Gaofen

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 (TSLC) into Sun-synchronous orbit, Gaofen-5 carries six payloads: an Advanced Hyperspectral Imagery sensor (AHSI), Atmospheric Infrared Ultraspectral Sensor (AIUS), Directional Polarization Camera (DPC), Environment Monitoring Instrument (EMI), Greenhouse-gases Monitoring Instrument (GMI), and Visual and Infrared Multispectral Sensor (VIMS).[2][9]

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.[10] 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.[10] In civilian applications, the AHSI allows analysts to conduct environmental monitoring and resource discovery while in a military application would allow analysts to detect and identify an adversary's equipment or spot non-multi-spectral camouflage.[10][11][12] AHSI has a 30 meter spatial resolution and 5 nanometer spectral resolution in the visible, near-infrared (NIR), and short-wave infrared (SWIR) wavelength ranges.[12]

The Atmospheric Infrared Ultraspectral Sensor (AIUS) payload aboard Gaofen-5 is China's first hyperspectral occultation spectrometer meaning it measures the spectra of imaged atmospheric particles between the sensor and the Sun.[13][14] AIUS allows scientists to monitor atmospheric circulation by tracing H
₂O (water vapor), temperature, pressure, and various carbon and halogen-containing gas pollutants such as chlorofluorocarbons (CFCs), dinitrogen pentoxide, and chlorine nitrate.[14][15] A Michelson interferometer, AIUS images wavelengths between 2.4 and 13.3 micrometers (near to mid-wave infrared) at a 0.3 centimeter resolution and a ±10° field of view.[14]

Gaofen-5's Directional Polarimetric Camera (DPC) is China's first space-based multi-angle polarimetric camera.[9] Prior to GF-5's launch, in September 2016, China had experimented with polarimetric imaging in 2016 aboard the Tiangong-2 space laboratory and launched its Cloud and Aerosol Polarimetric Imager (CAPI) aboard TanSat in December of that year.[9][16] CAPI imaged clouds within 670 and 1640 nanometer channels but was restricted to fixed-angle imaging. The DPC aboard Gaofen-5 enables atmospheric spectroscopy 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 to near-infrared (NIR). A step motor rotates the 512 × 512 pixel charge-coupled device (CCD) imager ±50° providing a 1,850 km swath of imagery at 3.3 km resolution.[9][17]