Sonar is an electronic device that uses sound waves in water to detect, locate and communicate underwater targets. It is the most widely used and important device in hydroacoustics. Sonar is an electronic device that uses sound waves in water to detect, locate and communicate underwater targets. It is the most widely used and important device in hydroacoustics. Traditionally, the main location for installing sonar on submarines is at the front end. Since modern submarines rely heavily on the detection effect of passive sonar, the huge radio device not only increases the diameter of the submarine, but also has to give way to the torpedo tubes originally located in this position. Get out of position and step aside. Other sonar types installed on submarines include passive sonar listening devices installed at other locations on the hull. Using the same signal received at different locations, after computer processing and calculation, rough positioning can be quickly carried out. It is more advantageous for submarines with larger hulls because the measurement baseline is longer and the accuracy is higher. Another type of sonar is called "towed sonar", because when this sonar device is used, it is connected to the submarine by a cable, and the sonar body is towed far behind the submarine for detection. The use of towed sonar greatly enhances the ability of the submarine to detect For all-round and different depth detection capabilities, especially the tail end of the submarine. This is because the tail end of the submarine is also the power output part. Due to the interference of the sound of water flow, the sonar located in the front cannot hear the signal in this area, forming a blind spot. After using towed sonar, you can eliminate this blind spot and find the target hiding in this area. Interestingly, sonar is not unique to humans. Many animals have their own "sonars". Bats use their throats to emit 10-20 ultrasonic pulses per second and use their ears to receive their echoes. With this "active sonar", they can detect very small insects and metal wire obstacles with a thickness of 0.1mm. Insects such as moths also have "passive sonar" and can clearly hear the ultrasonic sound of bats 40m away, so they are often able to escape attacks. However, some bats can use high-frequency ultrasound or low-frequency ultrasound beyond the listening range of insects, so that the hit rate of catching insects is still high. It seems that animals are engaged in "sonar warfare" just like humans! Marine mammals such as dolphins and whales have "underwater sonar", which can produce a very certain signal to find food and communicate with each other. The sensitivity of dolphin sonar is very high. It can detect metal wires with a diameter of 0.2mm and nylon ropes with a diameter of 1mm several meters away. It can distinguish two signals with a time difference of only 200 seconds. It can detect fish schools hundreds of meters away. Cover your eyes and move flexibly and quickly through a pool full of bamboo poles without touching the bamboo poles; dolphin sonar has a strong "target recognition" ability and can not only identify different fish, but also distinguish brass, aluminum, and bakelite , plastic and other different materials, it can also distinguish between the echo of its own sound and the sound wave that people record and replay; the anti-interference ability of dolphin sonar is also amazing. If there is noise interference, it will raise its cry The intensity of the sound can overwhelm the noise so that one's own judgment is not affected; moreover, dolphin sonar also has the ability to express emotions. It has been confirmed that dolphins are animals with "language", and their "conversation" is precisely through their sonar system. Especially the most precious of the only four freshwater dolphins that exist in the world - the white-tailed dolphin in the middle and lower reaches of the Yangtze River in my country. Its sonar system has a clear "division of labor", including positioning, communication and alarm. , and has the special function of modulating phase through frequency modulation. Many species of whales use sound to detect and communicate, using sounds at much lower frequencies and over much longer ranges than dolphins. Other marine mammals, such as seals and sea lions, also emit sonar signals for detection. Animals that spend their entire lives in the extremely dark depths of the ocean have to use sonar and other means to search for prey and avoid attacks. The performance of their sonar is far beyond the reach of modern human technology. Unraveling the mysteries of these animal sonar has always been an important research topic in modern sonar technology. Edit this paragraph Factors affecting the performance of sonar In addition to the technical status of the sonar itself, the influence of external conditions is very serious. The more direct factors include propagation attenuation, multipath effect, reverberation interference, ocean noise, self-noise, target reflection characteristics or radiated noise intensity, etc. Most of them are related to marine environmental factors.
For example, during the propagation of sound waves, they are affected and restricted by the uneven distribution of seawater media and the sea surface and seabed. They will produce refraction, scattering, reflection and interference, which will produce sound ray bending, signal fluctuation and distortion, causing changes in the propagation path and the occurrence of The sonar shadow area seriously affects the range and measurement accuracy of sonar. Modern sonar can appropriately select the working depth and pitch angle of the array according to the propagation conditions caused by the change of sound speed and depth in the sea area, and use different propagation paths of sound waves (direct sound, seafloor reflected sound, convergence area, and deep-sea sound channel) to overcome underwater sound. The adverse effects of propagation conditions increase the sonar detection range. For another example, the self-noise of the carrier platform is mainly related to the speed. The greater the speed, the greater the self-noise, and the closer the sonar range is, and vice versa; the greater the target's reflection power, the farther away it can be detected by the opponent's active sonar; The greater the intensity of the target's radiation noise, the farther away it will be detected by the opponent's passive sonar