High technologies are increasingly being introduced into our lives. Previously, the word lidar was associated with the most complex device available only to large companies and research institutes. Today, lidars have become so widespread that they can even be found in smartphones. What is this technology and where it is used, we will tell in detail.
Lidar – what is it and how does it work
The word “lidar” (LIDAR) comes from “Light Detection and Ranging” – a technology for measuring distances using a light beam.
The first mention of the term dates back to 1953. Earlier in meteorology, this was the name given to ordinary pulsed light sources. However, after the invention of the laser in 1960, the first lidars began to appear, in which a real laser was already used as an emitter. One of the first inventions in 1963 was the XM-23 laser rangefinder, which, after testing, was immediately adopted by the US Army.
Subsequently, the laser rangefinder became standard equipment for the M551 Sheridan tank, and this technology was widely popularized after the launch of Apollo 11 – astronauts installed the first corner reflector on the Moon, with which they managed to make accurate measurements of the distance from the Earth to the satellite.
In the USSR, experiments on laser ranging of the Moon began in 1963, and subsequently their own corner reflectors were launched on Lunokhod-1 and Lunokhod-2. The first Soviet laser rangefinder appeared in 1974 – KTD-1 was able to measure distances up to 10 kilometers with an error of only 1.8 meters.
The main problem of lidars was the extraordinary high cost due to the use of integrated circuits, so the scope was usually limited to military needs, space and meteorology. However, with the development and cheapening of microelectronics, the possibilities and areas of application have expanded significantly.
The principle of operation of the lidar is very similar to the radar familiar to us – the only difference is that in one case light is sent to the object, and in the other – a radio wave. One of the main problems with radio waves is that they reflect well only from large metal objects. Light does not have this disadvantage, and after the invention of the laser, engineers have the opportunity to send concentrated beams of light over long distances.
A lidar sends out a light wave (usually in the infrared), which bounces off an object and returns. By analyzing the time or reflected signal, you can calculate the distance to the object.
Distinguish pulse and phase methods of distance measurement. With the pulse method, a pulse is sent to the object, in parallel with which the device starts an internal counter. When the reflected beam returns, it stops the counter. After that, the microprocessor, using the counter time, calculates the distance to the object using the formula.
With the phase method, the radiation is modulated according to a sinusoidal law, and the reflected beam is shifted in phase. Based on the phase difference, the distance is determined.
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Most lidars use one of three wavelengths – 850, 905 or 1550 nm. Sources that generate waves of 850 and 905 nm at a sufficiently high power can damage the retina, but their production is as cheap and affordable as possible. A beam with a wavelength of 1550 nm is safe for the human eye even at high power, but the production of such emitters requires quite rare resources, for example, gallium-indium arsenide.
Application of lidars
Note that the term “lidar” can be understood in two different meanings. The first is a technology that uses a beam of light to measure the distance to an object. The second value is a separate device that sends out numerous beams of light to build a 3D map.
Most people are familiar with the technology from laser rangefinders . These gadgets are not commonly referred to as lidars because they only send out a single beam to measure distance. Compact devices the size of a phone can measure distances up to an average of 100 meters. An indispensable gadget during repair or construction.
The development of this technology has become rotating and scanning emitters. Such devices are already able not only to measure the distance to one point, but to build a full-fledged relief map or 3D object models. They are often referred to as lidars.
The technology is actively used in cartography and archeology, as it allows you to quickly create a map with an accuracy of up to 10 centimeters. Lidars can be mounted on aircraft or unmanned aerial vehicles, including small drones. The latter are used to obtain building models or maps of local agricultural land.
Powerful lidars are already installed on aircraft and are able to map entire regions using several different scanning methods. So oceanographers use lidars to track coastal erosion, and botanists to measure the changing structure of forests. Lasers are also used to study the gas composition of the atmosphere – volatile substances absorb the reflected beam to varying degrees, so that it is possible to calculate the concentration from scattering.
They even install lidars on spacecraft. For example, the ISS has a JEDI system, which has been used to study forests since 2018. Scientists managed to build a map of the height of forests around the world.
NASA also started building the MARLI lidar to study wind speed and atmospheric composition on Mars.
If we talk about more mundane devices, then lidars (LDS laser) are used in some robotic vacuum cleaners. A special block with a rotating head allows you to scan the area 360 degrees around the vacuum cleaner, thereby making a map of walls and obstacles.
Lidar is able to quickly and accurately build a map of premises, but it does not work well with mirrors, which it identifies not as an obstacle, but as another space.
Lidars are gradually making their way into consumer electronics such as smartphones. You have probably heard about the ToF cameras that the Samsung Galaxy S20+, Huawei P30 Pro, Sony Xperia XZ4 and other gadgets have. So these cameras use lidar technology – a sensor in the infrared range sends a beam of light and measures the time after which it will return. This opens up additional features: measuring the distance to objects, the effect of blurring the background, improved face recognition and more.
Apple took up the development of ToF cameras – for the first time in the iPhone 12 Pro, they introduced a full-fledged lidar. The key difference is that the lidar sensor sends light pulses not once, as the ToF sensor does, but constantly. This allows you to build full-fledged 3D models of objects in real time and provides more opportunities for working with augmented reality.
However, one of the most promising applications of lidars is unmanned vehicles. Together with other means of detecting obstacles, lidars allow you to create a fairly accurate map. For example, Yandex’s unmanned vehicles used lidars from one of the leading Velodyne brands.
One of the main deterrents to the development of the lidar market is their cost. Sufficiently powerful devices for automotive use, safe for human eyes, cost in the region of 800-1200 dollars. Lidars for household appliances like vacuum cleaners are already significantly cheaper, usually under $100.
But in Tesla cars, lidars are not used – there navigation is carried out exclusively by cameras, radar and ultrasonic sensors. Elon Musk is sure that lidars are an expensive and useless way of navigation, and with the development of computer vision technology, it will become completely useless. Whether he is right or not, time will tell, but even the well-developed obstacle detection system in Tesla cars is malfunctioning .
The scope of lidar is expanding every year – the rapid creation of virtual 3D models is required in a variety of industries, from design with three-dimensional printing to the study of the relief of other planets. It is possible that lidar will be the future for all unmanned vehicles, including cars and even aircraft.