title: Monitoring temporal opacity fluctuations of large structures with muon radiography: a calibration experiment using a water tower.
abstract: 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 ± 30 m 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.
authors.affiliation: Institut de Physique du Globe de Paris (CNRS UMR 7154), Sorbonne Paris Cité, Paris, France.
authors.forename: Kevin
authors.initials: K
authors.lastname: Jourde
authors.affiliation: OSUR-Géosciences Rennes (CNRS UMR 6118), Université Rennes 1, Rennes, France.|National Volcano Observatories Service, Institut de Physique du Globe de Paris (CNRS UMR 7154), Paris, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Gibert
authors.affiliation: Institut de Physique Nucléaire de Lyon, Univ Claude Bernard (UMR 5822 CNRS), Lyon, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Marteau
authors.affiliation: OSUR-Géosciences Rennes (CNRS UMR 6118), Université Rennes 1, Rennes, France.
authors.forename: Jean
authors.initials: J
authors.lastname: de Bremond d'Ars
authors.affiliation: Institut de Physique Nucléaire de Lyon, Univ Claude Bernard (UMR 5822 CNRS), Lyon, France.
authors.forename: Serge
authors.initials: S
authors.lastname: Gardien
authors.affiliation: Institut de Physique Nucléaire de Lyon, Univ Claude Bernard (UMR 5822 CNRS), Lyon, France.
authors.forename: Claude
authors.initials: C
authors.lastname: Girerd
authors.affiliation: Institut de Physique Nucléaire de Lyon, Univ Claude Bernard (UMR 5822 CNRS), Lyon, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Ianigro