brief analysis of the classification, application and prospect of lidar/激光雷达的分类、应用现状及前景简析
brief analysis of the classification, application and prospect of lidar
uestc Glasgow 2017 zhaojingyi（赵婧怡）
Foreword
Lidar has been widely used in both military and civil fields. Lidar is a kind of integrated optical detection and measurement system which works in optical frequency band. Compared with ordinary radar, geometric image, distance image and velocity image can be provided with high resolution and high radiation intensity. It was first used in the military, then in life. Among them, unmanned driving is the most widely used field. Now Google, Baidu, ford, BMW and other companies are gradually using the lidar perception solutions, has become the most basic configuration of unmanned driving technology. Similar to T as a principle of microwave radar, which USES optical frequency band of the electromagnetic wave to the target launch first detection signal, then the received wave signal with comparing with the emission signal, can achieve the target location (distance, azimuth and elevation), motion information such as speed, posture, implementation of aircraft, missile and target detection, tracking and identification.
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main part
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I. classification.
Lidar can be classified in different ways. For example, according to the transmitting waveform and data processing mode, it can be divided into pulse lidar, continuous wave lidar, pulse compression lidar, moving target display lidar, pulse doppler lidar and imaging lidar. According to the installation platform, it can be divided into ground lidar, airborne lidar, shipborne lidar and space lidar. According to the different tasks, it can be divided into fire control lidar, range measurement lidar, missile guidance lidar, obstacle avoidance lidar and aircraft landing guidance lidar. Then according to the line number graph, the product is also divided into 2D, 2.5D and 3D.
II. Application.
In the specific application, laser radar can be used alone or combined with microwave radar, visible light TV, infrared TV or LLL TV imaging equipment, so that the system can not only search for distant targets, but also achieve the precision tracking of the target, is a relatively advanced tactical application mode.
- Military aspects.
The radar used to indicate the target in the surface-to-air missile system mainly includes pulse radar, pulse doppler radar and continuous wave radar.
Pulse radar, this type of radar, the Soviet army is the most equipped. Except for a few models, most of them are from the 50s and 60s, and a few of them were in service in the 70s and 80s.Their work efficiency is low, mostly in E, F band, some in G/H band. The detection distance is tens of kilometers, generally 200 kilometers, and some of them can reach more than 500 kilometers. The anti-interference measures adopted are mainly side lobe suppression, fast automatic gain control, wide and narrow limits, constant frequency alarm, pulse repetition frequency hopping, etc. Pulse radar since 40 s service, all countries have a different number of equipment, is the use of common, a common radar system, the detection distance is farther, working frequency is low, but if cooperate to use, and other modern radar can receive improve the effectiveness of air defense system operational performance, in order to meet the needs of the future air defense combat, pulse radar as will in the future in the process of continuous development of new technology to be more perfect, pulse radar still has broad prospects for development.
Pulse doppler radar, in the past 20 years, the development of pulse doppler radar is rapid, in the short-range surface-to-air missile system applications. Pulse doppler radar can accurately measure the speed of the target, its speed sub-processing ability is not as good as other radar, the improvement factor of ground clutter, can reach more than 50, 60 dB, with good anti-chaff and ground object interference performance. Therefore, the application of pulse doppler radar in surface-to-air missile, especially short-range surface-to-air missile system energy, is increasing gradually.
The pulse doppler radar used in the ground anti-aircraft missile system has gone through two stages of development in terms of technology. The first stage was the 1960s and 1970s.This phase of the pulse doppler radar, adapt to the needs of detecting low fixed wing aircraft, mostly with a moving target indicator, constant false alarm receiver, feature interference and chaff interference resistance performance is good, some can work frequency can target type interference, can pass to multiple firepower unit three targets at the same time, operating distance within 1.5 ~ 20 kilometers, detection probability is greater than or equal to 90%.The second stage is since the 1980s, the pulse doppler radar in this stage has been mature in technology, the main characteristic is the synthesis, its antenna mostly USES the scanning method of mechanical and electronic combination, USES the solid state component, the reliability is higher, the maintenance operation is simpler. - Environmental aspects.
