Making a "super CT" for space: revealing the secrets of a world-class space weather "forecast station"

Today, let's learn about the Meridian Project, the first major national scientific and technological infrastructure in China's space science field. Recently, the Meridian Project Phase II, consisting of 16 observation stations and 58 observation points, has been initially completed. Together with the Meridian Project Phase I, it has formed a two-vertical and two-horizontal "well"-shaped "space environment" monitoring network covering the whole country, which is currently the largest ground-based comprehensive monitoring network in the world. It can be said to be a veritable "Skynet". Its mission is to reveal the process and laws of space weather changes and improve the forecast level of space weather. Among them, the detection of the ionosphere is one of the important contents.

News link: What is "space weather"?

So what is "space weather" compared to "wind, rain, thunder and lightning" on Earth? Here is a brief introduction. The space environment in the middle and upper atmosphere above the stratosphere 30 kilometers above the ground is affected by solar activity and will undergo drastic changes. This short-term change caused by solar activity is "space weather."

In particular, the upper atmosphere at an altitude of about 60 to 1,000 kilometers above the earth is called the ionosphere. Our daily communications, broadcasting, navigation, and positioning are inseparable from this area. The ionosphere is "naturally restless" and contains a large number of free charged particles. Sometimes disturbances suddenly occur, which seriously affect radio communications on the ground. Capturing and monitoring the "every move" of tiny electrons in space hundreds to thousands of kilometers away is like observing a candle hundreds of kilometers away with the naked eye. The difficulty can be imagined. One of the landmark equipment of the Meridian Project built this year, the Hainan Sanya Incoherent Scattering Radar, has mastered this key core technology. It is also the world's most advanced ground-based ionosphere detection equipment.

my country has built the world's most advanced ground-based ionospheric detection equipment

CCTV reporter Ren Meimei: Now we have come to the bottom of the entire radar array, where we can see that each antenna unit is connected to a component. These components are the core components of the radar array, which can transmit and receive signals.

Experts tell us that when 8,320 units radiate electromagnetic waves into the air in the same direction under unified instructions, the energy will be concentrated and the power will be greater.

Zhang Ning, an engineer at the Institute of Geology and Geophysics, Chinese Academy of Sciences: "8,320 components can radiate powerful energy to the ionosphere, which then scatters weak echo signals. We can then analyze the weak scattered signals through low-noise amplification and waveform encoding and decoding, obtain the parameters of the ionosphere, and magnify the state of electrons and ions in the ionosphere for scientists like a microscope."

The higher the altitude, the thinner the density of electrons in the ionosphere and the harder it is to detect. Currently, the international ionosphere detection altitude is several hundred kilometers. The Sanya incoherent scattering radar, as the world's largest and most powerful phased array incoherent scattering radar, has raised the ionosphere detection altitude to thousands of kilometers.

Moreover, its detection accuracy and sensitivity have reached the international leading level, and it can capture the changes of more subtle particles such as plasma. Since it was put into operation, the Sanya incoherent scattering radar has observed the cross-sectional structure of ionospheric plasma holes with high temporal and spatial resolution for the first time, laying a solid foundation for related physical research.

Le Xin'an, a researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences: The main station in Sanya has the functions of transmitting and receiving. There are two receiving stations in Danzhou in the northwest of Hainan Island and Wenchang in the northeast, forming an incoherent scattering radar system of "one transmit and three receive". It can be simply understood as a "super CT" facing space, which is equivalent to obtaining three CT sections at the same time, so as to better monitor the three-dimensional state of the entire space environment. The Sanya incoherent scattering radar is a major breakthrough in our country's ground-based space environment detection technology, filling a gap in our country's large-scale ground-based ionospheric detection equipment.

In addition, as a high-power radar, Sanya Incoherent Scattering Radar is also an ideal signal source for other radio astronomy equipment. It has been working with China's "Sky Eye" FAST and the Sichuan Daocheng Circular Array Solar Imaging Radio Telescope to carry out joint observations and has initially achieved a number of results. It is understood that the next step for Sanya Incoherent Scattering Radar is to expand its monitoring capabilities for the moon and small celestial bodies.

The circular array solar radio imaging telescope passed the process test on September 27. The telescope is one of the landmark equipment of the second phase of the Meridian Project (Source: Video screenshot)

The second phase of the Meridian Project was initially completed and entered joint commissioning operation

CCTV reporter Ren Meimei: At the National Space Science Center of the Chinese Academy of Sciences in Huairou, Beijing, we also saw array-type large-aperture laser radars, interplanetary scintillation monitoring telescopes, etc., which are the iconic equipment of the Meridian Project Phase II. We understand that 195 sets of space weather monitoring equipment have been completed in the Meridian Project Phase II.

Wang Chi, academician of the Chinese Academy of Sciences and general commander of the Meridian Project Phase II: For the Meridian Project Phase II, we are now in a stage of comprehensive commissioning, joint testing, and trial operation. We will strive to complete the national acceptance next year and officially enter the operation stage.

The Meridian Project is the first major national scientific and technological infrastructure in China's space science field. The first phase of the project started construction in 2008 and was officially put into operation in 2012. Along 120° east longitude and 30° north latitude, 15 comprehensive stations and 87 sets of monitoring equipment have been built. A series of original results have been achieved in understanding the characteristics of the near-Earth space environment of my country's 120° meridian chain, the propagation and evolution of space weather disturbances, etc.

The second phase of the project started construction in 2019, adding 16 new stations, 58 observation points, and 195 sets of monitoring equipment. In coordination with the first phase of the project, a two vertical and two horizontal "well" shaped ground-based space environment comprehensive monitoring network covering the entire country will be formed along 100° east longitude and 40° north latitude, with a wider coverage, higher detection altitude, and stronger monitoring capabilities.

Wang Chi, academician of the Chinese Academy of Sciences and general commander of the Meridian Project Phase II: After the Meridian Project Phase II, some of our "hardcore" products are in a leading position internationally. For example, the circular array in Daocheng is the solar radio telescope with the largest aperture in the world. Another example is the helium laser radar, which has a 6-meter aperture and all-weather detection capability for the middle and upper atmosphere. Its detection performance reaches 1,000 kilometers, which is the highest level among all the equipment in the world that we know of so far.

Together with Phase I, it will form the world's largest ground-based space environment monitoring network

The second phase of the Meridian Project adopts the design architecture of "one chain, three networks, and four focuses", and for the first time realizes the full-circle, multi-factor, and three-dimensional detection of the solar-terrestrial space environment above my country.

The "one chain" refers to the solar-interplanetary monitoring chain, which forms an all-weather monitoring capability of the solar-interplanetary-Earth; the "three networks" include the geomagnetic monitoring network, the middle and upper atmospheric monitoring network and the ionosphere monitoring network, which carry out "panoramic" monitoring; the "four focuses" refer to the "microscopic" detection of the four regions with special and strong space weather disturbances and sphere coupling, namely the Earth's poles, the northern mid-latitudes, Hainan's low latitudes and the Qinghai-Tibet Plateau.

Wang Chi, academician of the Chinese Academy of Sciences and general commander of the Meridian Project Phase II: The Meridian Project Phase II added monitoring of the source of space weather activities - the sun, forming an end-to-end monitoring of the space environment from the sun to the earth. This is the first and only space environment monitoring system in the world, achieving end-to-end observation of the entire solar-Earth space.

It is understood that in the future, the first and second phases of the Meridian Project will operate up to 44 types and nearly 300 instruments, which will be able to simultaneously cover the chromosphere, corona, solar wind, magnetosphere, ionosphere, middle and upper atmosphere, all the way to the lower atmosphere.

Wang Chi, academician of the Chinese Academy of Sciences and general commander of the Meridian Project Phase II: "By aiming at the forefront of world science and technology, we can answer how solar activity affects the Earth's space environment. In terms of meeting major national needs, we can provide data support for improving the accuracy of space weather forecasts and ensure the safety of a series of national space infrastructure and high-tech facilities such as aerospace, communications, and navigation."