In October 2020, the 'Belt and Road' lidar observation network-Roqiang station, led by Professor Huang Jianping and Professor Huang Zhongwei of the College of Atmospheric Sciences of Lanzhou University, was unveiled, marking the completion of seven stations in the domestic section of the radar observation network. Foreign section, with some 'Belt and Road' alongline country reached an agreement, which will be arranged 4 stations, including 3 identified stations.

 

Figure | Professor Wong Chi-ping and Ren Wei, Director of the Ruoqiang Meteorological unveiled the 'Belt and Road' lidar network Ruoqiang Station

 

       Each radar station is mainly monitored by multi-band Raman polarization lidar developed by Lanzhou University. From the improvement of hardware technology to the inversion of new algorithms, to the application of atmospheric remote sensing and environmental monitoring, the radar intelligence team of Lanzhou University has been working hard and upgrading iteration on the road of 'one-stop' research and development, and has laid out China's radar along the 'Belt and Road' line.

       Their stereo observation system aims not only to develop high-precision and high-resolution meteorological disaster forecasting and early warning systems covering countries and regions along the 'Belt and Road ', and to serve social and economic development fields such as railway and logistics transportation, but also to play an active role in global climate change research and correction of spaceborne lidar in China.

       At this time, Lanzhou University radar intelligence team lidar R & D has gone through 14 years. From relying heavily on imported lidar from abroad to independently developing and manufacturing 14 lidar, including the first multi-band Raman-fluorescence lidar system with independent intellectual property rights in China. This 14-year lidar R & D story started from a cross-professional research assessment.

 

 

       'Do you know lidar ?'

       'Do you have the confidence to build it later ?'

       In the fall of 2006, Huang Zhongwei, an undergraduate of the College of Physics Science and Technology of Grade 2003, was received the postgraduate assessment of the College of Atmospheric Sciences. Opposite him sat Professor Huang Jianping of the College of Atmospheric Sciences.

       Asked why he had chosen a student from the college of physics, professor Huang jianping explained:' Huang zhongwei is a physics student who is very interested in radar research. He has trained himself to build radar and conduct meteorological research. It can not only solve the problem of foreign monopoly lidar, but also expand new research fields.'

       Professor Huang Jianping said that in the field of atmospheric research, Lanzhou University used ground instruments before 2006 and a rice scattering lidar imported from abroad before 2014. Lidar is able to collect observations of the distribution of pollutants, water vapor and clouds in the atmosphere within a range of tens of kilometres from the surface. At present, China has an urgent demand for lidar technology in the fields of global climate change, environmental pollution, space environment monitoring and so on, but it has been relying on imported high-cost products from abroad, which seriously restricts the further development of related fields in China.

       It is not only expensive, but also limited in foreign lidar function. Generally, only a few bands can be measured, the signal analysis source is few, and the concentration and composition of solid particles cannot be accurately measured by ordinary radar. At the same time, it is difficult for these high-precision instruments to adapt to the arid and semi-arid difference and high concentration of particulate matter.

       'All I know is military radar. I never thought I could build a lidar one day.' Huang Zhongwei recalled.

       After passing the examination, Huang Zhongwei packed his luggage and went to Chengguan campus to finish his thesis, like other students. At this time, he received Professor Huang Jianping's phone call:' Don’t come to the Chengguan campus, directly to the top of the Cuiying Mountain.'

       On the top of Cuiying Mountain is the semi-arid climate and environment observation station built by Lanzhou University that year. It was here that Huang Zhongwei not only came into contact with Lidar for the first time, but also dismantled it.

       RMB 1.5 million is the price of buying a lidar from the United States in early 2006. In 2007, the laser radar on the top of Sui Ying failed, and Huang took a screwdriver and dismantled it.

       'Mr. Huang Jianping saw me and said that I was so courageous. Surrounded by classmates majoring in atmospheric sciences, they did not dare to dismantle such an expensive machine. However, my undergraduate degree majored in physics, snd I have been working on strength, heat, light, and electricity for four years. I’m used to disassembling the instrument when it’s broken, which helps me learn a lot.” Huang Zhongwei said.

       Professor Huang Jianping said: “Huang Zhongwei often disassembles and assembles this radar by himself. He is very familiar with the functions and principles of the radar, so he gradually began to conduct in-depth research in this area.”

       In the autumn of 2009, with the help of Professor Huang Jianping, Huang Zhongwei went to Northeast University of Japan for joint training. The goal of his trip is to learn lidar technology. Huang learned not only lidar technology in Japan, but also an additional 'super ability '——band measurement in Japan. At that time, the technology can only measure part of the fluorescence signal. Huang Zhongwei mastered the existing radar technology in Japan, and studied the technology of measuring fluorescence signal in multiple bands. At that time, there was little research on this aspect.

