Abstract: Phase noise estimation and cancellation as disclosed herein may allow cost-efficient increase of capacity in communications by enabling very high QAM levels. The proposed solution is potentially applicable to any single carrier applications where phase noise is a limiting factor and a required order of modulation is very high. For example, disclosed embodiments may enable high QAM levels for microwave backhauls despite severe phase noise sensitivity. One embodiment involves a pilot-aided and BCJR-based sequential search algorithm that accurately estimates and subtracts fast-varying phase noise symbol-by-symbol. Residual BER performance is evaluated under the most challenging phase noise scenarios. FPGA emulation results show detection and removal of a significant amount of phase noise and zero BER performance even for complex 1K-QAM and above.

Abstract: This invention provides a system apparatus and method for ship-towed deployment of a non-linear volumetric array of hydrophones, allowing line-intersect or line-transect sampling of marine mammal populations through passive acoustic monitoring, enabling unambiguous real-time three-dimensional localization of single sounds received through a low-cost, modular, robust, stable, small, light, neutrally to slightly negatively buoyant volumetric array having low self-noise and low flow noise, that avoids putting high tension on the tow cable and that is compatible with standard hydrophones, instrumentation, cabling, and analytical software.

Abstract: The invention concerns an underwater transceiver device, communications system and method of communicating sensor data underwater. The transceiver device comprises a sensor unit or a sensor connection for an external sensor unit for providing a sensor value and a communication unit functionally connected to the sensor unit or connection and comprising means for wirelessly transmitting the sensor value to another underwater device as data packets according to a timing scheme. According to the invention, the communication unit further comprises means for wirelessly receiving data packets of other underwater devices, and means for adjusting the timing scheme based on data packets received so as to avoid simultaneous transmitting of underwater devices. The invention enables energy-efficient and robust communications between diving equipment.

Abstract: Provided is a data processing device and a method of operating the same. The data processing device includes: a plurality of preprocessors configured to perform correction processing on a plurality of sensor data; a first switching circuit configured to selectively map and input the plurality of sensor data from at least two sensors to at least two preprocessors among the plurality of preprocessors; and a hybrid data processing engine configured to perform at least one of image enhancement and depth information determination on the plurality of sensor data received, via an on-the-fly method, from the at least two preprocessors.

Abstract: A relay supported method, system, and a RN for transmitting visible light information are provided. The method includes that UE sends information to a detected RN, and the RN processes and forwards the information from the UE to a VS. The RN is configured to process and forward the information from the UE to the VS in an uplink direction. According to the present disclosure, with adoption of visible light communication relay, visible light communication coverage may be broadened, and a visible light communication rate may be increased.

Abstract: A subsea electronics module for use in a subsea well installation, comprising: a backplane connecting a plurality of slots; a plurality of physical cards each supporting an electronic assembly having an identical architecture including a programmable logic module and a memory, the physical cards each being inserted into a respective slot of the backplane; and wherein the identical electronic assembly of each physical card is configured by program instructions stored in the memory thereon to be configured to perform in use a set of electronic functions of one of a plurality of different defined card roles in dependence on either one or both of: the position of the slot into which that card is inserted; an indication of a card role configuration selection for that card.

Abstract: A Doppler compensation system includes a transmitter unit for transmitting a signal, wherein the transmitted signal being associated with an emission time-scale, a receiving unit for receiving a signal, wherein the received signal is associated with a receive time-scale that is not equivalent to the emission time-scale, and a Doppler compensating unit configured to estimate an inverse temporal distortion function, wherein the Doppler compensating unit implements the inverse temporal distortion function to estimate the transmitted signal.

Abstract: A sample rate converter for an oversampled data stream develops interpolated samples at a first oversample rate, from samples at a second oversample rate; wherein the first oversample rate is a non-integer multiple of the second oversample rate. When the samples at the second oversample rate are changing state, at least two interpolated samples are generated or the interpolation is at least second order. When the sample at the second oversample rate is not changing state, the sample at the second oversample rate is passed substantially unchanged. In one embodiment of the invention, asynchronous sample rate conversion is performed, and the first oversample rate is a varying non-integer multiple of the second oversample rate.

