What types of LIDAR are used in self-driving cars?

There are many types of LIDAR. Categorized by function:

Laser Ranging Radar

Laser ranging radar is used to determine the distance between the object under test and a test point by emitting a laser beam at the object under test, receiving the reflected wave of that laser beam, and recording that time difference. Traditionally, laser radar can be used in the field of security detection in industry, such as the laser wall seen in sci-fi movies, where the system reacts immediately with an early warning when someone breaks in. In addition, laser ranging radar is also widely used in the field of space mapping. However, with the rise of the artificial intelligence industry, laser ranging radar has become an indispensable core component in robots, used in conjunction with SLAM technology, which can help robots to carry out real-time localization and navigation, and realize autonomous walking. The rplidar series developed by SLAM with SLAMware module is a typical representative of autonomous positioning and navigation for service robots, which can complete laser ranging tens of thousands of times per second within a 25-meter ranging radius and achieve millimeter-level resolution.

Laser Velocimetry Radar

Laser Velocimetry Radar (LVR) is a measurement of an object's moving speed, which is obtained by taking two laser ranging measurements of the object to be measured with a specific time interval.

Laser radar speed measurement methods are mainly two categories, one is based on the realization of the principle of laser radar ranging, i.e., a certain time interval to continuously measure the target distance, with the difference between the two target distances divided by the time interval can be known as the target's speed value, the direction of the speed according to the difference between the distance of the positive and negative will be able to determine. This method has a simple system structure, limited measurement accuracy, and can only be used for hard targets with strong laser reflection.

Another type of speed measurement method is to use the Doppler shift. Doppler shift is that when there is a relative velocity between the target and the LIDAR, there will be a frequency difference between the frequency of the received echo signal and the frequency of the transmitted signal, and this frequency difference is the Doppler shift.

Laser Imaging Radar

Laser Imaging Radar can be used to detect and track the target, obtain the target position and speed information. It can accomplish tasks that ordinary radar cannot, such as detecting submarines, mines, hidden military targets and so on. It is widely used in military, aerospace, industrial and medical fields.

Atmospheric Detection Lidar

Atmospheric Detection Lidar is mainly used to detect molecules in the atmosphere, the density of smoke, temperature, wind speed, wind direction and the concentration of water vapor in the atmosphere, in order to achieve the monitoring of the atmospheric environment and storms, dust storms, and other catastrophic weather forecasting purposes.

Tracking radar

Tracking radar can continuously track a target, and measure the coordinates of the target to provide the target's trajectory. It is not only used for artillery control, missile guidance, external ballistic measurements, satellite tracking, research on surprise defense technology, etc., but is also expanding in the fields of meteorology, transportation, and scientific research.

Categorized by working medium:

Solid-state LIDAR

Solid-state LIDAR peak power is high, the output wavelength range and the existing optical components and devices, the output long range and the existing optical components and devices (such as modulators, isolators and detectors) and atmospheric transmission characteristics, etc., and it is easy to realize the main oscillator-power amplifier (MOPA ) structure, coupled with conductors such as high efficiency, small size, light weight, high reliability and stability, solid-state lidar is prioritized for application in airborne and space-based systems. In recent years, LIDAR development has focused on diode-pumped solid-state LIDAR.

Gas Lidar

Gas Lidar CO2 Lidar as a representative, it works in the infrared band, atmospheric transmission attenuation is small, the detection distance is far, has been in the atmosphere of the wind field and environmental monitoring played a great role, but the volume is large, the use of the mid-infrared HgCdTe detector must be in the temperature of 77K work, restricting the development of gas Lidar.

Semiconductor LiDAR

Semiconductor LiDAR can work continuously with high repetitive frequency, has the advantages of long life, small size, low cost and little harm to the human eye, and is widely used in the backward scattering signal is relatively strong Mie scattering measurements, such as detecting the height of the cloud bottom. The potential applications of semiconductor lidar are visibility measurement, obtaining aerosol extinction profiles in the atmospheric boundary layer and recognizing rain and snow, etc., which are easy to make into airborne equipment.