Now, in the orbit of satellite 500 kilometers away from the earth, the mission of a " carbon star " has just begun. In the past, traditional carbon sink measurements had to rely on manual sampling and monitoring of forest vegetation. This time, carbon satellites carried a multi-beam lidar , which could make forest carbon sink monitoring more intelligent and accurate.
As my country's first active and passive joint observation remote sensing satellite , its main task is to monitor forest carbon sinks. Recently, the main load multi-beam lidar has officially "started". Analyzing the data back-received feedback, the lidar development team said: On-orbit normal operation and data played a role. my country's carbon sink monitoring has officially entered the era of space-based remote sensing.
multi-beam lidar test site. Photo provided by the 704th Institute of the Ninth Academy of China Aerospace Science and Technology Corporation
satellite-borne lifespan is twice that of European and American countries. The development of multi-beam lidar has been going on for ten years. Zhao Yiming, who is from the 704th Institute of the Ninth Academy of China Aerospace Science and Technology Corporation and is responsible for the development of this multi-beam lidar, said: "We have a doctor who started doing this when we were recruited into the institute, from the 20s to the 30s."
In her opinion, it is difficult to persevere without enthusiasm and responsibility for one thing. On the road of scientific research, no one can fully guarantee that a product can be "born" smoothly as scheduled.
In the past ten years, she successfully gave birth to two children. Sometimes, colleagues would occasionally say in private: "Mr. Zhao has given birth to three children in the past ten years." Another "child" that colleagues talk about refers to multi-beam lidar. Zhao Yiming called this "child" the eldest because the eldest son "has gone to heaven" and has become a talent.
On August 4, 2022, at the Taiyuan Satellite Launch Center , with the successful launch of Long March 4B launch vehicle , the terrestrial ecosystem carbon monitoring satellite equipped with four payloads: multi-beam lidar, multi-angle multi-spectral camera, ultraspectral detector, and multi-angle polarization imager, also successfully entered space.
From a functional perspective, this "carbon star" multi-beam lidar makes up for the gap in vertical profile observation of traditional passive remote sensors, and plays a role as an important atmospheric carrier for more accurately mastering aerosol - "carbon emissions".
aerosol subsystem identification part prototype field test site. Photo provided by Institute of 704, Ninth Academy of China Aerospace Science and Technology Corporation
"Two lidars in the load, one is used to detect the atmosphere, mainly for clouds and aerosols. This detection can obtain the distribution and type information of the two; the other is used to detect vegetation, which can detect the height of the global vegetation canopy, and the volume and distribution of vegetation can also be analyzed through the canopy height." Zhao Yiming explained.
Because multi-beam lidar targets two important directions, "terrestrial carbon" and "atmospheric carbon", it can actively and accurately detect vegetation and the atmosphere, aerospace people believe that this weapon will definitely provide important technical support for China's "dual carbon" strategy.
Currently, the maintenance capability of space-based products operating in space is almost zero. For developers, extending the onboard lifespan of multi-beam lidar has become a challenging problem. Project team member Pan Chao told the Beijing News reporter that in terms of long-loading lifespan, European and American countries generally have 3 to 5 years, but this time they proposed to extend the onboard lifespan of multi-beam lidar to 8 years, which is twice that of European and American countries.
"It's like a light bulb. If you use it for a long time, you will definitely have some problems. So we try to extend the on-orbit operation time of the star-borne product to obtain richer data." Pan Chao said that lidar roughly consists of three parts: light source emission system, large-diameter reception system, and information processing system that can detect. In the face of a complex optical system, each component needs to be carefully designed. Consider thoroughly and reduce mistakes to maximize the product's best condition.
According to reports, multi-beam lidar has innovatively realized active passive common caliber observation and vegetation atmospheric coordinated detection technology, and has overcome the problems of three active passive load common caliber composite detection problems, high-resolution ground imaging, 5-beam high-precision vegetation detection and 1064nm and 532nm polarization multi-channel atmospheric detection in the world.
Simply put, a load can simultaneously realize the functions of vegetation elevation measurement, atmospheric vertical profile detection and ground-high resolution imaging.
ensures the consistency of the test. The development team members basically do not drink water
project team members will feel that these ten years have passed quickly. They seem to have no concept of time in a sealed working environment. The laboratory of Zhao Yiming's unit is where they develop multi-beam lidar. The experiment is taboo, and the laboratory walls are covered with black shade cloth. After putting on the clean clothes, these people dive into the optical instruments and computer equipment.
