Elodie Cansot

Static Fourier transform spectroscopy breadboards for atmospheric chemistry and climate

New types of sounders dedicated to selected species could be used on small satellites to monitor atmospheric chemistry with simpler instruments. A new kind of Fourier transform spectrometer has been patented by CNES a few years ago. Based on a static configuration, two projects are being studied at CNES with laboratory breadboards. One is dedicated to CO2 concentration monitoring in near infrared. The other one works in thermal infrared to study CO and O3 atmospheric profiles. MoLI breadboard, with a new highly integrated interferometric core, will be used for a long time measurement of CO2 concentration. MOPI is another breadboard under development to transpose this concept in thermal infrared during the SIFTI phase A study. These new generation spectrometers consist in a Michelson interferometer with staircase mirrors assembled by molecular adhesion. They are adapted to narrow spectra sounding from space and could lead to totally static and highly stabilized instruments.

Static Infrared Fourier Transform Interferometer (SIFTI):Benefits of Phase Modulation Processing

SIFTI (Static Infrared Fourier Transform Interferometer) is a high resolution spectrometer, part of the TRAQ payload. This paper presents a description of this instrument and gives a preliminary radiometric performance in presence of phase modulation.

Progress in static fourier transform infrared spectroscopy: assessment of sifti preliminary performances

The concept of static Fourier transform interferometry at thermal infrared wavelengths is well suited in the case of narrow spectral bands that are looked at for targeted molecular species as CO and O3 for pollution and air quality monitoring, or H20 and CO2 for weather forecast, down to the troposphere. It permits a high spectral resolution and a very good radiometric performance, with the advantage of a static interferometer, including no moving part. Along with other molecules sounded in the UV-VIS domain, as for instance in the TRAQ mission, SIFTI will provide scientists with a complete set for pollution measurements and air quality survey. Our paper presents the principles of static Fourier transform spectrometry, the work led on the instrument performance model and our study of the SIFTI instrument. We describe the instrument, its main dimensions and characteristics, and its architecture and major subsystems. We eventually make a preliminary survey of the SIFTI performance budget items. As a conclusion, we introduce the future CNES phase A study of this instrument that is started in 2006

A new space instrumental concept based on dispersive components for the measurement of CO2 concentration in the atmosphere

Measuring the concentration of greenhouse gases from space is a current challenge. This measurement is achieved via a precise analysis of the signature of chemical gaseous species (CO2, CH4, CO, etc.) in the spectrum of the reflected sunlight. First at all, two families of spectrometers have been studied for the MicroCarb mission. The first family is based on the phenomena of interference between two radiation waves (Michelson Interferometer). The second family is based on the use of dispersive optical components. The second family has been selected for the forthcoming studies in the MicroCarb project. These instruments must have high radiometric and spectral resolutions, in narrow spectral bands, in order to discriminate between absorption lines from various atmospheric chemical species, and to quantify their concentration. This is the case, for example, for the instrument onboard the OCO-2 satellite (NASA/JPL). Our analysis has led us to define a new instrumental concept, based on a dispersive grating spectrometer, with the aim of providing the same accuracy level as the OCO-2, but with a more compact design for accommodation on the Myriade Evolution microsatellite class. This compact design approach will allow us to offer a moderate-cost solution to fulfil mission objectives. Two other studies based on dispersive grating are in progress by CNES prime contractors (ASTRIUM and THALES ALENIA SPACE). A summary of the main specifications of this design will be described, in particular the approach with the so-called “merit function”. After a description of such a space instrument, which uses a specific grating component, a preliminary assessment of performances will be presented, including the theoretical calculations and formula. A breadboard implementation of this specific grating has allowed us to show the practicality of this concept and its capabilities. Some results of this breadboard will be described. In addition, an instrument simulator is being developed to validate the performances of this concept. A grating component prototype has been built, and the specifications, together with the expected performances, will be described, in particular the polarisation ratio. Some elements about detectors will be also given regarding their suitability for the mission. This preliminary design is encouraging and shows that such a spectrometer may be compatible with a microsatellite platform (low mass, low power and compact design). Some prospects of improvements will also be considered.

Design and performances of microcameras and photometers instruments on TARANIS satellite for an advanced characterization of Transient Luminous Event in the upper atmosphere

The TARANIS mission aims at studying upper atmosphere coupling with a scientific nadir-pointing microsatellite - CNES Myriade family – at a low-altitude orbit (700 km). The main objectives are to measure the occurrence of Transient Luminous Event (TLE), impulsive energetic optical phenomena generated by storms according to recently discovered process, and Terrestrial Gamma-ray Flash (TGF), their emissions and trigger factors. TARANIS instruments are currently in manufacturing, assembly, integration and testing phase. The MicroCameras and Photometers instruments (MCP) are in charge of the remote sensing of the sprites and the lightning in optical wavelengths. MicroCameras instrument [MCP-MC] is an imager in the visible and Photometers instrument [MCP-PH] is a radiometer with four bands from UV to NIR, able to detect TLEs on-board and to trigger the whole payload. The satellite will provide a complete survey of the atmosphere in low resolution together with a high resolution data of sites of interest automatically detected on board. For MC and PH instruments, CEA defined scientific needs and is in charge of processing data and providing scientific results. CNES described the technical requirements of these two instruments and will run in-flight commissioning. Design, manufacturing and testing is under responsibility of Sodern for MicroCameras and Bertin Technologies for Photometers. This article shortly describes physical characteristics of TLEs and presents the final design of these instruments and first measured performances.

From the Concept to the Definition of the SIFTI Instrument: Static Infrared Fourier Transform Interferometer

SIFTI, a static interferometer using a pair of crossed staircase fixed mirrors, will provide high quality TIR spectra of O3and CO. At phase A mid-term, we review main technical choices, preliminary budgets and performances.