Laser Vision: The Mechanics of LiDAR Technology and Its Indispensable Role in the Modern World
From autonomous vehicles to space exploration, an in-depth explanation of how LiDAR technology creates three-dimensional maps using light pulses.
In the world of modern technology, when we talk about features like autonomous vehicles or Face ID in smartphones, there is an extremely powerful technology working behind the scenes called LiDAR. LiDAR is an acronym for 'Light Detection and Ranging,' which literally means identifying objects and measuring their distance using light. This technology uses laser light beams to measure the precise distance of objects and creates a detailed three-dimensional (3D) map of the world around it. Just as a bat uses sound waves to find its way in the dark, LiDAR uses laser light to give machines the power of sight.
To understand the basic working mechanism of LiDAR, we must focus on the speed of light. This system emits short pulses of light from a laser source, which travel through the atmosphere and strike an object. When this light strikes the object and bounces back, a sensor captures it. The distance is calculated based on how long it took for the light to travel from the sensor to the object and back. This process is called 'Time of Flight.' Since the speed of light is as fast as a millionth of a second, extremely precise electronics are required to perform this calculation.
- Laser EmissionThe sensor releases short pulses of laser light into the air.
- ReflectionLight beams hit an object in front (such as a car or tree) and bounce back.
- DetectionThe sensor captures the reflected light and records the exact time of its arrival.
- Distance CalculationThe exact distance of the object is determined based on the speed of light and time.
The history of LiDAR is quite old and interesting. The idea for this technology was first proposed in 1930 by E. H. Synge, who envisioned using powerful searchlights to investigate the atmosphere. However, the actual LiDAR system was developed in 1961 by the Hughes Aircraft Company, which came into existence shortly after the invention of the laser. Initially, it was called 'Colidar' (Coherent Light Detecting and Ranging). This system was used for military purposes and satellite tracking. The system named 'Colidar Mark II,' built in 1963, could measure distances up to 11 km with an accuracy of 4.5 meters.
The general public was introduced to the capabilities of LiDAR during the Apollo 15 mission in 1971. At that time, astronauts used a laser altimeter to map the lunar surface. Since then, this technology began to be used in meteorology to measure clouds and pollution. Today, the use of LiDAR has become so widespread that it is used for mapping the Earth's surface, measuring forest density, and even for the navigation of the 'Ingenuity' helicopter flying on the planet Mars.
A LiDAR system is primarily composed of four parts: a laser, a scanner and optics, a photodetector, and a positioning system. The laser is a light source that typically operates at a wavelength of 600 to 1,000 nanometers (nm). For non-scientific applications, laser power is kept limited for eye safety. Lasers with a wavelength of 1,550 nm are considered safer because they are absorbed by water before reaching the human retina. For this reason, such lasers can be used with higher power for long-range measurements.
| Wavelength (nm) | Main application | Features |
|---|---|---|
| 532 nm | Underwater mapping | Less absorbed in water and goes deeper. |
| 1,064 nm | Topographic mapping | Best for measuring accurate distance of land from the air. |
| 1,550 nm | Autonomous vehicles | Safe for human eyes and useful for long distances. |
The function of the scanner and optics is to distribute laser beams in different directions. Small mirrors that rotate at very high speeds are often used for this purpose. These mirrors scan the laser across the surrounding environment, making it possible to measure millions of points per second. The data obtained from this process is called a 'point cloud.' This point cloud is a collection of thousands to millions of points that represent the vivid 3D shape of any object. For example, if a LiDAR is mounted on a car, it can clearly identify potholes on the road, other vehicles, and pedestrians.
When laser light hits an object and reflects back, a photodetector is used to capture it. This is a highly sensitive sensor capable of detecting even weak light signals. Silicon avalanche photodiodes are a popular technology for this. These signals are processed and converted into digital data. If the LiDAR system is on a moving platform such as a drone or an aircraft, it is also integrated with a GPS and an Inertial Measurement Unit (IMU). These instruments determine the precise position and orientation of the sensor so that there are no errors in the map.
LiDAR employs two types of detection methods: incoherent and coherent. Incoherent detection primarily measures the intensity or amplitude of the reflected light. On the other hand, coherent detection is more complex and measures the phase or Doppler shift of the light. Coherent systems are more sensitive and can operate at lower power, but they are more expensive and complex to manufacture. Most commercial LiDAR systems are based on a pulse model, in which short bursts of light are emitted.
| Parameter | Detail |
|---|---|
| Maximum range | 11 km |
| Accuracy | 4.5 meters |
| First use | Military targeting |
The applications of LiDAR are not limited to roads alone. In oceanography, 'bathymetric' LiDAR is used, which utilizes green light at 532 nm. This specific wavelength can penetrate deep into water, making it possible to map the ocean floor. Using this technology, archaeologists have discovered ancient cities hidden beneath dense forests that were impossible to see with ordinary cameras or the human eye. An aircraft flying over a forest can map the surface beneath the trees by using LiDAR beams that reach the ground.
For autonomous vehicles, LiDAR is a boon. While companies like Tesla may place more emphasis on cameras, Waymo and many other companies believe that LiDAR is indispensable for safe driving. Cameras can be deceived at night or in bright light, but since LiDAR generates its own light, it works accurately in any lighting condition. It can determine the distance of an object with centimeter-level precision, which is extremely important for preventing accidents. In new technologies like Flash LiDAR, the entire field of view is illuminated at once, resulting in clearer images of dynamic objects.
In the future, LiDAR technology is expected to become smaller and more affordable. Currently, research is being conducted on solid-state LiDAR, which has no moving parts. This will make the system more durable and cost-effective. In India, too, the use of LiDAR is increasing in smart city projects and infrastructure planning. Whether it is landing on the moon or autonomous cars running on the road, LiDAR technology is permanently changing the way we see and the way machines perceive.
