Abstract: A robust underwater communication system, for communication between an acoustic signal transmitter and a remotely positioned acoustic signal receiver, wherein transmitted data is carried by a plurality of symbols each having two components one of which comprises a distinctive bit code and the other of which appertains to the character of the symbol as a whole wherein the character of successive symbols is stepped through a predetermined continuously repeating sequence of distinctive steps each of which occurs once in the sequence, the signal receiver being operated synchronously with the signal transmitter and comprising a correlator arrangement responsive both to the bit code and to the character of received signals for effecting demodulation and having a plurality of outputs one for each symbol, so that as each symbol is detected a signal on the output to which it corresponds pre-dominates and amplitude detector means responsive to the outputs from the correlator arrangement for providing an output signal c

Abstract: An embodiment of an apparatus includes a communication circuit and a transducer array coupled to the communication circuit. The communication circuit is operable to generate first and second information signals, and the transducer array is operable to generate in response to the first information signal a first sonar signal having a first frequency, and to generate in response to the second information signal a second sonar signal having a second frequency. The transducer array may generate the first and second sonar signals simultaneously to increase the transmission bandwidth. Where such an apparatus is a buoy, then the buoy may relay signals from an above-surface vessel to an unmanned underwater vehicle (UUV), and may relay signals from the UUV to the vessel. Therefore, the buoy allows the vessel to control the UUV without a cable linking the buoy and the vessel, and thus allows one to eliminate such a cable.

Abstract: Taps on a beam-interrupt button of an underwater signaling transceiver are encoded as binary frequency shift-key modulated Golay codes, which are transmitted via 56-58 kHz compression waves generated by a ring-shaped electromechanical transducer. Light emitting diodes flash to signal the content of received signals and provide monitoring of the distance between divers. All components of the transceiver—except outer portions of input/output leads and a suction cup for attaching to the transceiver to a diver's mask—are completely encased in transparent plastic. The input/output leads allow an internal battery to be recharged, provide access to the internal processor for programming and data retrieval, and monitor whether the transceiver is submerged so that the transceiver can operate in an underwater mode or an above-water mode. Transceivers only communicate with other transceivers which use the same communication channel.

Abstract: An analog multi-gigabit receiver and/or transceiver can be implemented for the reception and demodulation of multi-gigabits quadrature phase shift keying (QPSK) modulated using a CMOS (complementary metal-oxide semiconductor) process. Further, an analog multi-gigabit receiver and/or transceiver can be implemented for the reception and demodulation of multi-gigabits binary phase shift keying (BPSK), minimum shift keying (MSK), and/or amplitude shift keying (ASK) signal modulated in CMOS processes.

Abstract: An underwater communications system is provided that transmits electromagnetic and/or magnetic signals to a remote receiver. The transmitter includes a data input. A digital data compressor compresses data to be transmitted. A modulator modulates compressed data onto a carrier signal. An electrically insulated, magnetic coupled antenna transmits the compressed, modulated signals. The receiver that has an electrically insulated, magnetic coupled antenna for receiving a compressed, modulated signal. A demodulator is provided for demodulating the signal to reveal compressed data. A de-compressor de-compresses the data. An appropriate human interface is provided to present transmitted data into text/audio/visible form. Similarly, the transmit system comprises appropriate audio/visual/text entry mechanisms.

Abstract: An underwater communications system is provided that transmits electromagnetic and/or magnetic signals to a remote receiver. The transmitter includes a data input. A digital data compressor compresses data to be transmitted. A modulator modulates compressed data onto a carrier signal. An electrically insulated, magnetic coupled antenna transmits the compressed, modulated signals. The receiver that has an electrically insulated, magnetic coupled antenna for receiving a compressed, modulated signal. A demodulator is provided for demodulating the signal to reveal compressed data. A de-compressor de-compresses the data. An appropriate human interface is provided to present transmitted data into text/audio/visible form. Similarly, the transmit system comprises appropriate audio/visual/text entry mechanisms.

