Why does sonar use ultrasonic waves instead of infrasound waves?

Due to the short range of other detection methods, the penetration ability of light in water is very limited. Even in the clearest seawater, people can only see objects within a dozen meters to dozens of meters. Electromagnetic waves decay too fast in water, and the shorter the wavelength, the greater the loss. Even if high-power low-frequency electromagnetic waves are used, they can only propagate for tens of meters.

But the attenuation of sound wave propagation in water is much smaller. A few kilograms of bombs exploded in the deep-sea passage, and signals could be received 20 thousand kilometers away. Low-frequency sound waves can also penetrate the strata thousands of meters under the sea and obtain information in the strata. So far, there is no more effective means to measure and observe in water than sound waves.

Extended data:

It can be used to detect underwater targets and determine their moving elements, such as distance, azimuth, speed and heading. Active sonar emits some form of acoustic signal, which is detected by the echo reflected by obstacles or targets during underwater propagation. Because the target information is stored in the echo, we can judge the existence of the target according to the received echo signal, and measure or estimate the distance, azimuth, speed and other parameters of the target.

Traditionally, the main position of submarine sonar installation is at the forefront. Because the modern submarine relies heavily on the detection effect of passive sonar, the huge radio device not only increases the diameter of the submarine, but also makes the torpedo tube originally in this position give up and retreat to both sides.

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