Final answer:
Doppler Sonar is used for measuring water currents by analyzing frequency changes in sound pulses, reflecting a process similar to Doppler radar. It, along with related technologies such as the Hall effect for measuring fluid flow, relies on the principles of the Doppler effect.
Step-by-step explanation:
Doppler Sonar is useful in measuring currents because it utilizes sound pulses and analyzes the changes in pitch or frequency of particles suspended in the moving water. This technology is used to detect turbulence as a medical indicator in a process analogous to Doppler-shift radar used to detect storms. Sonar, an acronym for Sound Navigation And Ranging, makes use of the reflecting properties of sound waves to determine distances, such as the depth of the ocean from a ship. Another similar principle is the Hall effect, where a magnetic field is applied across a pipe, and the Hall voltage is measured to determine the velocity of fluid flow.
Digital meters, which can detect smaller currents, employ this principle to measure voltage and current with greater accuracy than analog meters using galvanometers. The Doppler effect is critical for this technology as it helps in comparing the perception of sound between a stationary observer and a moving sound source, as well as when both the sound source and observer are in motion.