Abstract: A system for rejecting wind noise at a plurality of sensors includes input logic, a processor and output logic. The input logic receives a signal from each of the plurality of sensors. The processor assigns a weight value to each of the received signals. The output logic derives a wind noise rejected output signal based on a function of the assigned weight values and the received signals.

Abstract: A method and system for processing received sonar signals. The method and system generate bearing data signals based on the received sonar signal. The method and system continuously determine the signal strength of the received sonar signal and also continuously determine the total noise from the received sonar signal in the ocean environment in which the target is located. The method and system provide a sensor gain in response to the determined total noise and the signal strength, and adaptively calculate filter coefficients from the sensor gain and the determined total noise. The method and system also filter the generated bearing data signals using a filter having the calculated filter coefficients.

Abstract: A transducer-based sensor system including a drive signal generator for generating a drive signal, a transducer coupled to the drive signal generator and configured to receive the drive signal, a mixer coupled to the transducer and configured to receive output from the transducer where such output results at least in part from physical movement of the transducer, and a diplexer operatively coupled with an output of the mixer and configured to present a substantially matched output impedance to the mixer over an operative range of output frequencies.

Abstract: A sonar quieting system for a forward-looking sonar array is provided. The sonar quieting system includes a cavitator for forming an envelope, a strut for supporting the cavitator to a marine platform, such as a ship, a forward-looking sonar array mounted to a forward face of the cavitator, and a ventilation system for pumping a gas, such as air, into the envelope to create a gas cavity which envelops the supporting strut and equipment downstream of and during a forward movement of the cavitator.

Abstract: The present invention provides for a method and system for identifying a sonic event of interest within a received audio signal. A sonic event is characterized by a predetermined rate of change in the perceived audio volume, and is associated with the loudness of the audio. The present invention detects a sonic event such as a percussive hit without requiring that the detector be disabled for a fixed time to avoid false triggering. Because the detector is not disabled during the detection process, sonic events occurring in close proximity are easily recognized and not ignored as in some conventional systems.

Abstract: The invention relates to the detection of the position of an object which can be moved along an acoustic-signal conductor of ferromagnetic material, in which an acoustic signal is incoupled in a clocked manner into the acoustic-signal conductor by means of a signal input coupler connected to a signal transmitter, extracted by means of a signal output coupler and the extracted signal is evaluated by an evaluating circuit for generating a signal representative of the instantaneous position of the object, wherein an opposite magnetic field for the magnetic field generated by the acoustic signal is incoupled in each case after the incouplion of the acoustic signal.

Abstract: A noise cancellation system and method for use with a seeker head of a marine vessel are provided according to the invention. The seeker head employs one or more hydrophones that generate one or more output signals. The noise cancellation system includes a plurality of motion sensors. The plurality of motion sensors generate a plurality of noise signals based on a hydrodynamic flow noise caused by the marine vessel and acting on the marine vessel. The noise cancellation system further includes a processor receiving the plurality of noise signals and the one or more output signals and applying an active noise cancellation to the one or more output signals to substantially cancel out the flow noise. The active noise cancellation is based on the noise signal.

Abstract: Acoustic field reconstruction is performed by expanding basis function which represent outgoing and incoming waves, without prior knowledge of the source geometry and dimensions. The reconstruction is based on acoustic pressures measured in the field only, and can be accomplished on a piece-wise basis. There are no restrictions on the locations of measurements. Moreover, the present invention can be used to reconstruct acoustic radiation from a plurality of sources or from a single source surrounded by multiple reflecting surfaces.

Abstract: A system and method are provided for an adaptive filter that is especially useful for sonar signal processing. The beam outputs of a conventional beamformer are provided as inputs to adaptive notch filters in accord with the present invention. The outputs of the plurality of adaptive notch filters are applied to a standard cross correlation process. In each of the adaptive notch filters, the beam outputs are split into two paths and in one path are applied directly to a signal combiner. In the second path, the beam outputs are delayed. The delayed beam outputs are applied to an adaptive finite impulse response filter, the output of which is an estimate of the narrowband interference contained within the beam output. The narrowband interference is then suppressed in the signal combiner prior to application to the standard cross correlation process.

Abstract: The present invention is directed to a method and system for significantly reducing the acoustic noise from near-surface sources using an array processing technique that utilizes Multiple Signal Classification (MUSIC) beamforming and the Lloyd's Mirror interference pattern at very low frequencies. Noise from nearby near-surface sources, such as merchant ships, super tankers, fishing trawlers, seismic profiling platforms, or other sources near the ocean surface can significantly interfere with the detection and tracking of a quiet target-of-interest (TOI) located well below the ocean surface. The present invention reduces the noise of the near-surface sources without degrading the signal level and quality of the TOI. The present invention utilizes a unique application of the MUSIC beamforming process to separate the noise and signal subspace. Next, eigenvalue beamforming is used to reduce narrowband energy in selected frequency bins wherein the near-surface noise is radiating.

Abstract: A method for characterizing degree of phase fluctuation of a signal and a signal processor for accomplishing such characterization, is described, in which a time series of complex data vectors are received, initial spectral processing is accomplished, an estimate of the excess phase rotation is made, and a quantity WSC equal to WSC = [ 1 M ⁢ ∑ i = 3 N ⁢ B ⁡ [ C ⁢   ⁢ Φ i ] L ] is calculated.

Abstract: A novel method and apparatus for signal processing are described which discriminate between signals and noise based on the magnitude of the phase fluctuations. In an embodiment of the invention, the governing equations of the process adaptively change in response to the phase and amplitude characteristics of the signals being received for processing. In an embodiment of the invention, an automatic detection method and apparatus is described which has the capability to alert an operator of the presence of signals having phase fluctuation characteristics which match a set of preset conditions (e.g. small fluctuations, medium fluctuations, or large fluctuations).

Abstract: A method and an apparatus for distinguishing systematic artifacts from noise involves localizing functional noise in the vicinity of predicted functional peaks. The method is particularly relevant to detection and tracking of time-varying signals. An apparatus implementing such an application of the method comprises a detection system (50) which monitors each component of a multi-component periodic signal via its basis repeat unit: a cyclet, of periodicity &tgr;. The signal is digitized and clocked through the system (50) in segments. A cyclet remover (62) subtracts predicted values of previously detected cyclets from the incoming signal segment to produce a residual signal. A cyclet detector (60) uses a sliding window procedure to detect further cyclets in this residual and to measure their amplitude profiles {overscore (b)}(&tgr;) and periodicities (&tgr;).

Abstract: An improved method is provided for operating a continuous wave sonar syst At time of transmission, a plurality of acoustic pulses are transmitted one right after another. Each pulse has a unique frequency and is of a time duration that is approximately one second long. The pulses are characterized by a separation frequency representing a difference in frequency between numerically successive frequencies. However, the pulses are staggered with respect to frequency. In the preferred embodiment, each successively transmitted one of the pulses is separated in frequency from an immediately preceding transmitted one of the pulses by an amount greater than the separation frequency. These multiple pulses seperated in time and in frequency, reduce the effects of frequency speading caused by the medium, resulting in a sonar with enhanced detection performance.

Abstract: A method for determining Doppler shifts and reflectivity data based on wavelet based sodars. Initially, a high powered sodar pulse of sound is transmitted from an antenna into the atmosphere. This pulse of sound consists of a string of concatenated wavelets. The reflected portion of this transmitted pulse is received, amplified and digitized as a string of samples of time correspond to the range of transmission. After sampling for a short time interval to cover the maximum range of sound, the sampled time series is divided into range gates. For Doppler shifts the power spectrum of the sampled time series is calculated and a peak surrounding the frequency of the transmitted sound is observed. From this peak the direction and velocity of the atmosphere at a given attitude is derived. To accurately arrive at a better velocity resolution, replication is used with wavelet coefficients and an inverse wavelet transform.

Abstract: A filter, and method of the filtering, for increasing the signal to noise tio of relatively small and constant amplitude signals in the presence of relatively large and varying amplitude signals. The filter produces a filtered power level a.sub.z proportional to: ##EQU1## where x.sub.i are power realizations of the signal in a selected frequency bin, and i=1, 2, . . . , N, and z is a non-zero real number not equal to -1, 0, or 1, and is preferably positive. For positive z, because filtered power level a.sub.z depends on a sum of (x.sub.i).sup.-z, sum a.sub.z disproportionately favors smaller, more stable, signals.

