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During the process of using remote sensing technology and equipment to observe surface cover and natural phenomena by remote sensing satellites, the positions on Earth where the satellite observes, the time of observation, and when it transmits the observed data need to be operationally managed by the ground systems. After the satellite remote sensing data is transmitted by the satellite data transmission system to the ground receiving station, a series of operations such as format decoding, decompression, and image data processing are required to produce usable image products. These operations are completed by the remote sensing satellite ground systems.
The remote sensing satellite ground systems are complex large-scale engineering system, typically consisting of seven subsystems: operations management, observation planning, data reception, data processing, data management, calibration evaluation, and distribution services.
The operations management subsystem is the control center of the entire ground system, responsible for managing the lifecycle of the entire ground system. It connects various subsystems from a hardware perspective and monitors and manages the operational status and security of the system's hardware and software resources. Additionally, it schedules tasks associated with data reception, data processing, data management, and data distribution for the ground system.
The observation planning subsystem is primarily responsible for organizing satellite work tasks. Many users request data services from the ground system, and the observation planning subsystem screens and filters these requests, creating the next day's satellite observation plan and reception plan based on the satellite payload's observation capabilities. The satellite observation plan is sent to the satellite control network and relayed to the satellite via control antennas for executing observation tasks. The satellite reception plan is transmitted to the satellite ground station network through the operations management subsystem.
Just like the visual neural system of the human brain receives what the eyes see, receiving the observational data acquired by the remote sensing satellite in orbit requires the receiving equipment of ground stations to capture and track the satellite according to the satellite reception plan. It receives, demodulates, and records the satellite remote sensing data and auxiliary data from the satellite in the form of electromagnetic signals, transmitting the received data to the data processing subsystem through the data management subsystem.
The ground station equipment mainly includes antenna feed systems, transceiver channels, data recording devices, and other station control management equipment. The antenna feed system, which receives signals like a dish antenna, converges the signal with a dish-shaped design, with diameters ranging from 5 to 20 meters. During satellite passes, the receiving antenna can automatically align with and track the satellite. Subsequently, the satellite's observational data signals are continuously transmitted down. Transceiver channel equipment, similar to set-top boxes, demodulates, amplifies, changes frequency, and processes the noise of received electromagnetic signals. Data recording devices record the data output from the demodulator onto storage devices like hard drives.
Currently, ground station receiving equipment is often utilizing multiplexed signals for both uplink and downlink, capable of receiving satellite-downloaded data and uploading data to the satellite. Data generation commands from the ground can be modulated into signals and sent to the satellites via antennas. Remote sensing satellites typically fly in sun-synchronous orbits around the Earth and can only transmit data when they reach a position visible to the receiving antenna. Due to the vast expanse of China's territory, a single ground station cannot cover the entire country, necessitating a network of ground stations for comprehensive reception. Commonly used ground stations in China are located in Beijing, Urumqi, Guangzhou, and Mudanjiang, among others.
After the satellite data is received by ground receiving stations, it is transmitted via network fiber to the ground data processing center. The raw remote sensing data undergoes rapid automated processing to convert the received digital signals into usable data. These processing steps include signal calibration, decompression, data format parsing, auxiliary data processing, data cataloging, digital information extraction, radiometric correction, geometric correction, and orthorectification, forming different workflows to generate standardized products of various levels according to user needs. Radiometric correction helps to eliminate distortions in raw images, making the images of ground objects clearer and more realistic through satellite image processing techniques.
Currently, China has dozens of remote sensing satellites in orbit, each equipped with multiple remote sensors, allowing each satellite to observe multiple times a day. For quick data query and extraction, satellite data management of remote sensing satellite product data is essential. The data management subsystem, akin to the memory neurons of the brain, handles long-term archival management of standard product data and metadata from remote sensing satellites. It provides access services for business databases, establishing an information system that supports querying, adding, and deleting database functions. Typically, graded storage methods, including online, near-line, and offline storage, are adopted to save storage costs while ensuring data security.
The calibration evaluation subsystem primarily tests and evaluates the quality of satellite observation data, akin to eye vision tests for ensuring optimal performance in data acquisition. It tracks performance changes of remote sensing satellite sensors, timely adjusts parameters needed for data processing, and provides a basis for adjusting satellite parameters. It regularly provides users with in-orbit absolute calibration coefficients for quantifying remote sensing data and offers analysis and quality evaluation of data products.
Data distribution delivers the most suitable data to users, providing data sharing services, much like retrieving the correct memory information from the brain. Users can order the required data after searching the data distribution network of the ground system, adding data order records in the order system. The backend system extracts relevant data from the data management subsystem based on the user's data service requirements, providing it to users via CD, HDD copy, and online transmission. The satellite ground systems are highly complex, and building the ground system involves knowledge and technologies from various disciplines. Only through the coordinated efforts and responsibilities of each subsystem within the ground system can the remote sensing satellite's operational management be successfully achieved. The operational activities of the satellite and ground system are akin to the human body, observing the outside world through "eyes", acquiring useful information through "brain" visual perception, and forming "memories". When such "memory" knowledge is needed, it is quickly retrieved through search to serve human activities.
Nowadays, the remote sensing satellite ground systems serve numerous users, processing hundreds to thousands of data orders daily, requiring high-performance computing, storage, network equipment, and information technology support. Currently, ground systems commonly use big data analysis technology, capable of intelligently recommending relevant remote sensing satellite data products to users based on their identity, location, and order history. Upon receiving remote sensing satellite data products, users interpret and analyze the information obtained by the satellites, converting it into terrestrial information required by specific disciplines, thereby enabling remote sensing information to play a role in the actual work of specific disciplines.
