The HY-1 satellite ground system is one of the five systems of satellite engineering (satellite, carrier, launch, Telemetry & Telecommand, ground application system). It consists of 7 components: data receiving and preprocessing, data processing, product archiving and distribution, radiometric calibration and validation, communication, operation control and the demonstration of application subsystem. The benefits of satellites are mainly reflected by the ground system. 

1. The basic tasks of the system are to receive and store 10-bands Ocean Color and Temperature Scanner (COCTS) data as well as the playback data of overseas detection, and 4-band CCD imager data transmitted in real time by HY-1A satellite.

The tasks also include the completion of satellite orbit prediction as scheduled time, comparison of satellite time and ground time, data preprocessing, the processing of ocean color, sea surface temperature image products and quantitative product.

The system is responsible for data archiving and distribution and has convenient retrieval and quick display capabilities. It could form a highly operational database and management system and provide data and product services. Using HY-1A satellite combined with other remote sensing data, establishing the demonstration of application system.

The system can carry out radiometric calibration of visible, infrared channels for COCTS and validate the retrieval results.

The system can achieve the communication between two ground receiving station and Xi'an satellite Telemetry & Telecommand center and build a network-wide management system.

The system is responsible for the exploration plan, Time uniformity, task operation, command and dispatch, counting and analysis of the quality of the system operation. When there is abnormality or unexpected event, related staff should organize troubleshooting on time to ensure the system running normally.

The system is compatible with the receiving of meteorological satellites and foreign marine satellite data.

2. The organization and function of system

The HY-1 satellite ground system consists of 7 components: data receiving and preprocessing, data processing, product archiving and distribution, radiometric calibration and validation, communication, operation control and the demonstration of application subsystem. The benefits of satellites are mainly reflected by the ground system, the framework is showed as below: 

(1) Data receiving and preprocessing subsystem

The subsystem is composed of Beijing ground station, Sanya ground station and data preprocessing subsystem. Beijing and Sanya station undertake the reception of real time and delayed data transmitted by two sensors of HY-1A satellite; data preprocessing subsystem is responsible for the preprocessing of the data received by the two ground stations to generate Level-0 and Level-1 data product. At the same time, the data receiving and preprocessing subsystem is also compatible with the receiving and pre-processing of the downlink data of the L-band NOAA series satellites and FY-1 series satellites, and the receiving of EOS satellite data. The data received by Sanya station is transmitted to Beijing station preprocessing subsystem through the communication subsystem.

① Beijing ground receiving system

The X-band receiving system introduced from SeaSpace, USA can receive HY-1A and EOS-MODIS data and has the ability to receive data of other marine satellites. The antenna of the L-band system has a diameter of 4.5m and a radome with a diameter of 5.5m. It is equipped with A-E plus a third-axis tilt antenna. It has a dual frequency feed with self-tracking performance. In order to reduce cable attenuation, the downconverter is installed on the antenna bracket inside the radome and the output power is 720MHz. The antenna control and servo system are controlled by computer. The receiver can be applied to 1-160Mbps rate and also can be applied to BPSK, QPSK, UQPSK, SQPSK, AQPSK modulation, etc. The time is controlled by GPS, data receiving and processing software runs on SUN workstation, and is equipped with DLT tape and UPS.

The L-band receiving system is used for receiving NOAA series HRPT and FY-1 series CHRPT data. The antenna diameter of the system is 1.5m and is equipped with A-E mounting. The diameter of the radome is 1.8m. The system can receive and process polar orbit meteorological satellite data by program tracking.

② Sanya ground receiving system

Sanya ground station is located at Haipo Resort, Sanya city, Hainan Province, China and the receiving system is developed domestically. The system is used for tracking, receiving, demodulation, data recording and real time display of the data from HY-1A and the data transmitted by X-band of its successor satellite. The station is also receiving data from EOS satellites, L-band data from NOAA series satellites and China's FY-1 satellite. The system is composed of antenna tracking, signal reception and demodulation, data recording, quick viewing, station management, calibration test subsystem and time-frequency equipment, etc. The antenna tracking subsystem consists of 5.2m standard parabolic antenna, L/S/X-band frequency feed, X-Y mounting, antenna servo control device, and antenna shaft encoder. The main objective of the signal reception and demodulation is to complete the reception and demodulation of satellites signals. The RF front end signals IF are 720MHz and 70MHz and the signals are demodulated respectively by high and low speed demodulator. The quick viewing subsystem can format HY-1A, NOAA, FY-1, EOS data and the data recording rate is between 0.1 and 160Mb/s. The quick viewing subsystem works on the Windows platform and is capable of automatic management based on satellite orbit parameter tasks.

③ Data preprocessing subsystem

The main objective of the data preprocessing subsystem is original data splitting, format conversion, track splicing (de-overlap), quality inspection, geometric positioning, calibration processing for the data received by Beijing and Sanya station, generating Level-0 and Level-1 products, quick viewing, automatically generate system operation report and automatic operation management. The data preprocessing subsystem is composed of the workstation and microcomputer platform.

(2) Data processing subsystem

The objective of the data processing subsystem is to generate Level-2, Level-3 products, various graphics, image and quantitative products from the HY-1A Level-1 data as scheduled. The system can automatically process and generates products, including normalized water-leaving radiance, chlorophyll concentration, suspended sediment concentration, dissolved organic matter, sea surface temperature, seawater diffuse scattering attenuation characteristics, atmospheric parameters from COCTS Level-2 products and its Level-3 products of daily, 10-day, monthly, yearly, and vegetation index and suspended sediment concentration products from CCD Level-2 products. The subsystem can automatically generate quick views of each level of products, and system can automatically generate reports for system management and query.