Abstract: A method for enhancing signal-to-noise ratio and resolution of amplitude stable signals wherein underwater acoustic data is first collected with an array of hydrophones, and then the data is digitally sampled. After producing spectra of sequential time snapshots of the digitally-sampled data, the spectra are beamformed for a single frequency. Next the low resolution beamformer response is deconvolved from the data by use of a calculated beam response pattern for the hydrophone array, so that many high-resolution estimates are created for each time snapshot. Finally, the resulting high resolution estimates are reduced to a single estimate for each spatial bin across all of the time snapshots, and the high resolution, high gain results are displayed.

Abstract: A broadband sonar system is configured to be coupled to a narrow band sonar sensor array having a plurality of sensor groups configured in subarrays. Each of the sensor groups within a subarray is spaced equidistantly from adjacent sensor groups within the same subarray. The sonar system includes a plurality of signal compensation filters, each being coupled to a respective one of the sensor groups for receiving signals from the respective sensor group and weighting the signals to generate respective output signals. The weighting of the signal from a first sensor group having a first SNR is greater than the weighting for the signal from a second sensor group that has a second SNR when the first SNR is greater than the second SNR, so as to maximize the SNR of the array. At least one broadband beamformer is coupled to the signal compensation filters for combining the output signals for determining ranges to targets.

Abstract: An acoustic sensing means such as a microphone or a thin-film sensor is located in a flowing medium. To prevent the sensing of flow generated noise, the sensing means is separated from the flowing medium by at least three stages of shielding. In a preferred embodiment, the sensing means is located within a foam shield which is located in a frame covered by a fabric shield and which is, in turn, located in a second frame covered by a second fabric shield. A spandex fabric is suitable for use in the present invention.

Abstract: A chaotic signal processing system receives an input signal provided by a nsor in a chaotic environment and performs a processing operation in connection therewith to provide an output useful in identifying one of a plurality of chaotic processes in the chaotic environment. The chaotic signal processing system comprises an input section, a processing section and a control section. The input section is responsive to input data selection information for providing a digital data stream selectively representative of the input signal provided by the sensor or a synthetic input representative of a selected chaotic process. The processing section includes a plurality of processing modules each for receiving the digital data stream from the input means and for generating therefrom an output useful in identifying one of a plurality of chaotic processes. The processing section is responsive to processing selection information to select one of the plurality of processing modules to provide the output.

Abstract: A method and system are provided to optimize filtering of compressional wave energy in the wavenumber domain for a given frequency range using a fluid-filled elastic cylinder. The fluid is selected based on its fluid density .rho..sub.i and dilatational wave phase velocity c.sub.i. The selected fluid must satisfy the relationship ##EQU1## for the given frequency range where P.sub.i is the magnitude of the pressure field in the fluid at a point within the fluid defined by a distance r.sub.1 from the cylinder's central longitudinal axis and P.sub.o is the magnitude of the impinging compressional wave, and must control at least one of the breathing wave response, the extensional wave response and the fluid P-wave response.

Abstract: Disclosed is an inverse method for measuring the breathing wave speed in a iquid-filled cylindrical shell. The model used with this method is based on an experimental configuration where a shell is attached to a mechanical shaker at the forward end, which initiates longitudinal wave propagation. The resulting spatial field in the shell consists of extensional and breathing waves. End-mounted accelerometers and force transducers are used to measure the extensional wave speed. Once this is accomplished, transfer functions between five equally spaced hydrophones that are in the fluid and a forward accelerometer are recorded. These data are then combined to yield a closed form value of the complex, frequency-dependent breathing wave speed. The experiment included to validate this method is extremely easy to implement and can be executed in a short period of time.

