Abstract: A standard non-destructive testing probe (4) may be coupled with a localization system (10) according to the invention so as to determine the position of the apparatus (4) on the surface to be analyzed (1) at any moment. The localization system (10) comprises an ultrasonic emitter (12) and two ultrasonic receivers (14, 16) coupled with means for determining the distance between the emitter (12) and the receivers (14, 16), each of the components being able to be moved freely relative to each other. The coupling between the emitter (12) and the probe (4) allows the position of the latter to be determined by triangulation. A localization and mapping method is also described.

Abstract: Systems and methods for locating the shooter of supersonic projectiles are described. The system uses at least five, preferably seven, spaced acoustic sensors. Sensor signals are detected for shockwaves and muzzle blast, wherein muzzle blast detection can be either incomplete coming from less than 4 sensor channels, or inconclusive due to lack of signal strength. Shooter range can be determined by an iterative computation and/or a genetic algorithm by minimizing a cost function that includes timing information from both shockwave and muzzle signal channels. Disambiguation is significantly improved over shockwave-only measurements.

Abstract: A location system including a base station (120, 200) and a responder tag (140, 250) that communicate using an acoustic signal to determine the location of the tag in a bounded 3D space (100). The base station transmits a request signal (310) encoded with the identifier of a particular tag. The particular tag responds after a fixed delay (t2?t1) with an acoustic response signal (330). The base station determines the location of the tag based on the received line of sight signal (330) and its reflections (340). The response signal may be encoded with data indicating a status of the tag, or data from associated sensors (270) or actuators (280). The request signal may also be encoded with data for controlling the tag or the associated sensors and actuators. A power management scheme may be carried out by the tag.

Abstract: In one embodiment, a tracking module (110) to select a plurality of pairs of digital ultrasonic signals to form two or more pairs of digital ultrasonic signals and estimate time difference of arrival (TDOA) for each of the two or more pairs of digital ultrasonic signals. The tracking module (110) may further determine an intersection of each pair of the TDOA estimated digital ultrasonic signals to form one or more intersections and a location of an ultrasonic signal generator (102) corresponding to at least one of the one or more intersections.

Abstract: This invention provides a system and method using wireless communication interfaces coupled with statistical processing of time-of-flight data to locate by position estimation unknown wireless receivers. Such an invention can be applied in sensor network applications, such as environmental monitoring of water in the soil or chemicals in the air where the position of the network nodes is deemed critical. Moreover, the present invention can be arranged to operate in areas where a Global Positioning System (GPS) is not available, such as inside buildings, caves, and tunnels.

Abstract: Systems and methods for compensation of sensor degradation in multi-shooter detection systems are described. In such systems, shooter position and trajectory can be estimated precisely from the shockwaves produced at the plurality of sensors by the incoming shots. However, sensor positions can shift and the performance of some sensors may degrade for various reasons. To compensate for sensor degradation that may occur over the life of a long-deployed system, the shooter estimation algorithms are dynamically adapted by performing a least-squares regression analysis of the shockwave arrival times to obtain a time residual for each shot, observing multiple shots, and weighting the individual contributions of the sensors as a function of the time residuals for the multiple shots.

Abstract: An embodiment of a method for conducting a bathymetric survey across a seismic spread includes the steps of emitting a signal from a pinger positioned within the seismic spread, measuring the arrival time of a bottom reflection of the signal at a receiver positioned within the seismic spread, measuring the arrival time of a direct arrival of the signal at the receiver, and determining the water depth utilizing the measured arrival times of the signal.

Abstract: This is an underwater acoustic ranging system for determining a range to a target object. An acoustic receiver is provided for detecting acoustic energy and determining an angle of arrival of said acoustic energy in at least one plane. An acoustic transmitter transmits an acoustic energy pulse. A receiver clock joined to the receiver, and a transmitter clock is joined to the transmitter. Acoustic energy is transmitted at a synchronized time. Range can be calculated based on the transmit time, the receive time and the reception angle. The system can also include a means for synchronizing the clocks.

Abstract: A method and apparatus for determining the geophysical position of an autonomous underwater system utilizing underwater acoustic modems that exchange broadband underwater acoustic signals. The method of the invention includes the steps of initiating an exchange of broadband acoustic signals between the autonomous system of unknown geophysical position and a base system of known geophysical position wherein the depths of both systems is known. A bearing calculation is made on one of the signals transmitted between the systems, preferably through the use of an array of hydrophones placed closely together at predetermined locations on either the autonomous or base system. Also, the range between the two systems is determined by measuring the time of travel of at least one signal.