2.1 development of lidar technology and its application in atmospheric environmental monitoring
Because of its short detection wavelength, strong beam orientation and high energy density, lidar has the advantages of high spatial resolution, high detection sensitivity, the ability to distinguish detected species and the absence of detection blind areas, etc., and has become an effective means of high-precision remote sensing detection of the atmosphere. Lidar can be used to detect aerosol, cloud particle distribution, atmospheric composition and vertical profile of wind field, so as to effectively monitor major pollution sources.
Observation of the distribution of atmospheric pollutants. When the laser emitted by lidar interacts with these floating particles, it will scatter, and the wavelength of incident light is of the same order of magnitude with the scale of floating particles, and the scattering coefficient is inversely proportional to the primary square of wavelength. Based on this property, mile-scattering lidar can complete the determination of aerosol concentration, spatial distribution and visibility.
Differential lidar is mainly used for the determination of atmospheric composition.Difference test principle of the laser radar is the use of laser radar of two different light, one of the wavelength tuning to the absorption line of the object under test, and the other wavelength tuning to online absorption coefficient smaller winger, then with high repetition frequency alternating the two wavelengths of light emission into the atmosphere, the laser radar measured to the two wavelength optical signal attenuation difference is caused by the absorption of the object under test, through the analysis of concentration distribution of the object under test can be got.
The fluorescence resonance scattering lidar is mainly used to observe the metallic vapor layer in the middle layer of the atmosphere. The principle is to use Na, K, Li, Ca and other metal atoms as tracers for atmospheric dynamics research. The Rayleigh scattering signal is very weak due to the low molecular density in the middle layer of the top atmosphere, and the resonance fluorescence cross section of the sodium metal atomic layer in this region is several orders of magnitude higher than the Rayleigh scattering cross section. Therefore, the sodium fluorescence radar is used to study the distribution of the sodium layer, and then the gravity wave and other related properties show its unique characteristics.
2.2 meteorological research using lidar
Lidar is a very important meteorological instrument, it is based on the electromagnetic energy will be reflected back from the target detection principle. Like radar, data about the nature, distance, Angle and so on of the target can be provided to us through the scattering of light. What makes it better than radar is that it can operate not only in the microwave region, but also in visible, infrared or shorter regions. Lidar is an extension of radar in the optical electromagnetic spectrum. A laser transmitter generates a short pulse of energy that is then fired at a target. Scattered waves radiated by the target are collected by the receiving optical system and concentrated on a sensitive detector. It converts the energy of incident light into an electrical signal, which is processed by amplifying the signal before being used.
The design of the first relatively primitive instrument developed at the Stanford institute clearly illustrates the application of lidar, such as detecting the location of clouds and fog layers through rain water or the structure of underlying clouds, and the height of the ascending limit. Lidar echoes clearly show a clear continuous aerosol layer from low altitudes, which is invisible to the naked eye.
2.3 monitoring of stratospheric ozone layer by lidar
The characteristics of the laser, such as its strong pulse energy, low divergence and high spectral purity, make it very suitable for remote sensing. Differential lidar is used to determine the trace components in the gas. It first emits two laser beams, and then completes the measurement based on the principle that the absorption coefficient of the gas against the two laser beams is different. Differential lidar is also commonly used for data on the micro composition of the air at a height of several kilometers, and its measurement range can completely obtain the vertical profile of the vapor layer and ozone layer. This paper mainly introduces the establishment of a system to monitor the ozone layer at an altitude of 50 km. The establishment of this system is of special significance for the establishment of a model to predict the ozone loss caused by the man-made release of chlorofluoromethane.
