Editorial Bonjour Je suis heureux de vous présenter la deuxième newsletter de CRITEX. Merci à tous les porteurs de WP d’avoir rédigé quelques lignes sur l’état d’avancement de leurs acquisitions ou de leurs développements. Comme vous le constaterez, CRITEX est bel et bien parti grâce à l’engagement de tous. La quasi totalité des équipements est désormais acquise, le reste le […]
Read moreCRITEX est un programme sur 10 ans impliquant beaucoup d’équipes, certaines en charge de l’équipement, et d’autres en charge des observatoires élémentaires des réseaux RBV ou H+. Un point clé pour le succès de CRITEX va être la capacité de l’ensemble du groupe à travailler ensemble et de partager l’équipement commun à travers des projets de recherche pertinents. CRITEX A SON […]
Read moreIn the perspective of a temporal and spatial exploration of aquatic environments (surface and groundwater), we developed a technique for field continuous measurements of dissolved gases with a precision better than 1% for N2, O2, CO2, He, Ar, 2% for Kr, 8% for Xe, and 3% for CH4, N2O and Ne. With a large resolution (from 1 × 10–9 to […]
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This paper describes a sensor dedicated to measuring the vertical profile of the complex permittivity and the temperature of any medium in which sensor electrodes are inserted. Potential applications are the estimate of the humidity and salinity in a porous medium, such as a soil. It consists of vertically-stacked capacitors along two conductive parallel cylinders of 5 cm in diameter and at a 10-cm […]
Read moreThe in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes, such as dispersion, channeling, trapping, matrix diffusion, ambient and density driven flows. We attempted to reduce this uncertainty by coupling push-pull tracer experiments with single-hole ground penetrating radar (GPR) time-lapse imaging. The experiments involved different injection fractures, chaser […]
Read moreWe show how a distributed borehole flowmeter can be created from armored Fiber Optic cables with the Active-Distributed Temperature Sensing (A-DTS) method. The principle is that in a flowing fluid, the difference in temperature between a heated and unheated cable is a function of the fluid velocity. We outline the physical basis of the methodology and report on the deployment […]
Read moreWhen applied to hydrogeology, seismicmethods are generally confined to the characterisation of aquifer geometry. The joint study of pressure- (P) and shear- (S) wave velocities (VP and VS) can provide supplementary information and improve the understanding of aquifer systems. This approach is proposed here with the estimation of VP/VS ratios in a stratified aquifer system characterised by tabular layers, well-delineated […]
Read moreRetrieving the Relaxation Time Distribution (RDT), the Grains Size Distribution (GSD) or the Pore Size Distribution (PSD) from low-frequency impedance spectra is a major goal in geophysics. The “Generalized RTD” generalizes parametric models like Cole–Cole and many others, but remains tricky to invert since this inverse problem is ill-posed. We propose to use generalized relaxation basis function (for instance by […]
Read moreAt the scale of a magnetic resonance sounding (MRS) field setup, the earth’s magnetic field in the subsurface may vary laterally with depth and over time. These variations can be caused by different natural factors and generally cannot be compensated for by accurate tuning of the measuring device. The varying geomagnetic field (GMF) causes non resonance conditions of excitation that affect the amplitude and phase of […]
Read moreWe develop an approach for measuring in-well fluid velocities using point electrical heating combined with spatially and temporally continuous temperature monitoring using distributed temperature sensing (DTS). The method uses a point heater to warm a discrete volume of water. The rate of advection of this plume, once the heating is stopped, equates to the average flow velocity in the well. […]
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