Abstract: A scheme for filtering noise from a signal, in which the noise fluctuates significantly in phase. The signal is sampled to produce N members of a time series and the phase of each signal extracted in the form of a magnitude and a phaser, i.e. for a time series .vertline.x.sub.1 .vertline.e.sup.i.theta..sbsp.1, .vertline.x.sub.2 .vertline.e.sup.i.theta..sbsp.2, . . . , .vertline.x.sub.N .vertline.e.sup.i.theta..sbsp.N, where .vertline.x.sub.n .vertline. is the magnitude of the nth member of the N time samples, and e.sup.i.theta..sbsp.N the phaser for the nth sample. The phasers are added to form a complex value s such thats=.SIGMA..sub.N=1.sup.N ?Re(e.sup.i.theta..sbsp.n)+iIm(e.sup.i.theta..sbsp.n)!.Phase noise which fluctuates strongly will tend cancel itself in the sum s, whereas phase resulting from a stable signal will tend to reinforce. Thus the scalar .vertline.s.vertline.

Abstract: A cavitation suppressor using acoustic energy to suppress flow field caviion is provided. The suppressor system has a plurality of pressure transducers located along the outer surface of a sonar dome. These transducers are powered through a controller which receives flow data, that is, pressure fluctuations in the flow field and in response operates acoustic arrays located aft of the pressure transducers. The controller provides a sonic impulse having frequency and pulse duration selectant to reduce cavitation in the flow field around the sonar dome.

Abstract: A method for reconstructing the acoustic field on the surface of a vibrating object based on measurements of the radiated acoustic pressure includes solving the Helmholtz equation directly using the expansion of a set of independent functions that are generated by the Gram-Schmidt orthonormalization with respect to the particular solutions to the Helmholtz equation. The coefficients associated with these independent functions are determined by requiring the assumed form of solution to satisfy the pressure boundary condition at the measurement points. The errors involved in these coefficients are minimized by the least squares method. Once these coefficients are specified, the acoustic pressure at any point, including the source surface, is completely determined.

Abstract: A structure-bone sound detector suppresses unwanted signals in a frequency range to be monitored, to enhance the immunity of the detector to false alarms. The output signal from a sound sensor undergoes preprocessing, and is then fed to a pair of comb filters that are connected in parallel. The comb filters have mirror image filtering characteristics. The filtered output signals from the two comb filters are provided to a minimum value stage, which selects the smaller of the two output signals. This selected signal is further processed to detect an alarm condition. With this arrangement, broad band signals of interest will produce approximately the same outputs from each of the two comb filters, and therefore be passed on for further processing. In contrast, a narrow band interference signal will be suppressed by one of the two comb filters, and therefore not selected for further processing.

Abstract: A wireless boundary monitor system used to monitor the integrity of a boundary surrounding an area uses at least two housings having at least one transmitting means for emitting ultrasonic pressure waves to a medium. Each of the housings has a plurality of receiving means for sensing the pressure waves in the medium. The transmitting means and the receiving means of each housing are aimable and communicably linked. At least one of the housings is equipped with a local alarm means for emitting a first alarm indication whereby, when the pressure waves propagating from a transmitting means to a receiving means are sufficiently blocked by an object a local alarm means or a remote alarm means or a combination thereof emit respective alarm indications. The system may be reset either manually or automatically. This wireless boundary monitor system has useful applications in both indoor and outdoor environments.

Abstract: The invention provides a method of suppressing a background noise signal in a sampled noisy voice signal. The method comprises the following steps: digital frequency-domain processing of the noisy voice signal to produce time-domain filtering coefficients, and digital time-domain processing of the noisy voice signal in accordance with the filter coefficients to produce a voice signal in which the background noise signal is substantially suppressed.

Abstract: It is an object of present invention to provide a low-cost photoelectric conversion module in which a signal for compensating noise caused by changes in temperature and variations in power supply is obtained. In the photoelectric conversion module according to the present invention, a first amplifier having an input terminal connected to the anode of a light-receiving element for converting an optical signal into an electrical signal amplifies the electrical signal to obtain an amplified signal. A second amplifier having an input terminal connected to one electrode of a capacitor outputs an amplified signal for compensating noise of the electrical signal amplified by the first amplifier. The other electrode of the capacitor is connected to the cathode of the light-receiving element. The capacitor has a capacitance value equal to the capacitance of the light-receiving element.

Abstract: The narrowband signal revealer comprises a sensor, a baseband generator, an daptive locally optimum processor (ALOP), and a complex signal spectral analyzer. The sensor generates an input signal representative of a tonal signal masked by wideband interference. The baseband generator transforms the input signal into a complex baseband signal. The ALOP processes the complex baseband signal to suppress the interference and generates a complex output signal representative of the tonal signal. The spectral analyzer then analyzes the complex output signal and displays tonal signal power.

