The IASI instrument observes and measures twice a day the spectrum of infrared radiation emitted by the Earth from a low altitude sun-synchronous orbit, over a swath width of 2000 km. These measurements are compatible in terms of sampling, resolution, accuracy and overall performances with the mission objectives of providing information on:

Profiles of temperature in the troposphere and lower stratosphere with an accuracy of 1 Kelvin, a vertical resolution of 1 km in the low troposphere and an horizontal sampling of 25 km.
Profiles of water vapour in the troposphere with an accuracy of 10% on relative humidity, a vertical resolution of 1 km in the lower troposphere and an horizontal sampling of 25 km.
Total amount of ozone with an accuracy of 5% and an horizontal sampling of typically 25 km, possibly also ozone vertical distribution with an accuracy of 10% and a vertical resolution providing two or three pieces of independent information.
Fractional cloud cover and cloud top temperature/pressure.
Sea and land surface temperatures.

IASI is a key element of the meteorological sounding package of EUMETSAT Polar System (EPS).

Some of the IASI features have been adjusted to be compatible to the other meteorological instruments. This refers to the simultaneous operation and identical geographical coverage for all instruments and co-registration between the infrared (IASI, HIRS) and microwave (AMSU-A, MHS) instruments.

Furthermore, co-registration of 1 km is required between the IASI sounder and the AVHRR imager. The IASI scan pattern have been synchronised with those of the microwave instruments MHS and AMSU-A.

The defined target life time for IASI is five years. The probability of IASI to being fully functional and operating without significant loss in performance after five years in orbit operation must be at least 0.8. For METOP-A, to this day, the 5 years ended. No redundancy nor performance decrease were reported during the successive REVEX (Exploitation Review) for the instrument.

The operation of IASI mission plan includes two distinct phases after the launch. The first one is the functional in-flight commissioning (duration for METOP-A: 10 weeks), and the second one is the CAL/VAL (duration for METOP-A: 25 weeks). The CAL/VAL enabled to disseminate the products to a restricted scientific community (early dissemination) since May 24th, 2007. The operational phase began on July 19th, 2007 and will last until the rest of the life-time of METOP-A satellite.

Very quickly, the IASI system, composed of the IASI instrument and its ground segment, enabled a daily permanent coverage of at least 95 % of the earth without any significant systematic gap in coverage was performed.

Over the Atlantic Ocean, Europe and the Mediterranean Sea the objective was to reach 99 % coverage per day. This objective has been attained.

The operational processing of IASI data on-ground provides the users community with sounding data not later than 135 minutes after sensing. The software for this processing has been developed by CNES (L1/PPF as known as OPS) and provided to EUMETSAT that integrated it to the METOP satellite data processing operational center.