Abstract: A communication system for obtaining predetermined information from an underwater terminal via a sonobuoy is provided. The system includes an underwater terminal for transmitting and receiving sound wave signals, a base station apparatus for transmitting and receiving radio wave signals, and a plurality of sonobuoys for transmitting and receiving the sound wave signals to and from the underwater terminal, and for transmitting and receiving the radio wave signals to and from the base station apparatus.

Abstract: To control activation of one or more communication units in a survey system that performs surveying of a subterranean structure, optical activity on at least one optical link connected to at least one communication unit that is part of a survey system is detected. In response to determining that the optical activity has a characteristic that satisfies a predetermined criterion, the at least one communication unit is awakened.

Abstract: A wireless communication system includes a transmitting device and a receiving device, in which the transmitting device generates a signal including information and transmits the signal by electromagnetic waves and ultrasonic waves in the same frequency in parallel, and in which the receiving device extracts the signal from at least one of the electromagnetic waves and the ultrasonic waves transmitted from the transmitting device and acquires the information included in the extracted signal.

Abstract: The present invention provides a communication device and a communication method of an underwater vehicle, which use an electromagnetic field (electromagnetic wave), having a higher propagation speed than that of an acoustic wave, for communication between an underwater vehicle and a mother vessel or the like so as to allow real-time control of the underwater vehicle and the like and further to make the communication little sensitive to noise and the like. The communication device performs wireless communication between an underwater vehicle in water and an object on land or on water, and is configured to compress data to be transmitted and transmit/receive the compressed data by the use of a low-frequency electromagnetic field.

Abstract: The present invention relates to methods and systems for enhanced signal acquisition through cross-ambiguity function (CAF) interpolation. In one aspect, the present invention provides methods and systems for CAF interpolation. In an embodiment, a first CAF generated using a low input sampling rate (e.g., 1 sample/chip) is interpolated to generate a second CAF having a higher sample per chip rate. By lowering the initial input sampling rate, cost and complexity of initial synchronization processing can be significantly reduced at the receiver. In another aspect, coherent and non-coherent interpolation methods and systems are provided for time and frequency CAF interpolation. Low cost and low complexity implementations of these methods and systems are also provided with associated CAF peak detection methods and systems.

Abstract: A method and system for determining a physical property as a function of position. A data series including data point from one or more channels is obtained by frequency modulation continuous wave. A number of data points correspond to Nda different values of frequency of modulation. One or more processing steps are performed including at least part of said primary data series to obtain at least one secondary data series comprising N (N>Nda) data points from the values of frequency of modulation. The secondary data series from frequency domain is transformed to obtain at least one back scattering curve in space domain, and optionally the back scattering curve(s) to one or more physical properties as a function of position.

Abstract: The present invention provides an undersea seismic monitoring network, the monitoring network comprises at least one underwater vehicle and at least two monitoring stations located on the seabed, where each of the monitoring stations comprises at least one sensor for gathering seismic data and a radio modem for transmitting and receiving data to and from the underwater vehicle via a first wireless connection and where a second wireless connection is established between the monitoring stations, wherein the first wireless connection is formed by electromagnetic radiation through the water and the second wireless connection is formed by the propagation of an electromagnetic signal at least partially through the seabed.

Abstract: Advantageous online and/or real-time OFDM-based underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. The apparatus, systems and methods employ a receiver with a bank of parallel branches, with each branch having a self-correlator matched to a different waveform scaling factor. A detection is declared when any of the branches leads to a correlation metric larger than a pre-defined threshold. The branch with the largest metric yields a Doppler scale estimate and a coarse synchronization point. The proposed apparatus, systems and methods use one OFDM preamble, thereby avoiding the need to buffer the whole data packet before data demodulation and enabling online and/or real-time operation. Thus, the disclosed apparatus, systems and methods are advantageously applicable to UWA communications.

Abstract: The autonomous waterproof electronic signaling device disclosed comprises an activator; a signal emitter, said signal emitter to emit a primary signal upon activation of said activator, said signal emitter comprising one or more of the following: a hydrophone, a siren, a speaker, or a transducer; and a head assembly, said head assembly positioned so as to alter at least a portion of said primary signal producing a notification signal.

