IASI – MetOp's key instrument

IASI scanning principle
19 July 2006

In a series of articles focusing on MetOp's European instruments, we take a look at the innovative IASI (Infrared Atmospheric Sounding Interferometer) – arguably the most sophisticated instrument in the payload.

Developed by the French Space Agency CNES, IASI is a state-of-the-art, sophisticated sounding instrument that will be used for global measurements of atmospheric temperature and moisture with unprecedented accuracy and spectral resolution to improve weather prediction.

Making a significant technological step forward, this instrument is also destined to provide a wealth of data on various components of the atmosphere to further our understanding of atmospheric processes and the interactions between atmospheric chemistry, climate and pollution. In addition, the IASI will deliver data on land-surface emissivity and sea-surface temperature (in cloud-free conditions).

IASI data product profile
IASI data product profile

IASI's ability to detect and accurately measure the levels and circulation patterns of gases that are known to influence the climate will therefore significantly contribute to climate change monitoring.

From MetOp's polar orbit at an altitude of about 800 km, the IASI instrument observes the Earth up to an angle of 48.5° perpendicular to both sides of the satellite track, which corresponds to a swath width of about 2,000 km on the ground so that global coverage will be achieved in 12 hours.

The instrument is a Fourier Transform Spectrometer based on a Michelson Interferometer coupled to an integrated imaging system that observes and measures infrared radiation emitted from the Earth. The optical interferometry process offers fine spectral samplings of the atmosphere in the infrared band between the wavelengths of 3.2 and 15.5 microns.

This enables the instrument to establish temperature and water vapour profiles in the troposphere and the lower stratosphere, as well as measure concentrations of ozone, carbon monoxide, methane and other compounds.

IASI will measure the infrared radiation emitted by the Earth
IASI will measure the infrared radiation emitted by the Earth

For optimum operation, the IASI measurement cycle is synchronised with that of the AMSU-A1 and -A2 (Advanced Microwave Sounding Units) – two of the U.S. instruments provided by the National Ocean and Atmospheric Administration (NOAA).

The instrument should provide nearly an order of magnitude improvement in the vertical resolution of temperature and humidity profiles in the atmosphere, which will result in significant improvements in weather forecasts.

MetOp's European instruments:

ASCAT (Advanced Scatterometer) to measure wind speed and direction over the ocean.

GOME-2 (Global Ozone Monitoring Experiment-2) to measure concentrations of atmospheric ozone and other gases.

GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) to measure atmospheric temperature and humidity.

IASI (Infrared Atmospheric Sounding Interferometer) to measure atmospheric temperature and moisture, and trace gases such as carbon monoxide, nitrogen oxides, methane, ozone.

MHS (Microwave Humidity Sounder) to measure atmospheric humidity and temperature.

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