The earth is surrounded by a thick layer of atmosphere. The atmosphere is divided into troposphere (about 10-20 km from the ground), stratosphere (about 20-50 km from the ground), and the middle layer (about 50-85 km from the ground). The upper layer is the upper layer. About 800 km) and escape layer. The atmosphere of the hot layer is also called the ionosphere because it is exposed to the sun, the temperature is high, and the gas molecules or atoms are largely ionized and can conduct electricity.
“We refer to the uncharged atmosphere below the thermal layer as the neutral atmosphere, and the APSOS system is to detect around the neutral atmosphere.” Lu Daren said, “Because the research in this area can open up atmospheric physics and space physics research, A deeper analysis of the relationship between human activities and atmospheric movements, climate change, etc."
APSOS is also the world's first large-scale active-passive integrated detection system for multi-component and multi-factory neutral atmospheres. It consists of five large laser instruments, a millimeter wave cloud radar, a terahertz superconducting radiation spectrometer and a combined telescope. Viewed from the sky, centered on the building where the combined telescope is located, the container compartments with equipment are distributed around the whole system, and the whole system is in the shape of a "meter".
Among them, Lidar as an active laser pointer optical remote sensing detection device has the advantages of high spatial and temporal resolution and high detection accuracy. Its working principle is to emit laser light into the atmosphere. The laser beam interacts with different substances in the atmosphere, and the scattered light is scattered. The signal is received by an optical telescope and converted into an electrical signal by a photodetector. Based on different laser radar principles, the content of different detected substances can be obtained by processing the received signals, and the atmospheric temperature and wind field are obtained by the Doppler effect. The millimeter-wave cloud radar in the system is known for its sensitive detection of high-volume clouds.
In addition, multiple laser radars share an optical telescope, using four 1.2-meter-diameter mirror splicing to achieve an equivalent diameter of 2 meters, which greatly improves the receiving capacity of the laser radar, making it an internationally advanced atmosphere. Detecting the lidar receiving telescope.
The only passive remote sensing device in the system is a superconducting radiation spectrometer operating in the terahertz band to detect the content of greenhouse gases such as water vapor and ozone in the middle atmosphere. The terahertz band is the last electromagnetic band currently exploitable and has a strong atmospheric penetration capability to detect more distant targets.
Pan Weilin, a researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, said that in the neutral atmosphere, APSOS emits dozens of pulses per second by emitting laser light, just like a "sword" that "cuts" the atmosphere every few tens of meters. Accurate access to atmospheric composition information, including PM2.5, which is of greatest concern in recent years.
Why is the system placed in Tibet? “Tibet is China's focus on global climate change research. The elevation is more conducive to the detection of lidar and terahertz spectrometers, which makes it more likely to acquire multiple atmospheric elements to detect results at the same time, and more reflect the scientific value and data of the equipment. Value." Lu Daren said.
It is understood that the visualization platform that has built the basic framework can realize the synchronous update of data and realize remote monitoring of the system operation. However, such a sophisticated instrument still has certain challenges in the long-term and stable operation of Tibet.
"The biggest problem is that the laser is running on the plateau. In order to obtain high-quality signals, the laser is the highest configuration and the technical requirements are relatively high," said Pan Weilin. However, she said that lasers can still last for years with proper maintenance.
Although the current laser radar can't work in daytime and thunderstorm days, its long-term, continuous and stable advantages in the fine detection of multiple elements of the atmosphere still make experts look forward to its development.