Potentials and limitations of new-generation multisource resistivity-meter: numerical modeling and applications

The resistivity method has recently boosted its potentials since the development of new-concept resistivity-meters. Key improvements include a much better data quality and the reduced logistics required to operate complicated surveys in rough terrains. The Multi-Source System (MS) incorporates both these two features. In particular, the signal-to-noise ratio is significantly improved by injecting current using several simultaneous transmitting dipoles. This approach represents a major breakthrough for Electrical Resistivity Tomography (ERT) although some theoretical developments along with applications to new scenarios are still missing. MS has been never tested systematically since its appearance less than 10 years ago. This research is a sort of base work to evaluate the system potentials and understand the system limitations. Numerical modeling and real data were jointly used for the purpose. The MS response was initially tested on simple subsurface models, in order to gain confidence on its resolving power over known resistivity distribution. The response of traditional arrays was also analyzed in the same context and compared to the MS. The MS was tested and compared to traditional arrays in two specific shallow and deep settings: a river embankment; a buried bedrock. Synthetic and real data were utilized for an exhaustive analysis. The real data were collected in controlled sites: the levees of the Brenta river near Venice and the Vajont rockslide in the North-Eastern Alps. Prominent results have been obtained from this study. Two key parameters were estimated at first. The first parameter is the minimum signal amplitude recordable by the MS electronics. The second parameter, correlated to the first, is the acceptable noise per each model cell during iterative inversion. MS layouts and transmitting schemes were optimized to detect and image a target sand body within and below a river embankment. A procedure for effectively imaging a pervious subsurface body was devised via a cascade combination of inline and crossline transmitters. A similar procedure was adapted and applied to the resolution of an inclined bedrock surface. MS has also some drawbacks, like the effective portability of the units and the number of electrodes managed by a single unit, or again the introduction of undesired noise in the shallower portions of inverted models in some scenarios. The propagation of artificial current in natural media from multiple simultaneous transmitters via MS needs to be further investigated, as well as the optimization of the acquisition procedures using this system.