"Radar" is an electronic device that uses electromagnetic waves to detect the position of an object. The functions of electromagnetic waves include searching for targets and finding targets; measuring motion parameters such as distance, velocity, angular position, etc.; measuring characteristic parameters such as target reflectivity, scattering cross section and shape.
The conventional radar is a radar in which electromagnetic waves in the microwave and millimeter wave bands are carriers. The laser radar uses a laser as a carrier. Information can be carried by amplitude, frequency, phase, and amplitude as an information carrier.
Lidar uses laser light waves to accomplish these tasks. Non-coherent energy reception can be used, which is mainly a pulse counting based ranging radar. It is also possible to receive signals by means of coherent reception and to detect by post signal processing. There is no essential difference between lidar and microwave radar, and it is very similar on the principle block diagram. See the figure below.
Lidar is a radar that operates in the optical band. Similar to the principle of microwave radar, it uses the electromagnetic wave in the optical frequency band to first transmit the detection signal to the target, and then compares the received co-wave signal with the transmitted signal to obtain the position (distance, azimuth and altitude) and motion of the target. Status (speed, attitude) and other information to achieve the detection, tracking and identification of the target.
The lidar consists of three parts: transmitting, receiving and post-signal processing and a mechanism for coordinating the three parts. The laser light velocity divergence angle is small, energy concentration, detection sensitivity and resolution are high. The Doppler shift is large and can detect targets from low speed to high speed. The size of the antenna and system can be made small. The use of different molecules for laser absorption, scattering or fluorescence at specific wavelengths allows the detection of different material compositions, a unique feature of lidar.
Type of lidar
At present, there are many types of laser radar, but according to the concept of modern laser radar, it is often divided into the following types:
According to the laser band: there are ultraviolet laser radar, visible laser radar and infrared laser radar.
According to the laser medium: gas laser radar, solid-state laser radar, semiconductor laser radar and diode laser-pumped solid-state laser radar.
According to the laser emission waveform: pulsed laser radar, continuous wave laser radar and hybrid laser radar.
According to the display method: there are analog or digital display laser radar and imaging laser radar.
According to the carrier platform: ground-based fixed laser radar, vehicle laser radar, airborne laser radar, shipborne laser radar, spaceborne laser radar, missile-borne laser radar and handheld laser radar.
According to function: laser ranging radar, laser speed radar, laser angle-measuring radar and tracking radar, laser imaging radar, laser target indicator and bio-laser.
According to the purpose: laser range finder, range laser radar, fire control laser radar, tracking and recognition laser radar, multi-function tactical laser radar, detection laser radar, navigation laser radar, meteorological laser radar, detection and atmospheric monitoring laser radar Wait.
In specific applications, lidar can be used alone or in combination with imaging equipment such as microwave radar, visible light television, infrared television or low-light TV, enabling the system to search for both long-range targets and precise targets. track.
Comparison between lidar and microwave radar
Lidars have wavelengths that are orders of magnitude shorter than microwaves and have narrower beams. Therefore, compared to microwave radar, laser radar has the following advantages:
1. High angular resolution, high speed resolution and high distance resolution. High resolution clear images of moving objects can be obtained using distance-Doppler imaging techniques.
2, strong anti-interference ability, good concealment; laser is not interfered by radio waves, can pass through the plasma sheath, when working at low elevation angle, it is not sensitive to ground multi-path efficiency. The laser beam is very narrow, and only at the point where it is illuminated, it can be received at that moment, so the probability that the laser emitted by the laser radar is intercepted is very low.
3. The laser radar has a short wavelength and can detect the target at the molecular weight level. This is powerless for microwave radar.
4. In the case of the same function, it is smaller than the microwave radar and light in weight.
Of course, Lidar also has the following disadvantages:
1. The laser is greatly affected by the atmosphere and meteorology. Atmospheric attenuation and severe weather reduce the range of action. In addition, atmospheric turbulence reduces the accuracy of the lidar measurement.
2. The laser beam is narrow and it is difficult to search for targets and capture targets. Generally, other equipment implements large airspace, fast rough catching targets, and then the laser radar is used to accurately track and measure the target.
Lidar detection principle
The most important performance parameter of a lidar is the system signal-to-noise ratio (SNR). The following figure shows a block diagram of the non-coherent and coherent receivers of the lidar.
