We are developing a lightweight Raman imager for detecting harzardous chemical compounds on surfaces in emergency settings such as industrial accidents, terrorist attacks, and chemical warfare. Our instrument is based on a compact Fourier-Transform hyperspectral sensor which records interferograms used as signatures of chemicals compounds. Two important challenges relating to the detection of small amounts of chemicals with our device are (i) crosstalk artefacts degrading the reproducibility of the measurements, and (ii) the mixture of signatures from target compound and substrate material. We report on advances on crosstalk correction, and chemical detection by linear unmixing of the signatures. The system is demonstrated on the detection of two organophosphorus compounds on PMMA, a polymer with mild Raman signal.
Estimating emissions of the main greenhouse gases (such as CO2 and CH4) is a challenge in studying climate change. The European project called SCARBO, which involves several partners, aims at evaluating the feasibility of a low-cost constellation of small satellites onboarding small instruments, which could be capable of quantifying greenhouse gases. In this context, we propose NanoCarb, a miniature snapshot Fourier-transform imaging spectrometer concept dedicated to the measurement of two greenhouse gases: CO2 and CH4. Its compact design makes it a good candidate for small satellites. It is based on a multi-channel architecture which provides a sparse interferometric sampling strategy. This multi-channel design only involves two specific optical components: a microlens array and an interferometric plate, which is a stepcase phase plate. We have developed and assembled two NanoCarb prototypes which have been experimentally validated through a dedicated airborne campaign. This paper focuses on the design and laboratory calibrations of the two prototypes. The tests include both imaging and spectral features of the instruments. An adequate laboratory calibration is essential to process the data acquired by the prototypes during the airborne campaign. Experimental results show the good quality of the prototypes.
In the context of the creation of a Distributed Space Weather Sensor System (D3S), the European Space Agency (ESA) is planning to fly a small payload for the monitoring of the auroral emissions with the project Wide Field Auroral Imager (WFAI). In order to meet ESA's requirements for an Auroral Optical Spectral Imager (AOSI), CSUG will build a breadboard as a proof of concept based on Imager Spectrometer on Chip (ImSPOC) technology.
Imaging Spectrometer on Chip (ImSPOC) technology consists of a matrix composed by multiple, low finesse, Fabry-Perot modules mounted in one unique structure. Each of these Fabry-Perot has a fixed optical path difference distributed between optical contact up to maximum elevation in order to have the desired spectral resolution and the spectral coverage. So, in one snapshot it is possible to ""scan"" several optical path differences and reconstruct the spectrum for each point of the field of view. The advantage of this technology is to reduce the mass and dimensions but also that it collects sufficient number of photons allowing the observation of the faintest aurora (Non visible with naked eye) with short integration time. This makes it a particularly well-suited technology for small satellite payload design in the framework of polar lights monitoring.
We present here the optimization of the ImSPOC technology in the context of WFAI mission. This optimization allows us to recorded polar lights spectra in the wavelength range of 350 to 950 nm within an exposure between 10 and 60 s. The field of view of the instruments is 56.7° × 56.7°, obtained by combination of 9 individual modules with small dimension (one module fits in a 60 × 45 × 55 mm3 box). The simulated performances of the instrument are really encouraging. The spectrometer must have a spectral resolution of 1 nm at 350 nm.
Silvère Gousset, Juana M. Rodrigo, Etienne Le Coarer, Hélène Ehrhardt, Eric Stadler, Zoltán Hubert, Yves Magnard, Laurence Croizé, Yann Ferrec, Florence de la Barrière, Roland Domel, Christophe Coudrain, Remi Gouyon, Mathieu Chambon, Philippe Perrault, Jumana Boussey, Cécile Gourgon, Marie Panabière, Nadine Gerges
The Space CARBon Observatory (SCARBO) European program aims at assessing the monitoring of anthropogenic emissions of Green House Gas (GHG) with the uncovered goal of a sub-daily revisit of the Earth at an affordable cost. One of the main project scopes is the feasibility study of a hybrid constellation including both high accuracy reference missions (Copernicus CO2M or CNES MicroCarb mission) and 24 small-satellites onboarding innovative miniaturized payloads. The key GHG-sensor of the smallsat constellation is the NanoCarb concept, an unprecedently kilogram-class Fourier Transform imaging spectrometer. We are reporting here some preliminary experimental results from a demonstration airborne campaign. A low cost, 2-bands prototype designed for CO2 and CH4 measurement has been developed then integrated over a Falcon-20 from SAFIRE, jointly to SPEX aerosol sensor from SRON. During October 2020, we flew over Spain, Italy, and towards Poland from Francazal airport in Toulouse, France. Even if we did not have the opportunity to flight over a powerplant, a lot of data has been acquired and are being processed. After presented the instrument, mission and data products, we assess the data quality and the reliability of the model. We derive finally an expected sensitivity over CO2 and CH4 columns according to the background respectively about 1.5-2.5% and 5%. We finally demonstrate the operability of this first TRL5 prototype of NanoCarb.
