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.
IASI was successfully launched on MetOP A on 19 October 2006. After the in-orbit commissioning, the performances
of IASI were evaluated during the Cal/Val of level 1. Key parameters of instrument and on ground processing have been
fixed for optimal performance and best quality data delivery. The first spectra and images of level 1 products show all
the potential of IASI data for expected applications. Some illustrations are given here with maps of pseudo channels
sensitive to trace gases, atmospheric profiles or maps of surface temperature qualitatively compared to maps from
models. Level 2 processing to get these parameters has been implemented at Eumetsat and some products are currently
under validation. The quality of IASI data paves the way to additional very promising products. A thorough analysis of
cloud free spectra has been performed to extract the small signature of minor species like CFCs and HNO3. Nevertheless,
the main limitation of IASI data remains clouds. It is showed here with the cluster analysis of AVHRR data registered in
the IASI pixels and delivered as level 1 products that only a few cloud free pixels can used for full retrieval. A method
making use of the cluster information has been developed. It permits to strongly increase the statistics where clear
column profiles or columns above clouds can be retrieved. This scheme will be applied to the retrieval of the CO2 where
large data set are needed to extract information from the spectra.
The Infrared Atmospheric Sounding Interferometer (IASI) is a key payload element of the 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. The IASI measurement technique is based on passive IR remote sensing using an accurately calibrated Fourier Transform Spectrometer operating in the 3.7 - 15.5 μm spectral range and an associated infrared imager operating in the 10.3-12.5 μm spectral range. The optical configuration of the sounder is based on a Michelson interferometer. Interferograms are processed by the on-board digital processing subsystem which performs the inverse Fourier Transform and the radiometric calibration. The integrated infrared imager allows the co registration of the IASI sounder with AVHRR imager on-board METOP.
The first model (proto-flight) of IASI has successfully completed a verification program conducted at ALCATEL SPACE premises in Cannes. This paper provides a brief overview of the IASI mission, instrument architecture and key performances results. A companion paper1 by Alcatel provides more information on instrument design and development.
Satellite remote sensing measurements in the thermal IR spectrum have existed since the beginning of the space era with the first Tiros satellites in the sixties. The low spatial resolution data provided up to now have been mainly used for mesoscale applications in meteorology and oceanography. To study and understand on a local scale those natural phenomena which can be characterized by their radiative temperatures, the users need high spatial resolution data in multi-spectral channels with a good radiometric sensitivity. Thanks to recent progress in IR detector technology, these specifications will soon be satisfied. The IRSUTE (infra red satellite unit for terrestrial environment) instrument is designed to provide high spatial (50 m), multi-spectral (4 channels in the IR), high repetivity data with a good radiometric sensitivity. Moreover, the IRSUTE payload has to be compatible with the limited resources (mass, power, volume, ...) provided by a small satellite. The design of the instrument is based on the push-broom technique which uses IR-CCD linear array detectors positioned in the focal plane of a collecting telescope. The first results of a pre-feasibility study on the inboard instrument are presented.
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