Integration of geochemical and geophysical data at a NAPL-contaminated site

The joint use of borehole geo-electrical measurements and the chemico-physical monitoring of the subsoi is discussed; it permitted in the specific case to locate the zone characterized by intense bio-degradation activity, demonstrating the effectiveness of the integrated approac

2D and 3D data processing of archaeo-magnetic data

Introduction. The Sabine Necropolis at Colle del Forno (700-300 B.C.) at Montelibretti, Rome is characterized by dromos chamber tombs, most of them unexplored till now. The tombs can be assimilated to cavities of a standard volume of some cubic meters; the entrance of the tombs is a corridor 6 m long with a 1 square meter section . The surficial geology of the area consists of a series of tuffs about 10 m thick overlying Pleistocene-Quaternary sandy-clayey sediments. A thin layer of top soil (20 - 30 cm) covers the tuff. The investigation of the Necropolis in the past decade has been performed by different geophysical methodologies: electrical, electromagnetic and magnetic methods have been widely adopted to investigate several chamber tombs (Piro et al, 2001). The aim of this paper is to analyze an integrated approach to the processing of magnetic survey data. The magnetic susceptibility contrast between topsoil, subsoil and rocks (topsoil is normally more magnetic than subsoil) permits to detect ditches, pits and other silted-up features that were excavated and then silted or back-filled with topsoil. Meanwhile back-filled areas produce positive anomalies, less magnetic material introduced into topsoil, including many kinds of masonry (for example, limestone walls) may produce negative anomalies of the order of some nanoteslas. The same behavior is related to the presence of cultural voids and tombs whose magnetic anomaly is generated by the lack of magnetic materials due to the cavities of the tombs. In the area a diffused magnetisation is manly due to the presence of top soil and tuff materials and high negative susceptibility contrasts can be expected because of the presence of the tombs. The magnetic survey was performed along a regular grid of 0.5 m x 0.5 m using a optical pumped Caesium-vapour magnetometer G858 (Geometrics), in the gradient configuration, on an area which is well known as far as the presence, size and position of tombs are concerne

Micro-geophysics to assess the integrity of some statues in the Museo Egizio of Turin, Italy

On request of the Soprintendenza in charge of the Museo Egizio of Turin, a quite large number of tests have been performed on four statues of the museum to assess their integrity both for practical (moving the statue) and archaeological purposes. Ultrasonic tomography and georadar have been used with fine results on sub-decimeter scale. In this paper we present the main results on the statues of the Pharaons Ramses II (Fig.1 left) and Tuthmosis I. (Fig.2 left). Both the statues belong to the collection set up by Bernardino Drovetti, Console Generale of France in Egypt in the early XIX century. Ramses II statue was restored in the first half of the XIX century. Few documents can be found on these restoration works: very likely the statue arrived broken to Turin and was reassembled with cement mortar (Hartleben, 1909) No news can be found neither on the type of mortar nor on the quantity of mortar actually used. The statue of Ramses was probably found at Tebe in 1818. It is made by basanite exploited from a quarry in Uadi Hammamat. The basanite is a basaltic extrusive rock also known as Lydian stone or lydite. It was almost exclusively reserved to the crafting of statues of pharaons or divinities. In many parts of the statue the mortar (as dark as the stone) is clearly visible (Fig.1 right). The statue of Tutmosis I was found by J.J. Rifaud , a Drovetti 's agent, in 1818 in Tebe, very likely in the Karnak temple. The king sits on a throne with many scripts on both the sides of the seat. The statue is made by a dark diorite with some light pink plagioclase crystals sizing few centimeters. Its conservation seems fairly goo

Flowmeter and Ground Penetrating Radar: comparison between hydrogeological and geophysical methods

We discuss a comparison between saturated hydraulic conductivity calculated with Electromagnetic Borehole Flowmeter (EBF) and water content obtained by Ground Penetrating Radar (GPR) Zero Offset Profile (ZOP

P-wave and surface wave survey for permafrost analysis in alpine regions

We discuss the results of seismic survey to delineate temporal and spatial changes of frozen layer in Alpine environments. The seismic characterization allows us to detect changes of soil deformability properties related to the temperature effect on subsoi

Application and comparison of three tomographic techniques for detection of decay in trees

