arXiv subjects

François Andrieu

Publications and source records attributed to François Andrieu.

8 recordsLinked to original sources

arXiv2026

Properties of Seasonal Ice at Sisyphi Cavi and Implications for Current Modification of Martian Gullies

Martian gullies are geologically recent landforms that may form either through liquid-water activity and/or through processes involving CO2 ice. We investigated the mechanisms responsible for the formation or modification of these features by focusing on the active site of Sisyphi Cavi (68°S, 1°E), located outside the typical latitude range of gully presence. Using CRISM and OMEGA infrared data, we characterized the composition and physical state of seasonal surface ices to test the relevance of H2O and CO2 ice driven mechanisms. Our analysis shows that H2O ice is not detected as an independent surface deposit, although it may be present as minor inclusions within the CO2 ice layer. In particular, during the final phase of CO2 ice sublimation in late spring, no H2O ice signature is observed. In the area, faint spectral signatures of sulfate salts are observed, but their distribution and amount do not suggest any direct link with gully activity. Available observations during early and mid-spring reveal that CO2 ice is translucent during these times, suggesting that it likely remains in this state through most of the ice season. However, a temporal mismatch between dark spot formation - indicative of CO2 geysers through translucent ice - and gully modification (respectively occurring late winter to early spring, and mid to late spring) exists. This does not suggest a systematic link between both processes. Overall, the available observations provide no evidence that liquid water contributes to present-day gully activity at Sisyphi Cavi, while offering no support either for the hypothesis that gully modifications are mainly driven by the formation of CO2 geysers. Gully modifications at Sisyphi Cavi, observed during the late sublimation stages of CO2 ice, may be rather more appropriately explained by CO2-ice-based fluidization or avalanche processes.

astro-ph.EP↗

arXiv2026

Simulation of laser travel-time on Mercury for BELA

Recent laser altimeters are able to not only measure the ranging distance between the spacecraft and the surface but also the full time-of-flight of the photons or pulse shape. This new capabilities allows to measure the intra-footprint properties: surface slope distribution and surface microtexture. Here we simulate and discuss for the first time the effect of surface microtexture, especially for ice covered surface with longer penetration depth. Using the WARPE simulation software, two kind of microtextures are simulated: compact slab and granular. Laser pulse shape for an ideal instrument is simulated using physical properties such as the grain size, material composition, thickness, compacity (filling factor, porosity) rather than radiative properties. The effects of these parameters on the pulse shape are discussed as well in the range that could be possibly be observed with actual BELA measurement. Finally, examples of WARPE's simulated pulse shapes are used as input in the precise simulation chain of the BELA measurement output, to further assess the capability to detect variation in surface microtexture.

astro-ph.EP↗

arXiv2023

Powering AI at the Edge: A Robust, Memristor-based Binarized Neural Network with Near-Memory Computing and Miniaturized Solar Cell

Memristor-based neural networks provide an exceptional energy-efficient platform for artificial intelligence (AI), presenting the possibility of self-powered operation when paired with energy harvesters. However, most memristor-based networks rely on analog in-memory computing, necessitating a stable and precise power supply, which is incompatible with the inherently unstable and unreliable energy harvesters. In this work, we fabricated a robust binarized neural network comprising 32,768 memristors, powered by a miniature wide-bandgap solar cell optimized for edge applications. Our circuit employs a resilient digital near-memory computing approach, featuring complementarily programmed memristors and logic-in-sense-amplifier. This design eliminates the need for compensation or calibration, operating effectively under diverse conditions. Under high illumination, the circuit achieves inference performance comparable to that of a lab bench power supply. In low illumination scenarios, it remains functional with slightly reduced accuracy, seamlessly transitioning to an approximate computing mode. Through image classification neural network simulations, we demonstrate that misclassified images under low illumination are primarily difficult-to-classify cases. Our approach lays the groundwork for self-powered AI and the creation of intelligent sensors for various applications in health, safety, and environment monitoring.

cs.ET↗

arXiv2021

Constraints on effusive cryovolcanic eruptions on Europa using topography obtained from Galileo images

Images of Europa's surface taken by the Galileo Solid State Imager (SSI) show smooth features measuring a few kilometers, potentially resulting from eruptions of low-viscosity material such as liquid cryomagma. We estimated the volume of four of these smooth features by producing digital elevation models (DEMs) of four Galileo/SSI images. We used the shape-from-shading technique with special care to estimate the uncertainties on the produced DEMs and estimated feature volumes to be between ($5.7*10^{7}$ m$^{3}$ and ($2.7*10^{8}$ m$^{3}$. We discussed the implications for putative sub-surface liquid reservoir dimensions in the case of eruptions induced from freezing reservoirs. Our previous cryovolcanic eruption model was improved by considering a cycle of cryomagma freezing and effusion and by estimating the vaporized cryolava fraction once cryolava spreads onto Europa's surface. Our results show that the cryomagma reservoirs would have to be relatively large to generate these smooth features (1 to 100 km$^{3}$ if the flow features result from a single eruption, and 0.4 to 60 km$^{3}$ for the full lifetime of a reservoir generating cyclic eruptions). The two future missions JUICE (ESA) and Europa Clipper (NASA) should reach Europa during the late 2020s. They shall give more information on those putative cryovolcanic regions which appear as interesting targets that could provide a better understanding of the material exchanges between the surface, sub-surface and ocean of Europa.

