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Heat transfers in terahertz nanostructured membrane: from near-field imaging of electromagnetic mode to THz imagery
No full textInternational audienceImaging in the Terahertz (THz) is an active field of research that finds numerous applications such as non-destructive industrial testing, security or chemical identification. However, the high cost and low sensitivity of terahertz detectors constitute a serious obstacle for a wide range of applications. In this perspective, exalted thermal conversion in metasurfaces promises to be a cost effective alternative technique. In this talk, I will present nanostructured ultra-thin PET membranes that are designed to absorb the THz light and effectively heat up thus emitting in the infrared. At first, we image the heat transfers in the terahertz metasurface from the first time of heating up to the steady states and compare it to finite element modelling coupling electromagnetic and thermal physics. Interestingly, the THz metasurface is easily resolved through an infrared camera leading to the demonstration of far field acquired image of the near field modes of the metasurface. Then, we use the optimized printed split-ring resonator based membrane adapted on an infrared camera to image defects on metallic lines and characterize a THz focused beam
Vertical and horizontal variability and representativeness of the water vapor isotope composition in the lower troposphere: insight from Ultralight Aircraft flights in southern France during summer 2021
No full textInternational audienceThe isotopic composition of water vapor can be used to track atmospheric hydrological processes and to evaluate numerical models simulating the water cycle. Accurate model–observation comparisons require understanding the spatial and temporal variability of tropospheric water vapor isotopes. The challenging task of obtaining highly resolved water vapor isotopic observations is typically addressed through airborne measurements performed aboard conventional aircraft, but these offer limited microscale insights. This study uses ultralight aircraft observations to investigate water vapor isotopic composition in the lower troposphere over southern France in late summer 2021. Combining observations with models, we identify key drivers of isotopic variability and detect short-lived, small-scale processes. The key findings of this study are that (i) at hourly and sub-daily scales, vertical mixing is the primary driver of isotopic variability in the lowermost troposphere above the study site; (ii) evapotranspiration significantly impacts the boundary layer water vapor isotopic signature, as revealed by the δ18O–δD relationship; and (iii) while water vapor isotopes generally follow large-scale humidity patterns, with separation distances that might range up to 100–300 km, they also reveal distinct small-scale structures (approximately hundreds of meters) that are not fully explained by humidity variations alone, highlighting sensitivity of water vapor isotopic composition to additional fine-scale processes. The latter are particularly evident for δD, which also exhibit the largest differences in horizontal and vertical gradients. Combined with other airborne datasets, our results support a simple model driven by surface observations to simulate tropospheric δD vertical profiles, improving surface–satellite comparisons
Port-Hamiltonian reduced order modelling of the 2D Maxwell equations
No full textInternational audiencePurpose This study aims to develop a systematic and efficient method for modeling and reducing the computational complexity of the Maxwell equations in 2D. By maintaining the port-Hamiltonian structure in both the full order model (FOM) and reduced-order model (ROM), this approach ensures that the essential dynamical properties are preserved. The ultimate goal is to create a reduced order model that is suitable for rapid simulations, control and analysis in electromagnetic applications, such as waveguides, which involve boundary control and observation, as well as interface discontinuities. Design/methodology/approach This research introduces an ROM procedure for the 2D Maxwell equations within a port-Hamiltonian framework. Using a mixed finite element method, the high-fidelity FOM is generated, which retains the original structure of the Maxwell equations. Model reduction is then achieved through the Loewner framework, allowing for a low-complexity model that is computationally efficient while preserving the port-Hamiltonian properties. A lifting operator is employed to recover the FOM’s internal variables from the reduced model, validating the accuracy of the ROM in reproducing the FOM’s dynamic behavior. Findings The proposed methodology effectively reduces the dimension of the Maxwell system by approximately 35 times, significantly decreasing computational time while maintaining high fidelity in the key output responses. Simulation results demonstrate that the reduced model accurately replicates the full order model’s dynamics and power balance. The approach also highlights the advantages of using a port-Hamiltonian structure for energy tracking, with ROMs exhibiting only minor discrepancies due to truncation. The findings validate the ROM as a reliable and efficient approximation of the original high-dimensional system, suitable for complex electromagnetic configurations. Originality/value This work provides a novel approach to reducing the 2D Maxwell equations within a port-Hamiltonian framework, preserving essential structure and dynamical properties. By leveraging the Loewner framework with a unique focus on passivity preservation, the method offers a practical solution for efficient simulation and control in electromagnetic systems. This ROM methodology, with its reduced computational burden and enhanced accuracy, is valuable for applications in electromagnetic field simulations and control design, where high computational efficiency and structure preservation are critical [1]
