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# What is SOFAR?

## SOFAR is an ocean “channel” that allows sound to carry great distances.

The ocean consists of many zones. Sound can travel through a zone for hundreds, sometimes thousands of miles. ** Download Infographic | Infographic Text

At the height of World War II, scientists tested a theory that          low-frequency sound could travel long distances in the deep ocean. They          deployed a hydrophone from their research vessel, which was anchored off of Woods Hole, Massachusetts. Some 900 miles away, another ship lowered a four-pound          explosive to a specific depth below the ocean surface. Once detonated, the          explosion propelled pulses of sound that traveled the 900 hundred miles          from one ship to the other. That’s nearly the distance from Washington, DC,          to Des Moines, Iowa!

For the first time, researchers heard what they termed *SOFAR*, or a **SO**und **F**ixing **A**nd **R**anging          transmission. As the scientists noted, “The end of the sound channel transmission was so sharp that it was impossible for the most unskilled observer to miss it.”

 How does SOFAR work? Think of the ocean as consisting of various  zones, or layers — sort of like oil and vinegar salad dressing before it’s shaken up — except          that ocean layers occur due to differences in salinity (salt content) and          temperature variations. Saltier and colder water lie beneath less salty, warmer water.   

 Because of SOFAR, sound emitted at a certain depth bounces between these          various layers and can travel for hundreds of miles. This up-and-down          bending of low-frequency soundwaves allows soundwaves to travel great          distances without the signal losing significant energy. By placing          hydrophones at the axis of the sound channel, researchers can record sounds          such as whale calls, earthquakes, and manmade noise occurring vast          distances from the hydrophones. In some instances, low-frequency sounds can          be heard across entire ocean basins.

## Infographic Text

### What is SOFAR?

This infographic illustrates how SOFAR works. It shows a ship with a deployed underwater hydrophone receiving the sounds of distant whales, thanks to the effects of the SOFAR channel. 

SOFAR, or Sound Fixing and Ranging Channel, is a naturally-occurring ocean "channel" that allows sound to carry great distances.

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          -  How far does sound travel in the ocean?  (Ocean fact)
          -  Sound in the Sea  (NOAA Ocean Explorer)
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Did you know?

 Whales tuned into the SOFAR channel long before scientists. As whales            migrate, they rely on SOFAR to  communicate over distances of hundreds and even thousands of miles. Ship traffic and            other human activities result in a noisier ocean, though—and studies show            that louder noise levels interfere with whale communication. This  “cocktail party effect” impedes many marine animals that depend on sound for their most basic            needs, including food, communication, protection, reproduction, and            navigation. 

**Last updated:**  01/20/23**Author:** NOAAHow to cite this article

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