Sonar refers to sound navigation ranging. It involves using and interpreting sounds to detect something's location underwater and is especially handy for two reasons: Bodies of water are often far too murky for sight, and sound actually travels quickly underwater, much faster than it does in air.
Sonar technology sends out sounds and waits for the sounds to bounce off other objects and come back (the same way an echo bounces back to us in a cave). This technology is called active sonar, as opposed to passive sonar, or simply listening for the noises of other active objects. Remarkably, with sonar, we can interpret vital information, such as exactly how far away enemy submarines are.
Unlike humans, however, dolphins have been using this skill, known as biosonar, for millennia. So they're pretty darn good at it. The tricks of sonar are built into their DNA, so much so that they can tell the difference between a BB gun pellet and a kernel of corn from 50 feet away [source: Gasperini]. A dolphin's sonar process, also used by bats and some whales, is called echolocation. If you've ever heard a dolphin, you'll immediately recognize its characteristic clicks and squeaks. But there's more than meets the ear: Many of the clicks are simply at frequencies too high for the human ear to detect. Essentially, dolphins use these clicks as active sonar mechanisms.
The dolphin's echolocation process goes like this:
1) The dolphin uses nasal passages to make a click and sends it through its forehead, which focuses the sounds together into a beam before sending it into the water.
2) When the sound hits an object in the water, it bounces back to the dolphin as an echo.
3) The dolphin absorbs this returning echo through its jaw.
4) A passage of fat from the jaw conducts the sound to the dolphin's inner ear, which exchanges nerve impulses with its brain to interpret the object's characteristics, such as size, shape and material.
One way to think about the echolocation process is to imagine you're in a pitch-black room with only a flickering flashlight to guide you. To help understand an object, a dolphin will move around and read it from multiple points of view, as you might in the dark room, as well as with varying kinds of clicks. They'll even adapt for noisy environments by adjusting the frequency of their clicks. Using this process, dolphins can determine the size and shape of objects and even, in some cases, distinguish different metals, such as brass and copper, from far away, which assists them in finding mines [source: Bechtel].
But scientists are not sure how a dolphin's brain interprets sonar information. So much of our human understanding relies on visual information that it's hard for us to wrap our brains around the idea of "seeing" particular objects with our ears. Because dolphins are so exceptionally good with sonar, studying them hopefully will help us improve our own sonar technology. Until then, however, we can certainly use the dolphins themselves to find dangerous underwater objects. Right?
Actually, some people question the ethics behind using dolphins for such purposes. On the next page, we'll investigate that side of the story.