Comparison between LiDAR and Microwave Radar and LiDAR Technology

The wavelength of LiDAR is several orders of magnitude shorter than that of microwaves, and it also has a narrower beam. Therefore, compared to microwave radar, LiDAR has the following advantages:



1. High angular resolution, high velocity resolution, and high distance resolution. The use of range Doppler imaging technology can obtain high-resolution and clear images of moving targets.
2. Strong anti-interference ability and good concealment; Laser is not affected by radio waves and can penetrate plasma sheaths. When working at low elevation angles, it is not sensitive to ground multipath efficiency. The laser beam is very narrow and can only be received at the moment when it is illuminated, so the probability of the laser emitted by the LiDAR being intercepted is very low.
3. Lidar has a short wavelength and can detect targets at the molecular level. This is beyond the power of microwave radar.
4. Under the same function, it is smaller in size and lighter in weight than microwave radar.


Of course, LiDAR also has the following drawbacks:

1. Laser is greatly affected by the atmosphere and weather. Atmospheric attenuation and adverse weather conditions reduce the effective distance. In addition, atmospheric turbulence can reduce the measurement accuracy of LiDAR.
2. The laser beam is narrow, making it difficult to search for and capture targets. Usually, other devices are used to quickly and roughly capture targets in large airspace, and then the targets are precisely tracked and measured by LiDAR.
Analysis of Key Technologies of Lidar



Space scanning technology

The spatial scanning methods of LiDAR can be divided into non scanning systems and scanning systems, among which scanning systems can choose mechanical scanning, electrical scanning, and binary optical scanning. The non scanning imaging system uses multiple detectors, which have a long operating distance. The detection system is different from the unit detection of scanning imaging, which can reduce the volume and weight of the equipment. However, in China, it is difficult to obtain multiple sensors, especially area array detectors. Therefore, domestic laser radars mostly use scanning working systems.

Laser transmitter technology

At present, the selection of light sources for LiDAR transmitters mainly includes semiconductor lasers, semiconductor pumped solid-state lasers, and gas lasers.
Semiconductor laser is a miniaturized laser that uses a Pn junction or Pin junction composed of direct bandgap semiconductor materials as the working material. There are dozens of working materials for semiconductor lasers, and currently, semiconductor materials that have been made into lasers include gallium arsenide (GaAs), indium arsenide (InAs), antimony steel (InSb), cadmium sulfide (Cd s), cadmium telluride (cdTe), lead selenide (PbSe), lead telluride (PbTe), etc. The excitation methods of semiconductor lasers mainly include electric injection, optical pumping, and high-energy electron beam excitation. The excitation method of the vast majority of semiconductor lasers is electrical injection, which applies a forward voltage to the Pn junction to generate stimulated emission in the junction plane region, which is a forward biased diode. Therefore, semiconductor lasers are also known as semiconductor laserdiodes. Since the world's first semiconductor laser was introduced in 1962, after decades of research, semiconductor lasers have made remarkable progress. Its wavelength ranges from infrared to blue-green light, coverage gradually expands, and various performance parameters continue to improve. The output power has increased from a few milliwatts to kilowatts (array devices). In certain important application areas, other lasers commonly used in the past have gradually been replaced by semiconductor lasers.

High sensitivity receiver design technology

The receiving unit of a LiDAR consists of a receiving optical system, a photodetector, and an echo detection and processing circuit. Its functions include signal energy convergence, filtering, photoelectric conversion, amplification, and detection. The basic requirements for the design of LiDAR receiving units are: high receiving sensitivity, high echo detection probability, and low false alarm rate. In engineering applications, it is more reasonable and effective to use the technical approach of improving receiver sensitivity to improve the performance of laser rangefinders than to use the technical approach of increasing transmitter output power. The main method to improve the sensitivity of laser echo reception is to select appropriate detectionmethods and photodetectors for the receiver.

The detector is the core component of a laser receiver and a key factor in determining receiver performance. Therefore, the selection and rational use of detectors are important aspects in the design of laser receivers. At present, detectors used for laser detection can be divided into photomultiplier tubes based on external photoelectric effects, photodiodes based on internal photoelectric effects, and avalanche photodiodes. Due to their high internal gain, small size, and good reliability, avalanche photodiodes are often the preferred detection devices in engineering applications.


Terminal Information Processing Technology

The task of the LiDAR terminal information processing system is to complete the synchronization, coordination, and control of various transmission mechanisms, lasers, scanning mechanisms, and signal processing circuits, as well as to process the signals sent by the receiver to obtain distance information of the target. For imaging LiDAR, it is also necessary to complete tasks such as the acquisition, generation, processing, and reconstruction of the system's three-dimensional image data.
At present, the terminal information processing system design of LiDAR mainly adopts large-scale integrated circuits and computers. The ranging unit can be implemented using FPGA technology, and precision timing technology is also required in high-precision LiDAR. For imaging LiDAR, the system also needs to solve technologies such as non-linear scanning correction of image rows and amplitude/distance image display. The amplitude quantization of the echo signal is achieved by using an analog delay line and a high-speed operational amplifier to form a peak holder, and a high-speed A/D is used to complete the amplitude quantization. Image data acquisition is completed by high-speed DSP, and image processing and 3D display can be completed by industrial control computers.

LiDAR technology has been widely applied in various fields. Feiyan Remote Sensing has applied LiDAR technology to the surveying and mapping industry and accumulated impressive experience, completing each LiDAR aerial photography project on time