Search

Uvsq-Sat NG is a French 6U CubeSat (10 × 20 × 30 cm) of the International Satellite Program in Research and Education (INSPIRE) designed primarily for observing greenhouse gases (GHG) such as CO2 and CH4, measuring the Earth's radiation budget (ERB), and monitoring solar spectral irradiance (SSI) at the top-of-atmosphere (TOA). It epitomizes an advancement in CubeSat technology, showcasing its enhanced capabilities for comprehensive Earth observation. Scheduled for launch in 2025, the satellite carries a compact and miniaturized near-infrared (NIR) spectrometer capable of performing observations in both nadir and solar directions within the wavelength range of 1100 to 2000 nm, with a spectral resolution of 7 nm and a 0.15° field of view. This study outlines the preflight calibration process of the Uvsq-Sat NG NIR spectrometer (UNIS), with a focus on the spectral response function and the absolute calibration of the instrument. The absolute scale of the UNIS spectrometer was accurately calibrated with a quartz-halogen lamp featuring a coiled-coil tungsten filament, certified by the National Institute of Standards and Technology (NIST) as a standard of spectral irradiance. Furthermore, this study details the ground-based measurements of direct SSI through atmospheric NIR windows conducted with the UNIS spectrometer. The measurements were obtained at the Pommier site (45.54°N, 0.83°W) in Charentes–Maritimes (France) on 9 May 2024. The objective of these measurements was to verify the absolute calibration of the UNIS spectrometer conducted in the laboratory and to provide an extraterrestrial solar spectrum using the Langley-plot technique. By extrapolating the data to AirMass Zero (AM0), we obtained high-precision results that show excellent agreement with SOLAR-HRS and TSIS-1 HSRS solar spectra. At 1.6 μm, the SSI was determined to be 238.59 ± 3.39 mW.m−2.nm−1 (k = 2). These results demonstrate the accuracy and reliability of the UNIS spectrometer for both SSI observations and GHG measurements, providing a solid foundation for future orbital data collection and analysis. [ABSTRACT FROM AUTHOR]

Monitoring atmospheric concentrations of greenhouse gases (GHGs) like carbon dioxide and methane in near real time and with good spatial resolution is crucial for enhancing our understanding of the sources and sinks of these gases. A novel approach can be proposed using a constellation of small satellites equipped with miniaturized spectrometers having a spectral resolution of a few nanometers. The objective of this study is to describe expected results that can be obtained with a single satellite named Uvsq-Sat NG. The SolAtmos end-to-end simulator and its three tools (IRIS, OptiSpectra, and GHGRetrieval) were developed to evaluate the performance of the spectrometer of the Uvsq-Sat NG mission, which focuses on measuring the main GHGs. The IRIS tool was implemented to provide Top-Of-Atmosphere (TOA) spectral radiances. Four scenes were analyzed (pine forest, deciduous forest, ocean, snow) combined with different aerosol types (continental, desert, maritime, urban). Simulated radiance spectra were calculated based on the wavelength ranges of the Uvsq-Sat NG, which spans from 1200 to 2000 nm. The OptiSpectra tool was used to determine optimal observational settings for the spectrometer, including Signal-to-Noise Ratio (SNR) and integration time. Data derived from IRIS and OptiSpectra served as input for our GHGRetrieval simulation tool, developed to provide greenhouse gas concentrations. The Levenberg–Marquardt algorithm was applied iteratively to fine-tune gas concentrations and model inputs, aligning observed transmittance functions with simulated ones under given environmental conditions. To estimate gas concentrations (CO2, CH4, O2, H2O) and their uncertainties, the Monte Carlo method was used. Based on this analysis, this study demonstrates that a miniaturized spectrometer onboard Uvsq-Sat NG is capable of observing different scenes by adjusting its integration time according to the wavelength. The expected precision for each measurement is of the order of a few ppm for carbon dioxide and less than 25 ppb for methane. [ABSTRACT FROM AUTHOR]