Abstract: An underwater wireless communication system and method includes a sensor node for transforming measured underwater data into ultrasound signals, and transmitting the transformed ultrasound signals and receiving other ultrasound signals.

Abstract: An underwater optical communications system and method particularly suitable for use in communications with automated equipment. A series of light beacons are dispersed throughout a communications zone. The light beacons are each provided with a plurality of light-emitting elements and light receiving elements which are positioned so that each beacon within the communications zone emits light in a plurality of directions and receives light from a plurality of directions. A submersible craft is similarly provided with light emitting elements and light receiving elements. The submersible craft is thus always in optical communication with one or more beacons when in the communications zone, regardless of the orientation of the craft and regardless of the position of the craft within the communications zone.

Abstract: Advantageous OFDM-based underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. In general, OFDM transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among OFDM subcarriers. The disclosed apparatus, systems, and methods use a two-step approach to mitigate frequency-dependent Doppler drifts for zero-padded OFDM transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling to convert a “wideband” problem into a “narrowband” problem; and (2) high-resolution uniform compensation on the residual Doppler. The disclosed apparatus, systems and methods are based on block-by-block processing and do not rely on channel dependence across OFDM blocks. Thus, the disclosed apparatus, systems and methods are advantageously applicable for fast-varying UWA channels.

Abstract: A method for transmitting data is disclosed having the following steps: emitting packets of at least two types: pure data (long packets) and acknowledgments of receipt (acknowledgment) (short packets). Each packet is formed of three components: a—an acquisition preamble, (1) for presence detection and the joint determination of the initial values of the time shift and of the frequency shift, and b—the data proper, (2) and c—a set of unmodulated fixed carriers (3) making it possible to permanently estimate the frequency shift.

Abstract: An underwater system (10) comprising a transmitter (12) for broadcasting an electromagnetic synchronisation signal and at least one node (14) that has a receiver for receiving that signal, the node being adapted to use the received signal for synchronisation.

Abstract: An extended underwater electromagnetic transducer is provided with an electrically insulated transmission line typically connected to a transmitter or receiver or transceiver system. The transmission line allows near-field communications with another transmitter or receiver or transceiver system. The transmission line provided is relatively long, the through water signal path length can be significantly reduced.

Abstract: Seabed sensor units, systems including same, and methods for acquiring seabed data are described, one seabed sensor unit comprising a base, the base containing at least one sensor able to detect a seismic signal, electronics comprising a clock and one or more electronic components enabling the sensor to communicate seismic data to one or more memory modules, and a local autonomous power source. This abstract is provided to comply with the rules requiring an abstract, which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).

Abstract: The present invention relates to a sensing system, in particular to sensing system for sensing undersea seismic events. A vibration sensor is provided for sensing seismic vibrations on the sea bed is provided. The vibration sensor is electrically coupled to a transmitter unit, the transmitter unit being arranged to transmit, in use, an acoustic wave from which the presence of a seismic vibration can be inferred. The acoustic wave modulates light travelling along a nearby optical cable, the modulation being recovered at a distant monitoring station. A flotation arrangement is provide for retaining the transmitter unit in a raised position relative to the sea bed to facilitate the coupling of the acoustic wave to the optical cable.

Abstract: An underwater communications system is provided that transmits electromagnetic and/or magnetic signals to a remote receiver. The transmitter includes a data input. A digital data compressor compresses data to be transmitted. A modulator modulates compressed data onto a carrier signal. An electrically insulated, magnetic coupled antenna transmits the compressed, modulated signals. The receiver that has an electrically insulated, magnetic coupled antenna for receiving a compressed, modulated signal. A demodulator is provided for demodulating the signal to reveal compressed data. A de-compressor de-compresses the data. An appropriate human interface is provided to present transmitted data into text/audio/visible form. Similarly, the transmit system comprises appropriate audio/visual/text entry mechanisms.

