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 system for determining the velocity and trajectory of an underwater vehe comprises a data acquisition processor coupled to a plurality of sensors providing depth, heading, pitch and yaw data for the underwater vehicle. The acquisition processor collects data from the sensors, correlates and assembles the collected data into batches and processes the batches to determine vehicle velocity and trajectory of the vehicle relative to an earth-fixed coordinate system.

Abstract: An underwater communication system by coded pulses, includes a transmitter placed at a surface of a body of water, for transmitting coded pulses, the transmitter having a transmitter circuit for generating the coded pulses, the transmitter circuit including a first shift register pre-programmed with a binary code corresponding to the coded pulses, and an underwater piezoelectric transducer for submersion in the water and electrically connected with the transmitter circuit for transmitting the coded pulses through the water; an underwater receiver for receiving the transmitted coded pulses, without any physical connection between the transmitter and receiver, the receiver having an underwater piezoelectric transducer, submerged in the water, for receiving the transmitted coded pulses, and a receiver circuit for comparing the received code pulses with stored coded pulses, the receiver circuit including an amplifier for amplifying the received coded pulses, an internal clock generator for generating a clock sign

Abstract: A method and apparatus for filtering particulate matter entrained in a fl entering a port from a reservoir. First and second ultrasonic wave generators produce ultrasonic waves to define a composite wave pattern. The patterns produce nodes and antinodes in a region through which fluid entering a port passes. The particulate matter in the portion of the fluid passing through the region accumulates along the nodes and antinodes. The accumulating particulate matter is thereby separated and is displaced from the fluid entering the port.

Abstract: Apparatus and methods for filtering particulate matter from a fluid traveg proximate a surface containing a port. First and second ultrasonic wave generators produce superposed ultrasonic waves to define a composite wave pattern in a region of the fluid body upstream of the port. Nodes and antinodes in the composite wave region define regions at which the particulate matter accumulates. The accumulating particulate matter is displaced out of the fluid that enters the port.

Abstract: An adaptive oceanographic sampling system includes several stationary acoustic tomography units distributed in an ocean volume, a processing and control system and at least one underwater vehicle movable within the ocean volume. Each of the acoustic tomography units includes an acoustic source for transmitting acoustic energy in the ocean volume, a receiver array for generating acoustic tomography data in response to received acoustic energy and a transmitter for transmitting the acoustic tomography data. The acoustic tomography data represents an ocean characteristic in the ocean volume. The processing and control system analyzes the acoustic tomography data and determines a region of interest within the ocean volume. The processing and control system then directs the underwater vehicle to move to the region of interest. The underwater vehicle includes a sensor for sensing an ocean parameter and providing sensor data representative of the ocean parameter in the region of interest.

Abstract: A method for detecting radiated and reflected acoustic signals from an unwater source, wherein the acoustic signals are present in a random noise environment and form an output therewith. The method includes the steps of operating an entropy-based acoustic receiver to receive the output, calculating the entropy of the received output, and comparing the calculated entropy with a selected entropy threshold value. A substantial difference is indicative of the presence of an acoustic signal from an underwater source. A less than substantial difference is indicative of a lack of presence of an acoustic signal from an underwater source.

Abstract: The present invention relates to a system for studying, identifying and cacterizing thermal gradients within a volume of water. The system includes a frame formed from a plurality of PVC tubing sections and connectors. The connectors are used to house at least one pair of acoustic transducers, which transducers are used to collect data for studying, identifying and characterizing the thermal gradients within the volume of water. A number of different frame configurations may be used to perform a number of different studies.

Abstract: A buoyed sensor array communications system comprises multiple sensor syss electrically connected to a signal transmission line which are positioned at predetermined locations along the signal transmission line to form a linear sensor array. Each of the sensor systems generates a data signal in response to receiving an address signal. The system further includes; a processor system electrically connected to the signal transmission line for transmitting address signals to enable any one of the sensor systems at a time in a selectively accessed order and has a data storage memory for storing the data signal from each of the sensor systems as stored data. A radio frequency transmitting system is coupled to the data processor and transmits the stored data at a predetermined time. A negatively buoyant structure connected to the signal transmission line pulls the communications system to the bottom of a body of water upon deployment.