Background noise
In addition to the signal optical power Ps, the non-coherent receiver has an additional term, the background optical power PBK. . It is radiated by the sun and the object itself. The unnecessary noise signal caused by the reflection, diffuse reflection and flicker of the object becomes an electrical signal and is amplified in the receiver nonlinear photodetector. And other noise suppression measures produce a valid signal for the video bandwidth.
In a coherent receiver, in addition to the signal light of the frequency f0 emitted by the laser, there is a local oscillator light passing through the beam splitter. The echo of the signal light is coupled to the local oscillator to the light detection. In addition to receiving the optical signal power PS, the external seismic power PLo, which competes with the background noise term PBK, suppresses the noise.
The background noise is:
In the above formula, ε is the radiation coefficient of the target; Ï is the reflection coefficient of the target; T is the temperature (K) of the target; Δλ is the wavelength range of the light (μm); AR is the sensitive surface area of ​​the receiver detector (m2); k1 Is the transmission coefficient of sunlight through the atmosphere; SIRR is the radiance of the sun ( 
Is the scattering coefficient of the atmosphere; ηSys is the optical efficiency of the system; ΩR is the solid angle of the energy radiated by the radiator; σT is the Sterling-Boltzmann constant.
Signal to noise ratio expression
Where is the mean square value of the signal current; is the mean square value of the shot noise current; is the mean square value of the thermal noise current; is the mean square value of the background noise current; is the mean square value of the dark current; is the local oscillator The mean square value of the current.
The above-mentioned current is substituted into the SNR equation to obtain the signal-to-noise ratio equation for incoherent and coherent lidar:
The SNR equation of the incoherent lidar can be expressed as:
The signal-to-noise ratio SNR equation for coherent lidar is expressed as:
Analysis of key technologies of laser radar
Spatial scanning technology
The space scanning method of lidar can be divided into non-scanning system and scanning system. The scanning system can select mechanical scanning, electrical scanning and binary optical scanning. The non-scanning imaging system uses multiple detectors, which have a long range of action. The detection system is different from the scanning unit imaging, which can reduce the volume and weight of the device. However, it is difficult for multi-sensors in China, especially the area array detectors. Obtained, so the domestic laser radar mostly uses the scanning work system.
Mechanical scanning can perform large field of view scanning, and can also achieve high scanning rate. Different mechanical structures can obtain different scanning patterns, which is a scanning method with many applications at present. The acousto-optic scanner uses an acousto-optic crystal to scan the deflection of the incident light. The scanning speed can be very high, and the scanning deflection accuracy can reach the micro-arc metric. However, the scanning angle of the acousto-optic scanner is small, the beam quality is poor, the power consumption is large, and the acousto-optic crystal must be cooled, and the amount of equipment will be increased in practical engineering applications.
Binary optics is an emerging important branch of optical technology. It is one of the frontier disciplines in the field of optics based on diffraction theory, computer-aided design and micro-machining technology. A microlens array smart scanner can be fabricated using binary optics. Generally, such a scanner is composed of a pair of microlens arrays with a pitch of only a few micrometers. One group is a positive lens and the other is a negative lens. The collimated light passes through the positive lens and begins to focus, and then passes through the negative lens to become collimated. Light. When the positive and negative lens arrays move laterally relative to each other, the collimated light direction deflects. Such a lens array requires only a small relative movement of the output beam to produce a large deflection, and the smaller the lens array, the smaller the relative movement required to achieve the same deflection. Therefore, the scanning rate of such a scanner can be very high. The disadvantage of the binary optical scanner is that the scanning angle is small (a few degrees) and the transmittance is low, which is not mature enough in engineering applications.
Laser transmitter technology
At present, the selection of the laser source of the laser radar transmitter includes a semiconductor laser, a semiconductor-pumped solid-state laser, and a gas laser.
A semiconductor laser is a miniaturized laser that uses a Pn junction or a Pin junction of a direct bandgap semiconductor material as a working substance. There are dozens of working materials for semiconductor lasers. The semiconductor materials that have been fabricated into lasers are gallium arsenide (GaAs), indium arsenide (InAs), antimony steel (InSb), cadmium sulfide (Cds), and cadmium telluride (cdTe). ), lead selenide (PbSe), lead telluride (PbTe), and the like. The excitation modes of semiconductor lasers are mainly electric injection type, optical pump type and high energy electron beam excitation type. Most semiconductor lasers are excited by electrical injection, that is, a forward voltage is applied to the Pn junction to generate stimulated emission in the junction plane region, that is, a forward biased diode. Therefore, the semiconductor laser is also called a semiconductor. Laser _ pole tube. Since the world's first semiconductor laser was introduced in 1962, after decades of research, semiconductor lasers have been amazingly developed. Its wavelengths range from infrared to blue-green, and coverage has gradually expanded, and various performance parameters have been continuously improved. The output power is increased from a few milliwatts to kilowatts (array devices). In some important applications, other lasers commonly used in the past have gradually been replaced by semiconductor lasers.
