GF-1 (Gaofen-1) High-resolution Imaging Satellite / CHEOS series of China

Overview     Spacecraft     Launch    Mission Status     Sensor Complement    References

Gaofen-1 (gao fen = high resolution) is the first of a series of high-resolution optical Earth observation satellites of CNSA (China National Space Administration), Beijing, China. The civilian HDEOS (High-Definition Earth Observation Satellite) program was proposed in 2006, it received government approval and was initiated in 2010. China plans to launch six HDEOS spacecraft between 2013 and 2016. ¹⁾

The main goal of the HDEOS series is to provide NRT (Near-Real-Time) observations for disaster prevention and relief, climate change monitoring, geographical mapping, environment and resource surveying, as well as for precision agriculture support. The major users of the observation data will be the Ministry of Land and Resources, Ministry of Environmental Protection, and the Ministry of Agriculture.

In 2010, the Chinese government approved to implement CHEOS (China High-resolution Earth Observation System), which is an extension of the HDEOS program. The CHEOS series will consist of seven optical/microwave satellites. EOSDC-CNSA (Earth Observation System and Data Center - China National Space Administration) is responsible for organizing the construction of the CHEOS program. The CHEOS program comprises the elements of the spaceborne system, the near-space system, aerial system, the ground system and application system as a whole to realize Earth observation at high temporal, spatial and spectral resolution. ^{2) 3) 4)}

China's push into high-resolution optical Earth observation through its seven-satellite CHEOS system is slightly delayed but will see the launch of a second satellite in 2014 and three more satellites by 2016, according to CNSA (China National Space Administration). ⁵⁾

The implementation plan of CEOS satellite series is as follows:

• Construction period: 2010-2020

• The second satellite (GF-2) will be launched in 2014 and be put into service.

• By 2016, the next three satellites will be launched.

• By 2020, the entire CHEOS series of satellites will be on orbit.

Table 1: Overview of the Gaofen missions in the CHEOS program of CNSA (Ref. 3)

Figure 1: Artist's view of the deployed GF-1 spacecraft (image credit: CAST, DFH)

Spacecraft:

Gaofen-1 is based on the CAST small satellite bus designed and developed by the China SpaceSat Co. Ltd. of Beijing (also referred to as DFH Satellite Co. Ltd.), the commercial subsidiary of CAST (Chinese Academy of Space Technology). The satellite is equipped with a pair of solar panel wings, each with three solar panels. The CAST-2000 bus is a small platform with high performance, expandability and flexibility. The CAST-2000 bus is of HJ (Huan Jing)-1A and -1B mission heritage, both spacecraft were launched in Sept. 2008.

ADCS (Attitude Determination and Control Subsystem): The spacecraft is 3-axis stabilized; it has the capabilities of highly precise control, large-range sway maneuver, flexible orbit maneuver, highly integrated housekeeping and highly effective power supply. The ADCS uses a 3-axis star tracker, gyroscope, infrared earth sensors and digital sun sensors. Actuators are reaction wheels, magnetic torques, solar array drivers with BAPTA (Bearing And Power Transfer Assembly) and a propulsion subsystem with 8 years' fuel.

Table 2: Test results of the attitude control capability

The ADCS of GF-1 has the capability of large angle rapid maneuvers, side-slither maneuvers (90º yaw), and two-dimensional data transmission antenna pointing control. In the star tracker and gyro mode, GF-1 realizes high accuracy pointing and attitude stability. GF-1 is China's first spacecraft with a side-slither calibration adopting a 90º attitude yaw maneuver to realize relative radiometric calibration using the side-slither technique. In this configuration, each detector on the focal plane is positioned parallel to the ground-track direction thereby exposing each detector from the same segment of the ground

Figure 2: Principle of side-slither calibration by yaw 90º (image credit: DFH)

On May 1, 2013, the GF-1 spacecraft yawed 90° and performed side-slither calibrations three times on orbit. This maneuver produced a radiometric flat-field input to the sensor so that the relative response of each detector was determined for the same exposure level ( Figure 16). The side-slither derived detector correction parameters were then used to improve the quality of the GF-1 imagery. A significant improvement in image correction was achieved (Ref. 14).

TCS (Thermal Control Subsystem): The TCS employs mainly passive thermal control methods (such as heat insulation, scatter heat, isothermal), aided with active thermal control methods.

RF communications: the spacecraft features an S-band TT&C subsystem and an X-band data transmission subsystem. The Pan imagery is compressed by a JPEG 3:1 algorithm, while the 8 m and 16 m MS data are compressed with a lossless algorithm to ensure image quality.

The Gaofen-1 spacecraft has a launch mass of 1080 kg. The design life is 5 years with a mission goal of 8 years. ⁶⁾

Figure 3: Photo of the Gaofen-1 spacecraft during AIT (image credit: CAST, DFH)

Long life design features:

- All instruments' life time are designed longer than 5 years.

- Key units and functions are redundant. Some safety modes can be operated autonomously in order to ensure power.

- Rotational units like BAPTA and the X-band rotating antenna are required to speedup tests of > 10 years.

- Li-ion batteries are required to test charge and discharge of 30%DOD

- The inclination offset technology is a key design feature which can realize LTDN (Local Time on Descending Node) range inside 10:30±30 min with no need to adjust inclination (fuel saving).

Table 3: Overview of Gaofen-1 parameters ⁷⁾

Note: The Gaofen-1 and the VRSS-1 (Venezuelan Remote Sensing Satellite-1) satellites were both developed at DFH Co. Ltd. using the same CAST-2000 platform.

Launch: The GF-1 spacecraft was launched on April 26, 2013 on a CZ-2D (Long March -2D) vehicle from the JSLC (Jiuquan Satellite Launch Center) in northwest China. The GF-1 spacecraft is the first demonstration mission of the CHEOS program (Ref. 2). ^{8) 9)}

Orbit: Sun-synchronous orbit, altitude 645 km, inclination = 98º, LTDN (Local Time on Descending Node) = 10:30 hours, revisit frequency of ≤4 days.

The secondary payloads were:

• TurkSat-3USat, a nanosatellite (3U CubeSat, ~ 4 kg) of ITU (Istanbul Technical University), Istanbul, Turkey.

• NEE-01 Pegasus, a CubeSat of EXA (Ecuadorian Civilian Space Agency), Ecuador.

• CubeBug-1 of INVAP, a 2U CubeSat of Argentina, sponsored by the Argentinian Ministry of Science, Technology and Productive Innovation, INVAP S.E., Satellogic SA, and Radio Club Bariloche.

Launch: The GF-2 spacecraft was launched on August 19, 2014 on a CZ-4B (Long March 4B) vehicle from the TSLC (Taiyuan Satellite Launch Center), China.

Secondary payload:

The BRITE-PL-2 nanosatellite, also referred to as Heweliusz, of SRC/PAS (Space Research Center/ Polish Academy of Sciences of Warsaw, Poland.

Figure 4: Overview of Chinese institutions involoved in the CNSA EOSDC (Earth Observation System & Data Center, Ref. 3)

Mission status:

• The GF-1 spacecraft and its payload are operating nominally in September 2016. Its data are widely used in the fields of land dynamic monitoring, mineral resources exploring, environment monitoring, disaster monitoring and mitigation, etc. ¹⁰⁾

• August 2015: The GF-1 spacecraft and its payload are operating nominally after more than 2 years on orbit. GF-1 has served a wide range of applications covering many topics. The typical applications with high resolution and wide swath satellite data include: ¹¹⁾

- Monitoring land cover change for environmental monitoring.

- Agricultural applications, such as crop monitoring and management to help food security.

- Detailed vegetation and forest monitoring and parameter generation (e.g. leaf area index, chlorophyll concentration, carbon mass estimations).

- Observation of coastal zones (marine environmental monitoring, coastal zone mapping).

- Inland water monitoring.

- Flood mapping & management (risk analysis, loss assessment, and disaster management during floods).

• On March 6, 2015, the Gaofen-2 spacecraft was declared operational. The services provided by the satellite will help boost development of the country's data application and spatial information sectors, said Xu Dazhe, head of the State Administration of Science, Technology and Industry for National Defense. ¹²⁾

- According to the project information, GF-2 has a spatial resolution of 0.8 m and a multispectral resolution of 3.2 m.

• The Earth Observation and Data Center of CNSA presented some images of GF-1 acquired in 2014 and presented in Feb. 2015. ¹³⁾

Figure 5: The coverage region of Gaofen-1 in 2014 (image credit: CNSA)

Figure 6: ADO (Aerosol Optical Depth) monitoring of the Beijing region on July 27, 2014 with the WFI on GF-1 (image credit: CNSA)

Figure 7: Monitoring of the water bloom over Tai Lake on Oct 15th, 2014 (image credit: CNSA)

• October 2014: The GF-1 spacecraft and its payload are operating nominally. ¹⁴⁾

Figure 8: Fused image of the Beijing Forbidden City with 2 m and 8 m resolution data of GF-1 (image credit: DFH)

• June 2014: The GF-1 spacecraft (a demonstration satellite in the GF family) and its payload are operating nominally. The agile GF-1 provides several acquisition modes. For example, the spacecraft can provide up to 4 different roll acquisitions in one orbit and/or provide a 90º side-slither calibration (Ref. 7).

• EOSDC-CNSA facilitates and provides GF-1 data to various clients including tens of national ministries and agencies, local governments, research institutions, universities, enterprises and organizations in China. EOSDC-CNSA is eager to distribute Gaofen data in international cooperation agreements (Ref. 3).

- By the end of March 2014, an amount of 550,000 scenes have been delivered. Among them, the 2 m Pan and 8 m MS data covering an area of about 93% of China effectively; the 16 m MS data cover China over 10 times effectively.

• Feb. 2014: The Gaofen-1 spacecraft and its payload are operating nominally. The in-orbit test demonstrates that the performance of GF-1 meets the design requirements completely (Ref. 5).

• December 30, 2013: Gaofen-1, China's high-definition Earth observation satellite, has been formally put into service, as reported by SASTIND (State Administration of Science, Technology and Industry for National Defense). ^{15) 16) 17)}

- The satellite has undergone eight months of in-orbit tests since it blasted off on April 26. It has met requirements and even performed better than expected by sending back high quality imagery, according to SASTIND.

- Thus far, the satellite has provided data on the Lushan earthquake in Sichuan, floods in northeastern China and the smog in northern and eastern China during the test period. It also provided Pakistan with images after an earthquake in the country on September 24, 2013.

• On September 29, 2013, the satellite finished orbital commissioning and tested application in the areas of land resources, environmental protection and agriculture. The result of orbital commissioning shows: the main test results are better than expected. The image quality is excellent. All kinds of functions and performances of GF-1 met the user's requirements (Ref. 14).

Figure 9: Heilongjiang river flood inundation map acquired on Sept. 9, 2013 (image credit: DFH)

• On June 6, 2013, SASTIND released the first 13 photos from the high-resolution earth observation satellite Gaofen-1. The images feature four cities, including Beijing, Shanghai, Yinchuan and Datong. ¹⁸⁾

Figure 10: On May 21, 2013, the WFI instrument of Gaofen-1 acquired this 16 m MS image of the Yellow River delta region in China (image credit: CNSA)

The Figures 11 and 12 are an example under the theme: "GF-1 satellite application in geological interpretation."

Figure 11: A 2 m Pan and 8 m MS camera fusion image of Gaofen-1 (image credit: CNSA)

Legend to Figure 11: The imaging region includes the Dongchuan District of Kunming City and Hami City of the Xinjiang Uygur autonomous region. ¹⁹⁾

Figure 12: Interpretation of the geology information in Figure 11, including six larger scale landslides of the Dongchuan District and the fold structure, shear zone, fault structure and exposed strata of the Hami District (image credit: CNSA)

Figure 13: Extract of Figure 14 of the PMC with 2 m Pan/ 8 m MS fusion data acquired on May 1, 2013 showing the Beijing District in China (image credit: CNSA)

Figure 14: First high-resolution image of Beijing acquired by Gaofen-1 (image credit: SASTIND)

• Engineering test mission: It took 6 days to finish the follow items test items (Ref. 7):

- Day 1: Solar arrays deployed, normal 3-axis attitude control, set up platform, antennas deployed