Abstract: The signal appearing at the receiver input of a pulse code active sonar dng a return echo period, is sampled, time compressed and stored in a memory. The time compressed sample is successive read-out of memory, with each individual "read-out" hetrodyned with a discretely different doppler compensation frequency signal. The successively processed read-outs are passed through an "on line" correlation detection device to determine presence of a correctly compensated pulse code echo.

Abstract: The present invention relates to a system for studying, identifying and cacterizing thermal gradients in a volume of water. The system includes a frame for supporting one or more measuring devices and a source of heat for generating a thermal plume in the volume of water. The frame includes a first plate to which the measuring devices are mounted by a plurality of mounting blocks spaced about the periphery of a hole in the first plate. The frame further includes a second plate, spaced from the first plate, to which the source of heat is mounted.

Abstract: A towed buoy is deployed to a known depth below the surface from a submar and this depth is maintained by a control system that includes movable fins on the buoy. The movement of the buoy body and the buoy fins are monitored and used to evaluate sea state parameters, such as wave height for example. The tow cable is coupled to the buoy by means that permits measurement of the angle between the cable and the longitudinal axis of the buoy. Cable tension is also monitored to evaluate other surface parameters such as ocean current.

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: A method and apparatus for classifying objects in images utilize means for selecting portions of those images which contain objects and means for classifying those objects based upon parameters of the selected portions, which parameters are useful for classifying the objects. The selecting means preferably is a shadow and highlight detector, a statistical window detector and a neural network window detector whose output is combined in a combined cuer. The parameters are determined from the greylevels and positions of pixels using one or more modules which perform certain mathematical operations on this data. Such parameters include edge parameters, smoothness, clutter, presence and characteristics of highlights and shadows, and texture. The invention is particularly useful for classifying objects in sonar images as natural or man-made.

Abstract: A navigational device (10) for assisting a scuba diver in determining a direction toward and a distance from a dive boat (12) or to a buoy near the shore at which point the dive originated. The navigational device (10) includes a transponder unit (16) carried by a boat (12) and an interrogator unit (34) carried by a diver. The interrogator unit (34) includes at least one transducer (68) positioned for detecting signals from the transponder unit (16). Direction and distance indicators (46,50) are carried on the surface of the interrogator unit (34) for visual indication to the diver. The transponder unit (16) repeatedly pulses an identification signal to be received by the interrogator unit (34). When a valid identification signal is received by the interrogator unit (34), the direction from which the signal was received is determined and displayed. When the distance to the boat (12) is required, a signal is emitted from the interrogator unit (34).

Abstract: A system for characterizing ocean bottom properties in real-time by explong the multipath structure of reverberation to extract values for the bottom loss and the bottom scattering coefficient. The system obtains environmental and navigational data and synchronizes the data with sonar state data and acoustic beam data to produce an input data stream to an extraction processor. The extraction processor utilizes a digital signal processing means to produce a reverberation energy envelope from the acoustic beam data and time correlate the reverberation energy envelope with the environmental, navigational, and sonar state data.

Abstract: A system of sonar platforms designed for use in moderate depth water is disclosed, with each platform having a plurality of transducer modules mounted thereon. Each transducer module has a plurality of sonar transducers mounted in columns. The transducers are electronically grouped in two groups for sensing of reflected signals, to provide a means of bearing calculation by the phase monopulse method. The transducer modules are identical and interchangeable, so that any module can be mounted in any position on any platform. Each platform is hexagonal, with up to six transducer modules mountable on each platform to provide the desired pattern of sonar coverage for the platform. The platforms can be arranged in any desired pattern to provide the desired sonar coverage of a particular body of water.

