I. Basic Classification of LiDAR
1. Mechanical LiDAR
Mechanical LiDAR was the earliest commercially available form, its core feature being the use of a mechanical rotating device to drive a laser emitter for 360° scanning. This type of LiDAR comprises one or more laser emitters and corresponding receivers, continuously rotating to generate continuous scan lines on a horizontal plane, while simultaneously employing a vertical scanning mechanism to achieve wide-area coverage in three-dimensional space. For example, Velodyne's HDL-64E is a classic example of a mechanically rotating LiDAR product, widely used in the early research and testing of autonomous vehicles.
2. Hybrid Solid-State LiDAR
Hybrid solid-state lidar combines the advantages of mechanical and solid-state technologies. While it still has a few moving parts, its rotating mechanism is more compact and less noticeable. This type of lidar reduces size and weight, improves reliability, and lowers production costs through MEMS (microelectromechanical systems) or other technologies, while retaining high scanning resolution. A typical hybrid solid-state lidar achieves a static layout in some dimensions, while using rotating or vibrating mirrors in other dimensions to expand the field of view.
3. Solid-state LiDAR
Solid-state lidar eliminates all mechanical rotating parts, adopting a completely solid-state design, which greatly improves stability and durability. Solid-state lidar is further subdivided into several categories:
Flash LiDAR: This type of radar uses a large-area two-dimensional array receiver to emit a flash-like laser pulse at once, enabling synchronous detection of the entire field of view. It is suitable for quickly acquiring near-low-resolution environmental mappings.
OPA (Optical Phased Array) LiDAR: By controlling the emission time difference of multiple laser sources, a beam with a controllable direction is formed, enabling electronic scanning without mechanical movement. This technology promises to achieve higher resolution and faster scanning speeds, but currently still faces technical challenges and cost issues.
MEMS LiDAR: Uses microelectromechanical systems, such as micromirror arrays, to guide and scan laser beams, achieving both solid-state operation and maintaining high angular resolution.
II. Classification based on function and application area
1. Time-of-Flight (ToF) LiDAR
Time-of-flight lidar calculates distance based on the time it takes for a laser pulse to travel to and from the target. This type of radar is widely used for precise ranging at short to medium ranges and is a key sensor in SLAM (Simultaneous Localization and Mapping) technologies for autonomous vehicles and robots.
2. Continuous Wave (CW) LiDAR
Continuous wave lidar determines the speed and distance of a target by analyzing the frequency or phase changes of the received laser beam. It is often used for the precise tracking of high-speed moving objects and for wind speed measurement.
3. Single-point ranging lidar
Single-point ranging radar is mainly used for simple short-range ranging applications, such as safety protection and material handling in industrial automation.
4. Holographic LiDAR
Using holographic interferometry, holographic lidar can capture complex target information, such as object shape, texture and minute deformation, making it an ideal choice for high-end applications such as geological exploration and biomedical research.
LiDAR sensing technology has a wide range of applications, covering multiple fields. Below are some of the main application areas and specific scenarios:
Autonomous driving and assisted driving:
LiDAR can help vehicles acquire information about obstacles on the road in real time, and then use computer algorithms to further process the information to determine the type and location of the obstacles so that they can be avoided.
LiDAR can also help vehicles perform precise positioning and navigation by acquiring three-dimensional information about the surrounding environment, including ground elevation, slope, road surface undulations, and information about surrounding buildings.
Traffic flow analysis and scheduling: By detecting the distribution of vehicle and pedestrian traffic on the road, traffic congestion can be detected in a timely manner, and then traffic can be diverted, scheduled, and roads can be rationally planned.
Robot Navigation:
LiDAR measurements enable robots to obtain accurate position information relative to their environment in real time, achieving precise positioning and path planning.
LiDAR can also help robots perceive their surroundings, quickly detect and identify obstacles, and achieve intelligent obstacle avoidance and environmental perception.
Topographic surveying and building quality control:
LiDAR reveals terrain features by showing subtle changes in ground elevation, which is helpful for geological exploration and urban planning.
Using LiDAR to scan buildings ensures that the building matches the Building Information Model (BIM).
Underwater topographic surveying:
Underwater surveys are typically conducted using depth-sounding lidar, which can measure all the way to the bottom and helps in mapping terrestrial and aquatic systems.
Precision agriculture:
Farmers can choose precision agriculture, using lidar to reduce the amount of fertilizer applied in the field, thereby improving the efficiency and sustainability of agricultural production.
Industrial Automation:
LiDAR sensors can monitor the entry of personnel or the location of items in a factory in real time, enabling automatic shutdown or alarm activation, thereby improving production safety.
Medical diagnosis and surgical assistance:
LiDAR can acquire a three-dimensional model of a patient's body to analyze the morphology and location of lesions, assisting doctors in making quick and accurate diagnoses.
During surgery, lidar can generate a 3D model of the surgical scene in real time, helping doctors to accurately locate the surgical cutting position and avoid misoperation.
Military applications:
LiDAR can be used in a variety of military applications, such as target imaging and recognition, helicopter obstacle avoidance, chemical warfare agent monitoring, and local wind field measurement.
In addition, lidar plays an important role in forestry mapping, environmental protection, and other fields. With continuous technological advancements, the application scenarios of lidar sensing technology will continue to expand, bringing innovation and convenience to more sectors.
With continuous technological innovation, LiDAR is developing towards miniaturization, lower cost, and higher reliability. New solid-state LiDAR technologies, such as silicon photonics LiDAR and quantum dot LiDAR, are constantly emerging, indicating that future LiDAR will further improve performance, broaden application areas, and inject new vitality into industries such as intelligent transportation, smart cities, virtual reality, and remote sensing mapping.
LiDAR sensing technology encompasses a wide variety of categories, with different design philosophies and technical approaches catering to diverse application scenarios and performance requirements. As the technology matures and market demand grows, LiDAR will leverage its unparalleled advantages in more fields, becoming a crucial supporting technology for the construction of an intelligent society.
