IASI instrumentation

The Infrared Atmospheric Sounding Interferometer (IASI) is a spectrometer, which is an instrument that measures the spectral distribution of incident radiation. The instrument scans through the long slit opening visible on the nadir-facing side of the spacecraft to measure infrared radiation emitted by the Earth. The control electronics and the data processing equipment are located inside the satellite. IASI's large square radiator can be seen at the side adjacent to the flight direction. The main components are a scan mirror, an internal blackbody, an optical bench containing the interferometer, a passive thermal cooler housing the cold optics and the detectors and an electronic compartment where the corner cube mechanism electronics, the scan mechanism electronics and the main acquisition electronics are installed. The IASI is slightly larger than one cubic metre and weighs about 200 kilograms.

The instrument concept is based on the Michelson interferometer. Incident radiation is divided into two beams by a beam splitter where the first beam follows a path of constant length and the other is reflected by a moving corner cube and follows a path of variable length. An optical path difference can be measured when the two beam paths are recombined. From this, data on atmospheric temperature and humidity as well as other atmospheric parameters are derived.