Abstract: A code division multiple access (CDMA) communications device includes a CDMA receiver to isolate a CDMA signal, and a processor to generate a quantized sample representation of the CDMA signal. The processor performs a hard correlation between the quantized sample representation of the CDMA signal and a quantized representation of a reference to generate a coarse time alignment. Based upon the coarse time alignment, the processor performs a soft correlation between actual values of the CDMA signal and the reference.

Abstract: An underwater communication system comprises a plurality of location and messaging units for sending and receiving ultrasonic energy through water. In accordance with one aspect, each of the location and messaging units comprising an array of transducers, a transceiver adapted to generate a code element, generate a data element, generate a modulation element, and combine the code element, the data element and the modulation element into an analog wave form. The system is further adapted to transmit the analog wave form through one of the ultrasonic transducers and receive the analog wave-form generated by at least one of the location and messaging units.

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: Systems, apparatuses, and methods for securing wireless communication using an acoustic signal are described. In one method involving a first and second device, the second device generates, when connecting to the first device, connection initiation information including key information for secure communication, converts the connection initiation information to an acoustic signal, and transmits the acoustic signal to the first device through an acoustic communication channel. Then the second device monitors a radio wireless channel, which is secured using the key information for secure communication, to determine whether a valid response is received from the first device and, upon receipt of the valid response, discontinues transmission of the acoustic signal and begins communicating with the first device securely on the radio wireless channel.

Abstract: A detection system of geological formations, particularly but not exclusively used for oil exploration, and for characterization and monitoring of hydrocarbon reservoirs. The detection system includes an electromagnetic transmission device positioned on a surface of a geological formation close to a first well having a vertical development direction, the first well being covered by a metal casing, and an electromagnetic reception device positioned deep inside the first well, the electromagnetic reception device including an electromagnetic detector. The electromagnetic transmission device includes a primary electromagnetic field generator configured to generate a primary electromagnetic field focalized in a direction of the metal casing, the metal casing irradiating the primary electromagnetic field into the geological formation.

Abstract: A system and method for monitoring biometric data of a diver and signaling those data from a first communication device to other communication devices, e.g., those of other divers, on a ship or buoy. A signal generated from a device of the diver can generate a diver identifier, an indication of a stress state of the diver and the diver's location.

Abstract: In one aspect a system for acoustic testing comprises a plurality of acoustic sensors mounted to a plurality of vehicles, a control system to control the plurality of vehicles, and a data acquisition system to receive data generated by the plurality of acoustic sensors in response to noise from a noise source proximate the plurality of vehicles.

Abstract: A device is provided for monitoring waters, particularly swimming pools, including at least one control unit assigned to one person which includes at least one sensor device, one analysis device and one transmitter; at least one receiving device disposed within the waters; at least one transmission device which is signal-connected to the receiving device; and at least one display unit which is signal-connected to the transmitter. The transmitter is designed such that it emits signals of a predetermined pattern in the event of an alarm, and the receiving device is designed such that it recognizes a case of alarm based on the predetermined pattern of the signal and emits an alarm signal to at least one display unit.

Abstract: A storage and/or reaction container system for fluids, includes a container and an electronic documentation device connected to the container. The documentation device further includes a timing device for capturing a point in time, at least one sensor, at least one input device for capturing inputs, and a storage device to store for readout at least one measured value captured by the at least one sensor device and/or an input captured by the at least one input device. The at least one measured value and/or the at least one input is associated by the timing device with the point in time of the capture.

Abstract: A signal generator generates an electrical signal that is sent to an amplifier, which increases the power of the signal using power from a power source. The amplified signal is fed to a sender transducer to generate ultrasonic waves that can be focused and sent to a receiver. The receiver transducer converts the ultrasonic waves back into electrical energy and stores it in an energy storage device, such as a battery, or uses the electrical energy to power a device. In this way, a device can be remotely charged or powered without having to be tethered to an electrical outlet.

