Lidar

Lidar, short for light detection and ranging, is a powerful tool that helps us measure distances using laser light. It works by sending out a laser beam toward an object and then timing how long it takes for the light to bounce back. This helps create detailed maps and images of surfaces, whether they're on the ground, in the air, or even under the ocean.

Lidar can be used from many places — on the ground, in airplanes, or in cars. It's helpful 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 even helped a helicopter named Ingenuity fly safely on Mars.

Because lidar can create three-dimensional pictures of areas, it's very useful for many jobs. It helps autonomous cars navigate safely and assists in planning where future space landers will touch down. With its ability to see clearly through forests and other complex areas, lidar continues to be an important technology 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 created 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," which 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 image objects. It can target many things, such as rocks, rain, chemical compounds, aerosols, clouds, and even single molecules. A narrow laser beam can map physical features with very high resolutions. For example, an aircraft can map terrain at a resolution of 30 centimeters or better.

Lidar determines the distance of an object or surface using a simple formula involving the speed of light and the time it takes for the laser light to travel to the object and back. There are two main types of lidar detection schemes: incoherent detection, which measures changes in the amplitude of the reflected light, and coherent detection, which is better for measuring changes in the phase of the reflected light. Both types can use different pulse models, either micropulse or high energy, depending on the application.

Components

Lidar uses lasers to measure distances by sending out light and timing how long it takes for the light to bounce back. Common lasers for lidar work in the 600–1,000 nm range and are designed to be 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 detailed measurements. These lasers are also used in military devices because they are invisible to night vision goggles.

Lidar systems also need special tools to capture and process the returning light signals. Sensors and electronic receivers help measure the 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 such as straight down, straight up, or to the side. It can be used to measure distances by sending out a laser beam and timing how long it takes for the light to bounce back.

There are different types of lidar uses. Airborne lidar is attached to airplanes to create detailed maps of landscapes from above. Terrestrial lidar is used on the ground to make 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 in different fields. It helps in detecting objects and measuring distances with high accuracy. The effectiveness of lidar depends on how well it can identify objects, the detail in its measurements, and how well it works in bright or reflective conditions.

Companies are trying to lower the cost of lidar sensors, which currently range from about US$1,200 to over $12,000. Cheaper prices would open up new uses for lidar in various industries.

Agriculture

Lidar is useful in farming. It can help in applying fertilizer by mapping fields and showing slopes and sunlight exposure. This helps farmers decide where to apply fertilizer to get the best crop yield. Lidar can also monitor insects in fields, track crop growth in orchards, and help in weeding by identifying plant species using 3D data and machine learning.

Archaeology

In archaeology, lidar helps in planning excavations and mapping areas hidden by forests. It can create detailed maps of sites, even those covered by trees or vegetation. This has led to discoveries of ancient structures and cities, such as hidden cities in jungles and ancient roads in forests.

Autonomous vehicles

Lidar is important for self-driving cars. It helps these vehicles detect obstacles and navigate safely. Lidar provides detailed 3D data that helps the car’s software understand its environment. This technology was key in early self-driving vehicles and continues to be used in many advanced driver-assistance systems.

Ecology and conservation

Lidar is used to study natural landscapes like forests, wetlands, and grasslands. It helps measure tree heights, biomass, and leaf area. This data is important for understanding ecosystems and managing natural resources.

Forestry

In forestry, lidar helps manage forests by measuring tree heights, crown sizes, and other details. This information is used to estimate forest resources, monitor bushfires, and manage forest health.

Geology and soil science

Lidar helps scientists study Earth’s surface. It can create detailed maps that show features like river banks, glacial landforms, and fault lines. This helps in understanding geological processes and changes over time.

Atmosphere

Lidar is used to study the atmosphere. It can measure clouds, aerosols, winds, and gases like carbon dioxide and methane. This helps in weather forecasting, climate research, and monitoring pollution.

Flood forecasting

In Japan, lidar technology is being used to improve flood forecasting. Researchers use lidar to study water vapor, temperature, and wind patterns. This data helps in predicting floods and managing water resources.

Military

Lidar has military applications, such as detecting targets and measuring speeds. It is used in systems for identifying threats and in research for advanced defense technologies.

Mining

In mining, lidar is used to measure ore volumes and detect obstacles for autonomous mining vehicles. This helps in efficient and safe operation of mines.

Physics and astronomy

Lidar is used in astronomy to measure distances to the Moon and other celestial bodies. It helps in testing theories of physics and studying planets. In atmospheric physics, lidar measures elements like potassium and sodium in the upper atmosphere.

Rock mechanics

Lidar is used to study rock surfaces and changes over time. This helps in assessing the stability of rock slopes and predicting landslides.

Robotics

In robotics, lidar helps robots understand their environment. It provides detailed 3D maps that robots use for navigation and mapping. This is important for both ground and airborne robots.

Spaceflight

Lidar is used in space missions to measure distances and study planetary surfaces. It helps in navigating spacecraft and understanding atmospheres on other planets.

Surveying

Lidar is widely used in surveying to create detailed maps of terrain. It can measure elevations, forest canopies, and even underwater depths with high accuracy.

Transport

In transportation, lidar is used to monitor road conditions and vehicle distances. It helps in adaptive cruise control systems for cars and in measuring cloud heights at airports.

Wind farm optimization

Lidar helps in optimizing wind farms by measuring wind speeds and turbulence. This data helps in placing wind turbines effectively and improving their performance.

Solar photovoltaic deployment optimization

Lidar assists in planning solar power installations by identifying suitable rooftops and assessing shading effects. This helps in maximizing solar energy production.

Video games

Lidar technology is used in some video games to create realistic environments. It helps in reproducing race tracks and terrain with high precision, enhancing the gaming experience.

Physical security

Lidar improves physical security systems by providing detailed detection of threats. It can monitor perimeters and critical infrastructure, offering precise and reliable surveillance.

Other uses

Lidar has been used in music videos, such as the 2007 Radiohead song "House of Cards," and in Apple products like the iPad Pro and iPhone for augmented reality and improved camera features. It has also been used in TV shows like Wheel of Fortune to track movements on the puzzle board.

Variants

Flash lidar uses a wide laser beam to light up a whole area at once, unlike regular lidar that lights up one point at a time. This lets it take pictures of distance instead of color, and it works better when things are moving. Both types use a special camera to record where the light hits and how bright it is.

Because flash lidar lights up everything at the same time, it can create quick, detailed 3-D images. This makes it useful for things like helping spacecraft land safely. However, it needs special materials to avoid hurting eyes, which can make it more expensive.

Alternative technologies

Further information: 3-D scanner

Computer stereo vision has been explored as a cheaper option to lidar for nearby applications. It can work well when the right conditions are met and costs less than lidar systems.