This paper presents a set of developed tools and methods for the stray light analysis of the Compact Gas Imager, a new sensor concept to capture images of gases, featuring a peculiar optical concept.The disruptive optical concept requires an adaptation of existing tools and the development of new technics for accurate stray light analysis.The described approach consists in deriving the stray light requirements from the requirements for the gas concentration by use of theoretical models and a set of approximations.The coupling of analytical models implemented in MatLab with conventional FRED modeling allows the assessment of stray light performance, i.e. the estimate of the impact of ghost (parasite interferograms) and diffuse stray light on the Compact Gas Imager performance.The analysis of the simulation results highlights the design changes and countermeasures required to achieve the system performance objectives.The Compact Gas Imager concept associates interferometric and multispectral push broom imager technologies, thus the stray light methods and techniques discussed in the paper are suitable for a wide range of space applications.

The paper presents the results of the 2021 CarbonCGI project, specified by ESA Future Earth Observation department, dedicated to high-resolution observations of GHG (Greenhouse Gas) with CGI (Compact Gas Imager). CarbonCGI aims at detecting and characterizing faint anthropogenic emissions of Carbon dioxide and Methane gas, from low orbit satellite to complement and extend CO2M mission [1]. CGI are developed in an integrated team of scientists and engineers involved in the framework of CarbonCGI project, the IRT (Research and Technological Institute) NS3 (New Space Small Sensor) project and the scientific activities of the industrial chair TRACE [2]. Compact Gas Imagers developments cover the atmospheric transport inverse modelling (level 4), the radiative transfer modelling (level 2), the simulation of acquisition chain, data correction, registration and calibration, as well as detailed design of sensor and critical components (level 0-1).

The SIFTI (Static Infrared Fourier Transform Interferometer) instrument aims at supporting an important part in a mission for atmospheric pollution sounding from space, by providing high spectral resolution and high Signal to Noise Ratio spectra of the atmosphere. They will allow to resolve tropospheric profiles of ozone (03) and carbon monoxide (C0), especially down to the planetary boundary layer (PBL), an altitude region of very high interest, though poorly monitored to date, for air quality and pollution monitoring. The retrieved profile of ozone, resp. C0, will contain 5 to 7, resp. 2.5 to 4, independent pieces of information. The French space agency CNES (Centre National d'Etudes Spatiales) has proposed and is studying an instrument concept for SIFTI based on a static interferometer, where the needed optical path are generated by a pair of crossed staircase fixed mirrors (replacing the moving reflector of dynamic Fourier transform interferometers like IASI or MIPAS). With the SIFTI design, a very high spectral resolution (~0.1 cm-1 apodised) is achieved in a very compact optical setup, allowing a large throughput, hence a high SNR. The measurements are performed in the 9.5 μm band for 03 and in the 4.6 μm band for C0. The science return of the sounder can be further increased if an "intelligent pointing" process is implemented. This consists in combining the TIR sounder with a companion TIR imager, providing information on the cloud coverage in the next observed scene. 0nboard, real-time analysis of the IR image is used to command the sounder staring mirror to cloud free areas, which will maximize the probability for probing down to the surface. After the first part of the phase A, the architecture of SIFTI was studied as a trade-off between performance and resource budget. We review the main architecture and functional choices, and their advantages. The preliminary instrument concept is then presented in its main aspects and in terms of main subsystem functions. The preliminary budgets of mass, volume, size and power are also evaluated. Eventually the science performances are estimated, at instrument level and at mission level, and are compared to the specifications. To finish, the ways forward are discussed.

This paper reviews the performance of the serie s of 3 Infrared Atmospheric Sounding Interferometer instruments. It provides also a first view on the flight performance of the IASI instrument on METOP A.

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 (EUMETS AT 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 coregisters :he 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.

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 mum spectral range and an associated infrared imager operating in the 10.3-12.5 mum 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 paper(1) by Alcatel provides more information on instrument design and development.

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(1).

The Infrared Atmospheric Sounding Interferometer (LASI), is part of the operational meteorological payload managed by EUMETSAT. The baseline platform for the first flight model of the instrument is the METOP-1 polar platform to be launched during 2002.IASI consists of a Fourier Transform Spectrometer (FTS) based on a Michelson Interferometer coupled to an Integrated Imaging System (IIS) which allows characterisation of cloudiness inside the FTS field of view. LASI will provides mainly H2O and temperature profiles in the free Troposphere and lower Stratosphere with 1 degrees K/1Km vertical resolution in the low troposphere.IASI phase B is running under CNES management. This paper gives the present status of LASI design and associated performances. (C) 1997 International Astronautical Federation. Published by Elsevier Science Ltd.

This paper introduces the 'complex instruments ranking with a new computational environment' or CIRCE software tool for aiding elaboration and exploitation of analytic models for performance management of optical instruments. CIRCE is currently developed by the optical instrument preliminary design team at the Aerospatiale Company's Cannes, France, Center, in cooperation with the Institut National de Recherche en Informatique et Automatique' or INRIA at the nearby Science Park of Sophia Antipolis. As a multiprogram tool, CIRCE incorporates the requirements at all stages of optical instrument development, from conception through manufacturing. It affords an original approach to creation and operation of performance models that facilitates know- how conservation through introduction of the notions of concepts (relations bases) and models (computation tree). It eases out the everyday tasks of engineers owing to generating capabilities for performance budgets or parametric analyses and to automatic numeric code generation.

From the functional analysis of the field-widened Michelson interferometer developed by A. Girard in 1970, this paper investigates the design of a new generation of interferometer with two input and output channels, combining the advantages of a simplified optical design with highly compact geometry and enhanced system performance. The optical design is characterized as follows: direct location of the interferometer in the front-end optics' focal plane, location of the fringes outside the interferometer (thereby directly over the detector plane), and optimization capability with a relatively low aperture number. The system-level performance of an on-board imaging Fourier Transform Spectrometer (FTS) based on such an interferometer is discussed.

The SIFTI instrument is presented, in particular the program, the mission, and the concept of this new type of sounder, and its preliminary performances. Developed by CNES for the monitoring of atmospheric pollution (ozone and carbon monoxide), the concept is based on static Fourier transform interferometry, which permits to get an interferogram with no translation mechanism in the interferometer. Very good radiometric performances are foreseen, and a high spectral resolution is obtained. The concept is well suited to get high performance spectra in narrow bands.