Semiconductor-pumped solid-state lasers combine the advantages of semiconductor lasers with solid-state lasers, featuring small size, light weight, and high quantum efficiency. By pumping the laser T as a substance, the pump light with good beam quality, temporal coherence and spatial coherence is eliminated, which eliminates the shortcomings of poor quality and mode characteristics of the semiconductor laser, and has a pump compared with the xenon-pumped homogeneous laser. High efficiency, long life, stable and reliable. The laser working substance can be selected from Nd, Tm, Ho, Er, Yb, Li (Li) Multiple waves. At present, many engineering application problems of semiconductor pumped solid-state lasers have been solved, and it is the laser with the best application prospect and the fastest development.
Gas lasers are currently one type of laser with the most abundant output laser wavelength and the most widely used. It is characterized by a wide range of laser output wavelengths; the optical uniformity of the gas is good, so the output beam quality is good, and its monochromaticity, coherence and beam stability are good.
High sensitivity receiver design technology
The receiving unit of the laser radar is composed of a receiving optical system, a photodetector and an echo detecting processing circuit, and its function is to complete functions such as signal energy convergence, filtering, photoelectric conversion, amplification and detection. The basic requirements for the design of the lidar receiving unit are: high receiving sensitivity, high echo detection probability and low false alarm rate. In engineering applications, the technical approach to improve the sensitivity of the receiver to improve the performance of the laser rangefinder is more reasonable and effective than the technical approach to increase the output power of the transmitter. The method for improving the sensitivity of laser echo reception is mainly to select an appropriate detection method and photodetector for the receiver.
The core components of the detector laser receiver are also the key factors determining the performance of the receiver. Therefore, the selection and rational use of the detector is an important part of the design of the laser receiver. At present, detectors for laser detection can be divided into photomultiplier tubes based on external photoelectric effect and photodiodes and avalanche photodiodes based on internal photoelectric effects. The avalanche photodiodes have high internal gain, small size, and good reliability. Other advantages, often the preferred detector component in engineering applications.
The echo signal circuit of the laser radar mainly includes an amplifying circuit and a threshold detecting circuit. The design of the amplifying circuit is to match the waveform of the echo signal. For different echo signals (such as pulse signals, continuous wave signals, quasi-continuous signals or FM signals), the receiver must have matching bandwidth and gain. . For the laser-radar of the pulse working system, the amplifying circuit should have a wide bandwidth, and at the same time, the time gain control technology should be adopted, and the gain of the amplifier is not fixed, but the control curve designed according to the curve of the lidar equation to suppress Close-range backscattering reduces false alarms and allows the amplifier to operate in a linear amplification region.
The threshold detection circuit is a pulse peak comparator. The criterion for determining the arrival of the echo is that the amplitude of the echo pulse exceeds the threshold. The advantage of this approach is simple, but there are two main drawbacks. First, as long as there is a pulse amplitude that first exceeds the threshold, the detection circuit will determine it as an echo, regardless of whether it is a coherent pulse or a clutter interference pulse, resulting in false alarms; secondly, the amplitude of the echo pulse changes. It will cause an error in the arrival time, resulting in a ranging error. In high-precision laser range finder, the peak sample-and-hold circuit and the constant-ratio timing circuit are usually used to reduce the time measurement error.
Terminal information processing technology
The task of the laser radar terminal information processing system is to complete the synchronization and control of each transmission mechanism, laser, scanning mechanism and each signal processing circuit, and to process the signal sent by the receiver to obtain the distance information of the target. Imaging laser radar also needs to complete the tasks of acquiring, generating, processing and reconstructing three-dimensional image data of the system.
