26 research outputs found
Joint inversion of muon tomography and gravimetry - a resolving kernel approach
Both muon tomography and gravimetry are geophysical methods that provide
information on the density structure of the Earth's subsurface. Muon tomography
measures the natural flux of cosmic muons and its attenuation produced by the
screening effect of the rock mass to image. Gravimetry generally consists in
measurements of the vertical component of the local gravity field. Both methods
are linearly linked to density, but their spatial sensitivity is very
different. Muon tomography essentially works like medical X-ray scan and
integrates density information along elongated narrow conical volumes while
gravimetry measurements are linked to density by a 3-dimensional integral
encompassing the whole studied domain. We develop the mathematical expressions
of these integration formulas -- called acquisition kernels -- to express
resolving kernels that act as spatial filters relating the true unknown density
structure to the density distribution actually recoverable from the available
data. The resolving kernels provide a tool to quantitatively describe the
resolution of the density models and to evaluate the resolution improvement
expected by adding new data in the inversion. The resolving kernels derived in
the joined muon/gravimetry case indicate that gravity data are almost useless
to constrain the density structure in regions sampled by more than two muon
tomography acquisitions. Interestingly the resolution in deeper regions not
sampled by muon tomography is significantly improved by joining the two
techniques. Examples taken from field experiments performed on La Soufri\`ere
of Guadeloupe volcano are discussed.Comment: Submitted to Geoscientific Model Developmen
Muon tomography applied to active volcanoes
Muon tomography is a generic imaging method using the differential absorption
of cosmic muons by matter. The measured contrast in the muons flux reflects the
matter density contrast as it does in conventional medical imaging. The
applications to volcanology present may advantadges induced by the features of
the target itself: limited access to dangerous zones, impossible use of
standard boreholes information, harsh environmental conditions etc. The
Diaphane project is one of the largest and leading collaboration in the field
and the present article summarizes recent results collected on the Lesser
Antilles, with a special emphasis on the Soufri\`ere of Guadeloupe.Comment: 7 pages, 7 figures, International Conference on New
Photo-detectors,PhotoDet2015, 6-9 July 2015, Moscow, Troitsk, Russia.
Submitted to Po
Monitoring temporal opacity fluctuations of large structures with muon tomography : a calibration experiment using a water tower tank
Usage of secondary cosmic muons to image the geological structures density
distribution significantly developed during the past ten years. Recent
applications demonstrate the method interest to monitor magma ascent and
volcanic gas movements inside volcanoes. Muon radiography could be used to
monitor density variations in aquifers and the critical zone in the near
surface. However, the time resolution achievable by muon radiography monitoring
remains poorly studied. It is biased by fluctuation sources exterior to the
target, and statistically affected by the limited number of particles detected
during the experiment. The present study documents these two issues within a
simple and well constrained experimental context: a water tower. We use the
data to discuss the influence of atmospheric variability that perturbs the
signal, and propose correction formulas to extract the muon flux variations
related to the water level changes. Statistical developments establish the
feasibility domain of muon radiography monitoring as a function of target
thickness (i.e. opacity). Objects with a thickness comprised between
50 30m water equivalent correspond to the best time resolution. Thinner
objects have a degraded time resolution that strongly depends on the zenith
angle, whereas thicker objects (like volcanoes) time resolution does not.Comment: 11 pages, 9 figures. Final version published in Scientific Reports,
Nature, 14 march 201
Muon dynamic radiography of density changes induced by hydrothermal activity at the La Soufrière of Guadeloupe volcano
paper submitted to Scientific Reports in june 2016. 15 pages. 8 figuresInternational audienceImaging geological structures through cosmic muon radiography is a newly developed technique particularly interesting in volcanology. Here we show that muon radiography may be efficient to detect and characterize mass movements in shallow hydrothermal systems of low-energy active volcanoes like the La Soufri\`ere lava dome. We present an experiment conducted on this volcano during the Summer and bring evidence that huge density changes occurred in three domains of the lava dome. Depending on their position and on the medium porosity the volumes of these domains vary from to . However, the mass changes remain quite constant, two of them being negative () and a third one being positive (). We attribute the negative mass changes to the formation of steam in shallow hydrothermal reservoir previously partly filled with liquid water. This coincides with the apparition of new fumaroles on top of the volcano. The positive mass change is synchronized with the negative mass changes indicating that liquid water probably flowed from the two reservoirs invaded by steam toward the third reservoir
