In the past, lidar has been difficult to deploy on a large scale due to cost and size issues. With the progress of technology and production efficiency, the cost of lidar has started to decline rapidly in recent years, and various Omanufacturers have gradually incorporated it into the ADAS sensor program. Among them, the new domestic forces are more radical in the deployment of lidar, taking Lidar as a new technology selling point and exploring its application function more actively, and the application of lidar is becoming more and more extensive. In the robot, unmanned driving, unmanned car and other fields can see its figure, there is a demand is bound to have a market, with the increasing demand for lidar, Lidar types have become dazzling, according to the use of functions, detection methods, load platforms and other lidar can be divided into different types. Lidar is a system that integrates laser, global positioning system (GPS) and IMU (inertial Measuring Device). Compared with millimeter-wave radar, Lidar has the advantages of high resolution, good concealment and stronger anti-interference ability.

Laser ranging radar

Laser ranging radar transmits laser beam to the measured object, receives the reflected wave of the laser beam, records the time difference, and determines the distance between the measured object and the test point.

Lidar can be used in industrial security detection, such as the laser walls seen in science fiction films. When someone breaks in, the system will react and give an early warning. In addition, laser ranging radar isalsowidely used in the field of space mapping. However, with the rise of the artificial intelligence industry, laser ranging radar has become an indispensable core component of the robot body. Combined with SLAM technology, it can help the robot carry out real-time positioning and navigation and realize autonomous walking.

Laser velocity radar

Laser velocity measurement radar is the measurement of the moving speed of the object, through the object to be measured twice with a specific time interval laser ranging, so as to get the moving speed of the object. There are two main categories of lidar velocity measurement methods, one is based on the principle of lidar ranging, that is, to continuously measure the target distance at a certain time interval, divide the difference of two target distances by the time interval to get the target velocity value, the direction of the speed can be determined according to the positive or negative of the distance difference value. This method can only be used for hard targets with strong laser reflection due to its simple system structure and limited measurement accuracy. Another kind of velocity measurement method is the use of Doppler frequency shift. Doppler shift means that when there is a relative speed between the target and the laser radar, there will be a frequency difference between the frequency of the received echo signal and the frequency of the transmitted signal, and this frequency difference is the Doppler shift.

Laser imaging radar

Laser imaging radar can be used to detect and track the target, obtain the target azimuth and velocity information. It can accomplish tasks that ordinary radar cannot, such as detecting submarines, mines, hidden military targets and so on. It is widely used in military, aerospace, industrial and medical fields.

Atmospheric detection lidar

Atmospheric detection lidar is mainly used to detect molecules in the atmosphere, the density of smoke, temperature, wind speed, wind direction and the concentration of water vapor in the atmosphere, so as to achieve the purpose of monitoring the atmospheric environment and forecasting severe weather such as storms and sandstorms.

Tracking radar

Tracking radar can continuously track a target, measure the coordinates of the target, and provide the trajectory of the target. It is not only used in artillery control, missile guidance, outer trajectory measurement, satellite tracking, penetration technology research, but also in the fields of meteorology, transportation, and scientific research.

Solid-state lidar

Solid state lidar has high peak power, output wavelength range matching existing optical components and devices, long output range matching existing optical components and devices (such as modulators, isolators and detectors) and atmospheric transmission characteristics, and it is easy to achieve master vibrator-power amplifier (MOPA) structure, Coupled with conductors of high efficiency, small size, light weight, high reliability and good stability, solid state lidar is preferred for airborne and space-based systems. In recent years, the focus of laser radar development is diode pumped solid state laser radar.

Semiconductor lidar

Semiconductor lidar can work continuously with high repetition frequency, has the advantages of long life, small size, low cost and little damage to human eyes, and is widely used in backscattered signal strong scattering measurement, such as detecting cloud base height. The potential applications of semiconductor lidar are to measure visibility, obtain aerosol extinction profile in atmospheric boundary layer and identify rain and snow, etc., which are easy to be made into airborne equipment.

Gas lidar

Gas lidar is represented by CO2 lidar. It works in the infrared band, with small attenuation of atmospheric transmission and long detection distance. It has played a great role in atmospheric wind field and environmental monitoring.

MEMS lidar

MEMS lidar can dynamically adjust its scanning mode to focus on special objects, collect details of further and smaller objects and identify them, which is impossible to achieve with traditional mechanical lidar. The MEMS system uses only a small mirror to direct a fixed laser beam in different directions. Because the mirror is small, it has a small moment of inertia and can move quickly, fast enough to track 2D scanning patterns in less than a second.

