Gaofen () is a series of Chinese

high-resolution Image resolution is the level of detail of an image. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail. Image resolution can be measured in various ways. Resolution quantifies ...

Earth imaging satellites launched as part of the China High-resolution Earth Observation System (CHEOS) program. CHEOS is a state-sponsored, civilian Earth-observation program used for

agricultural Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...

disaster A disaster is an event that causes serious harm to people, buildings, economies, or the environment, and the affected community cannot handle it alone. '' Natural disasters'' like avalanches, floods, earthquakes, and wildfires are caused by na ...

resource ''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...

, and

environmental monitoring Environmental monitoring is the processes and activities that are done to characterize and describe the state of the environment. It is used in the preparation of environmental impact assessments, and in many circumstances in which human activit ...

. Proposed in 2006 and approved in 2010, the CHEOS program consists of the Gaofen series of space-based

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

s, near-space and airborne systems such as

airship An airship, dirigible balloon or dirigible is a type of aerostat (lighter-than-air) aircraft that can navigate through the air flying powered aircraft, under its own power. Aerostats use buoyancy from a lifting gas that is less dense than the ...

s and

UAVs An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers onboard, but rather is controlled remotely or is autonomous.De Gruyter Handbook of Drone ...

, ground systems that conduct data receipt, processing, calibration, and taskings, and a system of applications that fuse observation data with other sources to produce usable information and knowledge. Although the first seven Gaofen satellites and their payloads have been heavily detailed, little to no details on Gaofen 8 and later satellites have been revealed prompting suggestions that Gaofen satellites may be dual purpose supporting both civilian and military missions. In 2003, the

China National Space Administration The China National Space Administration (CNSA) is a government agency of the People's Republic of China headquartered in Haidian District, Haidian, Beijing, responsible for civil space administration and international space cooperation. These ...

(CNSA) agreed with

Roscosmos The State Corporation for Space Activities "Roscosmos", commonly known simply as Roscosmos (), is a State corporation (Russia), state corporation of the Russian Federation responsible for space science, space flights, List of space agencies, c ...

to share Gaofen data for data from Russia's Earth observation satellites of similar capability. This agreement was expanded in August 2021 when leaders from

BRICS BRICS is an intergovernmental organization comprising ten countriesBrazil, Russia, India, China, South Africa, Egypt, Ethiopia, Indonesia, Iran and the United Arab Emirates. The idea of a BRICS-like group can be traced back to Russian foreign ...

space agencies Government space agencies, established by the governments of countries and regional agencies (groupings of countries) are established as a means for advocating for engaging in activities related to outer space, exploitation of space systems, ...

agreed to share space-based

remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...

data.

Notable satellites

Gaofen-5

Gaofen-5 has been lauded as the "flagship of the environment and atmosphere observation satellite in the CHEOS program". Launched on 8 May 2018 from

Taiyuan Satellite Launch Center The Taiyuan Satellite Launch Center (TSLC) also known as ''Base 25'' (), is a People's Republic of China space and defense launch facility (spaceport). It is situated in Kelan County, Xinzhou, Shanxi Province and is the second of four laun ...

(TSLC) into

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

, Gaofen-5 carries six

payloads Payload is the object or the entity that is being carried by an aircraft or launch vehicle. Sometimes payload also refers to the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of t ...

: an Advanced Hyperspectral Imagery sensor (AHSI), Atmospheric

Infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

Ultraspectral Sensor (AIUS), Directional

Polarization Polarization or polarisation may refer to: Mathematics *Polarization of an Abelian variety, in the mathematics of complex manifolds *Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...