The data processing subsystem consists of a high-performance HP N4000 server and several HP B2000 workstations, and two servers form a dual-system hot backup cluster system to ensure high reliability requirements of the system; The storage system consists of a high-performance EMC FC4500 disk array and a robotic STK 700 cassette library and 7TB of data can be stored online and nearline. The LAN network of the processing center is composed of a core network of Gigabit optical fibers and a secondary exchange of 100Mbps desktops and the network master switch is composed of CISCO 6505 and 3548 with Gigabit fiber ports. The processing subsystem’s software consists of HYDAS which is a specific software used for ocean color processing for HY-1A and commercial image processing software such as IDL, ERDAS, ENVI and PCI, etc.

(3) Data archiving and distribution subsystem

The main objective of data archiving and distribution subsystem is to archive and distribute data, including Level-0, Level-1, Level-2, and Level-3 products of HY-1A, NOAA series satellites data, Level-0, Level-1 products of FY-1C/D, raw data of EOS-AM satellite, radiometric calibration in-situ observations, and other ancillary data and thematic information products. The system has product library and product information library which are automatically generated and classified, mainly used for distributing products to fixed/authorized users, and provides users with product information query and retrieval and order submission services via web server.

The subsystem consists of a database server, a disk array, a cassette library, and a database management system and data storage management software running on the server. The main hardware devices of the subsystem include the UNIX primary database server, the Internet server, and the internal and external network-isolated Proxy server and several image processing workstations.

(4) Calibration and validation subsystem

The objective of the radiometric calibration and validation subsystem is to establish an observation and measurement system for radiometric correction and validation for the two sensors onboard HY-1A, complete in-orbit radiometric correction of sensors onboard HY-1A at sea and land radiometric correction field, obtain simultaneous observation of various in-situ data at sea radiometric correction field,

complete the validation of quantitative remote sensing data and geophysical parameter products, establish and improve the in-orbit radiometric correction and validation database of the two sensors onboard HY-1A. Through the acquisition of the in-situ data, the calibration coefficients of two sensors onboard HY-1A are given and updated, and the quality of the satellite data and products are analyzed and evaluated.

There are six main equipments for the radiometric calibration and validation subsystem:

1) Marine optical instrument: SAS-II, ASD, SPMR, AC9, HS6, etc.;

2) Atmospheric optical instrument: CE318, CE317, MicroTops-II, etc.;

3) Thermal infrared instrument: CE312, Mikron340, etc.;

4) Biochemical analysis instrument: HPLC, GBC, Millipore, etc.;

5) Optical instrument calibration system: NIST, NIM, radiant standard board, high precision power control system, high precision optical platform, etc.;

6) Hydrometeorological observation instrument.

(5) Communication subsystem

The objective of the communication subsystem is to complete raw data, scheduling and monitoring HY-1A data transmission between Sanya and Beijing station, complete the transmission of HY-1A satellite telemetry data, remote control data, orbit data between Xi'an Satellite Monitoring Center and Beijing, and complete the transmission of voice command and dispatch information between Beijing and Xi'an and Sanya stations. The communication subsystem connects the Beijing ground system, Sanya ground station and Xi'an measurement and control center through the VSAT network forming a remote integrated data transmission network for HY-1A ground system.

The communication subsystem is equipped with a 4.96Mbps high-speed VSAT communication system and a 2Mbps VSAT communication system in Beijing, the dual-machine hot backup HP A500 server and disk array form the core node of the communication network and is connected to the ground system core network through the network switch.

The communication subsystem is equipped with a high-speed VSAT communication system in Sanya and the highly reliable HP A400 communication server form the Sanya communication node, and is connected to the Sanya ground station receiving system LAN through a network switch.

The communication subsystem is equipped with a low-speed VSAT station at Xi'an measurement and control center and the high-reliability communication workstations which form the Xi'an communication node.

Data communication software automatically completes satellite raw data and scheduling information transmission and is capable of real time monitoring and remote configuration and realizes the automated operation of the communication subsystem.

(6) Operation control subsystem

The objective of the operation control subsystem is to complete the development of the payload exploration plan for HY-1A, the telemetry parameter monitoring of the satellite and sensors operation and the orbit prediction, complete automatic scheduling operation of data reception, preprocessing, processing and archiving of HY-1A, and complete real time monitoring of the operational status of the ground system.

The operation control subsystem is equipped with HP A500 dual-system hot backup server and shared disk array, workstation, high-performance microcomputer, large-screen projection equipment and other hardware devices, Oracle8i database, IBM MQ messaging middleware software, and operation control software. The operation control software includes telemetry/remote control data processing software, orbit prediction software, task scheduling software, operation status monitoring software, operation control data management and analysis software to achieve the functions of the operation and control subsystem.

(7) Application and demonstration subsystem

The objective of the application and demonstration subsystem is to conduct satellite remote sensing data application research based on all levels of products stored in the data archiving and distribution subsystem, and based on this, provide practical algorithms and corresponding software for HY-1 Level-3 products. Combining other satellites data to conduct operational application tests of sea surface temperature, sea ice and chlorophyll concentration (primary productivity). Mainly focusing on monitoring marine disasters nation-widely and for key sea areas including red tides, oil spills and sea ice, providing fishery environmental information service and dynamic monitoring applications for typical areas of the coastal zone. Demonstrating the application ability of HY-1A satellite remote sensing data in marine environmental monitoring.

The computer network equipment of the subsystem is composed of HP L2000 server, high-end image processing workstation, high-end PC and switched Fast Ethernet.