Abstract: The disclosed invention is a highly reliable cost effective sound direction detection system. In the preferred embodiment of the invention the system comprises a device which includes two microphones set at a spread of at lease 5 cm from each other, a digital signal processing (DSP) and a command processing board. A pattern recognition algorithm allows the system to recognize the signal of an actual event and distinguish it from echoes and reflections according to several parameters such as the signal's time of arrival, energy, amplitude levels and frequency. The pattern of the recorded signals is analyzed according to prevalent signal patterns and then the real event can be identified. By identifying the signal of the sound event and distinguishing it from background noises and from its reflections, the system can calculate its direction of arrival (DOA) using classical sound direction detection methods.

Abstract: Systems and methods for locating the shooter of supersonic projectiles are described. The system uses at least five, preferably seven, spaced acoustic sensors. Sensor signals are detected for shockwaves and muzzle blast, wherein muzzle blast detection can be either incomplete coming from less than 4 sensor channels, or inconclusive due to lack of signal strength. Shooter range can be determined by an iterative computation and/or a genetic algorithm by minimizing a cost function that includes timing information from both shockwave and muzzle signal channels. Disambiguation is significantly improved over shockwave-only measurements.

Abstract: A gunshot location system computes candidate gunshot locations [314] from angle-of-arrival information [304, 308] and time-of-arrival information [312] provided by acoustic sensors [300, 302]. In addition to an angle, each sensor calculates an angular uncertainty [306, 310] from impulses received at four or more microphones having rotational symmetry. An intersection of one or more time-of-arrival hyperbolas with one or more angle-of-arrival beams [322] is used to determine a candidate gunshot location. In simple environments, a location can be confirmed with just two sensors allowing sensor density to be significantly reduced, while in complex environments including reflections, blocking, and interfering acoustic events, the additional angle-of-arrival information improves location accuracy and confidence, allowing elimination of candidate locations inconsistent with the combined time-of-arrival and angle-of-arrival information.

Abstract: A position detection system comprising positional element and positioning device, wherein the positional element transmits a continuously modulated acoustic waveform and a synchronization signal that is a sequence of at least two synchronization packets, each bearing timing data for the continuously modulated acoustic waveform. Additionally, the synchronization signal uses time hopping to support concurrent positioning of a plurality of positional elements.

Abstract: A method for determining a mutual distance between two objects in a pipeline. The method includes the steps of: providing a pipeline which is filled with a medium having an acoustic impedance different from that of the material of the pipeline and/or a medium present outside the pipeline; providing each of the two objects with a clock; synchronizing the clocks; periodically transmitting an acoustic signal from a first to a second one of the two objects; measuring the reception time of the acoustic signal; determining the delay time from the first to the second object; and calculating a traveled distance of the signal between the two objects on the basis of a propagation speed of the acoustic signal in the medium and the measured delay time of the acoustic signal.

Abstract: A to method and system provide a range and depth localization of a passive sound generator, e.g., a submarine target. The method and system use an autocorrelation and/or a cross correlation to arrive at a plurality of range versus depth estimates, which are resolved and evaluated using likelihood factors in order to provide a range and depth localization.

Abstract: An accurate measure of normally operating noise is required for a useful noise measurement system. A device is needed to make a representative measure of the boat's acoustic power using measured boat sound level with integrated corrections for sensed distance to the boat and measured ambient sound level. This device needs to make this measurement process invisible, automatic, and accurate from a law enforcement point of view.

Abstract: Systems and methods for locating the shooter of supersonic projectiles are described. Muzzle blast signals are neither sought nor required. The system uses at least two sensors, with each sensor having a 3-axis accelerometer. The sensors are spaced apart at least 1 meter and have each a diameter of about one centimeter. The three accelerometer signals of each sensor represent pressure gradients and are processed to find the shockwave arrival angle unit vector, the shockwave arrival time instant and peak pressure. Noise signals seldom cause false detections with this sensing method because the sensors have maximum sensitivity at the high frequency characteristics of shockwaves, while their sensitivity to the low frequency characteristics of ambient noise is relatively low.

