Explainer: What are lidar, radar and sonar? | Science News for Students

Explainer: What are lidar, radar and sonar?

Three similar technologies rely on echoes to map the unseen
May 1, 2015 — 7:15 am EST
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.

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.

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.

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.

Power Words

(for more about Power Words, click here)

echo    To bounce back. For example, sound bouncing off walls of a tunnel, and returning to their source. Radio waves emitted above the surface can also bounce off the bedrock underneath an ice sheet — then return to the surface.

echolocation   (in animals) A behavior in which animals emit calls and then listen to the echoes that bounce back off of solid things in the environment. This behavior can be used to navigate and to find food or mates. It is the biological analog of the sonar used by submarines.

laser   A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.

lidar   (short for light detection and ranging) A tool to measure the shape and contour of the ground from the air. It bounces a laser pulse off a target and then measures the time (and distance) each pulse traveled. Those measurements reveal the relative heights of features on the ground struck by the laser pulses.

navigate   To find one’s way through a landscape using visual cues, sensory information (like scents), magnetic information (like an internal compass) or other techniques.

radar   (short for radio detection and ranging) A system for calculating the position, distance or other important characteristic of a distant object. It works by sending out periodic radio waves that bounce off of the object and then measuring how long it takes that bounced signal to return. Radar can detect moving objects, like airplanes. It also can be used to map the shape of land — even land covered by ice.

radio waves    Waves in a part of the electromagnetic spectrum; they are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals; it is also used in radar.

range   The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (In math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

sonar  (short for sound navigation and ranging) A system for the detection of objects and for measuring the depth of water. It works by emitting sound pulses and measuring how long it takes the echoes to return.

sound wave    A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

ultrasound    (adj. ultrasonic) Sounds at frequencies above the range that can be detected by the human ear. 

NGSS: 

  • MS-PS4-1
  • MS-PS4-2
  • HS-PS4-1
  • HS-PS4-3
  • HS-PS4-4
  • HS-PS4-5

Further Reading

S. Milius. “Bat signals jammed.” Science News for Students. December 2, 2014.

S. Ornes. “Drones put spying eyes in the sky.” Science News for Students. November 6, 2014.

S. Ornes. “Sound cloak.” Science News for Students. April 14, 2013.

A. Bridges. “Twister science.” Science News for Students. December 9, 2012.

E. Sohn. “Underwater racket.” Science News for Students. February 2, 2011.