Satellite ground system—the "nerve center" of Earth remote sensing satellites

The remote sensing satellite ground system is a complex large-scale engineering system, which is usually composed of seven subsystems: operation and management, observation planning, data reception, data processing, data management, calibration and evaluation, and distribution services.

Operation Management Subsystem

The Operations Management Subsystem is the central management hub of the entire ground system, responsible for managing the entire system's lifecycle. It connects the various subsystems at the hardware level and monitors and manages the operational status and security of the system's hardware and software resources. Furthermore, the Operations Management Subsystem schedules tasks related to data reception, processing, management, and distribution within the ground system.

Observation Planning Subsystem

The observation planning subsystem is primarily responsible for satellite mission scheduling. Numerous users submit data service requests to the ground system, which is then screened and filtered. Based on the satellite payload's observation capabilities, the subsystem formulates the satellite observation and reception plans for the following day and sends the observation plans to the satellite tracking and control network. These plans are then transmitted to the satellite via the tracking and control antenna, directing the satellite to carry out its observation tasks. The satellite reception plans are then transmitted to the satellite ground station network via the operation management subsystem.

Data receiving subsystem

Just as the human brain's visual nervous system receives what the eyes see, receiving observation data acquired by remote sensing satellites in their orbits requires ground receiving stations to acquire and track the satellites according to the satellite reception plan. The satellite remote sensing data and auxiliary data are received, demodulated, and recorded in the form of electromagnetic wave signals. The received data is then transmitted to the data processing subsystem through the data management subsystem.

Ground station equipment mainly includes antenna feeders, channel transceivers, data loggers, and other station control and management equipment. The antenna feeder, essentially a dish-shaped receiving antenna, focuses signals through its dish-like design, with a diameter ranging from 5 to 20 meters. When a satellite passes overhead, the receiving antenna automatically aligns with and tracks the satellite. During this time, the satellite's observation data signals are continuously transmitted. The channel transceiver, similar to a set-top box, demodulates, amplifies, converts, and processes the received electromagnetic signals. The data logger records the data output from the demodulator onto storage devices such as hard drives.

Currently, ground station receiving equipment often uses uplink and downlink signal multiplexing, capable of receiving data downlinked from satellites and uplinking data to satellites. It can modulate ground-generated satellite mission commands and other data, transmitting them to the satellite via antennas to direct satellite operations. Remote sensing satellites typically orbit the Earth in sun-synchronous orbits. Data transmission only occurs when the satellite is within the receiving antenna's range. Due to my country's vast territory, a single ground station cannot cover the entire country; therefore, a network of multiple ground stations is needed for comprehensive reception. Currently, commonly used ground stations in my country are located in Beijing, Urumqi, Guangzhou, and Mudanjiang.

Data Processing Subsystem

After receiving satellite data, the ground receiving station transmits it to the ground data processing center via fiber optic network. There, the raw remote sensing satellite data undergoes rapid, automated processing, converting the received digital signals into usable data. These processes primarily include signal calibration, decompression, data format parsing, auxiliary data processing, data cataloging, digital information extraction, radiometric correction, geometric correction, and orthorectification. Different workflows are created based on varying user needs, resulting in standardized products of different levels. Radiometric correction, in particular, eliminates distortion in the original image, making ground feature images clearer and more realistic.

Data Management Subsystem

Currently, my country has dozens of remote sensing satellites in orbit, each carrying multiple remote sensors. Each satellite can conduct multiple ground observations daily. To facilitate rapid data retrieval and extraction, effective management of remote sensing satellite product data is essential. The data management subsystem is analogous to the neuronal memory portion of the brain, primarily used for long-term archiving and management of standard remote sensing satellite product data and metadata. It provides access to the business database and establishes an information system capable of database query, addition, and deletion functions. Currently, a hierarchical storage approach—online, near-line, and offline—is generally adopted. This hierarchical storage approach saves storage costs while ensuring data security.

Calibration and Evaluation Subsystem

The calibration and evaluation subsystem primarily tests and evaluates the quality of satellite observation data. To put it simply, it's like testing a person's eyesight, ensuring the satellite acquires data in the best possible condition. It tracks performance changes in remote sensing satellite sensors, promptly corrects relevant parameters needed for data processing, and provides a basis for satellite parameter adjustments; it periodically provides users with on-orbit absolute calibration coefficients, facilitating the quantification of remote sensing data; and it analyzes and...

Distribution Service Subsystem

Data distribution delivers the most relevant data to users, primarily providing data sharing services, much like retrieving accurate memory information from the brain. After finding the required data on the ground system's data distribution network, users can order it, similar to ordering on Taobao. The order system adds a data order record, and the backend system retrieves the corresponding data from the data management subsystem based on the user's data service request, providing it to the user via CD-ROM, hard drive copying, or online transmission. The satellite ground system is highly complex, as shown in Figure 2. Ground system construction involves knowledge and technology from multiple disciplines. Only when each subsystem within the ground system fulfills its responsibilities and coordinates with each other can the operation and management of remote sensing satellites be successfully completed. The daily operations of the satellite and ground system, like the human body, observe the outside world through "eyes," acquire useful information from visual perception through the "brain," and form "memories." When these "memories" are needed, they are quickly retrieved to serve human activities.

Today, remote sensing satellite ground systems serve numerous users, processing hundreds or even thousands of data orders daily, requiring high-performance computing, storage, network equipment, and information technology support in the background. Currently, ground systems widely employ big data analytics, automatically and intelligently recommending relevant remote sensing satellite data products to users based on their identity, location, and order history. After receiving the remote sensing satellite data products, users interpret and analyze the information obtained from the satellites, transforming it into the ground feature information needed by specific disciplines, thus enabling remote sensing information to play a role in practical work within those disciplines.

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