Parametric study of lightning induced damage in carbon composite using X-ray phase contrast imaging
No full textInternational audienceThis study presents a parametric analysis of lightning-induced damage in Carbon Fibre Reinforced Polymers (CFRP) using X-ray Phase Contrast Imaging (XPCI) using MultiLateral Shearing Interferometry technique. Damage severity was evaluated at different electrical energies deposited in the CFRP and cross-validated with other non-destructive techniques. The results demonstrate the potential of XPCI for precise characterization and improved damage modeling in aerospace applications
Modeling 3D radiative transfer for maize traits retrieval: A growth stage-dependent study on hyperspectral sensitivity to field geometry, soil moisture, and leaf biochemistry
No full textInternational audienceThis study integrates a dynamic plant growth model with a three-dimensional (3D) radiative transfer model (RTM) for maize traits retrieval using high spatial–spectral resolution airborne data. The research combines the Discrete Anisotropic Radiative Transfer (DART) model with the Dynamic L-System-based Architectural maize (DLAmaize) growth model to simulate field reflectance. Comparison with the 1D RTM SAIL revealed limitations in representing row structure effects, field slope, and complex light–canopy interactions. Novel Global Sensitivity Analyses (GSA) were carried out using dependence-based methods to overcome limitations of traditional variance-based approaches, enabling better characterization of hyperspectral sensitivity to changes in leaf biochemistry, canopy architecture, and soil moisture. GSA provided complementary results to assess estimation uncertainties of the proposed traits retrieval method across growth stages. A hybrid inversion framework combining DART simulations with an active learning strategy using Kernel Ridge Regression was implemented for traits estimation. The approach was validated using ground data and HyPlant-DUAL airborne hyperspectral images from two field campaigns in 2018 and achieved high retrieval accuracy of key maize traits: leaf area index (LAI, R2=0.91, RMSE=0.42 m2/m2), leaf chlorophyll content (LCC, R2=0.61, RMSE=3.89 μg/cm2), leaf nitrogen content (LNC, R2=0.86, RMSE=1.13 × 10−2 mg/cm2), leaf dry matter content (LMA, R2=0.84, RMSE=0.15 mg/cm2), and leaf water content (LWC, R2=0.78, RMSE=0.88 mg/cm2). The validated models were used to generate two-date 10 m resolution maps, showing good spatial consistency and traits dynamics. The findings demonstrate that integrating 3D RTMs with dynamic growth models is suited for maize trait mapping from hyperspectral data in varying growing conditions
"Fast data processing method for multispectral radiation thermometry based on Euclidean distance optimization": comment
No full textInternational audienceA recent publication [ Opt. Express , 32 , 1342 ( 2024 ) 10.1364/OE.510084 ] presents a processing method for multiwavelength pyrometry (MWP) that claims to be accurate without requiring an a priori emissivity model. MWP is known to be an underdetermined problem which, as a result, has an infinite number of exact solutions. The proposed method can therefore only lead to one of these solutions (albeit approximately), with no way of telling whether it’s close or far from the real solution we’re looking for. Notwithstanding this, the results obtained by the authors systematically showed small errors. The reason is that they relied on the minimum and maximum values of the actual emissivity spectrum, knowledge of which is in fact very demanding a priori. By the way, when this knowledge is available, the temperature and the emissivity spectrum can be recovered directly using a conventional method. Without tight constraints on emissivity range or a priori emissivity model, MWP leaves us with an infinite number of permitted solutions , among which the actual solution is impossible to guess, leading to a deadlock.Une publication récente [Opt. Express, 32(2), 1342-1356] présente une méthode de traitement pour la pyrométrie multi-longueurs d'onde (MWP) ne nécessitant pas de modèle d'émissivité a priori et revendiquée comme étant précise. Cependant, la MWP est connue pour être un problème sous-déterminé qui, corrélativement, a un nombre infini de solutions exactes. La méthode proposée ne fournit donc qu'une seule de ces solutions, qui plus est approximative. De plus, il est impossible de dire si elle est proche ou éloignée de la solution réelle recherchée. En dépit de ce diagnostic pessimiste, les résultats obtenus par les auteurs présentaient systématiquement de faibles erreurs. La raison en est qu'ils se sont appuyés sur les valeurs minimales et maximales du spectre d'émissivité réel, dont la connaissance a priori est en fait très exigeante. Qui plus est, lorsque cette connaissance est disponible, la température et le spectre d'émissivité peuvent être identifiés directement à l'aide d'une méthode conventionnelle. En fin de compte, la MWP sans conditions contraignantes sur l'émissivité nous laisse avec un nombre infini de solutions permises, parmi lesquelles il est impossible d’isoler la solution réelle, ce qui conduit à une impasse
Développement d'une méthode de frontières immergées locales sur maillages curvilignes pour la capture des détails géométriques complexes dans les simulations aérodynamiques