In order to detect long-term trends in the profile of the ozone layer and to overcome natural changes in the ozone layer, long and accurate surveys are necessary. Lidar technology is well suited for this purpose. The effectiveness of the current lidar system model is greatly confirmed by detecting the ozone layer reduction at an altitude of 40 km. - Aviation
The range of rendezvous and docking is 100km-1m. In the actual space rendezvous and docking, when the distance is greater than 100km, astronauts can obtain the relative position between the two spacecraft through the on-board microblog rendezvous radar and periscope. With the approach of two spacecraft, when the relative distance is less than 100m, due to the limitation of hardware, microwave radar cannot provide enough accurate measurement information for the final approach. Due to the narrow laser beam itself, good coherence, high working frequency, the laser radar can in the SEC until the whole process of docking with high precision of relative distance, relative velocity, the precise measurement of the Angle and angular velocity, so it can be used for the homing, approach and the final manual approximation process operation, and can provide future unmanned docking mission with the expansion of the autonomous navigation function.
The principle of ranging, measuring and angle-measuring of lidar is basically the same as that of microwave radar. Therefore, the lidar for space rendezvous and docking consists of a continuous wave rangefinder and a position sensor.The two parts are combined by a common optical device.The doppler frequency shift of the echo signal is a reliable and accurate velocity measurement method of lidar.Conical scanning method and monopulse method can be used to track the Angle of laser radar.Lidar can now also be used for the final manual approach and docking phase, where it is primarily used to measure relative attitude.Laser ranging technology is mature, but laser attitude Angle measurement is a technical difficulty.
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Conclusion
**Application prospect
Lidar is too expensive and bulky to produce energy.To solve this problem, every big company is now actively developing new products to solve the number of applications, which has a promising future.
