What are the ranging methods of LiDAR?

With the development of artificial intelligence, auto-driving cars are no longer an imaginary scene. Do you know how cars can see the surrounding environment and realize autonomous driving? This has to mention the “eyes” of the robot’s three-dimensional imaging LiDAR. LiDAR, as its name suggests, is an active detection remote sensing device that uses lasers to measure the distance of objects. Similar to microwave radar, people first find inspiration from bats. Compared with them, LiDAR has higher ranging accuracy and can see more detailed features of objects, so it has a very wide range of applications in life.

In the 1960s and 1970s, developed countries have already begun the research of LiDAR in the field of 3D imaging. If the imaging of an object by LiDAR is likened to a blind person touching an elephant, then we can divide the process of “touching an elephant” into two steps: first, know the position and distance of the “elephant”, and then continue to explore the “elephant” to determine the “elephant”. ” And this corresponds to two major parts of the work of 3D imaging LiDAR: the laser distance measurement process and the laser 3D imaging process.

Using LiDAR for distance measurement, we have to prescribe the right medicine for different application scenarios.

Clairvoyance Pulse Laser Ranging Method in Laser Ranging

Pulsed laser has the characteristics of high peak power, which enables it to travel a long distance in space, so the pulsed laser ranging method can measure very far targets. How far is it? At present, the farthest laser measurement distance in human history is the distance between the earth and the moon, and they use the pulsed laser ranging method. Since June 2019, the Tianqin project team in my country has successfully measured the distance between the earth and the moon many times. Through accurate timing of the pulse flight time, the distance between the earth and the moon is 351,000 km to 406,000 km (elliptical orbit).

Pulsed laser ranging is a well-developed ranging system that can not only be used to detect distant targets but also can be used in measurement scenarios of several kilometers or even tens of meters. This method is also mostly used in the current automatic driving of automobiles, and its ranging accuracy can reach the order of centimeters, which is sufficient for most application scenarios.

How is LiDAR imaged?

After the first step of “Blind People Touching the Elephant”, we have successfully found the location and distance of the “elephant”. How do we know what the “elephant” looks like in the next step? This is the problem to be solved in the imaging process of LiDAR. Simply understand, LiDAR 3D imaging is actually based on measuring the distance of each point of the target, and at the same time obtaining the horizontal angle and the elevation angle between each point and the radar, so that we can get the 3D information of the target. According to the method of acquiring the three-dimensional information of each point of the target, the laser imaging system mainly includes scanning laser imaging and area array laser imaging.