Abstract: An underwater communications system is provided that transmits electromagnetic and/or magnetic signals to a remote receiver. The transmitter includes a data input. A digital data compressor compresses data to be transmitted. A modulator modulates compressed data onto a carrier signal. An electrically insulated, magnetic coupled antenna transmits the compressed, modulated signals. The receiver that has an electrically insulated, magnetic coupled antenna for receiving a compressed, modulated signal. A demodulator is provided for demodulating the signal to reveal compressed data. A de-compressor de-compresses the data. An appropriate human interface is provided to present transmitted data into text/audio/visible form. Similarly, the transmit system comprises appropriate audio/visual/text entry mechanisms.

Abstract: Underwater communication system comprising a plurality of communication modules, each provided with a microprocessor, a memory, a transmitter and a receiver unit; these communication modules are incorporated in an underwater computer and in a plurality of underwater equipment devices; the underwater computer and the underwater equipment devices form an underwater master/slave communication network for short and long ranges, in which each device forms a node and communicates in a bidirectional way with the other nodes of the network administered by a main underwater computer or master unit; each node of the network is identified by a unique identification code which is assigned dynamically by the master unit of the network, and is provided with at least one of said communication modules for short-range communication; a data and message transmission protocol is provided for this network, for administering the bidirectional network between the various nodes of the network.

Abstract: An underwater communications system is provided that transmits electromagnetic and/or magnetic signals to a remote receiver. The transmitter includes a data input. A digital data compressor compresses data to be transmitted. A modulator modulates compressed data onto a carrier signal. An electrically insulated, magnetic coupled antenna transmits the compressed, modulated signals. The receiver has an electrically insulated, magnetic coupled antenna for receiving a compressed, modulated signal. A demodulator is provided for demodulating the signal to reveal compressed data. A de-compressor de-compresses the data. An appropriate human interface is provided to present transmitted data into text/audio/visible form. Similarly, the transmit system comprises appropriate audio/visual/text entry mechanisms.

Abstract: Systems and methods for visual light communication in an underwater environment are provided. The system can include a master control station that determines an amount of impairment of a water medium and selects one of a wired and wireless communication transceiver for exchanging communications with communication device located in the water. The system can also include a first gateway that exchanges radio frequency signals with the master control station and provides visual light communication signals to devices located in the water. The system can also include a second gateway that can exchange both visual light communication signals and acoustic communication signals with other devices located in the water.

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

Abstract: A system for measuring acoustic signature of a target object in water includes a plurality of rigid segments connected to each other to form a longitudinal member and a plurality of floats connected to the longitudinal member. Two buoys are connected at two ends of the longitudinal member and two weights are suspended from the buoys, thus making the longitudinal member neutrally buoyant when suspended in water. A plurality of hydrophones and an acoustic projector of a known source level are connected to the longitudinal member. The system further includes a data acquisition system for receiving signals from hydrophones and a signal processing means for processing signals received by data acquisition and determining acoustic signature of the target object. A depth/pressure sensor may be included. A pinger is located on the target object to measure range of target object to hydrophones. Range to target object is displayed in real time.

Abstract: The present invention includes a system and method of use for communications from an in-air platform to a submerged platform. The system includes a laser positionable on the in-air platform above a water medium that sends a pulsed information-bearing laser beam containing a modulated communications signal to create and react in a non-linear regime manner with the water medium at an air/water interface. The beam vaporizes and optically breaks down a portion of the water medium, creates a shock wave and generates bubble oscillations at the vaporized portion. An acoustic sensor on the submerged platform detects these shock wave oscillations within the water medium and a demodulator-decoder that identifies these broadband acoustic transients that contain deterministically placed energy and demodulates-decodes the acoustic transients into the transmitted communications signals from the in-air platform.

Abstract: An environmental monitoring system including at least one underwater measurement device and a transmitter for transmitting data from the measurement device to an above water station using a magnetically coupled antenna.

