A new instrument concept for a Static Fourier Transform Spectrometer has been developed and characterized by CNES. This spectrometer is based on a Michelson interferometer concept, but a system of stepped mirrors generates all interference path differences simultaneously, without any moving parts. The instrument permits high spectral resolution measurements (≈0.1 cm−1) adapted to the sounding and the monitoring of atmospheric gases. Moreover, its overall dimensions are compatible with a micro satellite platform.
The stepped mirrors are glued using a molecular bonding technique. An interference filter selects a waveband only a few nanometers wide. It limits the number of sampling points (and consequently the steps number) necessary to achieve the high resolution.
The instrument concept can be optimized for the detection and the monitoring of various atmospheric constituents. CNES has developed a version whose measurements are centered on the CO2 absorption lines at 1573 nm (6357 cm−1). This model has a theoretical resolution of 40 pm (0.15 cm−1) within a 5 nm (22.5 cm−1) wide spectral window. It is aimed at the feasibility demonstration for atmospheric CO2 column measurements with a very demanding accuracy of better than 1%.
Preliminary measurements indicate that, although high quality spectra are obtained, the theoretical performances are not yet achieved. We discuss the causes for the achieved performances and describe foreseen methods for their improvements.
The Multi-viewing ,Multi-channel, Multi-polarisation Imager (3MI) of the EUMETSAT Polar System - Second Generation (EPS-SG) is a two-dimensional push broom radiometer dedicated to aerosol characterisation for climate monitoring, air quality forecasting and Numerical Weather Prediction (NWP). The purpose of the 3MI concept is to provide a multi-spectral (from 410 to 2130 nm), multi-polarisation (-60°, 0°, and +60°), and multi-angular (10 to 14 views) image of the Earth outgoing radiance at the top of the atmosphere (TOA) in order to accurately measure the aerosol load and thereby resolve the directional anisotropy and the microphysical properties of aerosol. The 3MI heritage comes from the Polarisation and Directionality of the Earth's Reflectances (POLDER) and Polarisation and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL), with 3 instruments launched since 1996.
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.
KEYWORDS: Calibration, Sensors, Cameras, Photons, Signal to noise ratio, Digital cameras, Charge-coupled devices, CCD image sensors, Image sensors, Global Positioning System
This paper presents the characterization and calibration of a new digital modular camera call PELICAN (French acronym for "Plateforme Et Logiciels Informatiques de Cameras Aeroportees Numeriques"). This system has been developed in 2003 as an IGN-ONERA-CNES cooperation project. The basic configuration is a set of four optical heads each equipped with a 4096 × 4096 pixels CCD detector working in the visible and near IR spectral range (from 400 nm to 950 nm). This
sensor provides synchronous images achieved with a TDI-like control of the CCD to avoid smearing, thanks to GPS data. This paper gives an overview of the instrument, its calibration facility and our approach of calibration. The first step consists of modeling the sensor. It conducts to the calibration equation and the proper number of correction point to acquire. Characterization includes all the necessary measurements to validate the previous model. This process also gives us accurate visions of the sensor use extent. After a possible model adjustment, we acquire flat-field images in the whole
range of configuration. These images provide an inter-pixel sensitivity matrix. We also perform a spectral sensitivity
measurement and an acquisition on calibrated source. These last steps allow calculation of the absolute sensitivity. As an example of the versatility of the system, first results from an experiment over urban area (Capitoul campaign) are described. For this airborne campaign held in February 2004, the system simultaneously acquires images of eight narrow spectral bands of 20 nm width, with a 20 cm spatial resolution.
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