Abstract: In an adaptive array beamformer, a spatial beamforming filter is connected to a sensor array for respectively filtering and summing array signals to produce a first filter output containing a target signal that arrives in a specified direction. First adaptive filters provide transversal-filtering the first filter output to produce a second filter output not containing the target signal, using a first error signal by restraining their tap weight coefficients. The array signals are further coupled to subtractors. Each subtractor detects a difference between the second filter output of the corresponding first adaptive filter and the corresponding sensor signal to derive the first error signal. Second adaptive filters provide transversal-filtering the first error signals of the subtractors to produce third filter outputs, using a second error signal, by restraining their tap weight coefficients.

Abstract: A preamplifier and pre-emphasis network is provided having a differential plifier exhibiting common mode noise rejection. The preamplifier is particularly suited for use with a double-sided sensor element and it includes a double-sided, balanced calibration circuit. First and second variable gain buffers are joined to the differential amplifier for preventing current noise degradation at the differential amplifier inputs. A pre-emphasis network is further provided in conjunction with the variable gain buffers for providing balanced differential gain of the sensor element signal. Further elements of the invention provide for high and low pass filtering, and differential buffering of the output signal.

Abstract: An algorithm for detecting and tracking dynamically-related sets of unstable passive sonar signals is disclosed. The algorithm detects, enhances, tracks and displays both stable and unstable passive sonar signals, while organizing them into dynamically-related groups. The algorithm is implemented as part of a general purpose digital computer/peripheral system that performs:power spectrum analysis on the segmented time-waveform from the hydrophone,processing of the spectra for detection and enhancement of the signal by the novel algorithms of the present invention and other methods,formatting and displaying of the detected and enhanced signals.The algorithm of the present invention (the ABT, or Automatic Band Tracking algorithm) detects persistent signals having related features by means of correlation and enhances by mathematical integration (or smoothing) of the detected signals.

Abstract: A control system which enables a diver to electronically switch between voice operated (VOX) operation and push-to-talk (PTT) operation by actuation of the existing momentary contact PTT switch used in most diver communication systems. A counter and multivibrator arrangement is employed to alternate between PTT and VOX modes in response to a pair of quick depressions of the PTT switch within a pre-determined time. An audio tone having a duration which identifies which mode of operation has been enabled is also generated and is available for input to the diver's earphone amplifier. The control system includes a frequency selective VOX enabling circuit which takes advantage of the repetition of vowel pitch pulses found in human speech. The circuit continually locks onto these pulses when they last for a few cycles but ignores noise (as found in diving masks) which has only random spikes without the periodic repetition of vowel frequencies in speech.

Abstract: Apparatus for processing a broadband signal, 1.2, 2.2, by determining the first and second moments of variation between frequency sub-bands, 1.4, 2.4, of the broadband signal, 1.2, 2.2, in order to either distinguish between man made objects and natural objects or detect shadows comprising splitters, 1.3, 2.3, which comprise analogue or digital filters, for separating the broadband signal into a plurality of frequency sub-band signals, 1.4, 2.4, detectors means, 1.5, 2.5, for processing each of the frequency sub-band signals, 1.4, 2.4, to either extract, identify or enhance a signal within the broadband signal, 1.2, 2.2, and combiners, 1.7, 2.7, for re-combining the processed frequency sub-band signals, 1.4, 2.4, by either summating the frequency sub-band signals, 1.4, 2.4, to produce the first moment of variation or enabling the amount of variation between the processed frequency sub-band signals, 1.4, 2.4, to be analyzed to produce the second moment of variation.

Abstract: An adaptive statistical filter system for receiving a data stream comprising a series of data values from a sensor associated with successive points in time. Each data value includes a data component representative of the motion of a target and a noise component, with the noise components of data values associated with proximate points in time being correlated. The adaptive statistical filter system includes a prewhitener module, a plurality of statistical filters of different orders and a selection module. The prewhitener module receives the data stream from the sensor and generates a corrected data stream comprising a series of corrected data values each associated with a data value of the data stream, each including a data component and a noise component with the noise components of data values associated with proximate points in time being decorrelated. The plural statistical filters are coupled to receive the corrected data stream in parallel from the prewhitener.

