Fabio Giannino - Electromagnetic Methods in Geophysics: Applications in GeoRadar, FDEM, TDEM, and AEM

1. Chapter 2
2. Chapter 3
3. Chapter 7

1. Chapter 2
2. Chapter 3
3. Chapter 4
4. Chapter 5
5. Chapter 6
6. Chapter 7

Fabio Giannino

IDS GeoRadar s.r.l.Pisa, Italy

and

Giovanni Leucci

Institute of Heritage Sciences (ISPC)

National Research Council of Italy (CNR)

Lecce, Italy

This edition first published 2022
2022 John Wiley & Sons, Inc.

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Library of Congress CataloginginPublication Data

Names: Giannino, Fabio, author. | Leucci, Giovanni, author.
Title: Electromagnetic methods in geophysics : applications in GeoRadar, FDEM, TDEM, and AEM / Fabio Giannino and Giovanni Leucci.
Description: Hoboken, NJ : Wiley, 2022. | Includes bibliographical references and index.
Identifiers: LCCN 2021027149 (print) | LCCN 2021027150 (ebook) | ISBN 9781119770985 (hardback) | ISBN 9781119770992 (adobe pdf) | ISBN 9781119771005 (epub)
Subjects: LCSH: Magnetic prospecting. | Ground penetrating radar.
Classification: LCC TN269 .G433 2022 (print) | LCC TN269 (ebook) | DDC 622/.153dc23
LC record available at https://lccn.loc.gov/2021027149
LC ebook record available at https://lccn.loc.gov/2021027150

Cover Design: Wiley
Cover Image: Fabio Giannino

Geophysical techniques have many environmental, archaeological, forensic, geological, geotechnical, or engineering applications, as well as in the oil and gas, the mining industry, or for general academic research. Because of this, all the aspects connected with the logistics, designing, data collection, analysis, interpretation, and visualization, must be evaluated on a casebycase basis.

Regardless of the geophysical technique deployed for a specific subsoil exploration campaign, the final objective is always to search for the variations of a specific physical property of the system to be investigated, and to infer the possible anthropogenic or natural factor(s), which caused the variation itself.

The properties which, more often, are the main subject of an applied geophysics measurements campaign are the electrical conductivity (electrical resistivity), the seismic waves velocity propagation (either in their vertical and/or horizontal component), the EM waves velocity propagation, the dielectric constant, the magnetic field, the gravity acceleration, and so on. Measuring of the abovementioned properties, in boreholes, on surface, in the sea, or airborne, is carried out with instrumentation specifically designed and manufactured, and the data gathered through these tools, are analyzed by means of specific software, whose proper use allows even very small variations of a given quantity to be highlighted. The survey and laboratory/office operations addressed to the acquisition and analysis of such specific data, result in those geophysical methodologies known as Geoelectrical techniques, EM induction methods, seismic methods (seismic refraction, seismic reflection, seismic tomography, MASW, Re.Mi.), ultrasound, Ground Penetrating Radar (GPR), Magnetic method, Microgravimetry, and so on.

The list outlined is obviously partial, but on the other hand may be useful to give an idea of the macroareas within which the most commonly used geophysical techniques can be allocated, with respect to the industry, the academic research, or in the professional services activities.

Tools deployed for the data acquisition, as well as the software to be used for the purposes of data processing and visualization, improved very much in the last three decades, and became rather complex and of a specific use. Moreover, the possibility to apply a specific technique for the purposes of a given project, cannot disregard the knowledge of the theoretical basis on which every geophysical technique is founded on. As a direct consequence of this, a poor awareness on the hardware, the software, and the theoretical aspects, will most likely lead to a geophysical approach, whose possibility of technical success is low.

Another very important factor in planning and performing a geophysical survey, is the collection of the greater possible amount of information relating to the nature, dimension, geometry, and burial depth of the target of the measurements campaign, and the (geological) background where the object is imbedded. In this case, the word target means every buried feature determining a contrast in physical properties detectable by the technique. The knowledge of this, can also positively contribute to selecting the geophysical technique, which increases the probability to maximize the differences of a given physical property between the background and the target. Hence, the possibility to locate the latter with a higher degree of confidence and increasing the resolution of the final result.

Many geophysical techniques are based on the propagation in the space of electromagnetic (EM) waves (wave field methods), and a unique classification of them can be difficult and, to a certain extent, of no use. However, in order to optimize the results deriving from their application to projectrelated issues, it is of a paramount importance to have a clear idea about the existing EM techniques and what are the characteristics differentiating one from another. To do this, it may be used as a classification factor, at a first instance, the fact that a known amplitude and frequency transmitter may be used as a source of EM energy, as it happens for the