At present, the design of the terminal information processing system of the laser radar is mainly implemented by using a large-scale integrated circuit and a computer. The ranging unit can be realized by using FPGA technology, and precision time measuring technology is also needed in high-precision laser radar. For imaging laser radar, the system also needs to solve the techniques of nonlinear scanning correction, amplitude/distance image display of image lines. The amplitude of the echo signal is quantized using an analog delay line and a high-speed operational amplifier to form a peak holder, which uses high-speed A/D to perform amplitude quantization. Image data acquisition is performed by a high-speed DSP, and image processing and three-dimensional display can be performed by an industrial control computer.
Lidar application
Application of Lidar Technology in Urban 3D Building Model
“Digital City†is an important part of the digital earth technology system, and the three-dimensional models that express the main objects of the city include three-dimensional terrain, three-dimensional building models, and three-dimensional pipeline models. These three-dimensional building models are one of the important basic information of digital cities.
The laser radar technology can quickly complete 3D spatial data acquisition, and its advantages make it have a broad application prospect. The components of the airborne radar system include: laser scanners, high-precision inertial navigation systems, global positioning systems using scoring technology, and high-resolution digital cameras. Through the integration of these four technologies, the acquisition of terrestrial three-dimensional geographic geographic information can be quickly completed, and the image data with coordinate information can be obtained through processing. A technique for modeling 3D buildings using lasers. First, data preprocessing is performed. It combines the posture parameters recorded by IMUU, the onboard GPS data, the ground station GPS observation data, the GPS eccentric component, the eccentric components of the scanner and the digital camera, and performs the GPS/IMU joint solution to obtain the scanner and camera exposure coordinates. Trace the file, and then get the foreign element. Secondly, the LIDAR data commercial processing software is used to separate the ground data from the non-ground data to generate the DEM, and the DOM is quickly generated by using the pure surface data to correct the image orientation elements by finding the same-name image point. The DEM and DOM are superimposed to form a three-dimensional terrain model. Finally, texture maps are applied to 3D building models in order to express the true urban appearance. Texture pasting methods are commonly used in manual pasting and texture mapping. There are two common methods for obtaining textures. The first method is to use aerial images on the top texture of the building, and the side texture information is taken in the field for handheld cameras. The second method is tilt aerial photography. After obtaining the texture, using professional software to select the texture surface, homogenizing treatment, etc., the image information of the current state of the reaction building is mapped to the corresponding model to achieve the purpose of reflecting the current status of the city.
Application of Lidar Technology in Atmospheric Environment Monitoring
Due to its short detection wavelength, strong beam orientation and high energy density, laser radar has the advantages of high spatial resolution, high detection sensitivity, ability to distinguish detected species and no detection blind zone, and has become a high-precision remote sensing of the atmosphere. An effective means of detection. Lidar can be used to detect aerosols, cloud particle distribution, atmospheric composition and vertical profiles of wind fields, enabling effective monitoring of major sources of pollution.
Observation of the distribution of atmospheric pollutants. When the laser emitted by the laser radar interacts with these floating particles, the wavelength of the incident light is of the same order of magnitude as that of the floating particles. The scattering coefficient is inversely proportional to the square of the wavelength. The Mie scattering laser radar can be based on this property. The determination of aerosol concentration, spatial distribution and visibility was completed.
Differential laser radar is mainly used for the determination of atmospheric components. The principle of differential lidar testing is to use laser radar to emit two kinds of unequal light, one of which is adjusted to the absorption line of the object to be tested, and the other wavelength is adjusted to the wing with smaller absorption coefficient on the line, and then repeated with high repetition. The frequency alternately emits the two wavelengths of light into the atmosphere. At this time, the difference in the attenuation of the two wavelengths of the optical signals measured by the lidar is caused by the absorption of the object to be measured, and the concentration distribution of the object to be tested can be obtained through analysis. .
The observation of the metal vapor layer in the middle layer of the atmosphere mainly uses a fluorescence resonance scattering laser radar. The principle is to use atmospheric metal dynamics such as Na, K, Li, Ca and other metal atoms as tracers. Due to the low atmospheric molecular density of the middle layer, the Rayleigh scattering signal is very weak, and the sodium metal atomic layer in this region is several orders of magnitude higher than the Rayleigh scattering cross section. Therefore, the sodium layer is used to study the sodium layer. Distribution, and then the study of gravity waves and other related properties show its unique characteristics.
Application of Lidar in Direct Investigation of Oil and Gas
The direct detection of hydrocarbon gas anomalies above oil and gas using remote sensing is a direct and rapid method of oil and gas exploration. Lidar is a combination of laser technology and radar technology, and it has become possible to apply it to oil surveys. The laser has a wide operating wavelength range, good monochromaticity, and the laser is directional radiation, which has the advantages of collimation and high measurement sensitivity, making it far superior to other sensors in remote sensing.
Lidar consists of two parts: the transmitting system and the receiving system. The transmitting system mainly includes a laser and a transmitting telescope; the receiving system is mainly composed of a receiving telescope, a photomultiplier tube and a display. Lidar technology is based on the phenomenon that the laser beam is scattered in the atmosphere, the dust particles and various gas molecules in the atmosphere scatter, laser Rayleigh scattering, Raman scattering and resonance fluorescence and resonance absorption, and then use the laser radar receiving system. Collect and record the backscattering spectra generated during the above phenomena to achieve the purpose of detecting atmospheric composition and concentration.
Hydrocarbon gas is the main indicator gas for oil and gas micro-leakage in oil and gas fields, and the near-surface hydrocarbon gas is mainly composed of early diagenesis, bacterial action and underground heat. Resonance absorption laser radar generally uses various tunable lasers to detect the gas molecule's detection sensitivity, which refers to the ability of the laser radar to receive subtle changes in laser power. The detected distance and the absorption cross section of the gas molecules to be measured are the main factors affecting the sensitivity of the probe. According to the research data, the larger the absorption cross section, the higher the sensitivity; the larger the detection distance, the higher the sensitivity. The relationship between the path and the sensitivity is that the longer the path, the stronger the absorption attenuation of the laser beam by the gas molecules, so that the detection sensitivity is greatly improved. However, due to the divergence of the laser spot and the dithering effect of the change of the laser transmission direction caused by atmospheric turbulence, the effective utilization of the laser is reduced, that is, the signal-to-noise ratio is lowered, thereby affecting the detection accuracy of the molecular content of the contaminated gas. Therefore, the detection distance is preferably several kilometers.
Using lidar for meteorological research
Lidar is a very important meteorological instrument based on the detection principle that electromagnetic energy will be reflected back from the target. Like radar, data about the nature, distance, and angle of the target can be provided to us by scattering of light. More excellent than radar, it can operate not only in the microwave region, but also in visible, infrared or shorter areas. Lidar is an extension of radar in the optical electromagnetic spectrum. A short pulse of energy is generated by the laser transmitter and transmitted to a target. The scattered waves radiated by the target are collected by the receiving optical system and concentrated on a sensitive detector, which converts the energy of the incident light into an electrical signal, which is processed by the amplified signal and then used.
The first primitive instrument design developed at the Stanford Institute clearly demonstrates the application of lidar, such as the location of clouds and fog layers through the structure of rain or underlying clouds, and the height of the rise limit. The lidar echo clearly reveals a clear continuous aerosol layer from low altitudes, which is invisible to the naked eye.
The SRI Mark III's lidar shows a higher level of detection of thin cirrus clouds. It shows that a very high peak power can penetrate the cloud while forming a reflection. Using this phenomenon, it is possible to prove the existence of cirrus clouds of several different layers when observed at different sea wave heights. Despite the superior performance of the Lidar, in addition to optimizing the parameters in the design system, many techniques are utilized to improve the performance of the Lidar system. For example, laser cooling is a problem that all lasers must solve. Air cooling can be used when the lidar pulse repetition frequency is low or the pump threshold is low, and the cooling system must be used to cool the laser with a larger laser pulse energy.
Lidar applications in the automotive and transportation sectors
Automatic parking technology
Automated parking systems typically have sensors mounted around the front and rear of the car that act as both a transmitter and a receiver. They send a laser signal that is reflected back when the signal hits an obstacle around the body. The onboard computer then uses the time it takes to receive the signal to determine the location of the obstacle. There are also some automatic parking systems that use a bumper to mount a camera or radar to detect obstacles. In general, the principle is the same. The car will detect the stopped vehicle, the size of the parking space and the distance from the roadside, and then drive the car into the parking space.
The mode of operation is as follows. When the car moves to the side of the front car, the system will give the driver a signal telling him when he should stop. Then, the driver reverses the gear, releases the brakes a little, and starts to reverse. Then, the computer system on the car will take over the steering wheel. The computer turns the wheel through the power steering system and completely pours the car into the parking space. When the car falls far enough back, the system gives the driver another signal telling him that he should stop and change to the forward gear. The car moves forward and adjusts the wheels in place. Finally, the system gives the driver a signal telling him that the car has stopped.
