The Infrared Atmospheric Sounding Interferometer (IASI) is a key element of the MetOp payload, dedicated to operational meteorology. IASI measurements allow to retrieve temperature and humidity profiles at a 1 km vertical resolution with an accuracy of respectively 1 K and 10%. The aim of this paper is to give a status of the instrument and to present some lessons learned after almost two years in orbit. As the first European infrared sounder, the IASI instrument has demonstrated its operational capability and its adequacy to user needs, with highly meaningful contributions to meteorology, climate and atmospheric chemistry studies. The in-flight performance of IASI is fully satisfactory. The sensitivity to radiative environment seems to be higher than expected: several SEU related anomalies were recorded, without any consequence on the instrument's health. The first decontamination since the commissioning phase was successfully performed in March 2008. The instrument globally shows a stable behaviour.
IASI is an infrared atmospheric sounder. It will provide meteorologist and scientific community with atmospheric spectra. The IASI system includes 3 instruments that will be mounted on the Metop satellite series, a data processing software integrated in the EPS (EUMETSAT Polar System) ground segment and a technical expertise centre implemented in CNES Toulouse.
The instrument is composed of a Fourier transform spectrometer and an associated infrared imager. The optical configuration is based on a Michelson interferometer and the interferograms are processed by an on-board digital processing subsystem, which performs the inverse Fourier transforms and the radiometric calibration. The infrared imager co-registers the IASI soundings with AVHRR imager (AVHRR is another instrument on the Metop satellite). The presentation will focus on the architectures of the instrument, the description of the implemented technologies and the measured performance of the first flight model.
CNES is leading the IASI program in association with EUMETSAT. The instrument Prime is ALCATEL SPACE.
Satellite radar altimetry, initially designed for studying ocean surface topography, demonstrated a strong potential for the continuous monitoring of ice sheets and land surfaces over the last 25 years. If radar altimetry is mostly used for its capacity to determine surface height, the backscattering coefficients provide information on the surface properties. Spatio-temporal variations of radar altimetry backscattering over land and ice sheets were related to the nature of the surface and its changes against time. This study presents the results of an along-track analysis of radar altimetry echoes over land, Antarctica and Greenland at Ku and S bands from June 2002 to July 2003 using the ERS-2 and ENVISAT datasets on their nominal orbit during the tandem phase of the two missions. Temporal average and deviations are presented at global scale for ascending and descending tracks for the two missions.
One way to calibrate space sensors on the visible part of the spectrum is to use acquisitions over Rayleigh scattering for
dark surface conditions. Oceanic sites are good candidates because of their behaviour in term of spatial homogeneity and
temporal stability. An appropriate selection is consequently required to identify the best oceanic areas. Nevertheless, the
knowledge of the surface reflectance of such sites remains a limitation while their stability (and/or homogeneity) is
usually not perfect. A previous study (Fougnie et al., 2002) has defined a selection of oceanic sites using one year of
SeaWiFS data and regarding their spatial homogeneity and temporal stability. A first characterization of their monthly
surface reflectances was derived (seasonal cycle) and used for several years as input for in-flight calibration processes.
The major oligotrophic sites are located in North/South Atlantic and Pacific oceans, in Indian ocean, and in the
Mediterranean Sea while some other mesotrophic sites were also defined for example in the Gulf of Mexico or Yucatan
strait. The goal of this study was to revisit the definition of these sites regarding their spatial homogeneity and to analyze
the annual cycle over 9 years of L3B R-2009 SeaWiFS products. Site behaviours are accurately defined with these
longer time series, hence new recommendations are drawn for all sites and an updated climatology is proposed to be used
for future in-flight calibrations.
IASI (Infrared Atmospheric Sounding Interferometer) is an infrared atmospheric sounder. The IASI instrument is
currently operating on the Metop-A satellite (launched in October 2006). The core of the instrument is composed of a
Fourier transform infrared spectrometer. The detection chain of the spectrometer includes 3 bands to cover the 3.4 to
15.5 μm spectral range. For each band, the IR detection is made by a 2 x 2 pixels array operating at ~93K. This paper
presents an analysis of the radiation tolerance of the infrared detectors for each band. On ground, radiation tests have
been performed to address sensitivity to gamma-rays and protons radiations. A special care has been taken to keep the
detectors at cold temperature during tests. Performance evolutions (responsivity, relative spectral response, noise,...
tested in CNES facilities) before and after radiations are given. First in orbit impacts of the radiations are also reviewed.
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 purpose of this paper is to present the IASI overall architecture and the IASI functional chain including optics and interferometer, analogue to digital acquisition, on board and on ground digital processing. It points out special features of IASI's design and critical technologies. The IASI technical description is followed by a development status including activities on breadboards, engineering models, proto flight and flight models with emphasis put on achieved critical steps. A companion paper by CNES will provide detailed information on the IASI mission and instrument key performance achievement.
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.