In the future, solid-state lidar is the trend, and its advantages are small size and low cost.Easy integration and installation.No mechanical rotating parts are needed to ensure higher reliability and stability.The specially optimized obstacle avoidance mode can customize the rectangular area of interest to focus on the obstacle location information within the detection range, accurately match the width of the machine, so that the machine can move unimpeded.At the same time, it supports multiple machines to work together and is resistant to strong light. It can be used in a broad range of fields, including unmanned driving and industrial automation.
reference：http://www.eeworld.com.cn/qcdz/article_2018052622947.html
https://wenku.baidu.com/view/a231ea0eb94ae45c3b3567ec102de2bd9605ded6.html
https://wenku.baidu.com/view/cad79e722f60ddccda38a0dd.html
激光雷达的分类、应用现状及前景简析
电子科技大学 格拉斯哥学院 2017 赵婧怡
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前言
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激光雷达无论在军用领域还是民用领域日益得到广泛的应用。激光雷达是工作在光频波段的雷达，是一种综合的光探测和测量系统。和普通雷达对比，能够提供的几何图像、距离图像、速度图像都是高分辨率且辐射强度高的。一开始只是在军事方面应用，后来才应用在生活中。其中无人驾驶领域使用最为广泛。现在谷歌、百度、奥迪、福特、宝马等企业都在逐渐使用激光雷达的感知解决方案，已经成为了无人驾驶技术中的最基本的配置了。与微波雷达的T作原理相似，它利用光频波段的电磁波先向目标发射探测信号，然后将其接收到的同波信号与发射信号相比较，从而获得目标的位置(距离、方位和高度)、运动状态(速度、姿态)等信息，实现对飞机、导弹等目标的探测、跟踪和识别。
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主体
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一、 分类。
激光雷达可以按照不同的方法分类。如按照发射波形和数据处理方式，可分为脉冲激光雷达、连续波激光雷达、脉冲压缩激光雷达、动目标显示激光雷达、脉冲多普勒激光雷达和成像激光雷达等；根据安装平台划分，可分为地面激光雷达、机载激光雷达、舰载激光雷达和航天激光雷达；根据完成任务的不同，可分为火控激光雷达、靶场测量激光雷达、导弹制导激光雷达、障碍物回避激光雷达以及飞机着舰引导激光雷达等；然后根据线数图通，产品还分为2D、2.5D和3D三类。
二、 应用现状。
在具体应用时，激光雷达既可单独使用，也能够同微波雷达，可见光电视、红外电视或微光电视等成像设备组合使用，使得系统既能搜索到远距离目标，又能实现对目标的精密跟踪，是目前较为先进的战术应用方式。
- 军事方面。
地空导弹系统中用来指示目标的雷达，主要有脉冲雷达，脉冲多普勒雷达和连续波雷达。
脉冲雷达，这类雷达，苏军装备最多。除个别型号外，大多是五、六十代的产品，少数是七八十年代服役的。它们的工作效率较低，大都在E、F波段内，个别的在G/H波段。探测距离，近者为数十公里，一般为200公里，个别的可达500余公里，采用的抗干扰措施主要有，旁瓣抑制、快速自动增益控制、宽限窄、恒频警、脉冲重复频率跳变等。脉冲雷达从四十年代开始服役以来，各国都有不同数量地装备，是使用普遍、常见的一种雷达体制，探测距离较远，工作频率较低，但若和其他新式雷达配合使用起来，则可收到提高防空系统作战性能的效果，为了适应未来防空作战需要，脉冲雷达今后任将在不断发展新技术的过程中更加完善，脉冲雷达仍有着广阔的发展前景。
脉冲多普勒雷达，近二十年来，脉冲多普勒雷达的发展较快，在近程地空导弹系统中的应用较多。脉冲多普勒雷达能准确测量目标的速度，其速度分辦能力是其它雷达所不及的，对地杂波的改善因子，可达五、六十分贝以上，具有良好的抗箔条与地物干扰性能。因此，脉冲多普勒雷达在地空导弹特别是近程地空导弹系能中的应用还逐渐增多。
地面防空导弹系统用的脉冲多普勒雷达，从技术方面看，大体经历了两个发展阶段。第一阶段是六、七十年代。这一阶段的脉冲多普勒雷达，适应探测低空固定翼飞机的需要，大多装有动目标指示器、恒虚警接收机，抗地物干扰和箔条干扰性能好，有的可变频工作，可抗瞄准式干扰，能同时向多个火カ单元传递3个目标的数据，作用距离在1.5~20公里内，探测概率大于或等于90%。第二阶段是进入八十年代以来，这一阶段的脉冲多普勒雷达在技术上已经成熟，主要特点是综合化，其天线多采用机械、电子相结合的扫描方式，采用固态元器件，可靠性更高，维护操作更简单。 - 环境方面。