Abstract: A method for operating a digital computer to suppress reverberation artifacts in an ultrasound image. The image includes an ordered array of pixels, each the pixel corresponding to the intensity of the echo generated by a corresponding voxel in an ultrasound energy field. The ordered array has axial and lateral directions defined therein, the axial direction corresponding to voxels on the same radial line from a transducer used to generate the ultrasound energy field. The method starts by dividing the image into a plurality of segmentation blocks thereby generating an ordered array of segmentation blocks. The columns of the segmentation block array are chosen such that all segmentation blocks in the same column correspond to the same axial direction in the ultrasound image. In the preferred embodiment of the present invention, at least one segmentation block is classified as having a strong edge.

Abstract: In the particular embodiment of the invention described herein, sonar signals in the range from 200-3600 cps. are analyzed by bandshifting selected segments of 100 cps. width to the range 300-400 cps. for analysis, and indications of signals in all of the bands are presented side-by-side on a continuous printer. in addition, the modulation envelope of the detected signal, which contains low frequency modulation components, is demodulated to provide indications of such low frequency components in a target signal.

Abstract: An adaptive statistical filter system for receiving a data stream compris a series of data values from a sensor associated with successive points in time. Each data value includes a data component representative of the motion of a target and a noise component, with the noise components of data values associated with proximate points in time being correlated. The adaptive statistical filter system includes a prewhitener, a plurality of statistical filters of different orders, stochastic decorrelator and a selector. The prewhitener generates a corrected data stream comprising corrected data values, each including a data component and a time-correlated noise component. The plural statistical filters receive the corrected data stream and generate coefficient values to fit the corrected data stream to a polynomial of corresponding order and fit values representative of the degree of fit of corrected data stream to the polynomial.

Abstract: The present invention provides a method and system for characterizing the sounds of ocean captured by passive sonar listening devices. The present invention accomplishes this by first generating a spectrogram from the received sonar signal. The spectrogram is characterized in terms of textural features and signal processing parameters. The textural features and signal processing parameters are fed into a neural network ensemble that has been trained to favor specific features and/or parameters. The trained neural network ensemble classifies the signal as either Type-I or clutter.

Abstract: An acoustic sensor for measuring acoustic waves contained in fluid flow flowing over the sensor. The acoustic sensor reduces any unwanted self-noise associated with the flowing fluid by providing a nose cone having proper aerodynamic properties and by positioning the diaphragm of a microphone of the sensor at a location where any unwanted noise is at a relatively low level. The nose cone has a rounded, blunt or even sharp tip neither of which creates any major disturbances in the flowing fluid which it intercepts.

Abstract: The present invention relates to a signal processing system for generating a nulling signal for attenuating a periodic noise component from an information signal. According to one aspect of the invention, the system includes two nested feedback networks. One network detects the phase angle and frequency of the noise component, and generates a nulling signal having a phase angle and frequency substantially equal to the phase angle and frequency of the noise component. The other network detects the amplitude of the noise component, and scales the nulling signal to have an amplitude substantially equal to the amplitude of the noise component. According to a further aspect of the invention, the system includes a combining network for attenuating the noise component by combining the information signal with the nulling signal. In this way, the invention preserves the high fidelity of the information signal except over a very narrow bandwidth, adjacent to the noise signal frequency.

Abstract: An array plate for use in an underwater craft. The craft having an array of sonar elements which has a selected range of operating frequencies. The array plate having at least one layer of material in which the layer(s) of material are designed to have selected natural frequencies of vibration throughout the range of sonar operating frequencies. The natural frequencies resulting in standing waves having selected wavelengths that develop along the layer(s) of material. The sonar elements are mounted upon the layer(s) of material such that adjacent sonar elements are spaced apart a distance of one half the average wavelength of the standing waves.

Abstract: A multistatic sonar system (50) employing a short duration automatic gain control (AGC) following beamforming of the return signal to reject spatial transients at the sonar waveform leading and trailing edges. The output of the beamformer (58) is delayed by a delay line (60A) before passing through a programmable gain (60B). The magnitude of an undelayed version of the beamformer output is also squared (60D) and averaged over a time window (60E). This average is used to normalize the delayed value of the beamformer output. The normalized output of the beamformer is compared (60C) with a threshold having a value much greater than unity, and the comparator output controls the gain circuit (60B). When the normalized value of the beamformer output exceeds the threshold value, the gain of the AGC is set to a value much smaller than unity. When the normalized value of the beamformer output does not exceed the threshold, the gain of the AGC is set to unity.