Camera (DPC), Environment Monitoring Instrument (EMI), Greenhouse-gases Monitoring Instrument (GMI), and Visual and Infrared Multispectral Sensor (VIMS). The Advanced Hyperspectral Imagery (AHSI) sensor payload aboard Gaofen-5 claims to be the first space-based hyperspectral imaging sensor utilizing both convex grating spectrophotometry and a three concentric-mirror (Offner) configuration. The AHSI uses spectrophotometry to measure the light spectra reflected, transmitted, or emitted by an imaged object to detect or identify objects on the ground. In civilian applications, the AHSI allows analysts to conduct

and

discovery while in a military application would allow analysts to detect and identify an adversary's equipment or spot non- multi-spectral camouflage. AHSI has a 30 meter

spatial resolution In physics and geosciences, the term spatial resolution refers to distance between independent measurements, or the physical dimension that represents a pixel of the image. While in some instruments, like cameras and telescopes, spatial resoluti ...

and 5 nanometer

spectral resolution The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum. It is usually denoted by \Delta\lambda, and is closely related to the resolvi ...

in the visible, near-infrared (NIR), and short-wave infrared (SWIR)

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

ranges. The Atmospheric Infrared Ultraspectral Sensor (AIUS) payload aboard Gaofen-5 is China's first

hyperspectral Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifyi ...

occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...

spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...

meaning it measures the spectra of imaged atmospheric particles between the sensor and the Sun. AIUS allows scientists to monitor

atmospheric circulation Atmospheric circulation is the large-scale movement of Atmosphere of Earth, air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth. The Earth's atmospheric circulation varies fro ...

by tracing (

water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...

), temperature, pressure, and various carbon and halogen-containing gas pollutants such as

chlorofluorocarbon Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly Halogenation, halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F). They are produced as volatility (chemistry), volat ...

s (CFCs),

dinitrogen pentoxide Dinitrogen pentoxide (also known as nitrogen pentoxide or nitric anhydride) is the chemical compound with the formula . It is one of the binary nitrogen oxides, a family of compounds that contain only nitrogen and oxygen. It exists as colourless c ...

, and chlorine nitrate. A

Michelson interferometer The Michelson interferometer is a common configuration for optical interferometry and was invented by the American physicist Albert Abraham Michelson in 1887. Using a beam splitter, a light source is split into two arms. Each of those light be ...

, AIUS images wavelengths between 2.4 and 13.3

micrometers The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

(near to mid-wave

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

) at a 0.3

centimeter upright=1.35, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is in-between 1 meter to 1 millimeter. A centimetre (International spelling) or centimeter (American ...

resolution and a ±10°

field of view The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...

. Gaofen-5's Directional Polarimetric Camera (DPC) is China's first space-based multi-angle polarimetric camera. Prior to GF-5's launch, in September 2016, China had experimented with polarimetric imaging in 2016 aboard the

Tiangong-2 Tiangong-2 () was a Chinese space laboratory and part of the Project 921-2 space station program. Tiangong-2 was launched on 15 September 2016. It was deorbited as planned on 19 July 2019. Tiangong-2 was neither designed nor planned to be a ...

space laboratory and launched its Cloud and Aerosol Polarimetric Imager (CAPI) aboard TanSat in December of that year. CAPI imaged clouds within 670 and 1640

nanometer 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling Despite the va ...

channels but was restricted to fixed-angle imaging. The DPC aboard Gaofen-5 enables

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

in three polarized bands (90, 670, and 865 nm; polarized at 0°, 60°, and 120°) and five non-polarized bands (443, 565, 763, 765, and 910 nm), all wavelengths from

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

near-infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

(NIR). A step motor rotates the 512 × 512

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

charge-coupled device A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...

(CCD) imager ±50° providing a 1,850 km swath of

imagery Imagery is visual symbolism, or figurative language that evokes a mental image or other kinds of sense impressions, especially in a literary work, but also in other activities such as. Imagery in literature can also be instrumental in conveying ...

at 3.3 km resolution.

Satellites

Since the program's start in 2013, the People's Republic of China has launched 32 Gaofen-series satellites with only one launch failure. Jilin-1 satellites described as 'Gaofen' are not part of the government's Gaofen series, rather are described as having high resolution ().

References

{{CNSA space program, state=collapsed Earth observation satellites of China Satellite series Spacecraft launched by Long March rockets

Notable satellites

Gaofen-5

Satellites

See also

References