Meteorological satellites have become an irreplaceable weather and ocean observing tool. There are totally 13 meteorological satellites that were launched into both sun-synchronous and geostationary orbit in China. All the satellites have been incorporated into the global constellations of operational meteorological satellites within the WMO framework.
As the second-generation geostationary-orbit meteorological satellite, FY-4 was launched on Dec.11, 2016. There are four payloads onboard. Two different type of infrared remote sensors, Advanced Geostationary Radiometric Imager (AGRI) and Geostationary Interfering InfraRed Sounder (GIIRS), are the main payloads on-board FY-4. AGRI has 14 spectral bands located on six focal plane assemblies (FPAs) with the highest spatial resolution of 500 meter, and will scan much faster than the current FY-2 radiometer. AGRI covers from visible band (0.45μm) to thermal infrared band (13.8μm). GIIRS is nadir and limb viewing infrared Fourier transform spectrometers (FTS), which could be able to provide sounding data with 0.625 cm-1 spectral resolution covering wavelengths in the midwave infrared (1650～2250 cm-1) and longwave infrared (700～1130 cm-1) to users, and to get the atmospheric temperature profile and humidity profile. China may be the first country that could get high spectral infrared data from both geostationary and polar-orbiting satellites.
Some tradeoffs have been made to build the infrared sensors. In accordance with specification and designing strategy, the following choices of single-pixel detector, linear detector and focal plane detectors, thermal cooler and mechanical cooler, different type of telescope, double-axis gimbaled mirror and single-axis scanning mirror, have been selected respectively. The characteristics of these infrared sensors, design overview conjoined with detector, cooling, optics, pointing, observation strategy, calibration strategy, etc. are introduced in this paper.