Lidar

Lidar, short for light detection and ranging, is a tool that measures distances using laser light. It sends out a laser beam toward an object and times how long it takes for the light to bounce back. This helps create detailed maps and images of surfaces on the ground, in the air, or under the ocean.

Lidar can be used from many places — on the ground, in airplanes, or in cars. It is useful for making precise maps used in surveying, archaeology, and studying forests and weather. Scientists use it to learn about Earth's surface and atmosphere, and it helped a helicopter named Ingenuity fly safely on Mars.

Because lidar can create three-dimensional pictures of areas, it is very useful for many jobs. It helps cars navigate safely and assists in planning where future space landers will land. With its ability to see clearly through forests and other complex areas, lidar is important in many fields.

History and etymology

The idea of lidar started in 1930 when E. H. Synge thought about using bright lights to study the atmosphere. The first lidar-like system was made in 1961 by the Hughes Aircraft Company, just after the laser was invented. This system was used to track satellites and was called "Colidar," short for "coherent light detecting and ranging."

Lidar was first used on the ground in 1963 with a device called the "Colidar Mark II." It could measure distances up to 11 kilometers. People began calling it "lidar" around this time, mixing the words "light" and "radar." It became well-known in 1971 when astronauts on the Apollo 15 mission used a laser to map the Moon's surface. Today, people write it as "LIDAR," "LiDAR," or "lidar," and it is used to study clouds and pollution.

Theory

Lidar uses ultraviolet, visible, or near infrared light to picture objects. It can target things like rocks, rain, chemical compounds, aerosols, clouds, and even single molecules. A narrow laser beam can map features very clearly. For example, an airplane can map the land with a resolution of 30 centimeters or better.

Lidar finds the distance of an object or surface using a simple formula with the speed of light and the time it takes for the laser light to reach the object and return. There are two main ways lidar can detect things: one measures changes in the strength of the reflected light, and the other is better at measuring changes in the light's phase. Both ways can use different types of laser pulses, depending on what they are used for.

Components

Lidar uses lasers to measure distances. It sends out light and times how long it takes for the light to bounce back. Lasers for lidar are safe for people on the ground. Some lasers, like the 1,550 nm type, are safer for eyes but may not work as well for close-up measurements. These lasers are also used in military devices because they are invisible to night vision goggles.

Lidar systems need special tools to capture and process the returning light signals. Sensors and electronic receivers help measure distances very accurately. When mounted on moving platforms like airplanes, lidars use GPS and other navigation tools to know exactly where they are. These systems can create three-dimensional images by using fast cameras and advanced chips that can process many signals at once, allowing them to map large areas quickly and with great detail.

Classification

Lidar can be pointed in different directions like down, up, or to the side. It measures distances by sending out a laser beam and timing how long it takes for the light to return.

There are different types of lidar. Airborne lidar is attached to airplanes to make detailed maps of landscapes from above. Terrestrial lidar is used on the ground to create 3D models of objects and areas. Mobile lidar is placed in cars or other moving vehicles to collect data while moving, such as mapping streets and their features.

Applications

Lidar has many uses. It helps detect objects and measure distances very well. Companies want to make lidar sensors cheaper so more people can use them.

Agriculture

Lidar helps farmers. It maps fields to show slopes and sunlight. This helps farmers know where to put fertilizer. Lidar can also track crop growth and help remove weeds.

Archaeology

Lidar helps archaeologists find hidden sites under forests. It makes detailed maps, even through trees. This has helped find ancient cities and roads.

Autonomous vehicles

Lidar is important for self-driving cars. It helps cars see obstacles and navigate. Lidar gives 3D data so cars can understand their surroundings.

Ecology and conservation

Lidar studies nature like forests and wetlands. It measures tree heights and leaf area. This helps care for ecosystems and natural resources.

Forestry

Lidar helps manage forests. It measures tree heights and sizes. This helps estimate forest resources and watch forest health.

Geology and soil science

Lidar helps scientists study Earth. It makes maps showing rivers, glaciers, and fault lines. This helps understand Earth changes.

Atmosphere

Lidar studies the air. It measures clouds, winds, and gases. This helps with weather forecasts and studying pollution.

Flood forecasting

In Japan, lidar helps predict floods. It studies water vapor, temperature, and wind. This helps manage water and predict floods.

Military

Lidar has uses in the military, like finding targets and measuring speeds. It helps in defense research.

Mining

Lidar helps in mining. It measures ore amounts and finds obstacles for mining vehicles. This makes mining safer and more efficient.

Physics and astronomy

Lidar measures distances to the Moon and planets. It helps test physics ideas and study planets. It also measures elements in the upper atmosphere.

Rock mechanics

Lidar studies rock surfaces. This helps check if rock slopes are stable and predict landslides.

Robotics

Lidar helps robots understand where they are. It gives 3D maps for robots to navigate and map places. This is important for robots on the ground and in the air.

Spaceflight

Lidar is used in space missions. It measures distances and studies surfaces of other planets. It helps spacecraft navigate and understand atmospheres.

Surveying

Lidar is used to make detailed maps of land. It measures heights, forests, and even underwater depths very accurately.

Transport

Lidar monitors roads and distances between vehicles. It helps cars with adaptive cruise control and measures cloud heights at airports.

Wind farm optimization

Lidar helps with wind farms. It measures wind speeds and turbulence. This data helps place wind turbines better and improve their work.

Solar photovoltaic deployment optimization

Lidar helps plan solar power systems. It finds good rooftops and checks for shading. This helps make the most solar energy.

Video games

Lidar is used in video games to make realistic worlds. It helps copy race tracks and terrain exactly, making games more fun.

Physical security

Lidar improves security systems. It can find threats and watch important places very well.

Other uses

Lidar has been used in music videos and Apple products like the iPad Pro and iPhone. It helps with augmented reality and better cameras. It has also appeared in TV shows.

Variants

Flash lidar uses a wide laser beam to light up an area all at once. Regular lidar lights up one point at a time. Flash lidar can take pictures of distance and works well when things are moving. Both types use a special camera to record where the light hits.

Flash lidar can create quick, detailed 3-D images. This helps with things like spacecraft landing safely. But it needs special materials to protect eyes, which can make it more expensive.

Alternative technologies

Further information: 3-D scanner

Computer stereo vision is another way to see objects that can cost less than lidar. It works best when the conditions are just right.