The concept of IASI is based on the spectral decomposition of thermal heat emission from the Earth, performed with a Michelson interferometer. After an inverse digital Fourier transform and radiometric calibration, performed on board to control data flow, the calibrated spectra are transmitted to the ground sector. After the data inversion, temperature and water vapour profiles in the troposphere and lower stratosphere are established, as well as the quantification of atmospheric chemical components — such as ozone, carbon dioxide and methane — that play a basic role in tropospheric phenomena and the greenhouse effect.

The temperature of the troposphere and lower stratosphere is measured under cloud-free conditions with a vertical resolution of 1 km in the lower troposphere; a horizontal resolution of 25 km, and an accuracy of 1 kelvin. The humidity of the troposphere is measured under cloud-free conditions, with a vertical resolution of 1–2 km in the lower troposphere; a horizontal resolution of 25 km, with an accuracy of 10%. IASI also measures the fractional cloud cover and cloud top temperature and pressure.

The total amount of ozone under cloud-free conditions is measured with a horizontal resolution of 25 km and an accuracy of 5%, and total column-integrated content of CO, CH₄ and N₂O with an accuracy of 10% and a horizontal resolution of 100 km.