What type of sonar is commonly known as a fathometer?

A fathometer is commonly known as a single-beam echo sounder. This device works by emitting a sound pulse from the transducer, which travels through the water column until it reaches the seafloor. The time taken for the pulse to return to the transducer is measured, allowing the system to calculate the water depth by applying the speed of sound in water. This method is specifically designed for depth sounding, which is why it is often referred to as a fathometer.

In contrast, while multi-beam echo sounders provide a wider swath of data by emitting multiple sound pulses simultaneously, they are not categorized as fathometers. Side-scan sonar is designed for mapping the seabed and detecting objects on the seafloor rather than measuring depth, and acoustic Doppler instruments are used primarily for current measurements and profiling, rather than depth sounding. Thus, the classification of a fathometer aligns specifically with the functionality of a single-beam echo sounder.