Abstract: The invention relates to a method and device for generating data about the mutual position of at least three acoustic transducers. The aim of the invention is to make it possible to continuously measure and calculate the mutual position of at least three acoustic transducers, particularly the rotation and the position of a human head wearing headphones within a room without using any additional transmitter element on the head, headphone, or body of the listener, during audio playback. This aim is achieved by connecting the acoustic transducers to a digitally operated system which comprises an output path emitting audio signals to first and second acoustic transducers, an input path receiving audio signals from the third acoustic transducer, an audio signal source that is connected to the output path, an ultrasound generator that is connected to the output path, and an information generator which indicates a position and is connected to the input path.

Abstract: An object producing an acoustic wave is located and identified by passive detection of the acoustic wave. The acoustic wave is defined by different sensors in an array having a plurality of passive acoustic detectors. The sensors produce signals in response to the detection of the acoustic wave. A wavelet derived from an acoustic wave of a known form with which each of the at least three signals correlates, is determined. Time difference of arrival measurements between the at least three signals using correlation intensity with the wavelet is used to performed acoustic reciprocity from each of the different detectors. The result of the acoustic reciprocity is a hemisphere centered around each of the different sensors. The hemispheres produced by the acoustic reciprocity are examiner to determine an intersection point of at least three hemispheres. The size of the hemispheres is increased according to the velocity of the acoustic wave and pre-determined intervals until an intersection point is found.

Abstract: A system for locating and identifying an acoustic event such as gunfire. The inventive system employs a plurality of man wearable acoustic sensors for detecting gunfire, each acoustic sensor having a display associated therewith for displaying information concerning the acoustic event to a user. In preferred embodiments, the sensor includes a microphone for receiving acoustic information; an A/D converter; a processor for processing the digitized signal to detect a gunshot and determine a time of arrival; a GPS receiver for determining the position of the acoustic sensor; and a network interface for bidirectional communication with a system server. Preferably the display comprises: an LCD; and an electronically readable compass. When the display and acoustic sensor are in separate housings, the acoustic sensor includes a transmitter and the display includes a receiver for transferring the gunshot information.

Abstract: A system and method is provided for determining the three dimensional location of an acoustic event using a system of five or more sound sensing elements. The sensing elements are positioned at substantially the same elevation and in spatially distributed locations with respect to the acoustic event. The sensing elements generate notification signals indicating occurrence of the acoustic event. A central processor receives the notification signals, associates the locations of each of the sensing elements with the time at which each sensing element sensed the sound, determines the speed of sound for the medium, and calculates a three dimensional location for the acoustic event using a linear error minimization algorithm. A system of six or more sensing elements enables the processor further to discriminate between near simultaneous acoustic events.

Abstract: Shockwave-only solutions that estimate shooter position and shot trajectory are extremely sensitive to the quality and precision of the shock time-of-arrival (TOA) measurements as well as the accuracy to which relative sensor positions in space are known. Over the life of a long-deployed system, the sensor positions can shift and the performance of some sensors may degrade for various reasons. Such changes can degrade the performance of deployed shooter estimation systems. Disclosed are systems and methods that can be used to calibrate sensor positions based on shock and muzzle measurements processed from a series of shots fired from a known location and in a known direction, as well as an approach for dynamically adapting shock-only shooter estimation algorithms to compensate for sensor degradation and/or loss.

Abstract: The invention relates to a device that is used to analyse the structure of a material. The inventive device comprises: probe elements (5) which are used to (i) emit a wave, in the material, with emission delay laws that correspond to several simultaneous deviations and (ii) receive, on the different probe elements (5), signals from the refraction of said wave by the material; detection channels, each detection channel being connected to a probe element (5), in order to collect the refraction signals and to transmit same to data processing means (4); and delay circuits that apply a delay on each detection channel according to the reception delay laws which are predetermined and which correspond to the different deviations of the wave emitted. The invention also relates to an analysis method which can be used, in particular, on said device.

Abstract: An object localising system comprises sensor devices at different sites, each sensor device being capable of detecting a signal from an object, and control means for repeatedly responding to the outputs of the sensor devices by selecting a sub-set of the devices and determining the amount by which the times at which the devices of the sub-set receive the signal are delayed with respect to each other to enable calculation of the current location of the object. Each sensor device can be switched between a master mode, in which the device is operable to transmit events derived from a signal from an object, and a slave mode, in which the device is responsive to such events from another sensor device for processing its own signal in order to determine the time delay between receipt of the signals by the sensors of the respective devices.

