An echo sounder or fathometer is a scientific device that is used to determine the depth of the ocean floor. Many boats have one aboard for a variety of reasons, and these devices are also extremely useful for scientific studies and sea floor mapping. While the basic technology behind the device is fairly simple, many modern machines are quite complex and extremely accurate, and the design is periodically refined for even better performance.
The device relies on the same principles that radar and ultrasound use. It works by emitting a pulse of sound and listening for its return. Since the speed of sound in water is a known constant, the device can calculate the ocean's depth by halving the time it takes for the pulse to return, and plugging in the known speed of sound to find out how far the pulse had to travel to reach the ocean floor. Sophisticated echo sounders may also have instrument pods that detect salinity, temperature, and the flow of current, all factors that can interfere with the pulse of sound and cause a variation in the depth reading.
The earliest echo sounders were designed in the 1910s, as increased shipping across the Atlantic led researchers to want more safety devices to make navigation less perilous. The original design was actually intended to help ships spot icebergs, which it wasn't terribly good at, but the design proved to be excellent for determining the depth of the ocean floor, and sailors quickly realized the potential applications.
At its most basic, an echo sounder is a safety device that can alert a ship to dangerous changes in the level of the ocean floor. It may be set up to trigger an alarm if a shallow area is reached, so that people on board the ship can take evasive action to avoid running aground. Even in the most perfectly charted area, anomalies in the sea floor can occur, and the devices can prevent costly and embarrassing mistakes.
They can also be used to map the sea floor, or to look for specific items of interest, such as underwater volcanoes or shipwrecks. These devices are used in the fishing industry to seek out and track shoals of fish so that fishermen know exactly where to drop their nets, and they are used in surveying to monitor changes in the ocean floor.
Modern echo sounders often feature an array of transducers to send and transmit sound, so that a wide swath of the ocean floor can be documented. Many return displays in color, so that the ocean's depths can be easily visualized, and some convert data into three-dimensional maps and charts on a computer.