Summary. A 3-D finite-element simulation of global electromagnetic induction is used to evaluate satellite responses in geomagnetic dipole coordinates for harm

Summary. Pointe du Hoc overlooking the English Channel in Normandy, France was host to one of the most important military engagements of World War II but is vu

This paper provides a theoretical overview of some of the fundamental concepts underlying electromagnetic (EM) induction exploration methods using marine controlled-source EMs as an exemplar. In particular, it will be shown, from different vantage points, that EM induction operates in the magnetoquasistatic regime in which inductive effects dominate, capacitive effects are ignored, and the displacement current is negligible; hence, charge polarization and dielectric phenomena play no role. We determine some of the major physical consequences of this approximation, and we make a distinction between wave physics and diffusive behavior, which is of particular interest in the special case of time-periodic excitation. We distinguish the fundamentally different roles of mobile charge carriers and bound charges in EM induction. It is emphasized that EM induction cannot be fully understood by comparing and contrasting Maxwell’s equations with governing equations from other disciplines that possess a similar mathematical structure. It is suggested that visualizations of energy flow using the Poynting vector and the Joule heating parameters provide a powerful tool to understand how the geologic medium shapes EM induction responses.

We have better maps of the surfaces of Venus, Mars, and the Moon than of the Earth’s seafloor. There is even less information available about the geologic structure below the seafloor. In particular, the transition zone deep beneath and crossing the coastline is a very poorly studied frontier resulting from limitations of technology and logistical barriers. Here, we point out the significance of this region for understanding fundamental geologic processes, geohazards, and especially coastal aquifers. One prominent example is the increasing awareness of the importance of groundwater exchange between land and sea. This Perspective defines the region beneath the coastal transition zone, or coastal white ribbon as an underexplored frontier, and highlights the need for characterization of this critical region to depths of tens of km. We discuss available geophysical methods and their limitations with coastal groundwater used as the primary illustration. Advances in geophysical and drilling technology, coupled with numerical modeling, are needed to enable better accounting of this poorly understood component of the geosphere.

Cassava as a world food security crop still suffers from an inadequate means to measure early storage root bulking (ESRB), a trait that describes early maturity and a key characteristic of improved cassava varieties. The objective of this study is to evaluate the capability of ground penetrating radar (GPR) for non-destructive assessment of cassava root biomass. GPR was evaluated for this purpose in a field trial conducted in Ibadan, Nigeria. Different methods of processing the GPR radargram were tested, which included time slicing the radargram below the antenna surface in order to reduce ground clutter; to remove coherent sub-horizontal reflected energy; and having the diffracted energy tail collapsed into representative point of origin. GPR features were then extracted using Discrete Fourier Transformation (DFT), and Bayesian Ridge Regression (BRR) models were developed considering one, two and three-way interactions. Prediction accuracies based on Pearson correlation coefficient (r) and coefficient of determination (R²) were estimated by the linear regression of the predicted and observed root biomass. A simple model without interaction produced the best prediction accuracy of r = 0.64 and R² = 0.41. Our results demonstrate that root biomass can be predicted using GPR and it is expected that the technology will be adopted by cassava breeding programs for selecting early stage root bulking during the crop growth season as a novel method to dramatically increase crop yield.