Abstract: In order to locate and display the source of a sound such as a noise at a factory or the like accurately even when it is outside, a pair of microphones (M1, M3) and another pair of microphones (M2, M4) are disposed on the X axis and Y axis with a distance L therebetween, respectively, the direction of the sound source is estimated from a difference between sound arrival times to the microphones (M1, M3) and a difference between sound arrival times to the microphones (M2, M4), an image around the estimated location of the sound source is picked up by a camera, and the above estimated location of the sound source is displayed on the above image displayed on the display of a personal computer.

Abstract: A system and method for protecting sensor positions in an array of acoustic sensors which make up a gunfire locator system. The inventive system includes a purity of sensors and a host computer. Each sensor includes: a microphone for receiving acoustic information; a processor for processing acoustic information to detect an acoustic event and determine a time of arrival; a GPS receiver; an encryption module for encrypting transmitted sensor positions; and a network interface for transmitting sensor positions and times of arrival. The host computer includes: a network interface for receiving sensor transmissions; an encryption module for deciphering sensor positions; and a CPU.

Abstract: Systems and methods for locating the shooter of supersonic projectiles based on shockwave-only measurements are described. Muzzle blast signals are neither sought nor required. The system uses at least five, preferably seven, acoustic sensors that are spaced apart at least 1 meter. The sensor signals are acquired with a time resolution in the order of microseconds and processed to find and disambiguate the shockwave arrival angle unit vector. Two different Time-Difference-Of-Arrival (TDOA) measurement techniques are described, with one technique using counters in each signal channel and the other technique using cross-correlation between signal channels. A genetic algorithm can be used to efficiently disambiguate the results.

Abstract: A passive vehicle acoustic data analyzer system having at least one microphone disposed in the acoustic field of a moving vehicle and a computer in electronic communication the microphone(s). The computer detects and measures the frequency shift in the acoustic signature emitted by the vehicle as it approaches and passes the microphone(s). The acoustic signature of a truck driving by a microphone can provide enough information to estimate the truck speed in miles-per-hour (mph), engine speed in rotations-per-minute (RPM), turbocharger speed in RPM, and vehicle weight.

Abstract: A system and method for issuing an alarm when the separation distance between a monitoring module associated with an object (animate or inanimate) and an alert module exceeds a preset threshold distance thereby forming a leadless electronic tether between the object and the object owner. A monitoring module comprises a portable transmitter provides a signal to an alert module comprising a receiver and a processor. The alert module is adapted to determine a separation distance between the monitoring module and the alert module based on an attribute of the signal. When the separation distance exceeds a predetermined threshold, the alert module issues an alert.

Abstract: A primary transceiver of a primary vehicle transmits a first transmission signal to a first transponder and a second transponder associated with a secondary vehicle. A first transponder antenna and a second transponder antenna are associated with secondary vehicular reference points. Upon receipt of the first transmission signal, the first transponder transmits a second transmission signal to a first beacon of the primary vehicle and the primary transceiver. A transmitter antenna and the first beacon antenna are associated with primary vehicle reference points. Upon receipt of the first transmission signal, the second transponder transmits a third transmission signal to the first beacon and the primary transceiver. A data processor or estimator determines propagation times associated with the first transmission signal, the second transmission signal, and the third transmission signal.

Abstract: An acoustic-propagation-time measuring apparatus includes an acoustic transmitting and receiving section having an acoustic element capable of transmitting and receiving acoustic waves, an A/D converter which converts an echo signal reflected from a target object to be measured into a digital signal, an inverse-analysis section that converts the digital echo signal into an impulse signal through inverse analysis where the digital echo signal is multiplied by an inverse matrix, a calculating section that measures an acoustic propagation time and a time difference based on the digital echo signal converted to the impulse signal, and a display section which displays the acoustic propagation time and time difference calculated by the calculating section.

Abstract: A simulated grenade for MILES-type simulations generates a unique RF signal and a unique audio signal. A detector utilizes the time between receipt of the RF signal and the slower-traveling audio signal to determine the distance between the detector and the simulated grenade.

Abstract: A proximity detector for use in a mobile telephone having at least a microphone and a loudspeaker operatively connected to a signal processor is presented. The proximity detector includes data processing and control modules having a module for controlling the signal processor for activating the loudspeaker to reproduce an acoustic control signal. A correlator correlates a control signal received directly by the microphone and a control signal being reflected from a user of the telephone and then received by the microphone to determine the distance between the telephone and the user. A signal level controller controls the signal processor to vary the signal level of an audible signal reproduced by the loudspeaker proportionally to the determined distance between the telephone and the user.

