LiDAR works on the same principles as radar ("radio detection and ranging," a location system that is often used by ships and planes) and sonar ("sonic navigation and ranging," a system that is typically used by submarines). All three technologies emit waves of energy to detect and track objects. The difference is that while radar uses microwaves and sonar uses sound waves, LiDAR uses reflected light, which can measure distance faster, with greater precision and higher resolution than either radar or sonar.

A typical LiDAR instrument is made up of several components:  

• a laser scanner that emits rapid pulses of near-infrared laser light
• a LiDAR sensor that is used for detecting and collecting the returning light pulses, and
• a processor for calculating the time and distance and for building the resultant data set, called a LiDAR point cloud. 

For the remote sensing to be accurate, measurements of time and space must be exact, so a LiDAR system will also use time-keeping electronics, an inertial measurement unit (IMU) and GPS.

The LiDAR instrument emits pulsed laser light into the environment. These pulses, traveling at the speed of light, bounce off surrounding objects and return to the LiDAR sensor. The sensor measures the time that it took for each pulse to return and calculates the distance that it traveled. Because the speed of laser light is constant, this “time of flight” can be used to calculate precise distances.

By repeating the process and sending out laser pulses across a larger area, time-of-flight measurements can be collected on billions of individual points and processed in real time into what is known as a LiDAR point cloud.

The data undergoes several processing stages to transform the LiDAR point cloud into a 3D map. First, it is checked for correctness and completeness and cleaned to remove anomalous noise. Then, ground surface features like buildings, riverbanks and forest canopy can be algorithmically identified and classified.

To simplify the analysis, algorithms downsample the point cloud to remove redundant data and reduce file size. The data is then converted into the industry-standard LAS (or LASer) file format used for exchanging 3D x, y, z data.

Finally, once converted into LAS, the point cloud data can be visualized and modeled into a 3D map of the scanned terrain. These computations are constant and ongoing for a moving LiDAR system such as those used in autonomous vehicles. According to one source, self-driving cars generate and process a terabyte of data every hour of operation.¹

Airborne LiDAR systems, also called airborne laser scanning systems, use LiDAR scanners mounted to aircraft (usually helicopters or UAVs) to generate 3D models of the ground surface.

Airborne LiDAR mapping has become a valuable tool for creating digital elevation models of the Earth’s surface, mainly replacing the older and less accurate photogrammetry method. Airborne LiDAR scanning is also used extensively in forestry to build LiDAR surveys of the forest canopy and topographic terrain models of the forest's ground surface.

Types of airborne LiDAR technology include:

Bathymetric LiDAR
Bathymetric LiDAR captures GIS data in shallow water and along coastlines.  Bathymetric LiDAR emits green laser beams at a wavelength that can penetrate water to measure the digital elevation of the seafloor, instead of using infrared laser light like typical LiDAR systems.

Space-based LiDAR
 

NASA and other space agencies use space-based LiDAR for spacecraft navigation and digital mapping of celestial bodies. LiDAR is also used to pilot NASA's autonomous vehicles and fly the helicopter Ingenuity on Mars.

Terrestrial LiDAR is a ground-based LiDAR system frequently used for terrain and landscape mapping. Terrestrial LiDAR can be used to collect more localized and short-range data, making it ideal for mapping smaller areas with high precision.

Types of terrestrial LiDAR include:

Static LiDAR
Some terrestrial LiDAR systems are static, fixed in one location, and used to take precise and repeated LiDAR scans of a single area. Static LiDAR is often used for archeological sites, construction projects and hazard assessments. It can monitor the ground surface of active volcanoes, earthquake faults and flood zones.

Mobile LiDAR
Mobile LiDAR is a form of terrestrial LiDAR that collects LiDAR data from a moving vehicle. Mobile LiDAR systems (MLSs) are instrumental to the automotive industry in developing driver assistance and autonomous driving: the data collection from real-time light detection and ranging allows self-driving cars to identify roadway assets and infrastructure quickly, accurately and cost-efficiently.