Understanding the phenomena that can occur in a given medium necessitates a clear grasp of its chemical composition. In this context, various techniques including infrared (IR) spectroscopy were developed. In this work, we determined the bond force constants of CO2 molecule in gas phase state and trapped in a nanocage by applying group theory to the normal vibrational modes of the symmetric (16O12C16O, 626) and the asymmetric (16O12C18O, 628) CO2 isotopic species. Wilson's force, F and inverse-mass, G matrices, were calculated for the CO2 (626 and 628) species. The effect of Fermi resonances was included in the analysis. Results are given in terms of bond force constants for stretching and bending modes of CO2 molecule trapped in nanocages of rare gas matrices and of clathrate hydrates. The comparison with the gas phase values demonstrated that the condensed phase effect can be constrained at the harmonic level. A database of vibrational frequencies can then be built from the calculated values with a pseudo-uncertainty range to enhance automatic analysis of observed data pertaining to CO2 in an unknown media by IR sensors. The study of CO2 trapped in nanocages using group theory to calculate force constants has received little theoretical consideration in previous works. Here, we provide an additional approach to evaluate the uncertainty measurement in IR spectroscopy. Similar outcomes should be achievable for other molecules, providing the possibility to improve spectroscopic IR observation and analysis from sensors specially designed for mobile sensing applications. Constrained external degrees of freedom of Carbon Dioxide molecule in a nanocage and anisotropic electric environment perturbing internal vibrational degrees of freedom which have an effect on the infrared signature of the molecule. The calculations show, that the unperturbed v1 mode peaks are at a lower value than the unperturbed 2v2 mode for both the 626 and 628 isotopologues when the molecule is trapped in a rare gas matrix or in a clathrate hydrate nanocage. [ABSTRACT FROM AUTHOR]

Understanding the phenomena that can occur in a given medium necessitates a clear grasp of its chemical composition. In this context, various techniques including infrared (IR) spectroscopy were developed. In this work, we determined the bond force constants of CO2 molecule in gas phase state and trapped in a nanocage by applying group theory to the normal vibrational modes of the symmetric (16O12C16O, 626) and the asymmetric (16O12C18O, 628) CO2 isotopic species. Wilson's force, F and inverse-mass, G matrices, were calculated for the CO2 (626 and 628) species. The effect of Fermi resonances was included in the analysis. Results are given in terms of bond force constants for stretching and bending modes of CO2 molecule trapped in nanocages of rare gas matrices and of clathrate hydrates. The comparison with the gas phase values demonstrated that the condensed phase effect can be constrained at the harmonic level. A database of vibrational frequencies can then be built from the calculated values with a pseudo-uncertainty range to enhance automatic analysis of observed data pertaining to CO2 in an unknown media by IR sensors. The study of CO2 trapped in nanocages using group theory to calculate force constants has received little theoretical consideration in previous works. Here, we provide an additional approach to evaluate the uncertainty measurement in IR spectroscopy. Similar outcomes should be achievable for other molecules, providing the possibility to improve spectroscopic IR observation and analysis from sensors specially designed for mobile sensing applications. Constrained external degrees of freedom of Carbon Dioxide molecule in a nanocage and anisotropic electric environment perturbing internal vibrational degrees of freedom which have an effect on the infrared signature of the molecule. The calculations show, that the unperturbed v1 mode peaks are at a lower value than the unperturbed 2v2 mode for both the 626 and 628 isotopologues when the molecule is trapped in a rare gas matrix or in a clathrate hydrate nanocage. [ABSTRACT FROM AUTHOR]

A concept of innovative rotational Raman lidar with daylight measurement capability is proposed to measure the vertical profile of temperature from the ground to the middle stratosphere. The optical filtering is made using a Fabry-Pérot Interferometer with line spacing equal to the line spacing of the Raman spectrum. The detection is made using a linear PMT array operated in photon counting mode. We plan to build a prototype and to test it at the Haute-Provence Observatory lidar facility. to achieve a time resolution permitting the observation of small-scale atmospheric processes playing a role in the troposphere-stratosphere interaction as gravity waves. If successful, this project will open the possibility to consider a Raman space lidar for the global observation of atmospheric temperature profiles.