Abstract: The invention relates to diver-to-diver communication apparatus. There is provided a communication apparatus (2) for diver to diver communication, the apparatus comprising a waterproof casing (4), power supply means (52), ultra acoustic transmission means (72), ultra acoustic reception means (72, 74), control means (56) for the ultra acoustic transmissions, monitoring means (56) for the ultra acoustic reception, and means (16) to actuate the transmission means (72); whereby upon actuation of the transmission means (72) a predetermined signal is transmitted by the transmission means (72) suitable for reception by the reception means (72, 74) of another diver using similar apparatus (2).

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 automatic method for finding mines in side scan sonar images using a two-stage detection/discrimination process is provided. This method improves the discrimination process by specialized processing of regions of interest found in the detection process to increase the probability of correctly identifying highlight and shadow regions associated with mine images. Features specifically selected for their ability to discriminate mines are then extracted from these areas for use in the Bayesian discriminator.

Abstract: A system and method for estimating a ship's far-field acoustic characteristics includes at least one reference hydrophone and at least one movable hydrophone, both of which are disposed in the water closely adjacent the ship. The movable hydrophone senses acoustic tonals at a plurality of points on the surface of an imaginary prolate spheroid surrounding the ship, the major and minor axes of which are roughly equal to one-half the length of the ship and the beam of the ship, respectively. The phase difference in the signals from the movable hydrophone and reference hydrophone are compared to generate a near-field data set. A computer is used to estimate a far-field data set representative of the ship's acoustic characteristics based on the near-field data set. Thus actual far-field measurements are not required.

Abstract: A method for eliminating false detections at the water column boundary in side scan sonar images is provided. Each image is filtered by computing the median greylevel value of a pixel and its four adjacent pixels to produce a median image. The median image is filtered with a first linear filter to produce an edge image. The edge image is then filtered with a second linear filter to produce an edge-smoothed image. The edge of the image is detected by searching each row of the edge-smoothed image for the maximum greylevel. A transition region is defined between the detected edge and a preselected right boundary and the average greylevels over the rows and columns in this transition region is computed. The sonar image is then normalized by computing the image mean grayness level of each pixel in the image.

Abstract: A method is described for providing an estimate of the state of a moving tact in a three dimensional ocean. The method comprises the steps of providing a device for estimating the state of the contact, inputting into the device information about a location of an observer during a sequence of time, information from at least one sensor about the position of the contact relative to the observer during the time sequence, and a knowledge vector, transforming the inputted information into a series of three dimensional geographical grids, and analyzing the geographical grids to produce an estimate of the state of the contact with respect to the location of the observer. The device for providing the estimate of the state of the moving contact is a neurally inspired contact estimation device.

Abstract: A method for characterizing ocean bottom properties in real-time by explong the multipath structure of reverberation to extract values for bottom loss and the bottom scattering coefficient. The bottom parameters are extracted from a measured reverberation energy envelope generated from the reverberation returns of one or more pings from a sonar system. The measured reverberation envelope is compared to a reference reverberation model to identify a period of time in which the measured reverberation energy envelope exhibits properties that allow the extraction of bottom parameters. The bottom parameters are then extracted by direct comparison of the measured reverberation to the reference reverberation model within the time period or by iteratively changing the value of bottom loss or bottom scatter coefficient and recalculating the reference reverberation for the identified time period until the reference reverberation matches the representative reverberation.

Abstract: A trajectory estimation system for estimating a trajectory of a target in sponse to a series of data items which generated in response to motion of the target. The trajectory estimation system includes a data segmentation means and a trajectory selection means. The data segmentation means processes the series of data items in accordance with a regression/multiple-hypothesis methodology to generate a plurality of segments, each having associated data items which have similar features. The trajectory selection means for processing said segments in accordance with a multiple-model hypothesis methodology to generate a corresponding statistically-supportable candidate trajectory motion estimate of target motion thereby to provide indicia of an overall trajectory of the target.