astro-ph.EP↗

arXiv2018

Ice state evolution during spring in Richardson crater, Mars

The Martian climate is governed by an annual cycle, that results in the condensation of CO$_{2}$ ice during winter, up to a meter thick at the pole and thousands of kilometers in extension. Water and dust may be trapped during the condensation and freed during the sublimation. In addition, ice may be translucent or granular depending on the deposition process (snow vs direct condensation), annealing efficiency, and dust sinking process. The determination of ice translucency is of particular interest to confirm or reject the cold jet model (also known as Kieffer model). This work is focused on the dune field of Richardson Crater in which strong interactions between the water, dust and CO$_{2}$ cycles are observed. We analyzed CRISM hyperspectral images in the near IR using radiative transfer model inversion. We demonstrate that among the states of CO$_{2}$ ice, the translucent state is observed most frequently. The monitoring of surface characteristics shows a decrease in the thickness of the ice during the spring consistently with climate models simulations. We estimate a very low dust content of a few ppmv into the CO$_{2}$ ice, consistent with the formation scenario of cold jets. The water impurities is around 0.1\%v, almost stable during the spring, suggesting a water escape from the surface of subliming CO$_{2}$ ice layer. The water ice grain size varies in a range 1 to 50 microns. From these results, we propose the following new mechanism of small water ice grain suspension: as a cold jet occurs, water ice grains of various sizes are lifted from the surface. These jets happen during daytime, when the general upward gas flux from the subliming CO$_{2}$ ice layer is strong enough to carry the smaller grains, while the bigger fall back on the CO$_{2}$ ice layer. The smaller water grains are carried away and integrated to the general atmospheric circulation.

astro-ph.EP↗

arXiv2015

Radiative transfer model for contaminated slabs : experimental validations

This article presents a set of spectro-goniometric measurements of different water ice samples and the comparison with an approximated radiative transfer model. The experiments were done using the spectro-radiogoniometer described in Brissaud et al. (2004). The radiative transfer model assumes an isotropization of the flux after the second interface and is fully described in Andrieu et al. (2015). Two kind of experiments were conducted. First, the specular spot was closely investigated, at high angular resolution, at the wavelength of $1.5\,\mbox{μm}$, where ice behaves as a very absorbing media. Second, the bidirectional reflectance was sampled at various geometries, including low phase angles on 61 wavelengths ranging from $0.8\,\mbox{μm}$ to $2.0\,\mbox{μm}$. In order to validate the model, we made a qualitative test to demonstrate the relative isotropization of the flux. We also conducted quantitative assessments by using a bayesian inversion method in order to estimate the parameters (e.g. sample thickness, surface roughness) from the radiative measurements only. A simple comparison between the retrieved parameters and the direct independent measurements allowed us to validate the model. We developed an innovative bayesian inversion approach to quantitatively estimate the uncertainties on the parameters avoiding the usual slow Monte Carlo approach. First we built lookup tables, and then searched the best fits and calculated a posteriori density probability functions. The results show that the model is able to reproduce the spectral behavior of water ice slabs, as well as the specular spot. In addition, the different parameters of the model are compatible with independent measurements.

physics.geo-ph↗

arXiv2015

Radiative transfer model for contaminated rough slabs

We present a semi-analytical model to simulate bidirectional reflectance distribution function (BRDF) spectra of a rough slab layer containing impurities. This model has been optimized for fast computation in order to analyze hyperspectral data. We designed it for planetary surfaces ices studies but it could be used for other purposes. It estimates the bidirectional reflectance of a rough slab of material containing inclusions, overlaying an optically thick media (semi-infinite media or stratified media, for instance granular material). The inclusions are supposed to be close to spherical, and of any type of other material than the ice matrix. It can be any type of other ice, mineral or even bubbles, defined by their optical constants. We suppose a low roughness and we consider the geometrical optics conditions. This model is thus applicable for inclusions larger than the considered wavelength. The scattering on the inclusions is assumed to be isotropic. This model has a fast computation implementation and thus is suitable for high resolution hyperspectral data analysis.

physics.optics↗

arXiv2013

Time-dependent relaxation of strained silicon-on-insulator lines using a partially coherent x-ray nanobeam

We report on the quantitative determination of the strain map in a strained Silicon-On-Insulator (sSOI) line with a 200x70 nm^2 cross-section. In order to study a single line as a function of time, we used an X-ray nanobeam with relaxed coherence properties as a compromise between beam size, coherence and intensity. We demonstrate how it is possible to reconstruct the line deformation at the nanoscale, and follow its evolution as the line relaxes under the influence of the X-ray nanobeam.

cond-mat.mtrl-sci↗