Explainer: What are lidar, radar and sonar?

Three similar technologies rely on echoes to map the unseen

A 3-D lidar scan of the Interstate 510 bridge in New Orleans, La. The U.S. Geological Survey used lidar in parts of Louisiana, Mississippi and Alabama to map flooding after 2012’s Hurricane Isaac.

Toby Minear/USGS

HELLLOOO! LOOH. Looh. looh.

If you have ever heard an echo, you’ll be familiar with the basic principle behind three similar technologies: radar, sonar and lidar.

An echo is the reflection of sound waves off of some distant object. If you shout in a canyon, the sound waves travel through the air, bounce off the rocky walls and then come back to you.

Sonar (SO-nahr) is the most similar to this scenario. This technology also relies on sound waves to detect objects. However, sonar is typically used underwater.

This sonar image shows the entrance to Portsmouth Harbor, N.H. Lower areas are in blue, higher areas in red. NOAA/NOS/Office of Coast Survey

Medical technicians also may use sound waves to peer inside the human body (which is mostly water). Here, the technology is known as ultrasound. When bats, dolphins and other animals use sonar naturally, usually to find prey, it’s called echolocation (EK-oh-lo-CAY-shun). These animals send out a series of short sound pulses. Then they listen for the echoes to determine what’s in their environment.

Radar and lidar (LY-dahr) rely on echoes, too. Only they don’t use sound waves. Instead, these two technologies use radio waves or light waves, respectively. Both are examples of electromagnetic radiation.

Scientists made up the words radar, sonar and lidar. Each reflects a technology’s usefulness:

·         Radar: ra(dio) d(etection) a(nd) r(anging)

·         Sonar: so(und) na(vigation) (and) r(anging)

·         Lidar: li(ght) d(etection) a(nd) r(anging)

Detection (or navigation) refers to locating objects. Depending on the technology, these objects may be underwater, in the air, on or below the ground, or even in space. Radar, sonar and lidar  can determine an object’s distance, or range. For that measurement, time plays an important role.

This radar image shows a December 19, 2009, snowstorm (blue, green and yellow) as it approaches the U.S. Mid-Atlantic region. NOAA/National Weather Service

Lidar, radar and sonar systems all include timing devices. Their clocks record the length of time needed for a wave to travel to an object and back. The farther the distance, the longer it takes for an echo to return.

Radar, sonar and lidar also can reveal information about an object’s shape, size, material and direction. Air traffic controllers use radar to spot aircraft in the sky. Police use it to detect speeders. Navies use sonar to map the ocean bottom — or to look for enemy submarines. And lidar helps read the lay of the land or features on Earth’s surface. Lidar’s laser pulses can penetrate forest cover to record the shape of the ground below. That makes this technology especially valuable for mapping.

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