Give the reason for using ultrasonic waves in SONAR.

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Detailed Solution

SONAR uses ultrasonic waves (above 20kHz) because they give narrow beams, high resolution, and accurate distance measurement under water.

Short wavelength → sharp detail: Higher frequency means smaller wavelength, so echoes distinguish small or closely spaced objects.
Better directionality: Easier to form narrow beams with practical-size transducers for precise mapping and target tracking.
Cleaner signal band: Many background ocean noises are lower frequency; ultrasonics reduce overlap and improve detection (within range limits).
Safe and controllable: Non-ionizing; piezoelectric transducers efficiently generate and detect these frequencies.

Trade-off: very high frequencies attenuate faster in water, so they suit short-range, high-detail tasks; lower frequencies travel farther for long-range search but with less detail.

Formula reminder: distance = (speed of sound in water × time-of-flight)/2; with v ≈ 1500 m/s.