Abstract: Methods for processing ultrasonic signal data to evaluate subsurface properties and tool orientation. Acoustic signals are transmitted into a plurality of azimuthal borehole positions. Formation echo signal transit time distributions are then determined in a plurality of azimuthal sectors for the acoustic signals. Front face echo signal transit times are also measured and farther-mode and closer-mode transit times are determined for the distribution of formation echo signals. Farther and closer tool standoffs are determined for the azimuthal sectors and a borehole diameter is determined from a summation including standoffs in opposing sectors. The standoffs are also used to determine a preferential tool position.

Abstract: A system and method for detecting, identifying, and fixing the location of the source of an acoustic event. The inventive system includes: a plurality of sensors dispersed at somewhat regular intervals throughout a monitored area; a communication network adapted to deliver information from the sensors to a host processor; and a process within the host processor for determining, from the absolute times of arrival of an event at two or more sensors, a position of the source of the event. Acoustic events are detected and analyzed at each sensor so that the sensor transmits over the network: an identifier for the sensor; an identifier for the type of event; and a precise absolute time of arrival of the event at the sensor. In a preferred embodiment, the system also identifies the type of weapon firing a gunshot.

Abstract: A control and motor arrangement for use in a model train includes a control arrangement integrally constructed with a motor. The control arrangement receives rotational speed and positional information from the motor and uses this information to determine how much power to supply to the motor, thus controlling the rotational speed of the motor. In this way, the control arrangement maintains a constant motor speed, if desired. In addition, the speed and positional information is optionally provided to a sound control arrangement for use in selecting appropriate sound effects.

Abstract: A system and method for detecting, identifying, and fixing the location of the source of an acoustic event. The inventive system includes: a plurality of sensors dispersed at somewhat regular intervals throughout a monitored area; a communication network adapted to deliver information from the sensors to a host processor; and a process within the host processor for determining, from the absolute times of arrival of an event at two or more sensors, a position of the source of the event. Acoustic events are detected and analyzed at each sensor so that the sensor transmits over the network: an identifier for the sensor; an identifier for the type of event; and a precise absolute time of arrival of the event at the sensor. In a preferred embodiment, the system also identifies the type of weapon firing a gunshot.

Abstract: The invention concerns a temporal and spectral submarine locating method, characterised in that it includes equipping the systems or mobile objects to be located and/or identified, with acoustic transmitters transmitting aperiodic signals with a predetermined pseudo-random sequence; deploying, over the working zone where the systems and moving objects to be located are found, one or several measuring points provided, each with an acoustic receiver, with a time scale reference and a measuring point locater; transmitting to a processing centre data derived from the measuring points where, at every time of detection on a given frequency band, precise dating is associated in a time scale referential with a position of the measuring point in a spatial referential; the whole set of data derived from the different measuring points being assembled at the processing centre to be operated on by level 2 correlation with the pseudo-random reference sequences corresponding to each of the searched transmitters.

Abstract: Method and apparatus for determining the positioning of volumetric detection array lines. In the case of a sonar array, ultrasonic frequencies are used. Transmitter subsystems including ceramic transducers, and sensors such as hydrophones, are deployed on the lines of the array and code division multiple access (CDMA) type pseudo-random numbers are used to identify each transmitter. Transit times between transducers and sensors, as determined by detector electronics, are sent to a ship-board receiver in any of various formats, so that array line position can be determined.

Abstract: A plurality of sound-detecting devices are configured to detect sound from an event of interest. Information about the sound is recorded that is dependent on a distance between the source position and the location of the sound-detection devices. The source position is approximated using the recorded information and the relative position of individual sound-detection devices to one another. The approximated source position is used as input for operating a electronic device.

Abstract: A time-difference process and apparatus for scoring supersonic aerial projectiles, such as military aircraft air-to-ground strafing projectiles fired at a strafe target, by detecting and measuring the acoustic shock waves propagated by the projectiles. The process and apparatus uses an array of at least six dynamic transducers to independently sample each projectile shock wave and transmit sampled signals to at least one all-purpose digital computer. The time-differences of arrival of the shock waves at each transducer are processed by an iterative algorithm implemented by the computer. The algorithm calculates projectile impact point, projectile velocity and other useful scoring data. The scoring data are used to quantitatively score the number of hits or misses by the strafing projectiles on the strafe target. Scoring data and other projectile data are selectably indicated to the operator by remote display and printout.

