In-flight performance of the infrared atmospheric sounding interferometer (IASI) on METOP-A

The Infrared Atmospheric Sounding Interferometer (IASI) is a key element of the payload embarqued on METOP series of European meteorological polar-orbit satellites. IASI will provide very accurate data about the atmosphere, land and oceans for application to weather predictions and climate studies. IASI measurements will allow to derive temperature and humidity profiles with a vertical resolution of one kilometer and an average accuracy of one Kelvin and 10 % respectively. The IASI measurement technique is based on passive IR remote sensing using a precisely calibrated Fourier Transform Spectrometer operating in the 3.7 - 15.5 μm region and an associated infrared imager operating in the 10.3-12.5 μm region. The optical configuration of the sounder is based on a Michelson interferometer. Interferograms are processed by the onboard digital processing subsystem which performs the inverse Fourier Transform and the radiometric calibration. The integrated infrared imager allows the coregistration of the IASI soundings with AVHRR imager onboard METOP. The first METOP satellite was successfully launched on 19th of October 2006. This paper summarizes the IASI instrument radiometric, spectral and geometric performance as measured in orbit during the Calibration and Validation Phase. Instrument noise, spectral and radiometric calibration stability and spatial pointing accuracy are discussed as well as the performance of the Level 1 Processing chain.