Flash lidar

Flash Lidar can quickly record the entire scene, avoiding the hassle of moving targets or lidar during scanning. It operates more like a camera. The laser beam diffuses directly in all directions, so a single flash can illuminate the entire scene. The system then uses an array of tiny sensors to pick up laser beams that bounce back in different directions. Flash Lidar has its advantages, of course, there are certain drawbacks. The larger the pixel, the more signals need to be processed. If a large number of pixels are crammed into the photodetector, it will inevitably bring all kinds of interference, and the result is a decline in accuracy.

Continuous lidar

From the principle of laser, continuous laser is always light out, just like the switch on a flashlight, its light will stay on (except in special circumstances). Continuous laser is to rely on continuous bright light to the height to be measured, to acquire data at a certain altitude. Because of the working characteristics of continuous laser, data can only be collected at one point at one time. Because of the uncertain nature of wind data, it is obviously partial to use a point to represent wind conditions at a certain height. Therefore, some manufacturers' compromise is to take a 360 degree rotation and collect points on the edge of the circle for average evaluation. Obviously, this is a concept of multi-point statistics in a virtual plane.

Pulse lidar

The output of the pulsed laser is not continuous, but in flashes. The principle of pulsed laser is to launch tens of thousands of laser particles, according to the international general Doppler principle, from the reflection of tens of thousands of laser particles to comprehensively evaluate the wind condition of a certain height, this is a three-dimensional concept, so there is a theory of detection length. From the point of view of laser characteristics, pulsed laser is dozens of times more than the point measured by continuous laser, and can accurately reflect the wind conditions of a certain height.

Airborne lidar

Airborne lidar is a technology that closely integrates laser ranging equipment, GNSS equipment, INS and other equipment. With the flight platform as the carrier, it scans the ground, records the attitude, position, reflection intensity and other information of the target, obtains the three-dimensional information of the surface, and deeply processes the required spatial information. It has extensive potential and prospects in both military and civilian fields. Airborne Lidar detection range is close, laser transmission in the atmosphere, energy attenuation by the atmosphere, lidar action range within 20 kilometers, especially in bad weather conditions, such as fog, heavy rain and smoke, dust, the action range will be greatly shortened, difficult to work effectively. Atmospheric turbulence also reduces the measurement accuracy of Lidar to varying degrees.

Vehicle-mounted lidar

Vehicle-mounted lidar, also known as vehicle-mounted three-dimensional laser scanner, is a mobile three-dimensional laser scanning system. It can analyze the return-back time after laser encounters the target object by transmitting and receiving the laser beam, calculate the relative distance between the target object and the vehicle, and use the collected three-dimensional coordinates and reflectivity of a large number of dense points on the surface of the target object. The 3D model of the target and various map data are quickly reconstructed, the 3D point cloud map is established, and the environment map is drawn, so as to achieve the purpose of environmental perception.

Spaceborne lidar

Satellite-borne radar uses a satellite platform, which has a high orbit and a wide field of observation, and can reach every corner of the world. It provides a new way for the acquisition of 3D control points and digital ground models in overseas areas, which is of great significance for national defense and scientific research. Spaceborne lidar also has the ability to observe the whole celestial body. The data provided by spaceborne lidar can be used to make a comprehensive three-dimensional topographic map of celestial bodies, which is included in the lunar and Mars exploration programs of the United States. In addition, measurements of vertical distribution of vegetation, sea surface height, vertical distribution of clouds and aerosols, and monitoring of special climate phenomena can also play an important role in spaceborne lidar measurements.

Phased array lidar

The phased array laser radar is equipped with an array of emitters that can change the direction of the laser beam by adjusting the relative phase of the signal. Most phased array lidar is still in the lab, and it's still in the era of rotary or MEMS lidar.

Mechanical rotary lidar

Mechanical rotary lidar is a relatively early developed lidar with relatively mature technology, but the structure of mechanical rotary lidar system is very complex, and the price of each core component is quite expensive, including laser, scanner, optical component, photodetector, receiving IC and position and navigation devices. Due to high hardware cost, the difficulty of mass production and the need to improve stability, solid-state lidar has become the development direction of many companies.

Coherent detection lidar

Coherent detection lidar can be monostable or bistable. In the so-called monostable system, the transmitting and receiving signals share an optical aperture and are isolated by a transmit-receive switch. The bistable system consists of two optical aperters, respectively for sending and receiving signals. The transmit-receive switch is no longer required naturally. The rest of the bistable system is the same as the single stable system.

Direct detection lidar

The basic structure of direct detection lidar is quite similar to that of laser rangefinder. When working, a signal is sent by the transmitting system, which is collected by the receiving system after being reflected by the target. The distance of the target is determined by measuring the time of the laser signal travelling back and forth. As for the radial velocity of the target, it can be determined by the Doppler shift of the reflected light, or the velocity can be obtained by measuring two or more distances and calculating the rate of change.