitude by multiplying said shading weight into the frequency domain beamformer equation.

Abstract: A method is provided for measuring the acoustic backscatter property of the floor of a body of water in which an acoustic multibeam echosounder employed on a ship is used to measure the sonic backscattered from a narrow transmission target strip on the sea floor that extends essentially vertically beneath the center of the transmitting antenna, transversely to the travel direction of the ship and which is successively exposed to sonic pulses by the transmitting apparatus. The measured backscatter is converted into sonic backscatter values allocated to receiving strips (115) of the multibeam echosounder. Calibration curves are constructed for all floor elements along the course line of the ship by echosounder measurements during a calibrating operation following a 90.degree. pivot of the echosounder around the vertical axis of the ship.

Abstract: A forward looking echosounder uses a non-scanning forward looking transducer inclined from the horizontal at a 45.degree. angle. The forward looking transducer produces a set of acoustic data signals indicative of echo signals received along the central axis of the sonic beam as produced by the transducer. Distance and depth coordinates are used in conjunction with vessel speed and pitch angle to determine where the source of the received echo is located relative to the moving vessel. This information is then displayed in a quasi-real time display format.

Abstract: A magnetic heading sensor alignment and roll reducing device is provided. A enerally cylindrical assembly has a first end and a second end. Each end has a plurality of grooves located equiangularly on a circle with the center thereof located at the cylindrical assembly's center longitudinal axis. Bearings, positioned at and supported by the first and second ends, support a magnetic heading sensor at either end thereof. The bearings provide the sensor with rotational freedom about the center longitudinal axis. A counterweight is affixed to the sensor such that its center of gravity and the sensor's center of gravity are located at a common axial loci. A plurality of longitudinal spring strips are provided to fit into corresponding ones of the grooves on the first and second ends of the cylindrical assembly. The spring strips cooperate with the inner surface of a tubular housing when the device is inserted therein. All materials used to construct the device are non-magnetic.

Abstract: Ship's attitude parameters, including pitch, roll and heading, provided in he form of synchro signals by redundant sensors, are distributed to various shipboard systems by a synchro selector binary switching tree under the control of a digital processor. The processor also generates dynamic simulations of pitch, roll and heading, which can be distributed to the shipboard systems by the switching tree.

Abstract: A sonar buoy 40 has narrow-beam sonar heads 80, 82 driven by a stepper motor 84. The heads produce sonar data for example accurately measuring the seabed. The buoy is handled by a crane wire 41 held taut by a float above the buoy and attached to a clump weight 46 resting on the seabed (although shown in retracted condition). A wire 50 runs from a winch 48 around pulleys 52 on the weight 46 and is connected to a lever 54 of a gimbal mechanism 56 which has two transducers 62, 70 giving measurements of the "X" position and the "Y" position of the buoy. A footage mechanism 76 is driven by the wire 41 and has a transducer giving a measurement of the heave position. A compass 88 and roll and pitch transducers at 86 give measurements of the heading position and the roll and pitch positions. The sonar data is compensated for the position of the buoy using a computer.

Abstract: For suppressing reflections of an acoustic reception signal at a transmitting/receiving ultrasound transducer, the ultrasound transducer is connected to a compensation circuit which supplies the ultrasound transducer with a compensation transmission signal during reception, which has a waveform similar to the acoustic reception signal, but with a polarity opposite that of the acoustic reception signal. A summing stage is connected in a reception channel of the ultrasound transducer, the summing unit having a first input supplied with a compensated reception signal, formed by a combination of the acoustic reception signal and the compensation transmission signal. A second input of the summing unit is connected to the compensation circuit, which supplies a signal at the second input which removes the contribution made by the compensation transmission signal from the compensated reception signal, so that the output of the summing unit generates a reception signal devoided of the compensation transmission signal.

Abstract: A transducer apparatus for marine pleasure craft employs only gravity-induced forces to always orient its electroacoustic transducer in a downward direction or other predetermined direction. The apparatus mounts on the transom or hull of a pleasure craft, and includes a housing having a smoothly shaped exterior to permit laminar water flow past it. The housing has an internal cavity of preferably spherical shape in which a transducer assembly is mounted. The assembly includes an electroacoustic transducer and a transducer support structure that allows the transducer to move freely on account of gravity about a center of rotation in at least two orthogonal directions as the craft pitches and/or rolls. The transducer assembly is preferably constructed to have an overall specific gravity about equal to that of the liquid so it essentially floats in the liquid.

Abstract: A motion dampening device is described that is efficiently and conveniently ackaged with sonobuoy components to reduce the effects of vertical motion caused by surface waves or internal buoyant forces. A plurality of spring steel spokes connected by sections of thin plastic sheet are fitted around a central core around a first-deployed element. As this element is packed, prior to deployment, the spokes and plastic sheet are wrapped around the core. Upon deployment, the stored spring forces push open to their extended positions and spread the plastic sheet, thereby impeding vertical motion of the element and reducing effects of flow noise on a sensor hanging therefrom.

Abstract: A method and apparatus for compensating sensitivity fluctuations in signals received from respective groups of hydrophones for the purpose of subsequent signal processing, the groups being arranged in a predetermined sequence (0, 1, 2, . . . i) to form a transducer arrangement, wherein the received signals are influenced by the sensitivity of the hydrophones and/or the gain of preamplifiers connected to the outputs of the hydrophones. The energy value (W.sub.i) for the received signals of each group of hydrophones is determined and a median energy curve (W.sub.m (.theta.)) is derived from the energy values (W.sub.i) as a function of the sequence of the groups of hydrophones. A correction value is formed for the signals received from each group of hydrophones from a comparison of the respective energy value (W.sub.i) with the energy curve (W.sub.m (.theta.)) and the received signals are corrected with the correction value.

Abstract: A floating sensor system is provided to detect very low frequency pressure ignals (down to 0.01 Hz). This system detects pressure fluctuations or pressure signals of interest in the ocean or other body of water in the presence of unwanted pressure signals generated by surface wave induced motion. A drifting sensor surface float follows the surface waves and in turn moves a suspended pressure sensor vertically, such that it detects the wave motion as a change in static pressure which then constitutes a noise source. A correlation circuit and a logic circuit discriminate between a first composite signal, comprised of the pressure signals of interest and wave motion noise, and a second reference signal, comprised only of the wave motion noise to provide an output signal transmitted to a monitoring station.