Modern atmospheric gas monitoring applications demand progressively better performances with regards to spatial, spectral and temporal resolutions. In this context, great potential is shown by a newly developed family of cutting-edge snapshot imaging spectrometers based on Fabry-Perot interferometry, whose conceptual design was patented under the name ImSPOC. Three different sensor prototypes based on the ImSPOC concept are under development: 1) in the near infrared wavelength range for CH4 or H2S detection, 2) in ultra-violet and visible range for NO2, O4, O3, and O2 characterisation and 3) specifically for CO2 monitoring. After the realisation of these prototypes there is the need arose to provide intelligible and well-calibrated acquisitions for the final users. This study presents the ImSPOC concept from the signal processing point of view, framing the optical transformations performed in the instruments under an appropriate mathematical model formulation. Additionally, preliminary developments are presented to address the first step of the signal processing pipeline for this instrument: the estimation of the thickness of each interferometer. This is a fundamental step for obtaining calibrated acquisitions that could then be used for gas monitoring.
In this paper, we describe the NanoCarb concept as well as its key elements. Then we will explain the design of the prototype followed by the development of characterization techniques. Finally, we will present how this tool can be used as part of end-to-end model. The key element of the NanoCarb concept is a matrix of silicon Fabry-Perot microinterferometers, which allows us to perform both imaging and interferometry with a field of view of 18° and several interferometric samples in a snapshot. This technique permits us to optimize the SNR for a much reduced volume. The very complex and unusual design of this component brings huge optical and technological challenges, and requires the development of characterization techniques at the nanometer scale. Upon achievement of this purpose, the next step will be the integration of this matrix in a NanoCarb prototype to demonstrate its effective performances. We present a test bench using the interferential metrology technique of Optical Coherence Tomography (OCT). In a first time, we managed to obtain optical path maps of different silicon wafers with nanometer accuracy. Then, we employed the technique to characterize the first micro-interferometers. In parallel, we realized the first prototype integration of NanoCarb with an InGaAs focal plane array and started its characterization
NanoCarb is an innovative Fourier Transform imaging spectrometer dedicated to the measurement of CO2 and CH4. Both its unusual optical principle and sampling strategy allows to reach a compact design, ideal for small satellite constellation as investigated by the European project SCARBO. The NanoCarb performance assessment as well as a proof of concept are required in this framework. A strategy of design is developed to optimize the performances and reach the sensitivity target of the space mission, demonstrating the potential of the concept without drastic complexity gain. A preliminary bias mitigation in the retrieval strategy is presented concerning water for CO2 measurement, illustrating the efficiency and the flexibility of the NanoCarb partial interferogram sampling technic. The presented design reaches a random error sub-ppm for CO2 and sub-10ppb for CH4, considering a 128 to 192 km swath, respectively, for 2 or 3 km of resolution at ground. A full mitigation of the water bias is performed on CO2 band thanks to partial interferograms.
Nanocarb is a snapshot imaging interferometer concept dedicated to the measurement of CO2. Thanks to its very compact design, it is a good candidate for small satellites, which would pave the way to a constellation of satellites to monitor emission of anthropogenic greenhouse gases from space. Nanocarb is based on a multiaperture design, with a stepcase interferometric plate to measure partial interferograms. It is developed in the framework of the Scarbo project, an European project involving several partners, the aim of which being to design and analyse the performances of the Nanocarb concept, complemented by collocated compact aerosol sensor and CO2 reference instruments. The overall measurement concept will be experimentally validated through a dedicated airborne campaign featuring instrument prototypes.
Earth's positive radiative forcing is significantly accelerated by massive anthropogenic emissions of greenhouse gases, like carbon dioxide and methane [1]. Since 2014 the concentration of CO2 exceeds 400 parts per million (ppm), and the concentration of CH4 climbs up to 1900 parts per billion (ppb) [2] with a constant annual increase.
Near-Infrared wave front sensing allows to enhance sky coverage with adaptive optics. The recently developed
HgCdTe avalanche photodiode arrays are promising, but still present an unperfect cosmetic. After the fine
characterization of such a HgCdTe array, we propose a statistical model of the pixel response. Assuming the
cosmetic is partially corrected, we simulate the impact of the residual error on a Shack-Hartmann wavefront
sensor measurement. The study shows the operability of such a real time correction, and of the HgCdTe APD
array characterized in this framework: the RAPID camera.
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