Marine acoustic technology

Marine acoustic technology

Underwater acoustic technology used in marine research and development, such as echo detection, passive detection, underwater acoustic communication, underwater acoustic telemetry and underwater acoustic remote control.
Echo detection   An acoustic signal is transmitted by a set of transducers, an echo signal reflected from the target is received by another set of transducers, and the parameters and properties of the target are determined by the processed signal.
Echo sounder   It emits a narrower sound pulse to the sea floor, measuring the time that the signal is reflected from the seabed and returned to the hydrophone. Under the condition that the speed of sound is known, the water depth at the vessel can be measured. Modern high-powered depth sounders that depict the deepest ocean shape. Multi-beam or multi-vibration depth sounder can simultaneously obtain data of multiple water depth points, and often use digital display, and automatically draw seabed topographic maps with computer.
Doppler Navigator (Doppler Sonar)   According to the Doppler effect, if the ship and the sea have relative motion, the echo signal will produce a frequency shift. 4 beams simultaneously measuring the frequency shift due to the relative motion of the seabed and the vessel appears, after signal processing, can accurately measure the velocity of the submarine vessel and to draw the track. Doppler sonar is also an effective tool to guide large ships.
Fish finder   The fish echoes obtained from it can roughly determine the location, extent and intensity of the fish. Commonly used vertical fish finder to detect underlying fish; horizontal fish finder to detect upper and middle fish. With advanced technologies such as electronic scanning, the range of detection is much larger.
Side scan sonar (submarine geomorphology instrument)   There are many types of underwater acoustic equipment used to investigate the geological features of the seabed, and this is one of them. A set of transducers with a wide vertical angle and a narrow horizontal angle are mounted on both sides of the ship, and the scattered echoes of the sea floor are recorded to obtain a fine seabed topographic sound map within a certain distance from the sides of the ship. In order to accommodate the needs of deep water detection, the transducer can also be placed in the towed body. This instrument can also be used in underwater engineering such as laying inspection of submarine tubing and searching for buried objects. The shallow formation profiler uses low-frequency acoustic signals to penetrate the formation and obtain structural data of the substrate from the analysis of its echoes, so it is widely used in geological exploration of underwater engineering. The seismic detection system uses high-power low-frequency sound sources, multi-channel receiving tow cables and multi-channel data processing and recording systems to obtain deep geological structure data for exploration of submarine oil and other minerals. High-power low-frequency sound waves from explosion sources can penetrate deep into the bottom layer. If a series of hydrophones are placed at a distance from the source of the explosion, refracted waves from different strata can be received to provide valuable data for submarine geological structures and underwater petroleum resources.
In ocean hydrological observations, hydroacoustic measuring instruments have been increasingly used. If the echo detector is modified accordingly and placed on the sea floor to make it emit sound pulses to the sea surface, the wave height and period can be measured, and the change of the tide level can be obtained from the change of the wave height average. If the transducer is mounted on the outside of the ship's side, the elements of the wave can also be measured. By using the Doppler shift characteristics of the echoes of the scatterers moving with the current, a Doppler current meter can be fabricated, which can measure the instantaneous low-speed current without destroying the flow field. According to the relationship between the transmission time of sound waves through a fixed distance and the speed of sound, a sound velocity meter can be made, which can measure the sound velocity of seawater in real time. The widespread use of underwater acoustic instruments in marine hydrological surveys is a major technological improvement.
Passive detection   It detects the acoustic information from the water and determines the position and characteristics of the sounding body. The sound source of the sound can be divided into two types: natural sound source and artificial sound source.
Natural sound source   Many animals in the ocean can make a sound (see the sounds of marine life ). Therefore, the passive detection system can be used to monitor the migratory characteristics of the fish population, and to determine the species of the fish according to the characteristics of the fish sound, and provide valuable data for marine fishing. The hydrophone system under deep seawater can also accurately measure the location of underwater earthquakes, underwater volcanic eruptions and estimate their strength.
Artificial sound source   Fish are very sensitive to sound and have a good and bad point. Therefore, they can make their favorite sounds to gather and send out the sounds they do not like to hear. Acoustic fish traps and fish repellents made according to this principle have begun to be used in marine fishing. Depending on the purpose, a small, audible or other modulation signal source is used to bind a small sound message to the fish body or into the stomach, using passive sonar tracking, which is suitable for the scene of marine life habits. the study. Tracking the small sounding body placed on the seabed, able to understand the movement state of the seabed gravel, etc., an acoustic beacon of the vessel and the flying opportunity, can emit an acoustic signal to indicate it during a certain period of time when the vessel and the aircraft are submerged under water. s position. Deep neutral currents, such as deep equatorial flows, can be measured using neutral buoys with acoustic beacons.
Underwater communication   Use sound waves to transmit information underwater. Both sides of the communication are provided with a transmitter and a receiver under water. There are two ways to communicate this: 1 carrier language to modulate sound waves or directly radiate speech sound waves. The latter is used for communication between divers who are closer. 2 Digital coding is a communication method commonly used as command and control in underwater acoustic equipment. The widely used underwater acoustic transponder is a typical device for digital coded communication. It performs communication between each transponder and the host by itself according to a pre-arranged procedure. The underwater acoustic transponder can be used for navigation and tracking of underwater carriers, helping drill ships and platforms to accurately find wellhead locations, monitoring underwater construction, and transmitting hydrological parameter signals for underwater telemetry systems.
Underwater acoustic telemetry system   After the underwater environment parameters to be measured are converted into underwater acoustic information, they are transmitted to the processing vessel or the shore station, processed by the underwater acoustic receiver, and converted into corresponding environmental parameter information.
Hydroacoustic telemeter for marine hydrological parameters   It replaces the troublesome cable with acoustic transmission. The instrument can be combined with a telemetry buoy system. A series of underwater buoys are used to transmit the measured parameters to the parent buoy through the underwater acoustic channel, which is then converted by the parent buoy into a radio signal for transmission to the survey vessel or shore station. This telemetry method has the advantages of real-time, large-area, fast and continuous measurement.
Net position meter   The underwater component is attached to the mesh port of the trawl, and the obtained information is converted into a hydroacoustic signal and transmitted to the ship, thereby monitoring the height of the fish net, the state of the opening, the pulling force of the tow rope, the state of the fish net and distribution, and the telemetry network port. The surrounding water temperature, etc., is very helpful for increasing the amount of fish caught.
Water acoustic remote control system   This includes onboard sound command transmitters, underwater acoustic command receivers and corresponding control mechanisms. For example, the underwater sound pontoon is released by the underwater sound release command by the underwater sound release command to make it float out of the water surface for the vessel to track and recover. This remote control technology is widely used in marine surveys, underwater engineering, oil drilling and seismic surveys. It can be used for underwater flow, blowout preventer racks, oil pipeline valves and underwater explosions. the way. Various marine automatic machines, such as unmanned submersibles, submarine self-propelled vehicles, and manipulator movements, can also be used with water-acoustic remote control.
In short, underwater acoustic technology has been widely used in various aspects of marine research and marine development, but because the seawater medium is a complex and variable and multi-channel acoustic channel, the underwater acoustic interference is very strong, and the detection of underwater acoustic information still exists. A series of difficulties have made certain improvements in the reliability and resolution of underwater acoustic instruments limited. To this end, in the future, it is necessary to strengthen the study of basic theories such as the law of waterborne sound transmission, and pay attention to exploring the possibility of applying new technologies in water sound.

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