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. Additional presentation content can be accessed on the supplemental content page.
The detection and quantification of greenhouse gas (GHG) emissions, in particular carbon dioxide (CO2) and methane (CH4), is presently one of the main goals of remote sensing of atmospheric gasses on a global scale, for the strong impact these molecules have on climate change. Of particular urgency is the quantification of emissions from anthropogenic sources, a high-priority task addressed by the ESA Copernicus mission CO2M, which will provide global coverage detection of CO2 and CH4. The observation of CO2M, capable of quantifying emissions from the major sources, can be complemented by other observation systems addressing the smaller, and more numerous, sources. In this domain, static interferometers can offer several advantages. This paper reports on the main results of two activities completed within the ESA Future Missions activities in the Earth Observation Program, for the development of small instruments based on static interferometer designs, for the detection of CO2. The two studies, named Carbon-HIGS and Carbon-CGI, investigated two instruments operating in the SWIR and NIR bands, with a targeted precision of 2 ppm and an accuracy of 1 ppm for CO2 atmospheric concentration, covering a relatively small swath of 50 km at a spatial sampling better than 300 m. We summarize the general detection principles, the result of the design activities, and the estimated instrument performances. Both concepts are suitable candidates to work in conjunction with the Copernicus mission offering a zoom-mode observation, for quantification of medium-sized GHG sources and improved localization and understanding of anthropogenic emissions. Additional presentation content can be accessed on the supplemental content page.
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 impact on an optical surface by a micrometeoroid gives rise to a specific type of stray light inherent only in the space optical instruments. This causes a double source of light scattering: the impact crater and the ejected contamination. We propose a method of stray light estimation and apply it to the case of the Laser Interferometer Space Antenna telescope. We estimate the backscattering fraction for nominal (4 years) and extended (10 years) mission durations.
We describe a setup based on Michelson interferometry for coherent measurements of the backscattered light from a low roughness optical surface under test. Special data processing was developed for the extraction of the useful signal from the various stray contributions to the coherent signal. We achieve coherent detection of light scattered by a mirror down to -130 dB in optical power. We characterize the dependence of the backscattered light with spot position and incidence angle. Results of cross-polarization scattering coherent measurements and preliminary results of dust deposition experiment are presented here. This work represents the first step in the experimental evaluation of the coherent perturbation induced by the scattered light in the space gravitational wave detector of the LISA mission.
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