Principle of laser radar ranging

What is the principle of lidar ranging?

The basic principle of laser radar ranging is to calculate the distance of the target by measuring the round-trip time of laser emission signal and laser echo signal. First of all, the laser radar emits a beam of laser, which is reflected after being hit by an obstacle, and is received and processed by the laser receiving system, so as to know the time interval between laser emission and reflection and reception, that is, the time of laser flight. According to the flight time, the distance of obstacles can be calculated. According to the different forms of emitted laser signals, laser ranging methods can be divided into two types: pulse laser ranging and phase laser ranging.

(1) Pulse laser ranging: The pulse method is that after the laser beam is emitted by the laser radar, part of the laser beam is reflected back to the obstacle and received by the receiver of the laser radar. Meanwhile, the time interval between transmission and reception can be recorded in the lidar, and the distance to be measured can be calculated according to the speed of light.

(2) Phase-based laser ranging: Phase-based laser transmitter sends out continuous laser signal with intensity modulation. After being illuminated by obstacles, it reflects back. The measuring beam will change phase during the round trip. By calculating the phase difference between the laser signal in the radar and the object flying back and forth with obstacles and the distance of obstacles, the conversion is carried out.

2. What are the types of lidar?

According to whether there are mechanical rotating parts, lidar can be divided into mechanical lidar, solid-state lidar and mixed solid-state lidar. (1) Mechanical lidar: Mechanical lidar has rotating parts to control the laser emission angle. It is bulky, expensive and has relatively high measurement accuracy, and is usually placed on the top of the car.

(2) Solid-state lidar: Solid-state lidar relies on electronic components to control the laser emission angle. It does not need mechanical rotating parts, so it is small in size and can be installed in the car body.

(3) Hybrid solid-state laser radar: Hybrid solid-state laser radar has no large-capacity rotating structure and needs multi-angle detection. It changes the direction of laser beam by rotating the inner glass sheet, so it is embedded.

According to the number of wire harnesses, lidar can be divided into single-line lidar and multi-line lidar.

(1) Single-beam lidar only produces one scan line at a time, and the obtained data is 2D data, which cannot distinguish the three-dimensional information of the target object. However, single-line lidar is used in safety protection, topographic mapping and other fields because of its fast measurement speed and low data processing ability.

(2) Multi-line lidar can generate multiple scanning lines at one time. At present, there are 4, 8, 16, 32 and 64 multi-line lidar products on the market. Suitable for 2.5D lidar and 3D lidar. The biggest difference between 2.5D lidar and 3D lidar is that lidar is vertical.