Technique for detecting the pressure of objects under water by acoustical echo is called:

Explanation

Option A: The Doppler effect is the change in frequency of a wave due to the motion of the source or the observer. The Doppler effect can be used to detect the speed of objects, such as cars or trains. However, it is not used to detect objects underwate Option B: Sonar stands for SOund NAvigation and Ranging. It is a system that uses sound waves to measure the distance, direction, and speed of objects underwater. Sonar systems emit sound waves into the water, and the sound waves are reflected back by objects underwater. The time it takes for the sound waves to travel to the object and back is used to calculate the distance to the object. The direction of the object is determined by the direction of the sound waves. The speed of the object is determined by the difference between the frequency of the emitted sound waves and the frequency of the reflected sound waves. Option C: Radar stands for RAdio Detection And Ranging. It is a system that uses radio waves to measure the distance, direction, and speed of objects. Radar systems emit radio waves into the air, and the radio waves are reflected back by objects in the air. The time it takes for the radio waves to travel to the object and back is used to calculate the distance to the object. The direction of the object is determined by the direction of the radio waves. The speed of the object is determined by the difference between the frequency of the emitted radio waves and the frequency of the reflected radio waves. Option D: Red shift is the increase in the wavelength of light due to the expansion of the universe. Red shift is not used to detect objects underwater.