The doctor who has been in his 20s to his 30s is Li Jing. When she was debugging in the laboratory, she needed to use a photosensitive film, with the purpose of converting invisible light into visible light. In order to accurately see the light, she had to turn off the light in the laboratory.
In and out of personnel will also affect the ultra-clean environment required by laser experiments. Usually, to complete the established workload of an experiment, the developer must control the eating. After the instruments and equipment are started, people must be in front of you. Most people need to power off the equipment when they leave, so in order to save time and to ensure the consistency of the test, they basically do not drink water during the experiment. Because you need to avoid going to the toilet, you need to save time in changing clothes.
multi-beam lidar subsystem assembly and testing site. Photo provided by Institute 704, Ninth Academy of China Aerospace Science and Technology Corporation
In the eyes of colleagues, Li Jing is very resilient. In an interview with the Beijing News reporter, she also said: "As long as this matter is left to me, no matter what method I use, I will definitely solve it. The laser I made myself can be used in aerospace, and I feel a sense of accomplishment."
Zhao Yiming is the first national doctoral student in recruited by the 704th Institute of the Ninth Academy of Aerospace. Li Jing has also joined since then. More than ten years ago, the development level of domestic lasers was still a certain gap with that of foreign countries. There were very few students like Li Jing who made lasers. At that time, Li Jing, who was about to end his studies at Aachen University of Technology in Germany, met Li Yanhua, who was the director of the 704th Institute at a job fair. After some in-depth exchanges, Li Jing decided to "face the difficulties" and return to China to stay at 704 institutions.
In the early years, my country's ground lidar applications were relatively few, and satellite-based lidar applications were urgently needed. "No one can say very clearly how much the lidar on the planet can play in the sky and how much its effectiveness can be achieved." Zhao Yiming said that it must be both application-oriented and technologically advanced, which has made the multi-beam lidar project questioned from the beginning.
has a lot of rich data and experience in ground lidar verification. In 2014, my country's first multi-wavelength lidar hang-flying comprehensive test for detecting the atmosphere was successfully completed. Two years later, the comprehensive test for airborne system of large spot lidar detection was also successfully completed. In addition, the developers have also worked on some key engineering technologies and verified the feasibility of the technology and principles of active loads looking from the sky to the ground.
solved problems such as the application of satellite-borne lidar, the demonstration of technical indicators, and the research and development of individual key technologies. At the end of 2016, nearly 50 experts gathered in the lobby of a hotel in Beijing to conduct consultation and review. Before the meeting ended, the experts unanimously agreed: feasible and possible.
Pan Chao feels that under the existing conditions, it is a difficult process to follow, run side by side and lead. "But I also think that as much as you pay, you will gain," he said. The
project team grew from 10 people to more than 50 people. In Zhao Yiming's view, this group of people truly love the lidar industry. Zhao Yiming told the team members: "You will become grandparents in the future, so you will tell your grandchildren that I made something back then, and now I can still cast light to the earth in space and have a mark on the earth.You guys say, is this a great thing? "
project team installed and tuned the multi-beam lidar atmospheric laser. Photo provided by the 704 Institute of the Ninth Academy of China Aerospace Science and Technology Corporation
receives laser echo signal, and the automatic centering system is particularly critical. When working, it is necessary to ensure that the laser emitted by the laser just enters the telescope to receive the field of view after being reflected by the atmosphere, so that the lidar can receive the echo signal.
Because the laser divergence angle and the telescope field angle are very small, this process is as difficult as looking for a needle in a haystack. At this time, automatic centering system is particularly critical.
"Simply put, the automatic centering system is a high-precision, high-resolution two-dimensional laser pointing adjustment device. "Zhou Shuchun, the technical director of the automatic centering system, told reporters.
According to him, at present, since high-precision real-time optical axis pointing feedback signals cannot be obtained, the system accuracy depends entirely on the precision mechanism and control system's own design and processing accuracy, which is very difficult. The
technical team took nearly seven years to develop the entire automatic centering system from the early technical research, to the development of electrical parts and identification parts, and then to the final regular development.
atmospheric lidar will experience violent vibration during transmission, and after the satellite is launched into orbit, the gravity environment will also undergo tremendous changes, and these factors will cause changes in the originally adjusted light transmission and reception axis.