Abstract: Method for determining the location and/or speed of at least one swimmer, swimming through water, comprising: —sending acoustic signals through the water, using stationary acoustic transmitter means (AT) having a stationary position, or using mobile acoustic transmitter means (AT?) being carried by said swimmer (S); —receiving the acoustic signals using mobile acoustic receiver means (AR) being carried by said swimmer (S), or using stationary acoustic receiver means (AR?) respectively; —determining the time difference between the time of sending and the time of receiving each acoustic signal; —determining a location and/or speed of said swimmer (S) with respect to said stationary transmitter means (AT) or stationary receiver means (AR?), using said time differences and a predetermined propagation speed of the acoustic signal through the water.

Abstract: A method for transmitting data is disclosed having the following steps: emitting packets of at least two types: pure data (long packets) and acknowledgments of receipt (acknowledgment ) (short packets). Each packet is formed of three components: a—an acquisition preamble, (1) for presence detection and the joint determination of the initial values of the time shift and of the frequency shift, and b—the data proper, (2) and c—a set of unmodulated fixed carriers (3) making it possible to permanently estimate the frequency shift.

Abstract: A wireless communication system includes a transmitting device and a receiving device, in which the transmitting device generates a signal including information and transmits the signal by electromagnetic waves and ultrasonic waves in the same frequency in parallel, and in which the receiving device extracts the signal from at least one of the electromagnetic waves and the ultrasonic waves transmitted from the transmitting device and acquires the information included in the extracted signal.

Abstract: The present disclosure provides an underwater detector including a power source for applying a predetermined voltage, a voltage control circuit for controlling the voltage based on a control signal, a gate signal generating module for outputting a gate signal, a switching circuit for outputting a reference signal based on the voltage controlled by the voltage control circuit and the gate signal outputted from the gate signal generating module, and a transducer for transmitting an ultrasonic signal underwater, an envelope of which being controlled based on a waveform of the control signal by being applied with the reference signal.

Abstract: Advantageous OFDM-based underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. In general, OFDM transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among OFDM subcarriers. The disclosed apparatus, systems, and methods use a two-step approach to mitigate frequency-dependent Doppler drifts for zero-padded OFDM transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling to convert a “wideband” problem into a “narrowband” problem; and (2) high-resolution uniform compensation on the residual Doppler. The disclosed apparatus, systems and methods are based on block-by-block processing and do not rely on channel dependence across OFDM blocks. Thus, the disclosed apparatus, systems and methods are advantageously applicable for fast-varying UWA channels.

Abstract: An acoustic method and apparatus for an acoustic system use a transceiver module, which can transmit to a transmit acoustic element of a transmit sonar array and receive from a receive acoustic element of a receive sonar array in accordance with a common transmit/receive control signal.

Abstract: The present application provides a linear mechanism for optical-to-acoustic energy conversion for optoacoustic communication from an in-air platform to an undersea vehicle. Signals used in underwater acoustic telemetry applications are capable of being generated through the linear optoacoustic regime conversion process. A number of issues concerning linear optoacoustic communication is addressed that lead to a formulation of a linear regime optoacoustic communication scheme. The use of oblique laser bean incidence at an air-water interface to obtain considerable in-air range from the laser source to the vehicle is also addressed. The effect of oblique incidence on in-water range is addressed as well. Optimum and sub-optimum linear optoacoustic sound-generation techniques for selecting the optical wavelength and signal frequency for optimizing in-water range are identified.

Abstract: A system and a method for conveying data using the vector components of the acoustic field, in addition to the scalar component is described. Receivers capable of determining the transmitted data values by measuring one or more parameters of an acoustic field are utilized. Measured parameters of the acoustic field may include both the scalar and vector components. The described system and method may optimize the conveyance of communications through a fluid.

Abstract: Described is a device for generating an acoustic signal in an electrically conductive medium such as salt water. The device of the present invention has a broadband frequency response and supports high bandwidth data transmission. Reliability is improved in comparison to conventional underwater acoustic transmitters as the device includes no moving components. In one embodiment, the device includes a parallel and alternating arrangement of electrodes and magnets. Neighboring electrodes have different voltages and neighboring magnets have opposite pole configurations such that the magnetic fields overlap the currents between the electrodes in the medium. The currents or the magnetic fields are modulated according to a data signal to generate an acoustic signal in the medium.