Abstract: A system for automatically detecting the event of a person or object falling overboard from a vessel into water includes a portable ultrasonic transmitter worn by each person or attached to selected objects on board and designed to be activated upon immersion in water, and an alarm control unit carried by the vessel containing an ultrasonic receiver. When the receiver detects a signal produced by a portable transmitter, it sounds an alarm and displays the vector velocity of the vessel relative to the portable transmitter, allowing rescue operations to be initiated and carried out even in conditions of zero visibility.

Abstract: A deployment system is disclosed for deploying a vertical, sub-surface bud, underwater acoustic sensor array in the ocean which includes a mechanical load transfer and cable separation mechanism which is embodied as a rigid triangular member. The vertical, sub-surface buoyed underwater acoustic sensor array is attached to a support cable which is connected at one end to the sub-surface buoy and at its other end to one of the vertices of the rigid triangular member. An anchor is attached to another vertex of the rigid triangular member and the third vertex of the triangular member is fitted with a strain relief/cable support, rotatable leg that is in turn attached to the deployment or shore cable. After deployment, the triangular member becomes the mechanical link between the array anchor and the array's vertical support member. It also acts as a mounting surface for the necessary electrical cable junction boxes or other required instrumentation and hardware.

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: A method and apparatus for navigating underwater a killer vehicle towards a mine emitting a magnetic field by using measurements of the mine's magnetic field, by two magnetic sensors affixed to the killer vehicle, in calculating the relative position of the killer vehicle with respect to the mine.

Abstract: A viewing screen apparatus for helmets or face masks of the type having a viewing area covered by a face plate is disclosed. The apparatus includes an enclosure adapted to be mounted on a helmet or face mask adjacent the face plate, a solid-state flat panel display screen and associated circuitry contained within the sealed enclosure for displaying visual images on the screen responsive to electronic signals, and a signal receiver connected with the screen for enabling the screen to receive electronic signals from an electronic signal transmission source. In one embodiment the enclosure is selectively movable between a viewing position adjacent the face plate and a position out of the wearer's field of vision to allow an unobstructed field of vision through the face plate.

Abstract: Target detection apparatus wherein a pulse of acoustic energy transmitted toward a target area of the sea bottom is reflected back to two spaced-apart receiver transducers. The sum and difference of the transducer outputs are obtained with the phase relationship therebetween being detected. An acoustic return from a target above or on the bottom will cause two returns to arrive at the receiver transducers at very slightly different times and at different angles thereby resulting in a phase relationship different than a return from the bottom. An output signal indicative of a target or no target condition is provided and is normalized so that its amplitude is independent of target strength.

Abstract: This invention provides an apparatus including a plurality of omnidirectional hydrophone sensors in a particularly configured array comprised of ring members which are carried between a plurality of tensioned cables, the cables being tensioned by an anchor weight at the bottom end of the array and a capsule float at the top end, the configuration enabling simplified signal processing techniques to achieve sound source discrimination in both azimuth and elevation within an underwater environment.

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: The identity of an aquatic organism is determined by a signature derived from a broadband acoustic signal transmitted and received by a broadband transducer or transmitted by a an broadband acoustic transmitter and received by an array of broadband acoustic receivers. The signature is a set of classifier coefficients created from a training processing that learns to discriminate between various size/taxa of aquatic life forms using features extracted from the received broadband echoes. The signature database used for classification during operation is stored on a portable storage medium. The degree to which the signals collected from an unknown aquatic life form matches the predefined known aquatic life form is then reported to a utilizing device.

Abstract: One embodiment that is shown relates to a reconnaissance and/or weapons system for underwater use and comprises a vehicle 1, which may be a torpedo, and a support 2. The support is connected with torpedo 1 with a control wire 3. The wire has a density lower than that of water and will therefore float. The control wire is stored in a magazine and supported by buoyant means 4.

