The China High-resolution Earth Observation System “CHEOS” or Gaofen is a Chinese civil earth observation project. It is driven by the Chinese space agency and the Chinese academy of science.
The aim of the program is the following:
- Building a high spatial, spectral and radiometric resolution earth observation capability
- Being weather and daytime independent in earth observation
- Providing global information on agriculture, disaster management, environment, natural ressources, etc.
- Improve international cooperation, especially in the Belt and Road Initiative (BRI)
The program was launched in 2010 and consists of a space segment as well as an aerial segment (stratospheric balloons and aircrafts as observing platforms). The program is comparable to the European earth observation program “Copernicus”, however the Chinese Gaofen program is thought to be also much more used in military applications due to the high spatial resolution of the sensors.
Satellites:
As of 2020 the Gaofen Constellation consisted of 20 satellites, most of them in low earth orbits. The platforms have an estimated life expectancy of 8 years.
Gaofen-1:
FirstSatellitof CHEOS, started on 26th of April 2013, with a high resolution multispectral sensor PMC-1 (GSD: 2 m PAN, 8 m MS), as well as an wide field camera (WFC) (GSD: 16 m).
Gaofen-1 (Nr. 2,3,4):
Follow up to the Gaofen-1, started in March 2018, also equipped with a PMC-1 sensor.
Gaofen-2:
Improved version von Gaofen-1, started on 19th of August 2014, equipped with a higher resolution sensor (PMC-2). The spatial resolution is 0.8 m (PAN) and. 3.24 m (MS). The tilting capability is 35°.
Gaofen-3:
First SAR (Radar) satellite in the series, started on 9th August 2016, equipped with a polarimetric C-band SAR with a spatial resolution choosable from 1 m to 500 m, depending on swath.
Gaofen-4:
First geostationary satellite in CHEOS, equipped with a multispectral sensor in VIS and Infrared. The satellite is positioned on 105.6° east.
Gaofen-5:
There are six different sensors equipped, for example a hyperspectral sensor with a spatial resolution of 30 m and a multispectral imager including a thermal IR band.
Gaofen-6:
Almost identical to Gaofen 1.
Gaofen-7:
The satellite has a stereo imaging capability aith a spectral resolution of 0.65 m, as well as a laser altimeter – and therefore is used for topographic mapping. It was started in November 2019.
Gaofen-8:
Almost identical to Gaofen-2, started in June 2015.
Gaofen-9 01:
Almost identical to Gaofen-2, started in September 2015.
Gaofen-9 (Nr. 2,3,4,5):
Almost identical to Gaofen-2, started between May and August 2020.
Gaofen-10 R:
Almost identical to Gaofen-2, started in October 2019.
Gaofen-11:
Almost identical to Gaofen-2, started in Juli 2018. Has a realys-capability.
Gaofen-11 02:
Almost identical to Gaofen-11, started in September 2020.
Gaofen-12:
Radar-satellite, almost identical to Gaofen-3, started in November 2019.
Gaofen-12 02:
like Gaofen-12, started inMarch 2021.
Gaofen-13:
Geostationary, comparable to Gaofen-4, started in October 2020.
Gaofen-14:
Similar to Gaofen-7, started in December 2020.
Gaofen-Duomo:
Started in July 2020, no other information available.
The 5 (known) ground segments are located in: Miyun (near Beijing) Kashgar (Xinjiang), Sanya (Hainan), Kunming Yunnan), und Kiruna (Sweden).
In a military context the sensors PMC-2 and the SAR are of high interest:
PMC-2:
| Band | Spectralrange [microm] | GSD [m] |
| Panchromatic | 0.450 – 0.900 | 0.8 |
| Blue | 0.450 – 0.520 | 3.24 |
| Green | 0.520 – 0.590 | 3.24 |
| Red | 0.630 – 0.690 | 3.24 |
| NIR | 0.830 – 0.890 | 3.24 |
The swath width is 45 km and the revisit time is 5 days (per satellite).
Image example (Gaofen 2):
SAR:
| Mode | Polarisation | Swath [km] | GSD [m] | |
| Spotlight | Single | HH, VV | 10 | 1 |
| Ultra-fine stripmap | Single | HH, VV | 30 | 3 |
| Fine stripmap | Dual | HH/HV, VH/VV | 50 | 5 |
| Wide finestripmap | Dual | HH/HV, VH/VV | 100 | 10 |
| Standard stripmap | Dual | HH/HV, VH/VV | 130 | 25 |
| Narrow ScanSAR | Dual | HH/HV, VH/VV | 300 | 50 |
| Wide ScanSAR | Dual | HH/HV, VH/VV | 500 | 100 |
| Global observation | Dual | HH/HV, VH/VV | 650 | 500 |
| Quad-pol stripmap | Quad | HH/HV/VH/VV | 30 | 8 |
| Wave | Quad | HH/HV/VH/VV | 5 | 10 |
| Expandedincidence angle | Quad | HH/HV/VH/VV | 130 | 25 |
| 80 | 25 |
Image example:
