The IASI system aims at observing and measuring 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.

The global sounding and imaging mission has been recognized as having the highest priority for the EUMETSAT Polar System. IASI is a key element of the meteorological sounding package.

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 will be synchronised with those of the microwave instruments MHS and AMSU-A.

The currently 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.

The operation of IASI mission plan will includes three distinct phases after the launch. The first is the commissioning and in orbit validation phase which is anticipated to last six months. The pre-operational assessment phase follows. This second phase should covers 12 months. It will be succeeded by the operational phase for the rest of the life-time of METOP-A satellite.

Under nominal conditions starting with the pre-operational assessment phase the IASI system, composed of the IASI instrument and its ground segment, should allow a daily permanent coverage of at least 95 % of the earth without any significant systematic gap in coverage.

Over the Atlantic Ocean, Europe and the Mediterranean Sea the objective is to reach 99 % coverage per day.

The operational processing of IASI data on-ground should provide the users community with sounding data not later than 135 minutes after sensing. The software for this processing has been developped by CNES and provided to EUMETSAT for integration to the METOP satellite data processing operational center.