Abstract: A signal generator generates an electrical signal that is sent to an amplifier, which increases the power of the signal using power from a power source. The amplified signal is fed to a sender transducer to generate ultrasonic waves that can be focused and sent to a receiver. The receiver transducer converts the ultrasonic waves back into electrical energy and stores it in an energy storage device, such as a battery, or uses the electrical energy to power a device. In this way, a device can be remotely charged or powered without having to be tethered to an electrical outlet.

Abstract: A system and method measures the time offsets of a plurality of acoustic sensor nodes relative to a reference time. The system includes an acoustic transceiver arranged to transmit a first signal to each acoustic sensor node and a processing resource arranged to record the transmission time of the first signal relative to the reference time. The acoustic sensor nodes receive the first signal and transmit a return second signal to the acoustic transceiver after a predetermined time delay, the second signal including the current acoustic sensor node internal time. The acoustic transceiver receives the second signal, and the processing resource records the time at which the second signal was received relative to the reference time and records also the combined time of flight of the first and second signal. From this data the time offset between the sensor node internal time and the reference time is calculated.

Abstract: Disclosed is an orthogonal frequency division multiplexing (OFDM)-based acoustic communications system. At an acoustic transmitting end, original data is modulated through channel coding into an acoustic signal of a data frame formed by multiple OFDM symbols and the acoustic signal is transmitted through a loudspeaker; at an acoustic receiving end, after a microphone receives the acoustic signal, and the acoustic signal is restored to the original data through demodulation and channel decoding. In a communication process, symbol synchronization is implemented through pilot information, and data frame synchronization is implemented in a manner of inserting baker codes, thereby simplifying processing, having a low bit error rate, improving acoustic communication efficiency, promoting development of acoustic communication, and having a good application prospect.

Abstract: A method for mobile underwater acoustic communications includes double differentially (DD) encoding a communication signal to produce a DD-encoded communication signal, applying direct sequence spread spectrum (SS) to the DD-encoded signal to produce a DD-SS communication output signal, and transmitting the DD-SS communication output signal. The method i) increases the SNR via processing gain, ii) eliminates the ISI through multipath suppression, and iii) enables bandwidth efficiency improvement via data multiplexing. The method is shown capable of facilitating simple receiver processing and offering performance robustness against unpredictable channel fluctuations.

Abstract: The invention relates to an underwater communication system and method. The system comprises at least one underwater remote device comprising a processing unit and functionally connected to the processing unit first magnetoinductive communication means capable of communicating with other underwater devices using magnetic induction, and a wearable underwater monitor device comprising second magnetoinductive communication means capable of communicating with said remote device using magnetic induction. According to the invention, the remote device further comprises functionally connected to said processing unit acoustic communication means capable of transmitting acoustic signals. The invention helps to keep the monitor device small and energy efficient, still allowing for long-distance underwater communications.

Abstract: A method of locating an underwater based system, the method including determining the underwater based system's geo-location, encoding the underwater based system's geo-location for RF transmission, encoding the underwater based system's geo-location for acoustic transmission, and transmitting RF and acoustic signals containing the encoded geo-location to a receiving station. A locator for locating an underwater based system including a buoy, a global positioning system having an antenna and a receiver, an RF transmission system including an antenna and a transmitter, an underwater acoustic transducer, and a locator control unit adapted to determine the underwater based system's geo-location, encode the underwater based system's geo-location for RF transmission, encode the underwater based system's geo-location for acoustic transmission, and transmit RF and underwater acoustic signals containing the encoded geo-location.

Abstract: Injectable acoustic tags and a process of making are described for tracking host animals in up to three dimensions. The injectable acoustic tags reduce adverse biological effects and have a reduced cost of manufacture compared with conventional surgically implanted tags. The injectable tags are powered by a single power source with a lifetime of greater than 30 days. The injectable tags have an enhanced acoustic signal transmission range that enhances detection probability for tracking of host animals.