No full textInternational audienceIn this paper, we propose an approach based on an Immersed Boundary Method (IBM), to deal with geometrical complex details in CFD simulations. A body-conformal hexahedral mesh describes a simple geometry, while details can be added onto the original geometry using an Immersed Boundary Condition that is local to each detail. The proposed Local Immersed Boundary Method (LIBM) avoids to generate a body-conformal mesh around the details, simplifying mesh generation process and enabling parametric studies on the shape and position of the details. The IBM method consists in forcing the solution through a wall function at some discretization points close to the immersed details. When the background mesh is too coarse in the vicinity of the immersed obstacles, hierarchical mesh adaptation is performed to properly capture the flow physics induced by the presence of the immersed obstacle. The preprocessing is achieved with the Cassiopée pre-/post-processing library and the flow simulation is performed by solving the compressible Reynolds-Averaged Navier-Stokes (RANS) equations with the industrial flow solver CODA. This approach has been validated on three test cases involving different flow topologies in the immersed boundary vicinity: a turbulent flow with an attached boundary layer over a 2D multi-element airfoil, a massively separated flow around a 2D horn-shaped iced-airfoil and a 3D iced-swept wing. The results obtained demonstrate the ability of the LIBM approach to reproduce the fundamental flow features induced by the immersed obstacles. They also highlight the relevance of using this approach as an efficient simulation tool to deal with geometrical complex obstacles, with a significant reduction in mesh generation effort and a good level of solution accuracy during the early stages of the aerodynamic design process
High speed fs/ps-CARS thermometry for supersonic H 2 /air combustion studies
No full textInternational audiencePrecise and robust measurement methods are needed to probe the complex and reacting media met in aerospace engines. Indeed, experimental data acquired in representative test benches provide a necessary database to improve and validate the numerical models describing the thermo-fluid dynamics inside the combustion chamber. We present the results of a hybrid femtosecond/picosecond coherent anti-stokes Raman scattering (fs/ps-CARS [1]) thermometry campaign performed on the H2/air research supersonic scramjet combustor LAPCAT II model at ONERA/LAERTE facility [2]. In-situ vertical and horizontal temperature profiles were retrieved upstream and downstream the combustion zone during short gusts [3]. Single shot measurements were demonstrated at kHz rate to catch the high-speed temperature fluctuations (Figure 1a). They effectively captured turbulence and temperature distributions in fluctuating zones. Spatially resolved histograms could be built in a single facility run using single shot measurements within the turbulent combustion (Figure 1b). The measurements were also compared to a numerical unsteady fluid dynamic simulation developed at ONERA called CFD3D-CEDRE [4] (Figure 1c). The temperature profiles obtained for various flow configuration on the reactive, hot burnt and cold gas regions inside the combustor, have provided valuable inputs for refining the model as some discrepancies were observed depending on the model hypothesis
Revisiting the mineralogy of multi-metallic indicators in the basement and sedimentary fill of the Permian Lodève Basin
No full textInternational audienceWe present a reassessment of the mineralogy of the multi-metallic indicators found in the basement and Permian sediment fill of the Lodève basin.This work is part of the development of hyperspectral remote sensing techniques, conducted in partnership with ONERA, BRGM, and the University of Paris-Saclay. It contributes to the inventory of mineral resources led by BRGM
Active Correction of Aperture Discontinuities-Optimized Stroke Minimization. I. A New Adaptive Interaction Matrix Algorithm
No full textInternational audienceFuture searches for bio-markers on habitable exoplanets will rely on telescope instruments that achieve extremely high contrast at small planet-to-star angular separations. Coronagraphy is a promising starlight suppression technique, providing excellent contrast and throughput for off-axis sources on clear apertures. However, the complexity of space- and ground-based telescope apertures goes on increasing over time, owing to the combination of primary mirror segmentation, the secondary mirror, and its support structures. These discontinuities in the telescope aperture limit the coronagraph performance. In this paper, we present ACAD-OSM, a novel active method to correct for the diffractive effects of aperture discontinuities in the final image plane of a coronagraph. Active methods use one or several deformable mirrors that are controlled with an interaction matrix to correct for the aberrations in the pupil. However, they are often limited by the amount of aberrations introduced by aperture discontinuities. This algorithm relies on the recalibration of the interaction matrix during the correction process to overcome this limitation. We first describe the ACAD-OSM technique and compare it to the previous active methods for the correction of aperture discontinuities. We then show its performance in terms of contrast and off-axis throughput for static aperture discontinuities (segmentation, struts) and for some aberrations evolving over the life of the instrument (residual phase aberrations, artifacts in the aperture, misalignments in the coronagraph design). This technique can now obtain the Earth-like planet detection threshold of 10^10 contrast on any given aperture over at least a 10% spectral bandwidth, with several coronagraph designs