2.1激光雷达技术的发展及其在大气环境监测中的应用
激光雷达由于探测波长短、波束定向性强，能量密度高，因此具有高空间分辨率、高的探测灵敏度、能分辨被探测物种和不存在探测盲区等优点，已经成为目前对大气进行高精度遥感探测的有效手段。利用激光雷达可以探测气溶胶、云粒子的分布、大气成分和风场的垂直廓线，对主要污染源可以进行有效监控。
对大气污染物分布的观测。当激光雷达发出的激光与这些漂浮粒子发生作用时会发生散射，而且入射光波长与漂浮粒子的尺度为同一数量级，散射系数与波长的一次方成反比，米氏散射激光雷达依据这一性质可完成气溶胶浓度、空间分布及能见度的测定。
差分激光雷达主要用于大气成分的测定。差分激光雷达的测试原理是使用激光雷达发出两种不等的光，其中一个波长调到待测物体的吸收线，而另一波长调到线上吸收系数较小的边翼，然后以高重复频率将这两种波长的光交替发射到大气中，此时激光雷达所测到的这两种波长光信号衰减差是待测对象的吸收所致，通过分析便可得到待测对象的浓度分布。
在大气中间层金属蒸气层的观测主要采用荧光共振散射激光雷达。其原理是利用Na、K、Li、Ca等金属原子作为示踪物开展大气动力学研究。由于中间层顶大气分子密度较低，瑞利散射信号十分微弱，而该区域内的钠金属原子层由于其共振荧光截面比瑞利散射截面高几个数量级，因此，利用钠荧光雷达研究钠层分布，进而研究重力波等有关性质更展示其独有的特性。
2.2利用激光雷达进行气象研究
激光雷达是一种非常重要的气象仪器，它是基于电磁能量会从目标反射回来的检测原理。像雷达一样，有关目标的性质、距离、角度等数据都可以通过光的散射给我们提供出来。其比雷达更为优秀的是它不仅可以在微波区域进行操作，而且可以在可见光、红外光或更短的区域进行操作。激光雷达是雷达在光学电磁频谱上的一个延拓。由激光发射机生成一个短脉冲的能量再针对一个目标发射出去。目标辐射出的散射波由接收光学系统收集并且集中到一个敏感的探测器上，它将入射光的能量转换成一个电信号，经过放大信号处理后再进行使用。
在斯坦福研究所开发的第一个比较原始的仪器设计清楚地表明了激光雷达的应用，如通过雨水或底层的云的结构探测云和雾层的位置，上升限度的高度。激光雷达回波可以清楚的从低海拔地区观察到一个清晰的连续气溶胶层，而这对于肉眼来说是不可见。
2.3通过激光雷达平流层臭氧层的监测
激光的特性，比如它的强脉冲能量，低发散度和高频谱纯度，使这种光源非常适合远程遥感。用于测定气体中微量成分的是差分式激光雷达，它先发射两束激光，再利用气体对着两束激光的吸收系数不同的原理来完成测量。对于几千米高空的空气微量成分的数据也常使用差分式激光雷达，它的测量范围完全可以得到蒸汽层和臭氧层的垂直剖面。文章主要介绍了搭建一个监视50千米高空臭氧层的系统，这个系统的搭建对于建立模型来预测由于人为释放氟氯甲烷而造成的臭氧损耗是具有特殊意义的。
为了检测臭氧层轮廓的长期变化趋势，并且克服对臭氧层的自然变化，长时间的精确的调查是必需的。激光雷达技术非常适合于这个目的。检测40千米高空臭氧层的减少量极大地证实了当前这个激光雷达系统模型的有效性。 - 航空方面
交会对接范围为100km—1m，在实际的空间对接中，当距离大于100km时，航天员可以通过机载微博交会雷达和潜望镜获得两个航天器之间的相对位置。随着两航天器的逼近，当相对距离小于100m时，由于硬件的限制，微波雷达不能为最后逼近提供足够精度的测量信息。由于激光本身的波束窄、相干性好、工作频率高等优点，激光雷达能在交会阶段直到对接的整个过程中提供高精度的相对距离、速度、角度和角速度的精确测量，因此它既能用于目前的自动寻的、接近和最后的手动逼近操作过程，又能为未来无人交会对接任务提供自主导航的扩展功能。
激光雷达的测距、测度、和测角原理与微波雷达基本相同。因此用于空间交会对接的激光雷达包含连续波测距器和位置敏感器两个部分。这两个部分通过公用光学装置混合起来。激光雷达比较可靠和精确的测速方法是测量回波信号的多普勒频移。激光雷达对目标的角跟踪可采用圆锥扫描法和单脉冲法。现在，激光雷达也能用于最后的手动逼近和对接阶段，此时主要用来测量相对姿态。激光测距技术比较成熟，但是激光测量姿态角是一项技术难点。
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结语
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应用前景
激光雷达价格高昂，体积太大，使其不能量产。为了解决这一问题，现在每个大公司都在积极研发新产品来解决在数量上的应用，其前景可观。
在未来，固态化的激光雷达是趋势，其优点是体积小、成本低。方便集成和安装。无需任何机械旋转部件，保证更高的可靠性与稳定性。特别优化的避障模式，可自定义矩形兴趣区域，以聚焦于探测范围内的障碍物位置信息，精准匹配机器宽度，让机器畅行无阻。同时支持多机协同工作，且抗强光，能够用于广义的领域：包括无人驾驶和工业自动化等。
reference：http://www.eeworld.com.cn/qcdz/article_2018052622947.html
https://wenku.baidu.com/view/a231ea0eb94ae45c3b3567ec102de2bd9605ded6.html
https://wenku.baidu.com/view/cad79e722f60ddccda38a0dd.html