Zhou Shuchun said that at this time, the automatic centering system needs to be "showed out its skills". It has an efficient search strategy to ensure that the best centering position is accurately found. The centering is completed. The first step in the work of lidar is also the main reason why the project is paying special attention to this sub-system in general.
has not learned from previous experience, and the automatic development process of the centralized system is very difficult. We encountered many difficulties. The solution of each problem embodies the huge contribution of the project team designers.
When doing thermal vacuum experiments, as a key indicator of the sub-system, the stability of the laser pointing seriously exceeds the standard. The development team regards the laboratory as home, eats, lives and works together, and spends more than a month to do all the experiments in various working conditions and check them one by one.
multi-beam lidar thermal vacuum test site. Photo provided by Institute 704, Ninth Academy of China Aerospace Science and Technology Corporation
"We have touched the characteristics of each component of the system in a thermal vacuum environment, and finally found the crux of the problem. As an astronaut, if you want to succeed, you have to be more cruel to yourself. "Zhou Shuchun said.
It is understood that at present, the automatic centering system has successfully completed the in-orbit centering process and accurately calibrated the optimal position of the laser emission optical axis. The system accuracy and stability fully meet the index requirements.
did not shed tears due to illness, but cried bitterly at the launch site
In order to achieve high-precision carbon sink monitoring, the developers also need to make an innovation, putting the lidar and optical camera on the same load to achieve active and passive joint observation. The team has no experience to learn from, the plan has been repeatedly demonstrated, and the test experiment failed and started again. After more than two years, the obstacles were finally overcome with difficulty.
In addition to the laser that is already in-orbit operation, it is also on the ground. There is a similar laser. The developer designed it to assess the on-board life of the laser. The verification test of this 1:1 ground laser has lasted for nearly 2 years and 8 months, and has emitted 1.4 billion laser pulses . This test proves that the laser has far exceeded the relevant requirements of the design at that time and has stable performance.
Over the years, Zhao Yiming, who became a mother, has had two fractures. She has used crutches and splint , and she has never fallen behind. The task is coming, and everyone is pursuing the task. "In order to ensure the development cycle of the project, Dr. Li Jing also postponed her surgery twice, and forced herself to complete the entire load development before she performed the surgery. "Zhao Yiming said.
According to Li Jing's recollection, during the period when she was doing the project to demonstrate , she always felt unbearable pain in her stomach. After going to the hospital for examination, she found that she was 7 weeks pregnant. After the baby was born, she was just taking a simple rest and then she was involved in the development of the laser.Li Jing's husband is also an astronaut. They are both busy. In addition, their parents are old and have difficulty moving. The child has to be vaccinated with the state-mandated children's vaccine, but it has been delayed for two and a half years.
Last year, Li Jing felt a stomachache again intermittently. "I am the kind of person who doesn't know hunger or pain when I get to work. When I rest, I feel extremely uncomfortable. "Li Jing told reporters that dreaming at night will dream of anxiety about the problems that arise from the product. In order to avoid making any mistakes in the products she made, she did not sleep for 70 hours in a row while doing thermal vacuum monitoring for atmospheric environment experiments. Later, Li Jing discovered that the reason for her acute and severe abdominal pain was the ruptured cyst in her body.
For this working state, Pan Chao also mentioned that they were not looking at the time, but the completion of the task that day. Sometimes, when they left the laboratory, they found that it was two or three in the morning.
Li Jing, who did not cry due to illness, cried at the launch site of the "Carbon Star" in early August this year. She stood on a small hill closest to , Taiyuan satellite launch base at , staring at the rocket. The colleague beside her asked her, "Did you feel the earth shake?" Li Jing turned her head and looked at her colleague, and tears fell down. "I really couldn't help it. I cried for almost half an hour. After the launch, the leader of the Institute (704) came, and I was still crying. Really, I'm very proud." Li Jing said.
In fact, the multi-beam lidar was successfully launched with the "Carbon Star", which made the entire project team members very excited. After the satellite took off, Zhao Yiming wrote a limerick poem, with two lines in the poem: No regrets and fear, just wait for the flowers to be better next year.
is operating normally in orbit, and has excellent detection data. Next, the lidar will play a crucial role in the future quantitative monitoring of "carbon sinks" and the global "carbon funds" survey.
Li Jing, who is in cultivation, also told reporters: "I hope I can adjust as soon as possible and contribute to the motherland for another 30 years."
Beijing News reporter Zhang Jianlin
Editor Chen Jing Proofreader Liu Yue
