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.