Abstract: A sonar system using closely spaced or interleaved projector and receiving transducer elements with a power inductor connected in series with the projector array transmits three separate frequencies and utilizes a resonant circuit connected across the projector array, and a switch alternately connecting the array to the transmitter or the resonant circuit. The resonant circuit has two parallel branches with an inductor in one branch and an inductor, a capacitor and a resistor in the parallel branch. An alternate embodiment includes a variable capacitor in series with the parallel circuit to simplify the tuning for individual installations. Values of the components were chosen to provide impedances looking into the resonant circuit which tend to maximize the "stiffness" of the projector elements for all the received frequencies, thus inhibiting the tendency of the projector elements to receive and reradiate echo signals during the receiving cycle of the sonar system.

Abstract: The present invention shows a system for the continuous echo analysis of a body of liquid, surrounded by walls of known dimension, for the presence of an object. Such a system comprises:a transmitting component capable of translating an electrical pulse into intermittent instigative pulses of sonic energy emitted into the body of liquid, wherein such pulses of sonic energy permeate the body of liquid, reflecting off the walls and any object within the body of liquid, and returning as a set of echo information;a receiving component capable of receiving such echo information and translating that echo information into a waveform equivalent of that echo information; and,an analysis component comprising a microprocessor-controlled electronic circuit capable of receiving each waveform and comparing that waveform against stored data on previous waveforms to provide an alarm activation signal when the variance exceeds a predetermined settling.

Abstract: A sonar transducer includes an electro-mechanical transducer coupled to a front mass and a back mass. Annular rings space a compliant diaphragm from the front mass, the diaphragm being in communication with the liquid to which the sonar transducer is exposed. The compliance of the diaphragm is selected to tune the sonar transducer to eliminate reactive components of the impedance of the combined sonar transducer and liquid medium load, and to maximize the radiation resistance of the system.

Abstract: A covert attacking swimmer is discovered and acquired by an echo-search aratus. Once acquired, a search and destruct vehicle type weapon is launched which seeks out the attacking swimmer and when in range therewith shoots him with lethal electric fields or spears.

Abstract: An underwater object detection system and method are described which util changing phase relationships between radio waves received by a moving underwater receiver, via a retransmitting underwater object, and radio waves received through air directly from a transmitter. The moving underwater receiver is characterized by an envelope or encapsulation of material of different radio wave propagation rate than that of the water medium, so that a markedly different phase change relation exists when the underwater receiver is in contact with the object.

Abstract: A regenerative radio-frequency wire detector is disclosed which incorpora a radio antenna and a radio receiver connected thereto. A radio transmitter is timely energized by an output signal from the aforesaid radio receiver which, in turn, causes the transmitting of electromagnetic energy within the environment ambient to the wire to be detected. A commercial radio station or other source is employed as a covert initial energizer of the wire to be detected. When so energized, said wire re-radiates electromagnetic energy to the receiving antenna which starts the regenerative processing within the system loop constituting the radio receiving antenna, the radio receiver, the radio transmitter, the transmitting radio antenna, the wire, and the environmental medium or mediums within which it is disposed. Due to the amplification effected by the aforesaid regeneration process, the detection of marine mine command wires, for example, is facilitated.

Abstract: A new method for measurement of the directional spectra of surface gravity (water) waves. Measurements are made at a single point by orthogonally mounted seismometers buried below the seabed surface and a pressure sensor resting on the seafloor or buried below the seabed. The maximum entropy principle is used to find the directional distribution function for the waves traveling through the sediments as measured by the seismometers. This function is combined with the frequency spectra of the ocean surface waves to form the directional spectra of the surface gravity waves. The method produced high directional resolution for instruments that were adequately coupled with the seabed. The method is also capable of detecting objects moving through water, such as surface ships and submarines.

