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What is an Echo Sounder?

Mary McMahon
Updated May 16, 2024
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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.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a EasyTechJunkie researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By lluviaporos — On Sep 10, 2012

@bythewell - Yeah, but a depth sounder isn't the problem in this case. You can set fishing limits so that the stocks aren't going to be depleted and, if anything, a sounder can help by helping you to figure out how big the fish school, or individual sports fish is before you try to catch it.

I remember reading a book when I was a kid where people had hand held echo sounders which they used to find big fish while scuba diving underwater so that they could hunt them. I wonder if people use it now in order to find fish to swim with.

By bythewell — On Sep 09, 2012

@JackWhack - In that case it sounds like your father isn't doing any harm, but in some ways I think it's a bad thing that the fishing industry uses echo sounders. It's yet another way they can over-fish and deplete stocks which are taking a long time to rejuvenate.

It really worries me, because fish is such a valuable part of the human diet and the ocean ecosystem is such an important part of our lives and we might not have left our children much to work with.

By JackWhack — On Sep 05, 2012

@giddion – I suppose a person who is competing with others and trying to catch the biggest fish would be shamed for using a fish finder. However, if you are fishing to catch dinner for that night, there is nothing wrong with it.

My dad uses a fish finder to locate catfish on the weekends. We absolutely love fried catfish, and since he doesn't want to disappoint the family, he has a little help from the echo sounder. It can't tell him what kind of fish is below, but there are so many catfish in the lake where he fishes that chances are that is what the echo sounder has found.

By giddion — On Sep 04, 2012

Isn't using a fish finder kind of like cheating? I would think that it would take the sport out of fishing. Is it looked down upon among people who fish for sport?

By wavy58 — On Sep 03, 2012

@healthy4life – These mysterious creatures always seem to live in lakes that are extremely deep. Your post reminds me of the Loch Ness monster.

I know that people have used echo sounders to try and locate it, as well. I remember hearing that they once picked up on something that they believed to be the monster 200 feet beneath the water's surface! It's crazy that echo sounders can detect objects that deep.

By healthy4life — On Sep 03, 2012

Echo sounders can also be used to track mythical underwater creatures. I watched a documentary about researchers trying to find a giant creature that resembled a dinosaur in Lake Champlain.

They used an echo sounder and found something about twenty feet long beneath the boat. It passed under them, and though they couldn't see it from the surface, the echo sounder let them know it was there.

I think I would have been terrified to have been on that boat! What if the creature had suddenly decided to surface? The boat would have been catapulted into the air!

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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