ACC active cruise technology
The ACC system includes a radar sensor, a digital signal processor, and a control module. The driver sets the expected speed. The system uses the low-power radar or infrared beam to get the exact position of the preceding vehicle. If the front vehicle is decelerated or a new target is detected, the system sends an execution signal to the engine or braking system to reduce the speed and make the vehicle Keep a safe distance from the front car. When the current road has no car, it will accelerate to the set speed, and the radar system will automatically monitor the next target. The active cruise control system replaces the driver to control the speed of the vehicle, avoiding the frequent cancellation and setting of the cruise control, making the cruise system suitable for more road conditions, providing the driver with a more relaxed driving style.
The radars currently applied to the ACC system mainly include single pulse radar, millimeter wave radar, laser radar, and infrared detection radar. The monopulse radar and the millimeter wave radar are all-weather radars, which can be applied to various weather conditions, and have the advantages of long detection range, large detection angle range, and many tracking targets. Lidar has higher requirements on the working environment and is sensitive to weather changes. The detection results in bad weather such as rain, snow, wind and sand are not ideal, the detection range is limited, and the tracking target is less, but its biggest advantage is that the detection accuracy is relatively high. And the price is low. Infrared detection is unstable in bad weather conditions, and the detection range is short, but the price is cheap.
Automatic brake technology
Car accidents with high fatality rates have driven the development of automatic emergency braking systems. The automatic emergency braking system monitoring system consists of a radar embedded in the grille, a camera mounted on the front of the interior mirror and a central controller. The radar monitors the objects and distances in front of the car, while the camera detects the type of object. The HD camera monitors pedestrian and bicycle trajectories. The central control controller monitors global information and analyzes traffic conditions. When a situation occurs, a warning signal is sent to alert the driver that if the driver fails to respond in time, the system will also force the vehicle to brake.
Unmanned driving technology
Ford launched in unmanned self-driving cars. The name is “Lidar Systemâ€. The system is equipped with four rotatable lidar sensors on the roof, which continuously emits a weak laser beam to the surrounding area, thus realizing a 360-degree 3D streetscape around the car in real time, and combining 360 cameras to help the car observe. In the surrounding environment, the system analyzes the collected information to distinguish constant solids (lane dividers, exit ramps, park benches, etc.) and moving objects (frightened deer, pedestrians, oncoming vehicles, etc.) And put all the data together, and then judge the surrounding environment according to the algorithm developed by the University of Michigan, and respond accordingly.
Automotive rapid prototyping technology
In 1990, the rapid prototyping technology of laser radar was developed under the development of computer technology, polymer material technology, laser technology, CAD/CAM technology, precision mechanical technology, etc. The rapid prototyping technology of laser radar scanning system was mainly applied to prototype car. The production of the model and the bursting of the mold, this technology can greatly shorten the bursting cycle of new products, reduce the cost of development, and can improve the market competitiveness of new products. It can also be applied to automotive parts and components, and is used to analyze and inspect the process performance, assembly performance, related tooling molds and test motion characteristics, wind tunnel experiments and entities expressing finite element analysis results. Using laser radar's non-contact measurement, high precision, fast detection speed, etc., laser radar has been widely used in the process of 3D inspection and burst design of automobile body. The laser beam radar is used to measure the point cloud data of the vehicle body, and the vehicle body is reversely designed. The point cloud data is preprocessed, and then the curve, the surface and the solid model are reconstructed, and finally the vehicle body model is reproduced.
Lidar and intelligent traffic signal control
Integrate a ground 3D laser scanning system into the important traffic intersection signal control system of the city, and continuously scan the road at a certain distance through the laser scanner to obtain real-time and dynamic traffic flow point cloud data on the road, and obtain the vehicle through data processing. Parameters such as flow rate, based on the comparison of east-west and north-south traffic volume and short-term traffic flow prediction, automatically adjust the east-west and north-south direction signal cycle.
Lidar and traffic accident investigation
The 3D laser scanner is used to perform 3D scanning on the scene of the accident, and the data of the scanner can generate high-quality images and detailed diagrams of the scene of the accident, which is convenient for later investigation and court trial.
The survey showed that the 3D laser scanner was used to collect the accident scene data and the average road closure time was reduced by 90 minutes each time.
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