Abstract: A diver navigation system which provides reliable position information to able a diver to locate and when required repair existing underwater devices such as cables, leg moorings and the like. The diver navigation system comprises a synchronous range-range navigation system operating on a repeating timing cycle, which is accurately duplicated in a master transmitter, a slave transmitter and a receiver. Within the master and slave transmitter the timing cycle is subdivided into two equal approximately one second subcycles, the first subcycle being for the master transmitter and the second subcycle being for the slave transmitter. The master transmitter sends out a tone burst signal at the beginning of the first subcycle and the slave transmitter sends out a tone burst signal at the beginning of the second subcycle. Each tone burst signal, in turn, comprises a 34 kilohertz signal followed by a 32 kilohertz signal each of which has a time period of approximately one millisecond.

Abstract: A method for combating a submerged target object through the intermediary of an active body which is deployable in an airborne mode, and which picks up a sonar contact with the target object from a helically descending searching trajectory below the water level. Also disclosed is an arrangement for combating a submerged target object, especially a double-hulled submarine, through the intermediary of an active body deployable in an airborne mode which is equipped with a sonar installation and with guidance media for the traversing of a helical gliding search trajectory. Upon contacting a target through the intermediary of a searching sonar which is more simply constructed in comparison with a homing sonar, the active body launches an effector which is equipped with an extremely rapid drive into linear attacking trajectory tangentially to the searching trajectory, and wherein the effector will detonate a warhead upon impact against a target.

Abstract: An air supply system which communicates between the compressed air supply and the mouth of a scuba diver utilizes a sealing cup which surrounds the mouth to define a breathing/microphone chamber into which the diver can speak. In addition to this chamber into which the diver can breath, a mouthpiece on an airpipe which passes through the sealing cup can be quickly forced into the mouth for direct breathing through the mouth into the air tube, bypassing the breathing chamber defined by the sealing cup in the event this chamber becomes flooded.

Abstract: An apparatus for detecting a person in a body of water includes a transmitter for generating an electrical swept frequency signal having a frequency that continuously varies between upper and lower limits, at least one pair of transducers disposed in a body of water including a transmitting transducer connected to receive the swept frequency signal for launching a beam of acoustical waves in response to the swept frequency signal in the body of water and a receiving transducer disposed opposite the transmitting transducer for receiving the acoustical waves and for converting received acoustical waves into an electrical received signal, and a receiver connected to the receiving transducer for producing a detected signal in response to the received signal, for producing a threshold signal in response to the detected signal, and for initiating an alarm when the detected signal falls below the threshold for at least a predetermined length of time.

Abstract: An acoustic transducer system employs a seawater return cable as a receiver lement. The cable is either open ended or short circuited with the seawater. A carrier frequency is applied at one end of the cable. Acoustic pressure waves impinging the cable change the characteristic input impedance of the cable. The changes in the impedance amplitude and phase angle are processed to derive information descriptive of the acoustic source.

Abstract: To detect and classify features in a sonar image comprised of a matrix of pixels each pixel having a known greyness level a set of windows is defined such that each window is comprised of a set of adjacent pixels such that every pixel of the image is included in at least one window. Properties of the greyness level for the pixels in each window are defined to enable selection of those windows having specific features of greyness level in excess of a predetermined threshold. Matched filter correlations are performed on the pixels in the selected windows to identify highlights and shadows. The identifying highlights and shadows are classified as targets, anomalies or background.

Abstract: The present invention relates to a method and system for generating signals which represent a map that depicts one or more submerged objects within an underwater area; detecting acoustic energy emitted from means carried by a diver within said underwater area, or scanning said area with sonar energy, to develop signals which indicate the location of said diver within said area; and combining said diver location signals with said map representing signals for producing a composite visual display to said diver which shows his location with respect to the location of one or more submerged map objects within said area. A remote station also may be provided at which several of these functions are performed.

Abstract: Pulsed ultrasonic apparatus for monitoring a swimming pool includes a transmitter housing securable to a child and provides a swept frequency pulsed output from a transducer within the housing when an electrical circuit is completed by having a pair of tabs on the outside of the housing immersed in water. The output from the transducer is detected by a receiving hydrophone and the hydrophone is connected to receiver circuitry which provides an appropriate alarm signal.