       'When I was in Japan, I was measuring fluorescence at 5 a.m. in an empty lab, and I could only hear crows outside the window.' With unremitting efforts, Huang Zhongwei and his mentor finally successfully developed the first multi-band Raman-fluorescence lidar in China in 2014.

 

 

       In 2011, Huang Zhongwei returned home and set up a lidar laboratory at Lanzhou University. In January 2014, the first multi-band Raman-fluorescent lidar was born in this small 'radar processing workshop' with a total area of less than 40 square meters, and became the reference standard for the production of other radars. In six years, they have built 14 lidars. Nowadays, in Lanzhou University lidar atmospheric remote sensing laboratory, two 'black boxes' of different sizes are the second generation multi-band Raman-fluorescence lidar.

 

Figure｜In 2014, Huang Zhongwei's team discussed the design plan and assembled the radar in Guanyun Building

 

       Lidar consists of a laser transmitter, an optical receiver, a turntable, and an information processing system. The laser emits light pulses, and the optical receiver restores the light pulses reflected from the target into electrical pulses, which are sent to the display.

       'Each radar is like a baby. It is not easy to manufacture. From the beginning of drawing and designing with SolidWorks software, to assembling and debugging the purchased parts and accessories, they are all made step by step by themselves.' Huang Zhongwei said.

       'A lidar has more than 100 parts. In order to improve the accuracy of the inversion algorithm and improve the performance of the radar.Mr. Huang Zhongwei asked us to come up with 2-3 plans for each part,, even for a small frame. All designs must be held in meetings and discussions, and Mr. Huang is careful and cautious, considering issues from multiple angles.' said Li Wuren, the team's research assistant.

 

Figure｜The second-generation multi-band Raman fluorescence lidar in the Lidar Atmospheric Remote Sensing Laboratory of Lanzhou University

 

       Before the multi-band lamman-fluorescent laser radar is developed, there were multi-band laser radar, Raman laser radar, and fluorescent laser radar on the market, but truly combining 'multi-band' 'Raman' 'fluoresce' is not as simple as '1 + 1 + 1 = 3', but it is necessary to overcome the factors of various mutual interference between them. Repeated trials can obtain the optimal combination of multi-band lamman-fluorescent laser radar, and truly realize the fine detection of atmospheric aerosol (Aerosol, generally referred to as atmospheric particulate matter, is a general term for all kinds of solid and liquid granular substances present in the atmosphere. ) full fluorescence spectroscopy.

       If a single-band lidar is compared to taking photos of particles in the atmosphere, the photos taken are only flat; the multi-band lidar is like taking multi-dimensional panoramic photos, so that we can see the different sides of the atmospheric particles. The measured atmospheric data are more comprehensive, three-dimensional and accurate.

       Professor Huang Jianping introduced that the so-called 'fluorescence' is the release of suspended particles in the atmosphere that people are gradually discovering. It is not only solid like sand and dust, but also microorganisms or organic matter suspended. 'Multi-band' plus 'fluorescence', it is not the dream to'see bacteria and viruses 20 kilometers away', but is the power of fluorescence, and it is a right-hand man for observing bacteria and viruses in the atmosphere. 'This can only be detected with fluorescence. The next challenge for the team is how to distinguish them one by one.'

       Multi-band Raman-Fluorescence Lidar uses technologies such as weak signal detection, high-precision spectroscopy, optical machine design and processing, and uses high-power lasers to simultaneously emit three lasers, including ultraviolet, visible, and near-infrared beams, into the sky, that is, three bands. After the ultraviolet laser interacts with atmospheric particles, it will release fluorescence. The large-aperture telescope is used to receive the signals reflected from the atmosphere. These weak signals are separated, extracted and detected, mainly by receiving signals, such as green light, infrared light, and purple light. The sequence is segmented through the optical lens, and then analyzed by a photomultiplier tube and a spectrometer. It can measure 38 wavebands, of which 32 are measured with a spectrometer and 6 are measured with a detector. The laser energy of the lidar is 350mJ, the telescope diameter is 35cm, the spatial resolution is 3.75m, and the time resolution is 1 minute (of which the fluorescence signal is 5 minutes), and it can detect atmospheric particulate matter information up to 20 kilometers. By receiving the fluorescence signal and Raman signal of 180 nanometers wide and 32 bands, not only the inversion accuracy of the signal data is greatly improved, but also the material composition can be measured for the frequency of the scattering change.

 

 

       If hardware technology is compared to the torso of radar, the inversion algorithm is the brain of radar. Good hardware provides high-quality signals, and good algorithms calculate accurate data. The two complement each other. Huang Zhongwei is well aware of the key to making the lidar made by Lanzhou University more effective. Therefore, after studying in Japan, he and his team have been committed to the research and development of new inversion algorithms in addition to studying the improvement of hardware technology.

