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LiDAR, also known as Light Detection and Ranging, is a system that combines laser, Global Positioning System (GPS), and Inertial Measurement Unit (IMU) technologies to collect data and generate precise Digital Elevation Models (DEMs). By combining these three technologies, LiDAR can accurately locate the spot where the laser beam hits an object and achieve centimeter-level ranging accuracy. The greatest advantages of LiDAR are its precision and efficiency in operation.
LiDAR can accurately and precisely obtain information such as the distance and speed of a target or achieve target imaging. The working principle of LiDAR involves the laser beam being directed through a scanning unit to form a beam angle deviation, which interacts with the target to produce reflection/scattering echoes. When the receiver is active, echoed photons from the original path can reach the receiver. The receiver forms signal reception through a photodetector and obtains information such as the distance and speed of the target or achieves three-dimensional imaging through signal processing.
LiDAR consists of four basic systems: the laser emission system, the laser reception system, the information processing system, and the scanning system. These four systems work together to obtain a large amount of positional information in a short period of time and use this information to achieve three-dimensional modeling.
1. Laser emission system: A laser source periodically drives the laser emitter to emit laser pulses. The laser modulator controls the direction and number of emitted laser beams through a beam controller, and the emitted laser is directed onto the target object through the emission optical system.
2. Laser reception system: A photodetector receives the laser reflected by the target object through the reception optical system and generates a reception signal.
3. Information processing system: The received signals are amplified, processed, and converted into digital signals. The information processing module then calculates the surface shape, physical properties, and other characteristics of the target object to establish a target model.
4. Scanning system: It rotates at a stable speed to scan the plane and generate real-time positional information.
The classification of LiDAR be done based on different factors:
1. Functional and Usage Classification: Tracking LiDAR (for range and angle measurement), Motion Target Indication LiDAR (for obtaining target Doppler information), Flow Velocity Measurement LiDAR (for measuring Doppler information), Wind Shear Detection LiDAR, Target Identification LiDAR, Imaging LiDAR (for measuring the reflected intensity and distance signals of different parts of a target), and Vibration Sensing LiDAR.
2. Working System Classification: Doppler LiDAR, Synthetic Aperture Imaging LiDAR, Differential Absorption LiDAR, Phased Array LiDAR, Portable LiDAR, Ground-based LiDAR, Vehicle-mounted LiDAR, Airborne LiDAR, Shipborne LiDAR, Spaceborne LiDAR, and Missile-mounted LiDAR.
3. Working Medium Classification: Solid-state LiDAR, Gas LiDAR, Semiconductor LiDAR, Diode-Pumped Solid-State LiDAR, etc.
4. Detection Technology Classification: Direct Detection Type, Coherent Detection Type.
5. Platform Classification: Portable LiDAR, Ground-based LiDAR, Vehicle-mounted LiDAR, Airborne LiDAR, Shipborne LiDAR, Spaceborne LiDAR, and Missile-mounted LiDAR, among others.
Lidar can be classified according to several factors:
1. Function and Purpose: This includes tracking radar (for distance and angle measurements), motion target indication radar (to obtain target Doppler information), flow velocity measurement radar (to measure Doppler information), wind shear detection radar, target recognition radar, imaging radar (to measure the reflection intensity and distance of different parts of a target), and vibration sensing radar.
2. Operating System: This includes Doppler lidar, synthetic aperture imaging lidar, differential absorption lidar, phased array lidar, portable lidar, ground-based lidar, vehicle-mounted lidar, airborne lidar, shipborne lidar, and satellite-based lidar.
3. Working Medium: This includes solid-state lidar, gas lidar, semiconductor lidar, diode-pumped solid-state lidar, etc.
4. Detection Technology: This includes direct detection type and coherent detection type.
5. Platform: This includes portable lidar, ground-based lidar, vehicle-mounted lidar, airborne lidar, shipborne lidar,-based lidar, and missile-carried lidar.
Advantages of laser radar include:
1. High resolution: Laser radar can achieve high angular, distance, and velocity resolution, which means it can produce very clear images using Doppler imaging techniques.
2. High accuracy: Laser beams propagate in straight lines, have good directionality, narrow beams, and low dispersion, resulting in high accuracy.
3. Strong resistance to active interference: Unlike microwave and millimeter-wave radar, which can be easily affected by electromagnetic waves widely present in nature, laser radar has few sources of interference in nature, making it highly resistant to active interference.
4. It has extremely high distance, angle, and velocity resolution: Detection accuracy is within centimeters, enabling precise identification of the specific contours and distances of obstacles without missing or misjudging obstacles ahead.
5. Rich information acquisition: Laser radar can directly obtain information such as distance, angle, reflection intensity, and velocity of targets, and can generate multidimensional images of targets. High-frequency lasers can obtain approximately 1.5 million position point information in one second, accurately recovering the three-dimensional features of the surrounding environment using the distance information from these point clouds.
6. All-weather operation: Unlike millimeter-wave radar, laser radar can detect human bodies, and its detection range is longer than that of cameras.
7. Long detection range: Laser radar's wavelength is in the range of thousands of nanometers, with good directionality, no steering, and no diffusion with increasing distance. It is not limited by pixels and light.