Design, Construction and In Situ Testing of a Muon Camera for Earth Science and Civil Engineering Applications
The MUST2 (MUon Survey Tomography based on Micromegas detectors for Unreachable Sites Technology) camera is based on a thin Time Projection Chamber read by a resistive Micromegas. This innovative combination presents interesting distinctive features compared to existing muon detection technologies. It allows a wide angular acceptance of the detector with a low weight and compact volume, well adapted for confined spaces or underground operation. The current work presents the results obtained during the calibration measurements at the reference site, the Low Background Noise Laboratory (LBNL). Preliminary results from field measurement campaign carried out at the dam overlooking the village of Saint-Saturnin-les-Apt (South-East of France) are presented and discussed
The muon tomography Diaphane project : recent upgrades and measurements
International audienc
Tracking the interfacial dynamics of PNiPAM soft microgels particles adsorbed at the air?water interface and in thin liquid films
International audienceWe report the behavior of thermosensitive soft microgel particles adsorbed at the air-water interface. We study the effect of temperature on the adsorption, interfacial diffusion, and surface rheology of pure N-isopropylacrylamide (NiPAM) microgel particles at the air-water interface. We find that the surface tensions of the solutions are the same as those of polyNiPAM solution; hence, their adsorption properties are dominated by the surface activity of the NiPAM repeat units of the particles. Particle-tracking experiments show that the particles adsorb irreversibly at the interface and form stable clusters at very low concentrations, e.g., 5.10(-3) wt%. We suggest that attractions between dangling arms or capillary interaction may be responsible for the formation of these clusters. For concentrations above 10(-2) wt%, the interface is filled with particles, and their Brownian diffusivity is arrested. The compression elastic moduli-measured using the pendant drop method-are one or two orders of magnitude below those obtained for hard particles and NiPAM chains, and their value is probably dominated by the intrinsic compressibility of the particles. The thin liquid films made from microgels exhibit a symmetric drainage, consistent with a high surface viscosity, but their lifetime is surprisingly short, illustrating the fragility of the films. We observed the formation of a monolayer of microgels bridging the two interfaces of the film outside the dimple. This zone grows and thins over time to a point where the microgels are highly compressed and stretched, resulting in the rupture of the fil
Radiographier lesvolcans avec des rayons cosmiques : instrumentationet applications
National audienceLes muons d’origine cosmique sont des particules éphémères de hauteénergie pouvant traverser plusieurs kilomètres de roche. Le principede la radiographie par muons consiste à déterminer la densité d’unmassif rocheux en mesurant l’atténuation qu’il produit sur le flux demuons. Les principes physiques et les difficultés de cette nouvelle méthoded’imagerie seront décrites ainsi que les télescopes de terrain quenous avons conçus et réalisés. Les performances de la méthodes serontillustrés à l’aide des résultats d’expériences réalisées sur des volcans(Soufrière de Guadeloupe, Etna, Mayon) et en laboratoire souterrain(Mont Terri)
DIAPHANE: Muon tomography applied to volcanoes, civil engineering, archaelogy
International audienceMuography techniques applied to geological structures greatly improved in the past ten years. Recent applications demonstrate the interest of the method not only to perform structural imaging but also to monitor the dynamics of inner movements like magma ascent inside volcanoes or density variations in hydrothermal systems. Muography time-resolution has been studied thanks to dedicated experiments, e.g. in a water tower tank. This paper presents the activities of the DIAPHANE collaboration between particle- and geo-physicists and the most recent results obtained in the field of volcanology, with a focus on the main target, the Soufrière of Guadeloupe active volcano. Special emphasis is given on the monitoring of the dome's inner volumes opacity variations, that could be ascribed to the hydrothermal system dynamics (vaporization of inner liquid water in coincidence with the appearance of new fumaroles at the summit). I also briefly present results obtained in the fields of civil engineering (study of urban underground tunnels) and archaelogy (greek tumulus scanning)