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Accurately support dual carbon targets to reveal the first laser carbon dioxide detection satellite |
In the early morning of April 16, 2022, the atmospheric environment monitoring satellite was launched with the Long March 4C carrier rocket, becoming the world‘s first satellite capable of carbon dioxide laser detection. The satellite will promote the application of remote sensing in my country’s ecological environment, meteorology, agriculture and rural areas, and is of great significance to improving the comprehensive application efficiency of satellite resources and promoting environmental protection.
In addition to passive detection payloads such as high-precision polarization scanners, multi-angle polarization imagers, ultraviolet hyperspectral atmospheric composition detectors, and wide-field imaging spectrometers, the satellite is also equipped with an active detection payload of atmospheric detection lidar for the first time in the world. , which can realize all-day and high-precision detection of carbon dioxide, and provide important data support for my country to achieve the goal of “carbon peaking and carbon neutrality”.
Multiple “firsts” record highs
The reporter learned from the Eighth Academy of China Aerospace Science and Technology Corporation, the general research and development unit of the satellite, that the atmospheric environment monitoring satellite has created three world firsts in the detection method and accuracy of carbon oxide, the active and passive detection of fine particles and the polarization crossfire detection system.
Carbon dioxide detection, lidar is amazing. For the first time in the world, the atmospheric environment monitoring satellite has realized the high-precision, all-day, global detection of active laser carbon oxidation. The most accurate remote sensing data support. At the same time, the atmospheric detection lidar has achieved the acquisition of vertical distribution information such as global aerosol optical thickness, shape and size for the first time in China by performing layered “CT” scanning of the atmosphere.
PM2.5 monitoring, comprehensive means hit a new high. For the first time in the world, the atmospheric environment monitoring satellite adopts an active-passive combination and a multi-means integrated detection system. By loading different types of payloads with different principles, it combines the echo signals received by actively transmitting lasers with the reflected signals of sunlight received passively. Comprehensively invert various remote sensing data to achieve high-precision monitoring of the concentration of near-ground fine particles (PM2.5, etc.), and provide scientific data support for the precise prevention and control of air pollution.
Polarization crossfire, information fusion efficiency is high. The Atmospheric Environment Monitoring Satellite is the first in the world to use fusion inversion-level polarization crossfire detection technology to obtain aerosol optical thickness, particle size and other parameters. level. In addition, the ultraviolet hyperspectral atmospheric composition detector and the wide-range imaging spectrometer will also greatly improve the monitoring capabilities of gaseous pollutants and surface environment, and the spatial resolution of hyperspectral atmospheric observation in the ultraviolet spectrum and wide-range multi-spectral observation will be doubled.
Precise control to achieve “active detection”
“It is equivalent to five passengers joining a special space vehicle. Each of them holds various measuring instruments to continuously and dynamically measure the atmospheric environment such as atmospheric fine particles, greenhouse gases, gaseous pollutants, clouds and aerosols, and ecological environment elements such as water environment. Comprehensive monitoring.” said Zhang Yanzhao, deputy chief designer of the satellite attitude and orbit control subsystem of the Eighth Academy of China Aerospace Science and Technology Corporation.
“Especially the ‘honored guest’ of atmospheric detection lidar has put forward high requirements for the driving skills of special drivers.” According to Zhang Yanzhao, when the atmospheric detection lidar is working, it emits lasers of different bands to the ground in real time, and receives them. The echo signal of the laser is used to invert the information on the concentration of carbon dioxide columns in the global atmosphere and the vertical distribution of clouds and aerosols through the received echo signals. The carbon dioxide detection concentration index of atmospheric detection lidar is 1ppm, which requires lidar to have extremely high pointing measurement accuracy, which is reflected in the satellite attitude and orbit control subsystem, which is the high-precision attitude and pointing control of the payload.
“The simple understanding is that lidar needs to accurately know where on the earth the emitted light waves are reflected back.” Zhang Yanzhao said. “We all know that when a wave encounters a moving object, it will produce a Doppler frequency shift, and the rotation of the earth will also produce a Doppler frequency shift in the laser echo signal. Different positions have different rotation speeds and different frequency shifts. To accurately compensate for the influence of this factor during inversion, it is necessary for the lidar to know exactly where the shot ‘bullet’ landed, which is the pointing measurement accuracy.”
In response to this feature of atmospheric environment monitoring satellites, the satellite attitude and orbit control subsystem adopts a three-axis zero-momentum “driving” technology, and the “driver” first steps on the first accelerator in space. Re-confirmation, that is, performing on-orbit absolute calibration. This is because the relative positional relationship between the load and the star sensor and other attitude measuring instruments, which are fixed together by mechanical structures on the ground, will change slightly in the space environment due to the release of structural stress, which will lead to measurement The link produces an initial error. The attitude and orbit control subsystem sets two calibration modes: laser ranging calibration and ground target absolute calibration, so as to correct the error of the whole link to the minimum, so as to ensure that the absolute attitude and pointing information of the lidar can be obtained.
“My eyes are rulers”
The atmospheric environment monitoring satellite is deployed in a sun-synchronous orbit and can fly 14 orbits around the earth every day. The lidar works all day, day and night. It can be described as a conscientious “model worker”. In addition to being dedicated, it is also a complete “obsessive-compulsive disorder”, never forgetting to straighten its posture to ensure extremely high pointing measurement accuracy. For this reason, it has also innovatively applied laser optical axis self-calibration without control points for the first time in China. technology.
The premise for the successful implementation of this “magic skill” is to have a “ruler” that can provide absolute posture information in real time, that is, the “eye” of the “driver” – the star sensor. The light source emitted by the lidar itself is split and reflected by the prism on the star sensor bracket to establish an on-orbit calibration system between the lidar and the star sensor, so that the lidar can use the star sensor to be a pair of “eyes”. “Where are you”.
According to Sun Shang, deputy chief designer of the satellite attitude and orbit control subsystem of the Control Institute of the Eighth Academy of China Aerospace Science and Technology Corporation, in order to provide high-precision on-orbit three-axis inertial measurement accuracy, the attitude and orbit control subsystem uses high-precision multi-head star sensors. “It’s like positioning with ‘three eyes’ at the same time, and using a ‘brain’ to fuse and process higher-precision attitude measurement data. “
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