LiDAR (Light Detection and Ranging) technology has revolutionized the realm of autonomous vehicles, environmental monitoring, and various other applications. To fully grasp the intricacies of LiDAR, this article delves into its classification based on scanning and detection methods. By understanding the distinct characteristics of each type, readers can gain a deeper appreciation of LiDAR’s versatility and capabilities.
Introduction
LiDAR has emerged as a transformative technology, enabling precise 3D mapping and object detection through the utilization of laser pulses. Its applications span across a wide spectrum, including autonomous vehicles, robotics, archaeological surveys, and environmental monitoring. To effectively comprehend the nuances of LiDAR, it is essential to categorize it based on its scanning and detection methodologies.
Classification by Scanning Methods
1. MEMS LiDAR
MEMS (Microelectromechanical Systems) LiDAR offers unparalleled flexibility by dynamically adjusting its scanning pattern. This enables it to focus on specific objects, capturing intricate details of distant or small targets, a capability beyond the reach of traditional mechanical LiDAR systems. The MEMS architecture employs a single, compact mirror to direct the fixed laser beam towards various directions. Owing to the mirror’s diminutive size, its inertial moment is negligible, allowing for rapid movement. This agility enables MEMS LiDAR to track 2D scanning patterns in less than a second.
2. Flash LiDAR
Flash LiDAR captures the entire scene instantaneously, circumventing the challenges posed by target or LiDAR movement during the scanning process. Its operation resembles that of a camera, with the laser beam directly illuminating the entire scene in a single flash. Subsequently, an array of miniature sensors gathers the reflected laser beams from diverse directions. While Flash LiDAR boasts distinct advantages, it also harbors certain limitations. As pixel size increases, the volume of signals to be processed escalates. Integrating a vast number of pixels into the photodetector inevitably introduces interference, compromising precision.
3. Phased-Array LiDAR
Phased-Array LiDAR employs an array of emitters that can manipulate the laser beam’s emission direction by adjusting the relative phase of the signals. Currently, most Phased-Array LiDAR systems remain confined to laboratory environments, with the field still dominated by rotating and MEMS LiDAR technologies.
4. Mechanically Rotating LiDAR
Mechanically Rotating LiDAR represents an early iteration of LiDAR technology and has reached a high level of maturity. However, its intricate system structure and the substantial cost of its core components, including lasers, scanners, optical components, photodetectors, receiver ICs, and position and navigation devices, hinder mass production and raise concerns regarding stability. Consequently, solid-state LiDAR has emerged as a promising alternative for many companies.
Classification by Detection Methods
1. Direct Detection LiDAR
Direct Detection LiDAR closely resembles a laser rangefinder in its fundamental structure. During operation, the emission system transmits a signal, which is reflected off the target and collected by the receiving system. The target’s distance is determined by measuring the round-trip propagation time of the laser signal. The radial velocity of the target can be ascertained by analyzing the Doppler shift of the reflected light or by measuring two or more distances and calculating their rate of change.
2. Coherent Detection LiDAR
Coherent Detection LiDAR can be categorized into single-mode and dual-mode systems. In single-mode systems, the transmitted and received signals share a single optical aperture and are isolated by a transmit-receive switch. Dual-mode systems, on the other hand, employ separate optical apertures for transmitted and received signals, eliminating the need for a transmit-receive switch. The remaining components are analogous to those of single-mode systems.
Classification by Laser Emission Waveform
1. Continuous-Wave LiDAR
Continuous-Wave LiDAR, as the name suggests, emits a continuous laser beam, akin to a flashlight’s steady illumination. Continuous lasers collect data at a specific altitude by maintaining a constant light source. Due to the inherent nature of continuous lasers, data is only acquired for a single point at a given instant. The stochastic nature of wind data renders the representation of wind conditions at a particular altitude using a single point somewhat simplistic. To address this limitation, some manufacturers employ a 360-degree rotation mechanism to collect data from multiple points along the circular path and perform an average assessment. This approach essentially involves statistical analysis of multiple data points within a virtual plane.
2. Pulsed LiDAR
Pulsed LiDAR emits laser pulses in a non-continuous manner, resembling a series of flashes. The principle behind pulsed lasers involves transmitting thousands of laser particles and applying the universal Doppler principle to comprehensively evaluate wind conditions at a specific altitude based on the reflection patterns of these laser particles. This approach offers a three-dimensional perspective, enabling the determination of detection range. From a laser characteristic standpoint, pulsed LiDAR offers significantly more measurement points compared to continuous-wave LiDAR, enabling a more accurate depiction of wind conditions at a specific altitude.
Conclusion
This article has provided a comprehensive exploration of LiDAR classifications based on scanning and detection methods. By delving into the unique characteristics of each type, we have gained valuable insights into the versatility and potential of LiDAR technology. As LiDAR continues to evolve, its applications are poised to expand across various industries, revolutionizing numerous fields from autonomous vehicles to environmental monitoring and beyond.