       The high precision inversion algorithm based on lidar is another core achievement of Huang Zhongwei's team. There is no ready-made data acquisition and control software for related inversion algorithms in the market. Huang Zhongwei's team writes code through independent programming， which improves the accuracy of inversion algorithm.

       Using the principle of Raman-fluorescence scattering, Huang Zhongwei's team can convert the signals collected by lidar into atmospheric data that can be adopted by professionals, namely 'products', such as atmospheric water vapor, particulate matter and other attributes and concentrations, and learn about atmospheric pollutants, which highlights the analysis of the composition and concentration of atmospheric particulate matter, and fills the gap in the research and development of multi-band Raman-fluorescence lidar in our country.

       Many peers have developed inversion algorithms for PM2.5 and PM10 signals. Huang Zhongwei's team has further improved the inversion accuracy of the algorithm through algorithm technology. Their research results were published in the foreign high-level journal Science of The Total Environment with the title of 'Ten Years of Spaceborne CALIPSO Lidar Observation of Global Particle Mass Concentration Calculation'. This technology is not only applied to self-made radars, but also applied to lidars of American satellites.

       In 2010, Huang Zhongwei's team proposed an effective Lidar aerosol optical properties inversion algorithm, and carried out the inversion test using the Lidar data from the semi-arid climate and environment observation station of Lanzhou University from April to October 2007.

 

Figure | Semi-arid Climate and Environment Observatory of Lanzhou University at the top of Cuiying mountain

 

       Huang Zhongwei said: “At present, few people can calculate the effective particle radius of aerosols at different heights. I guided a student to calculate it and have applied for an invention patent.” In 2012, Huang Zhongwei’s team tried to develop hardware technology and new reaction algorithms to further improve the atmospheric remote sensing capabilities of lidar, and develop a new algorithm based on lidar data to retrieve aerosol volume concentration and particle effective radius. They used the optical characteristic parameters such as extinction backscattering coefficient, depolarization ratio and color ratio obtained by the dual polarization meter scattering lidar of the Semi-arid Climate and Environment Observatory of Lanzhou University, as well as the inversion  result of the solar photometer (CE-318) to study the quantitative relationship between the optical characteristic parameters observed by the lidar and the physical information of the particles.

       At present, it can be calculated based on the inversion algorithm: the mass concentration of PM2.5 and PM10, the microphysical characteristics of aerosols, the profile of aerosol absorption coefficient, and the types of aerosols and clouds.

 

 

       'With hardware design, algorithm development, and later applications, our entire R&D industry chain is complete.' Huang Zhongwei said.

       The lidar manufactured by Huang Zhongwei’s team is mainly used for atmospheric remote sensing and environmental monitoring research. Aiming at atmospheric aerosols, using lidar as the main research method, they systematically study the main work of lidar atmospheric aerosol remote sensing from three aspects: hardware technology improvement, new algorithm inversion and atmospheric remote sensing applications. Multi-channel scanning lidar is also used to monitor the 3D distribution of atmospheric pollutants.

       The lidar can be used not only in the study and early warning of atmospheric haze detection, but also in the fields of satellite data correction, meteorological observation, meteorological intervention and so on. For example, the signals collected by radar about clouds can be converted into cloud data for reference in the artificial rainfall of meteorological department. 'Artificial rainfall requires anti-aircraft fire to hit the clouds with a catalyst, when to hit, how many, how to hit, and we need data to provide accurate guidance .' Professor Huang Zhongwei said.

       From a multi-band Raman-fluorescence lidar system, a laser device for online monitoring of atmospheric bioaerosols, a three-dimensional scanning multi-parameter lidar system for environmental monitoring, and a lidar system with multi-channel echo signal conversion Connecting devices to gas samplers and systems that can measure aerosol concentration, multi-functional multi-gas path adjustable flow gas samplers and systems, mass concentration analysis methods and devices... These invention patents range from radar hardware system design to data inversion Algorithm; from multi-band Raman polarization lidar data acquisition control software V1.0 to V2.0, and three-dimensional scanning environment monitoring lidar data acquisition control software V1.0, lidar control and data display system V1.0, etc. In the past 14 years, Huang Zhongwei's team has developed 6 international and domestic invention patents and 4 computer software copyrights in data acquisition control software, radar control systems, and data display systems.

       Today, this 'lidar processing workshop' of Lanzhou University can not only meet the scientific research needs of Huang Zhongwei's team, but also be used by environmental protection departments and brother colleges and universities. The Department of Ecological Environment of Gansu Province has purchased three of the lidar for the monitoring of sandstorms and haze to realize the transformation of scientific and technological achievements. Huang Zhongwei said that the production of lidar has not reached the level of mass production, self-made radar mainly for their own scientific research needs, but also for patent conversion applications.

       More than that, these lidar from Lanzhou have gone out of the country and extended to the 'Belt and Road' alongline countries.

