What does a depth sounder primarily measure?

A depth sounder primarily measures the depth of water beneath a vessel, which is crucial for navigation. By sending sound waves (or sonar pulses) from the vessel to the seabed and measuring the time it takes for the waves to return, a depth sounder calculates how deep the water is. This information is essential for ensuring that a vessel avoids running aground in shallow areas and can navigate safely through various water depths.

The measurement of water depth is vital for a variety of maritime activities, including safe passage planning, fishing, and marine research. By knowing the depth, mariners can make informed decisions regarding the vessel's route and operation in relation to underwater hazards. This particular function of the depth sounder makes it an indispensable instrument in navigation.