Abstract: Disclosed are a filtered hydrophone circuit and a method of filtering hydrophone output signals. The circuit, in its most elemental embodiment comprises: (1) a hydrophone having first and second output conductors, the hydrophone producing an electrical signal of varying frequency, (2) an operational amplifier having first and second inputs and an output, the first amplifier input coupled to the first hydrophone output conductor, (3) a first resistor coupling the amplifier output to a second resistor, the second resistor further coupled to an electrical ground and (4) a capacitor coupling the second amplifier input to a point between the first and second resistors to thereby define a feedback path between the amplifier output and the second amplifier input for portions of the hydrophone electrical signal above a selected cutoff frequency, an output signal of the amplifier thereby substantially freed of the portions of the output signal below the selected cutoff frequency.

Abstract: An apparatus for reducing acoustic radiation from an enclosure containing a fluid includes one or more vibration sensors in communication with surfaces of the enclosure. The vibration sensors feed signals corresponding to detected vibrations in the surface to a radiation filter. The radiation filter assigns weights to the signals and generates a summation signal which is then input to a control unit, with the summation signal ideally representing only those vibrations that will actually radiate from the enclosure. The control unit uses a reference signal and the summation signal to calculate a cancellation waveform to offset the cause of the detected vibrations. The cancellation signal is input to a fluid displacement unit which applies pressure oscillations to the fluid corresponding to the cancellation waveform.

Abstract: An apparatus for enhancing the signal to noise ratio of piezoelectric hydhone outputs by decoupling the turbulent velocity pressure noise from the imbedded acoustic signal. An electromagnetic turbulent velocimeter is positioned coaxially with a piezoelectric hydrophone and flush mounted in a shell structure. The velocimeter senses the changes in the electric potential caused by the velocity of a conductive fluid passing through a magnetic field normal to the shell structure surface. The velocimeter responds to electromagnetic signals and is insensitive to acoustic signals. The piezoelectric hydrophone is positioned so as to contain the electromagnetic turbulent velocimeter magnetic field within the hydrophone field of view. The hydrophone responds to conductive fluid velocity pressure variations and is insensitive to electromagnetic signals. The output frequency components of the velocimeter are correlated or coupled with those of the hydrophone.

Abstract: An active adaptive noise canceller that inserts delays into the weight update logic of an adaptive filter to keep the filter stable. The noise and residual noise are sensed and the respective sensor signals are digitized at a given sample rate for processing in the adaptive filter. To eliminate the need for high sample rates while maintaining flexibility in the frequency regions over which the adaptive filter is stable, the delay introduced into the weight update logic is a non-integer multiple of the sample period. The non-integer sample delay is obtained by a sample interpolation and decimation procedure.

Abstract: A system and method are provided to reduce a structure's far field acoustic adiation signature. A plurality of acoustic sensors are positioned in the acoustic near field of the structure for measuring the near field acoustic radiation of the structure. A programmable controller generates a prediction of the structure's far field acoustic radiation signature using the near field acoustic radiation. The prediction is then used to generate a noise control signal applied to a plurality of acoustic radiators suspended within the structure. The radiators convert substantially all of the noise control signal to airborne acoustic energy within the structure.

Abstract: A multi-dimensional acoustic, data processing and display system arranges acoustic data in a three-dimensional matrix. The three-dimensional matrix is compressed using singular value decomposition into singular vectors and singular values. A historical database is created and maintained and is also concatenated with the three-dimensional data. This database allows reverberation and noise to be diminished and other, weaker features in the data to be enhanced. Once the data is compressed, the data can be analyzed efficiently. The singular vectors are partitioned into one or more groups on the basis of their singular values or other criteria. Certain of the compressed data elements are enhanced or diminished by modifying the singular values within each of the groups of singular vectors. Selected singular vectors are processed further by other techniques for further enhancement, detection, isolation, feature extraction and classification.