In sonar technology, what function is provided by the Doppler effect?

The Doppler effect in sonar technology is crucial for understanding how sound waves change as they interact with moving objects. Specifically, it measures the speed of a target relative to the sonar source by observing the frequency shift of the sound waves that are returned to the sonar system. When a target is moving towards the sonar, the frequency of the returned sound waves increases, while if the target is moving away, the frequency decreases. This frequency shift allows sonar operators to calculate the velocity of the target, which is essential for tracking and engaging potential threats or monitoring environmental conditions.

The other functions described in the options do not pertain to the Doppler effect. While sonar can define range, indicate directional information, and measure depth through other technological means, these processes do not utilize the frequency changes related to the movement of objects, which is the hallmark of the Doppler effect. Thus, the measurement of target speed in relation to the sonar source accurately captures the essence of how the Doppler effect operates within sonar technology.