Abstract: A method and system are described that can be used for scanning underwater structures. The method and system allow a user to gain a better understanding of an existing underwater structure. For example, the method and system allow for building a three dimensional model of an underwater structure. A sonar wave is directed toward an underwater structure, and a reflected sonar wave is received. Initial 3D data points are obtained from the reflected sonar wave, and are configured to provide a three-dimensional image of the underwater structure. A working alignment model of the underwater structure is generated by the initial data points. As new 3D sonar data is collected, the new 3D sonar data is aligned with and added to the alignment model.

Abstract: An underwater communication system comprises a plurality of location and messaging units for sending and receiving ultrasonic energy through water. In accordance with one aspect, each of the location and messaging units comprising an array of four ultrasonic transducers positioned such that they define a generally tetrahedral shape, a transceiver adapted to generate a code element, generate a data element, generate a modulation element, and combine the code element, the data element and the modulation element into an analog wave form. The system is further adapted to transmit the analog wave form through each of the four ultrasonic transducers and receive the analog wave-form generated by at least one of the location and messaging units.

Abstract: Various embodiments of the invention provide a buoy and system for monitoring divers and other underwater objects. In many embodiments, the buoy has capabilities to monitor a diver, obtain position information about the diver and use that information to move itself to an effective range for continued monitoring. The buoy can connect and communicate with a communication device attached to a diver to communicate, position, biometric and other data. In one embodiment, the buoy comprises a propulsion system for propelling the buoy, an acoustic communication module for communicating with the diver and a propulsion controller for controlling the propulsion system to move to the effective range. Other embodiments provide a power generation system using a power generating buoy comprising an inertial weight, an energy converter and a connecting linkage. The system may comprise a single or multiple buoys and can include an electrical storage such as an electrical battery.

Abstract: A method of underwater communication between a link initiator and a link receptor, by transmitting a link acquisition waveform from the initiator to the receptor, and establishing communications channel parameters from such a received waveform. Data is then transmitted according to these parameters, which may include range, direction, frequency band and Doppler, with greater efficiency and robustness.

Abstract: An environmental monitoring system comprises at least one underwater environmental measurement device and a transmitter for transmitting data from the measurement device to an above water station using electromagnetic and/or magnetic signals, and/or a receiver for receiving data and/or commands from the above water station using electromagnetic and/or magnetic signal.

Abstract: The autonomous waterproof electronic signaling device disclosed comprises an activator; an audible signal emitter and a visual signal emitter, the audible signal emitter to emit a primary signal upon activation of the activator, the audible signal emitter comprising one or more of the following: a hydrophone, a siren, a speaker, or a transducer; and a head assembly, the head assembly positioned so as to alter at least a portion of the primary signal producing a notification signal. The visual signal emitter comprises at least one of incandescent bulbs, compact fluorescent bulbs, strobe bulbs, high intensity discharge (HID) bulbs, and light emitting diodes (LED) bulbs. The audible signal emitter and a visual signal emitter are operative singly or in combination, continuously or intermittently.

Abstract: The present invention relates to a transfer system for providing wireless data transfer, electrical power transfer and navigation between a mobile subsea vehicle and a deployed subsea station that uses acoustic and electromagnetic carrier signals for wireless communication and navigation. An inductive connector is provided for power transfer between mobile subsea vehicle and a deployed subsea station without conductive contact.

Abstract: An underwater communication system comprises a plurality of location and messaging units for sending and receiving ultrasonic energy through water. In accordance with one aspect, each of the location and messaging units comprising an array of four ultrasonic transducers positioned such that they define a generally tetrahedral shape, a transceiver adapted to generate a code element, generate a data element, generate a modulation element, and combine the code element, the data element and the modulation element into an analog wave form. The system is further adapted to transmit the analog wave form through each of the four ultrasonic transducers and receive the analog wave-form generated by at least one of the location and messaging units.

Abstract: A communication device includes: an ultrasonic oscillating unit which detects or generates an ultrasonic wave; a communication unit which transmits and receives information using the ultrasonic wave; a storage unit which stores a table to which a communication command to designate communication with the another communication device is allocated in time series, the table being shared by the another communication device; and a control unit which shifts the communication unit to one of a transmitting state, a receiving state, and a standby state that is neither the transmitting nor the receiving state, synchronously with the another communication device on the basis of the communication command in the table.

