Detailed explanation of LiDAR detection technology




On the Luojia Mountain of Wuhan University, a beam of green fluorescence often shines into the sky at night, complementing the surrounding buildings and becoming a unique scenery on the campus. This is the Wuhan National Atmospheric Remote Sensing Program led by Professor Yi Fan from the School of Electronic Information at Wuhan University

On the Luojia Mountain of Wuhan University, a beam of green fluorescence often shines into the sky at night, complementing the surrounding buildings and becoming a unique scenery on the campus. This is the Wuhan National Field Science Observation and Research Station for Atmospheric Remote Sensing, led by Professor Yi Fan from the School of Electronic Information at Wuhan University, conducting radar night operations.

Night working diagram of radar station on Luojia Mountain

Recently, the national major scientific research instrument and equipment development project "Advanced Raman Lidar for Rapid and Accurate Measurement of 0-35 km Atmospheric Temperature and Aerosols" led by Yi Fan passed the final acceptance organized by the National Natural Science Foundation of China and was awarded excellent.



Over the past five years, the project team has successfully developed an advanced Raman LiDAR system with high spatiotemporal resolution for precise measurement of atmospheric temperature and aerosols. Under the spatiotemporal resolution of 15 minutes/90 meters, the statistical error of the system's temperature measurement is less than 1K within 18 kilometers, less than 2K within 35 kilometers, and the relative measurement error of the aerosol backscatter coefficient is less than 5% within 12 kilometers. This provides strong support for the study of atmospheric structure and dynamics from the near surface to the lower troposphere.

Advanced Raman LiDAR on-site working diagram

The Yifan team has long been committed to the development of LiDAR remote sensing detection technology and has received support from the National Natural Science Foundation of China's Outstanding Youth Science Fund and Innovation Research Group Project. The team has relied on the advantageous resources and strength of the Wuhan University Remote Sensing National Field Science Observation and Research Station to carry out effective research and achieve a large number of original scientific research results. The team's achievement of building the most powerful mid to high level atmospheric lidar comprehensive detection platform in Asia has been selected as one of the top ten major scientific, technological, and engineering advances in China by Science and Technology Daily.


 
What is a LiDAR system

Light Detection And Ranging (LiDAR) is a laser detection, ranging, and positioning system that can be installed on different remote sensing platforms. It integrates technologies such as laser ranging, inertial measurement, and high-precision positioning. By recording the time it takes for a single laser signal to travel from emission to reception of energy reflected by ground objects, and based on the position and attitude of the laser scanning system measured by the positioning and attitude system (POS) at the moment of signal emission, the three-dimensional coordinates of ground objects can be calculated and topographic maps can be drawn.
　　
Schematic diagram of airborne LiDAR imaging principle
　　
Compared with conventional photogrammetry and remote sensing technology, the use of LiDAR technology for remote sensing data acquisition has the characteristics of fast acquisition speed, high degree of automation, less weather influence, short data production cycle, and high geometric accuracy. It is a new technological means to obtain high-resolution three-dimensional geospatial information.
 
The carrying platforms used in LiDAR remote sensing operations include various remote sensing platforms such as ground, vehicle, airborne, ship, and satellite. Among them, commercial LiDAR systems are mainly based on ground, vehicle, and airborne platforms. The manned airborne platforms include large fixed wing aircraft and helicopter platforms, while unmanned aerial platforms include fixed wing drones, unmanned helicopters, multi rotor drones, etc.
　　
Taking airborne and vehicle mounted LiDAR systems as examples, a typical system generally consists of the following main components: a high-precision positioning and attitude determination system (POS), which mainly includes a dynamic differential GNSS receiver used to determine the spatial position of the scanning projection center, and an inertial measurement unit (IMU) used for high-precision sensor spatial attitude parameter measurement; Laser scanning ranging system, used to measure the distance from sensors to ground points; A set of imaging devices (mainly digital cameras) used to obtain color digital images of the corresponding ground, for the final production of orthophoto images; A control and storage system for controlling the operation of laser scanning ranging systems, GPS, IMU, and imaging devices, and storing the acquired data; An operation terminal for operators to operate and monitor the status of equipment; Supporting data processing software, such as POS data processing software, point cloud generation software, etc.
　　
During homework, based on the echo angle and distance measured by the laser scanner, combined with the spatial position and attitude measured by the inertial measurement unit (IMU) and differential GNSS, as well as their geometric positional relationships, the high-density three-dimensional point cloud spatial position information of the target object can be directly obtained through geometric post-processing, as shown in the figure.