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 presence detection system includes a reader device attached to a first body, and a tag device attached to a second body. The reader device has an ultrasonic transducer for generating and transmitting ultrasonic pulses at a first rate of occurrence; an RF receiver for receiving a RF signal; and a microcontroller coupled to the ultrasonic transducer and the RF receiver for receiving signals from the ultrasonic transducer and the RF receiver and for controlling the operation of ultrasonic transducer and the RF receiver. The tag device has an ultrasonic receiver for receiving ultrasonic pulses from the ultrasonic transducer of the reader device; and an RF pulse generator for generating and transmitting an RF pulse.

Abstract: A two-way ultrasonic positioning and navigation system and method involve a plurality of objects each capable of transmitting and receiving ultrasonic signals. A first object transmits an initiating ultrasonic signal and identifies a second object for responding to the initiating ultrasonic signal. The second object transmits a responding ultrasonic signal after a predetermined time delay from receiving the initiating ultrasonic signal. The first objectives the responding ultrasonic signal, and determines a distance between the first object and the second object based on a time period starting at the transmission of the initiating ultrasonic signal and ending at the reception of the responding ultrasonic signal, and on knowledge about the predetermined time delay and other known in advance time delays.

Abstract: A system and method for determining a sound speed profile of a water column. A free falling sound source is deployed in the water at a known location and time. The sound source transmits acoustic pulses omnidirectionally therefrom at predetermined times after deployment. An acoustic receiver located at a known location detects each acoustic pulse. The time differential between each predetermined time and a time of arrival for each subsequent acoustic pulse is determined. Speed of sound for each portion of the water column is then determined as a function of the time differential, the known locations of sound source deployment and the acoustic receiver, and the known rate of descent of the sound source. The sound source can be constructed from a hydrodynamic body housing a power source, timing electronics, and spark gap electrodes. A bubble, generated by the spark gap electrodes, implodes to create the acoustic pulse.

Abstract: Given a trajectory and unit pointing vectors determined based on a planar or other approximation of a shock wave, a method and apparatus are provided to calculate times the sensors should have detected, based on a conical geometry of the shock wave. A difference between the calculated times and the actual times measured by the sensors may be minimized. The minimization may be performed by perturbing the unit vectors. When the perturbation of the unit vectors results in an acceptable difference between the calculated times and the measured times, an accurate trajectory of the projectile can be generated from the perturbed unit pointing vectors.

Abstract: The present invention relates to a positioning system for use in underwater/subsea hydrographic surveying and positioning applications The system comprises a submersible having a transponder formed and arranged for communication with a remote receiver. The transponder is formed and arranged to transmit a continuous water propagatable data signal, which signal includes a binary signal sequence, preferably a “gold code”, each of the transponder and the receiver being provided with an internal clock. The clock on the receiver and transponder are in substantial synchronisation. The remote receiver is provided with processing means for determining the position of the submersible by calculating the time taken for a signal to be transmitted by the transponder to be received by the remote receiver utilising the clock time of transmittal with respect to the clock time of reception at the remote receiver. Means for determining clock variation and resynchronising the clocks is described.

Abstract: Signals from microphones 1, 2 are first stored in memory circuits 4, 6 and then supplied to a cross-correlation arithmetic circuit 7, following which a cross-correlation operation is carried out and cross-correlation function values are calculated for each time difference. An evaluation function circuit 8 carries out addition processing of particular time intervals based on the cross-correlation function values and then searches for the maximum value to calculate time differences. Signals from the microphones 2, 3 are first stored in memory circuits 6, 5 and then supplied to a cross-correlation arithmetic circuit 9, following which a cross-correlation operation is carried out and cross-correlation function values are calculated for each time difference. An evaluation function circuit 10 carries out addition processing of particular time intervals based on the cross-correlation function values and then searches for the maximum value to calculate time differences.

Abstract: A system is provided having a transmitting transducer for transmitting a burst of energy in response to an electrical drive waveform. The system includes a receiving transducer for generating an electrical signal in response to arrival of the transmitted burst of energy.

Abstract: A subsurface object location apparatus for determining the position of an object 2 located below a surface S such as a land surface, the surface of the sea or a seabed. A subsurface unit 1 having transmitter means for transmitting inductive signals is mounted on the object 2. A plurality of surface units 3 are disposed at spaced locations at the surface S. Each surface unit 3 has receiver means arranged for receiving the inductive signals. Processing means 4 are provided for determining the location of the object 2 using time difference of arrival techniques in respect of the signals received at the surface units. Cyclic correlation is used in determining the times of reception of signals at the surface units.