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: An ultrasonic system including an ultrasonic transmitter and an ultrasonic receiver is provided. The ultrasonic transmitter emits a transmission signal, which includes a synchronous burst and multiple data bursts. The ultrasonic receiver receives a synchronous echo, and determines whether the amplitude of the synchronous echo is larger than a first threshold. If the amplitude of the synchronous echo is larger than the first threshold, then the ultrasonic receiver interprets the multiple data echoes corresponding to the data bursts to obtain a digital signal.

Abstract: A method and apparatus are present for managing a transmission of photons. The number of parameters for transmitting the photons as a beam in a liquid are identified using a number of characteristics of the liquid to form a number of selected parameters. The photons are transmitted in the liquid as the beam to a target using the number of selected parameters to form the transmission of the photons.

Abstract: A modulation device, a demodulation device, and a transmission system and acoustic signal transmission method using them which can carry out a synchronization process for data signals without using a carrier frequency for a synchronization signal. The modulation device transmits an acoustic signal superposed with a PN sequence set according to a carrier frequency and a data signal. A demodulation device receives the acoustic signal, determines the PN sequence having the highest maximum correlation value with the acoustic signal in a plurality of PN sequences, detects a symbol synchronization point according to the correlation value between the thus determined PN sequence and the acoustic signal, and performs a synchronization process. Thereafter, according to the detected synchronization point and determined PN sequence, an OFDM demodulation processing unit decides the carrier frequency band of the data signal superposed on the acoustic signal and demodulates the data signal.

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 metrology device, computer program product and computer-implemented method generating survey data without having the device touch subsea objects being surveyed. The metrology device may be used with an underwater vehicle or diving personnel, and may comprise an inertial navigation system having gyroscopes to detect angular velocity and accelerometers for the detection of linear velocity and transported by an underwater robotic apparatus or diver, the inertial navigation system outputting position and orientation data of the device for storage; an aiding device for collecting image data of the subsea objects, the aiding device being positioned so that the distance and orientation between the optical scanner and the inertial navigation system is known; and a computer for using the position information and image data between a successively visited known point to determine the drift of the metrology device and to use the drift of the metrology device to correct measurements of same.

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 sensing and communications node includes an underwater vehicle, target sensing capability mounted on a forward portion of the underwater vehicle, at least three passive acoustic sensors evenly distributed about a first circumferential region of the underwater vehicle, and at least three transceiving hydrophones evenly distributed about a second circumferential region of the underwater vehicle. A controller governs collection of sensed data and transmission of the sensed data into the underwater environment.

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: 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 system and method for generating an underwater acoustic waveguide suitable for guiding acoustic energy between a source and a receiver to enable underwater communications. Electrolysis of water by electrically powered terminals continuously creates a bubble field having a volume fraction of less than 0.01% gas. The bubble field has a lower sound speed than the surrounding water, resulting in the bubble field acting as a waveguide to transmit sound over the length of the bubble field. By maintaining small bubble radii, the bubble field can be stable for long periods of time. By keeping the volume fraction and bubble radii small, the power requirements for the terminals are minimized.

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: Sensor and communications systems for communicating measurements from subsea equipment, such as at an offshore well, to the surface. A sensor for a physical parameter, such as pressure or temperature at a blowout preventer, capping stack, or conduit in communication with the same, is electrically connected to a subsea acoustic transponder. An acoustic monitoring transponder deployed near the well periodically interrogates the acoustic transponder with an acoustic signal, in response to which the acoustic transponder transmits an acoustic signal encoded with the measurement. The measurement data are stored at the acoustic monitoring transponder. An acoustic communications device later interrogates the acoustic monitoring transponder to receive the stored measurement data for communication to a redundant network at the surface.

Abstract: An underwater system (10) comprising a transmitter (12) for broadcasting an electromagnetic synchronization 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 synchronization.