- Day 2: Set up of star sensors, RF of DTS (Data Transmission System) test

- Day 3: Cameras took photos with different roll angles

- Day 4 and 5: Payload and DTS test, different working modes, adjust focus, DTS transmit to double stations

- Day 6: Spacecraft in yaw angle configuration of 90º and side slither calibration; continues to roll 4 times in one orbit. GF-1 is China's first spacecraft which adopted an attitude yaw configuration of 90º to realize relative radiometric calibration using the side-slither technique. In this configuration, each detector in the focal plane was positioned parallel to the ground-track direction thereby exposing each detector from the same segment of the ground.

Figure 15: Illustration of the 90º yaw angle configuration (left) and the side slither target areas (right) acquired on May 1, 2013 (image credit: DFH)

Figure 16: Side-slither raw image (left) on May 1, 2013 and shift of each detector image (right), image credit: DFH

• On April 28, 2013, the RADI Miyun Ground Station succeeded in receiving the first track of image data from the Gaofen-1 spacecraft. ²⁰⁾

Sensor complement: (PMC, WFI)

The satellite is configured with two 2 m barrel-mounted panchromatic/8 m MS (Multispectral) cameras, and a set of 4 WFIs (Wide Field Imagers) with 16 m MS medium-resolution and a combined swath of 830 km. The revisit frequency of the spacecraft is ≤4 days and the observation range of the mission covers a region between 80ºN to ~80ºS. The data of the GF-1 mission are being used in the following application areas: land resource investigation, mineral resource management, atmospheric and water environment quality monitoring, and natural disaster emergency response and monitoring.

The complete camera set of PMC and WFI (6 cameras) may observe simultaneously, or each camera set (PMC or WFI) may observe separately, if required. ²¹⁾

PMC (PAN and Multispectral Camera)

PMC is a high-resolution pushbroom imager (2 cameras) with TDI (Time Delay Integration) capability observing in the visible range at a resolution of 2 m in PAN, and of 8 m in MS (Multispectral)mode. Note: the PMC is also referred to as HR (High Resolution). The PMC features a TMA (Three Mirror Anastigmat) optical system with PAN and 4 MS TDI (Time Delay Integration) CCD focal planes.

Table 4: Parameters of the PMC instrument

Figure 17: Obervation scheme of the 2 PMC (HR) cameras (image credit: DFH)

WFI (Wide Field Imager)

WFI is a medium-resolution pushbroom camera set with TDI (Time Delay Integration) capability observing in the VNIR range at a spatial resolution of 16 m in MS mode. There are four barrel-mounted cameras (WFIs) with a combined overlapping swath of 830 km. In Figure 3, the WFI camera set window is visible in the elongated slot underneath the two openings for the high-resolution PMC set. The four WFI cameras are mounted side by side in this slot, coverging the wide FOV (Field of View). The mounting on the platform pointing covers the range from -24º, -8º, +8º to +24ºas shown in Figure 18. Each camera has 4 multispectral bands using prism to realize beam-splitter. The spectral bands span from the visible (VIS) to the near infra-red (NIR).

Table 5: Parameters of the WFI instrumentation

Figure 18: Obervation scheme of the 4 WFI cameras (image credit: DFH)

Figure 19: GF-1 satellite on-orbit trace and swath of 2 HR (red) and 4 WFI (green) cameras, image credit: DFH

2) H. Qi, "China High-resolution Earth Observation System (CHEOS) and its Latest Development," Proceedings of the 51^st Session of Scientific & Technical Subcommittee of UNCOPUOS, Vienna, Austria, Feb. 11-22, 2014, URL: http://www.unoosa.org/pdf/pres/stsc2014/tech-47E.pdf

3) Guang Zhou, "Construction and Development of China High-Resolution Earth Observation System," 42nd session of the Coordination Group for Meteorological Satellites (CGMS), Guangzhou, China, 19-23 May 2014, URL: http://www.eumetsat.int/website/wcm/idc
/idcplg?IdcService=GET_FILE&RevisionSelectionMethod=LatestReleased
&Rendition=Web&dDocName=CWPT_1299

