Scientific results

The IASI (Infrared Atmospheric Sounding Interferometer) instrument was launched for the first time with the Metop A satellite in October 2006. It was financed by CNES and EUMETSAT. IASI is a Michelson interferometer used for atmospheric sounding. It can be used to measure spectra in the infrared range, covering wavelengths ranging from 3.62 µm to 15.5 µm. The contribution of IASI lies mainly in weather forecasting, atmosphere composition and climate monitoring.

Use in weather forecasting

The main purpose of the IASI mission is to provide temperature and humidity measurements. The IASI instrument provides a reading of the state of the atmosphere (temperature and humidity profiles) that is used as the initial state for weather forecasting. Forecasting precision is highly dependent on the precision of our knowledge of the initial state of the atmosphere. Performance objectives are 1K for temperature and 10% for humidity, with a vertical precision of 1 km.
The data is used operationally in most weather forecast centres worldwide, in both global and fine-scale models. For now, only 200 channels maximum are used. However, the impact of IASI on forecast quality is the greatest of all weather forecasting instruments currently used. The assimilation of IASI data is still the subject of research, in particular to make better use of cloudy observations, water vapour channels and profiles measured above continental surfaces.

CO Total column Courtesy Clerbaux et al., 2009

Use for atmosphere composition studies IASI also plays a major role in monitoring the composition of the atmosphere. Its excellent radiometric performance can be used to obtain the vertical composition or the integrated column of some 20 trace gases, in particular ozone and carbon monoxide. The latter is used mainly for air quality forecasts. IASI data has shown that it is possible to detect species that were believed to be undetectable from space, such as ammonia. It can also be used to detect certain events such as fires and volcanic eruptions.

Use for climate monitoring The performance of IASI and its long operating life (more than 15 years with three successive 5-year missions) can be used to construct time series of several key climate variables such as temperature, humidity, clouds, aerosols, the properties of continental surfaces and greenhouse gases influenced by human activity, such as CO2 and CH4. IASI makes it possible to monitor these variables by day or night, on land or at sea. In addition, the exceptional spectral and radiometric stability of IASI makes it the perfect instrument for inter-calibration of earth observation instruments within the framework of the international GSICS program.

Surface temperature July 2008 Courtesy LMD/CNRS