 

 

       In 2017, this is another conversation between Huang Zhongwei and Huang Jianping, ten years after the last examination.

       ''Belt and Road' Lidar Network, do you dare to build ?' Huang Jianping asked.

       Huang Zhongwei said :' Let's do it, just increase the working time.' In fact, Huang Zhongwei, who had just graduated from Dr. Huang for five years, had no idea. Before 2017, lidar was placed in the laboratory as a 'porcelain doll '. If you want to build lidar out of the laboratory to' Belt and Road ', it involves research and development, engineering, and communication.

       'I admire Mr. Huang Zhongwei. He is bold and innovative. If he hadn't tried, radar would n' t have been able to get out of the lab at first.' Li Wuren said.

       Lidar is a precision optical instrument, which has high requirements for the stability of power, network and ambient temperature. If it does not meet the requirements, a lidar with a price of RMB million may face the risk of scrapping.

       When the team members were worried about the lidar going out of the laboratory, Huang Zhongwei advocated that only by deploying the lidar can we discover and solve problems. Manufacturing prefabricated lidar - the direction of letting the radar 'into the box and go out' was formally determined.

       On the roof of the Urumqi Environmental Protection Bureau at minus 20 degrees Celsius, Huang Zhongwei's team guarded the first radar to go out for more than 20 days， which has accumulated experience and laid the foundation for their future research on fabricated lidar to improve thermal insulation performance, install battery life, install power outage alarm systems, and then improve its adaptability to the external environment.

       After solving the problem of lidar going out, the next step is how to make it go far.

       A panoramic map of the “Belt and Road” lidar observation network is posted on the wall of Huang Zhongwei’s office. It has 14 stations from Lanzhou in the east and Algeria in the west. It is over 8,000 kilometers across a straight line and can provide overall data for global atmospheric monitoring in arid and semi-arid regions. The completed sites are marked with red flags, and the sites to be constructed are marked with yellow flags. According to the observation requirements, each radar station is equipped with a single-band, multi-band, with or without fluorescence, and other functional combinations of lidars. In addition, it is also equipped with a multi-channel microwave radiometer, a sun-sky-moon photometer, and an online particulate matter monitor, MODIS, CALIPSO, CLOUDsat, and Fengyun-4.

 

Figure | Distribution of Proposed Layout of 'Belt and Road' Lidar Observation Network

 

       'The construction of the'Belt and Road' lidar observation network has the value of scientific research, talent training and international cooperation.' Huang Zhongwei said. Through the deployment of lidar observation network, the source of dust in the atmosphere along 'Belt and Road' can be tracked, and the trend of dust in the air can be analyzed, which is helpful to understand the causes of dust weather in China. In recent years, using the data from lidar observations, Huang Zhongwei’s team published 'Research on the Characteristics of Atmospheric Bioaerosols on the Transport Path of Asian Dust in Aerosol Movement' and 'A Shortcut Path for Asian Dust Transport Directly to the Arctic: A Case Study' and other related application results in international and domestic journals. As of September 2020, there have been 30 undergraduates, masters, and doctoral students who have participated in the Lidar Intelligent Manufacturing Project. They are still engaged in research related to air pollution monitoring after graduation.

       China provides lidar and related testing equipment, and the 'Belt and Road' countries provide the venue environment. The two sides strengthen international cooperation. 'In 2019, we also invited five young experts from the Umarov Institute of Physics and Technology of the Tajikistan Academy of Sciences and the Peshawar University of Pakistan to visit Lanzhou University to get the training. After returning home, they will also maintain the ‘Belt and Road' radar station. Huang Zhongwei said, 'The University of Peshawar in Pakistan also plans to establish a College of Atmospheric Sciences. I hope that we will provide teachers here to teach.'

       Almost every night, near student apartment No .12, Chengguan Campus, Lanzhou University, several white iron boxes emit green light, with——Raman polarized lidar on them. Soon, these white tin boxes will take Central Europe to Tajikistan and Pakistan. In the future, more lidar will be sent to countries along the Belt and Road by assembly and transportation. Belt and Road, a little green light, in series, woven into a lidar observation network spanning tens of thousands of kilometers. Through international cooperation, joint monitor and research on atmospheric composition.

 

Figure｜Laser emitted from a white observation box equipped with a radar on the Chengguan campus of Lanzhou University

 

       Huang Jianping’s team is continuously improving the lidar detection function, the accuracy of the inversion algorithm, and doing a good job in application development. At the same time, it has begun to make the data collected by the “Belt and Road” lidar observation network public through the network platform to achieve data sharing. Hopefully it will open a broader door for related research.

       Content Source | 'Lanzhou University News' Issue 974

       Text | Xu Wenyan Li Hui

       Editor | Yang Shuting

       Editor in charge | Zhang Tiantian

       Editor-in-Chief | Xiao Kun