4) "Chiina Hiigh-resollutiion Earth Observatiion System (CHEOS) and iits Lastest Devellopment," The Earth Observation System and Data Center , CNSA, 2014-2, URL: http://www.oosa.unvienna.org/pdf/pres/stsc2014/tech-47E.pdf

5) Peter B. de Selding, "China Pushing Ahead on Hi-Res Satellite System," Space News, Feb. 28, 2014, URL: http://spacenews.com/article/civil-space/39665china-pushing-ahead-on-hi-res-satellite-system

6) Rui C. Barbosa, "China back in action with Long March 2D launch of Gaofen-1," NASA Spaceflight.com, April 25, 2013, URL:
http://www.nasaspaceflight.com/2013/04/china-back-in-action-long-march-2d-gaofen-1/

7) Chunling Lu, Zhaoguang Bai, "GF‐1 Satellite On‐Orbit Test and Evaluation," Proceedings of the 4S (Small Satellites Systems and Services) Symposium, Port Petro, Majorca Island, Spain, May 26-30, 2014

8) Stephen Clark, "Four satellites launched on China's Long March rocket," Spaceflight Now, April 26, 2013, URL: http://www.spaceflightnow.com/news/n1304/26longmarch/#.UXuGc0okS2o

9) Patrick Blau, "Long March 2D performs China's first Orbital Launch of 2013," Spaceflight 101, April 26, 2013, URL: http://www.spaceflight101.com/long-march-2d-gaofen-1-launch.html

10) Ming Li, Pan Teng, Cao Haiyi, "An Overview of Satellite Project of the National High Resolution Earth Observation System (NHREOS)," Proceedings of the 67th IAC (International Astronautical Congress), Guadalajara, Mexico, Sept. 26-30, 2016, paper: IAC-16,B1,2,1

11) Chunling Lu, Zhaoguang Bai, "Characteristics and Typical Applications of GF-1 satellite," Proceedings of the IGARSS (International Geoscience and Remote Sensing Symposium) 2015, Milan, Italy, July 26-31, 2015

12) "Chinese HD earth observation satellite comes into service," Space Daily, March 9. 2015, URL: http://www.spacedaily.com/reports
/Chinese_HD_earth_observation_satellite_comes_into_service_999.html

13) S. Cheng, "Introduction to Application Achievement of GF-1 and GF-2 Satellite," 52^nd session of the Scientific and Technical Subcommittee, UNOOSA (United Nations Office for Outer Affairs), Vienna, Austria, Feb. 2-13, 2015, URL: http://www.unoosa.org/pdf/pres/stsc2015/tech-63E.pdf

14) Cunling Lu, Zhaoguang Bai, Changjun Li, Damin Li, "GF-1 satellite high resolution & wide swath system design and technology characteristics," Proceedings of the 65^th International Astronautical Congress (IAC 2014), Toronto, Canada, Sept. 29-Oct. 3, 2014, paper: IAC-14-B4.4.2

15) "China's HD observation satellite opens its eyes," Space Daily, Dec. 31, 2013, URL: http://www.spacedaily.com/reports/Chinas_HD_observation_satellite_opens_its_eyes_999.html

16) "Gaofen-1 satellite goes into service," Xinhua, Dec. 31, 2013, URL: http://www.shanghaidaily.com/national/Gaofen1-satellite-goes-into-service/shdaily.shtml

17) "China's HD Earth Observation Satellite Put into Use," CRIEnglish.com, Dec. 30, 2013, URL: http://english.cri.cn/6909/2013/12/30/2743s805813.htm

18) "China publicizes Earth observation satellite's HD photos," Xinhua, June 6, 2013, URL: http://www.china.org.cn/china/Off_the_Wire/2013-06/06/content_29045699.htm

19) Information provided by Joaquin Guo, Representative of Latin America, China Great Wall Industry Corporation (CGWIC)

20) "Reception of the First Image Data from Gaofen-1," Institute of Remote sensing and Digital Earth (RADI), URL: http://english.radi.cas.cn/Research/RP/201307/t20130717_106431.html

21) Information provided by Chunling Lu of DFH (Dong Fang Hong) Satellite Co. Ltd., Beijing, China.
 

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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