Abstract: An embodiment of an apparatus includes a communication circuit and a transducer array coupled to the communication circuit. The communication circuit is operable to generate first and second information signals, and the transducer array is operable to generate in response to the first information signal a first sonar signal having a first frequency, and to generate in response to the second information signal a second sonar signal having a second frequency. The transducer array may generate the first and second sonar signals simultaneously to increase the transmission bandwidth. Where such an apparatus is a buoy, then the buoy may relay signals from an above-surface vessel to an unmanned underwater vehicle (UUV), and may relay signals from the UUV to the vessel. Therefore, the buoy allows the vessel to control the UUV without a cable linking the buoy and the vessel, and thus allows one to eliminate the tether between the UUV and the vessel for applications in which a tethered UUV may be unsuitable.

Abstract: A water submersible communications device for use on a body of water includes a housing and a communications module. The housing has a geometric centroid. The housing is submersible in and floatable on the body of water. The communications module is mounted on and/or in the housing. A center of buoyancy of the communications device is located substantially at the geometric centroid of the housing.

Abstract: A Manually Agitated Underwater Signaling Device used for SCUBA divers, snorkelers and other water-sport enthusiasts. The Manually Agitated Underwater Signaling Device includes a water tight right circular cylindrical body containing one or more rigid spheres inside, an integrated slot for the connection of a lanyard to one end of the right circular cylindrical body and a spherical base integrated into the other end of the right circular cylindrical body. The right circular cylindrical body is comprised of two body halves, a right half and a left half. The right half includes a tongue ridge with an energy director around the perimeter forming a mating surface. The left half includes a recessed groove around its perimeter forming a mating surface that intersects with the right half when aligned together. The Manually Agitated Underwater Signaling Device includes an exterior surface texture to improve the grip.

Abstract: Taps on a beam-interrupt button of an underwater signaling transceiver are encoded as binary frequency shift-key modulated Golay codes, which are transmitted via 56-58 kHz compression waves generated by a ring-shaped electromechanical transducer. Light emitting diodes flash to signal the content of received signals and provide monitoring of the distance between divers. All components of the transceiver—except outer portions of input/output leads and a suction cup for attaching to the transceiver to a diver's mask—are completely encased in transparent plastic. The input/output leads allow an internal battery to be recharged, provide access to the internal processor for programming and data retrieval, and monitor whether the transceiver is submerged so that the transceiver can operate in an underwater mode or an above-water mode. Transceivers only communicate with other transceivers which use the same communication channel.

Abstract: An underwater wireless communication system and method includes a sensor node for transforming measured underwater data into ultrasound signals, and transmitting the transformed ultrasound signals and receiving other ultrasound signals.

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

Abstract: A system and a method for conveying data using the vector components of the acoustic field, in addition to the scalar component is described. Receivers capable of determining the transmitted data values by measuring one or more parameters of an acoustic field are utilized. Measured parameters of the acoustic field may include both the scalar and vector components. The described system and method may optimize the conveyance of communications through a fluid.

Abstract: A water submersible communications device for use on a body of water includes a housing and a communications module. The housing has a geometric centroid. The housing is submersible in and floatable on the body of water. The communications module is mounted on and/or in the housing. A center of buoyancy of the communications device is located substantially at the geometric centroid of the housing.

Abstract: In a first preferred embodiment, an underwater alert system (10) includes a transmitter assembly (12), carried by a first diver (14), that transmits a predetermined wireless signal (36) to a receiver assembly (16), carried by a mask (18) worn by a second diver (20), that generates an alert to gain the attention of the second diver (20). In a second preferred embodiment, the underwater alert system (10) includes a first transceiver assembly (232), carried by a mask worn by a first diver (14), communicating a predetermined wireless signal (36) with a second transceiver assembly (254), carried by a mask (18) worn by a second diver (20), to permit the first diver and second diver to gain each other's attention.