This paper reports application of electric, ultrasonic, and georadar tomography for detection of decay in trees and their comparison with the traditional penetrometer. Their feasibility in arboriculture is also evaluated, critically considering some "open problems." The experiments were carried out in an urban environment on two plane (Platanus hybrida Brot.) trees. Both trees, after felling, showed extensive white rot in the central cylinder. The electric tomography revealed low resistivity zones roughly centered in the trunk. A comparison with the successively cut sections showed a fine correspondence to decayed areas and a strong correspondence between high moisture zones and low resistivity zones. Ultrasonic tomography demonstrated to be a very effective tool for the detection of internal decay, accurately locating the position of the anomalies and estimating their size, shape, and characteristic in terms of mechanical properties. With the georadar technique, the high contrast of electromagnetic impedance measured between the inner decayed section and the outside sound section allowed the detection of the interface between the sound and decayed section of the tree, using radar acquisition in reflection modality. The penetrometer profiles detected the low-resistance areas inside the two trunk

Particle swarm optimization for simultaneous analysis of Magnetotelluric (MT) and Time Domain EM (TDEM) data

We present an innovative, simultaneous 1D optimization of electromagnetic data. The proposed scheme is suitable for the simultaneous analysis of magnetotelluric (MT) and time-domain EM (TDEM) data based on the probabilistic and evolutionary particle swarm optimization (PSO) algorithm. The simultaneous optimization also identifies and removes the static shift from the MT data. In the proposed scheme, the static shift of the MT apparent resistivity curve is considered an additional parameter S to be optimized. We tested the suggested method on synthetic data and then applied it to the data from an electromagnetic geophysical study carried out in the geothermal area of Larderello-Travale (Tuscany, Italy). Apart from the novelty of using the PSO algorithm to estimate the model parameters by joint analysis, the simultaneous optimization of the static shift parameter addresses a major problem in MT: i.e., how to define and remove the galvanic effects on MT curves according to independent information, such as that provided by TDEM data. The procedure is expected to strongly influence the application of MT, particularly in geothermal exploration, which commonly relies extensively on EM methods

Drone-Borne Ground-Penetrating Radar for Snow Cover Mapping

Ground-penetrating radar (GPR) is one of the most commonly used instruments to map the Snow Water Equivalent (SWE) in mountainous regions. However, some areas may be difficult or dangerous to access; besides, some surveys can be quite time-consuming. We test a new system to fulfill the need to speed up the acquisition process for the analysis of the SWE and to access remote or dangerous areas. A GPR antenna (900 MHz) is mounted on a drone prototype designed to carry heavy instruments, fly safely at high altitudes, and avoid interference of the GPR signal. A survey of two test sites of the Alpine region during winter 2020-2021 is presented, to check the prototype performance for mapping the snow thickness at the catchment scale. We process the data according to a standard flow-chart of radar processing and we pick both the travel times of the air-snow interface and the snow-ground interface to compute the travel time difference and to estimate the snow depth. The calibration of the radar snow depth is performed by comparing the radar travel times with snow depth measurements at preselected stations. The main results show fairly good reliability and performance in terms of data quality, accuracy, and spatial resolution in snow depth monitoring. We tested the device in the condition of low snow density (<200 kg/m(3)) and this limits the detectability of the air-snow interface. This is mainly caused by low values of the electrical permittivity of the dry soft snow, providing a weak reflectivity of the snow surface. To overcome this critical aspect, we use the data of the rangefinder to properly detect the travel time of the snow-air interface. This sensor is already installed in our prototype and in most commercial drones for flight purposes. Based on our experience with the prototype, various improvement strategies and limitations of drone-borne GPR acquisition are discussed. In conclusion, the drone technology is found to be ready to support GPR-based snow depth mapping applications at high altitudes, provided that the operators acquire adequate knowledge of the devices, in order to effectively build, tune, use and maintain a reliable acquisition system

A Review of Geophysical Modeling Based on Particle Swarm Optimization

This paper reviews the application of the algorithm particle swarm optimization (PSO) to perform stochastic inverse modeling of geophysical data. The main features of PSO are summarized, and the most important contributions in several geophysical felds are analyzed. The aim is to indicate the fundamental steps of the evolution of PSO methodologies that have been adopted to model the Earth’s subsurface and then to undertake a critical evaluation of their benefts and limitations. Original works have been selected from the existing geophysical literature to illustrate successful PSO applied to the interpretation of electromagnetic (magnetotelluric and time-domain) data, gravimetric and magnetic data, self-potential, direct current and seismic data. These case studies are critically described and compared. In addition, joint optimization of multiple geophysical data sets by means of multi-objective PSO is presented to highlight the advantage of using a single solver that deploys Pareto optimality to handle diferent data sets without conficting solutions. Finally, we propose best practices for the implementation of a customized algorithm from scratch to perform stochastic inverse modeling of any kind of geophysical data sets for the beneft of PSO practitioners or inexperienced researchers