The Transient Electromagnetic Field above Atmospheric Surface Duct

The transient electromagnetic field generated by vertical electric dipole in evaluation duct is investigated theoretically. A vertical electric dipole in the surface layer is taken as the source of the electromagnetic field. We determine the electric field strength exactly at some fixed point in the duct layer expansion with time, the image of the primary source permits us to apply the method first for Cagnaird and later extended by De Hoop and Frankena to the cases .Hence, we can give a physically intuitive description of polarization dependence at the time of the electrical field strength. The distinction of different cases where the distances between the receiving and transmitting ends at greater or lesser than the total reflection distance is studied. Keywords: Electromagnetic field, Magnetic dipol

The Transient Electromagnetic Field above Atmospheric Surface Duct

The transient electromagnetic field generated by vertical electric dipole in evaluation duct is investigated theoretically. A vertical electric dipole in the surface layer is taken as the source of the electromagnetic field. We determine the electric field strength exactly at some fixed point in the duct layer expansion with time, the image of the primary source permits us to apply the method first for Cagnaird and later extended by De Hoop and Frankena to the cases .Hence, we can give a physically intuitive description of polarization dependence at the time of the electrical field strength. The distinction of different cases where the distances between the receiving and transmitting ends at greater or lesser than the total reflection distance is studied. Keywords: Electromagnetic field, Magnetic dipol

A Comparative Overview of Geophysical Methods

This report was prepared with support from the Air Force Research Laboratory, under contract FA8718-07-C-0021.The shallow subsurface structure of the Earth is important to understand for many economic and safety reasons. The problem is usually difficult due to complexity of the earth’s subsurface processes especially near the surface. A number of geophysical methods are used for this purpose using different physical characteristics of the Earth materials. A particular geophysical method illuminates part of the problem, but a reliable solution can only be found by combining results of different methods. In order to synthesize information from different geophysical methods, it is important to understand their similarities and differences. The aim of this study is to correlate the basic principles of geophysical methods side-by-side starting from fundamental equations. This study reveals that many analogies exist among these methods both in their mathematical formulation, and sometimes, in ways they are used in the geophysical applications

Magnetism and the interior of the moon

The application of lunar magnetic field measurements to the study of properties of the lunar crust and deep interior is reviewed. Following a brief description of lunar magnetometers and the lunar magnetic environment, measurements of lunar remanent fields and their interaction with the solar plasma are discussed. The magnetization induction mode is considered with reference to lunar magnetic permeability and iron abundance calculations. Finally, electrical conductivity and temperature calculations from analyses of poloidal induction, for data taken in both the solar wind and in the geomagnetic tail, are reviewed

On electric fields produced by inductive sources on the seafloor

The transient electromagnetic (TEM) method has recently been proposed as a tool for mineral exploration on the seafloor. Similar to airborne TEM surveys conducted on land, marine TEM systems can use a concentric or coincident wire-loop transmitter and receiver towed behind a ship. Such towed-loop TEM surveys can be further augmented by placing additional stationary receivers on the seafloor throughout the survey area. We examine the electric fields measured by remote receivers from an inductive source transmitter within a 1D layered earth model. At sea, it is conceivable to deploy either a horizontal transmitter (such as the analogous standard airborne configuration) or a more exotic vertical transmitter. Therefore, we study and compare the sensitivity of the vertical and horizontal towed-loop systems with a variety of seafloor conductivity structures. Our results indicate that the horizontal loop system is more sensitive to the thickness of a buried conductive layer and would be advantageous over the vertical loop system in characterizing the size of a shallowly buried mineralized zone. The vertical loop system is more sensitive to a resistive layer than the horizontal loop system. The vertical electric field produced by the vertical loop transmitter is sensitive to greater depths than the horizontal fields, and measuring the vertical field at the receivers would therefore be advantageous. We also conducted a novel test of a towed horizontal loop system with remote dipole receivers in a marine setting. The system was tested at the Palinuro volcanic complex in the Tyrrhenian Sea, a site of known massive sulfide mineralization. Preliminary results are consistent with shallowly buried material in the seafloor of conductivities >1  S/m

Selected examples of induction studies in continental regions, including AMT prospection, for natural resources

Cet article présente une revue des techniques de prospection électromagnétique ainsi que quelques exemples de leur application à la détection de ressources naturelles. Les méthodes "au sol" sont considérées séparément des méthodes "aéroportées", en distinguant d'autre part les méthodes utilisant les "ondes planes" des "autres méthodes

Electromagnetic Wave Theory and Applications

Contains reports on eleven research projects.Joint Services Electronics Program (Contract DAAG29-83-K-0003)Joint Services Electronics Program (Contract DAAL03-86-K-0002)National Science Foundation (Grant ECS82-03390)National Science Foundation (Grant ECS85-04381)Schlumberger-Doll Research CenterNational Aeronautics and Space Administration (Contract NAG 5-141)National Aeronautics and Space Administration (Contract NAS 5-26861)National Aeronautics and Space Administration (Contract NAG 5-270)U.S. Navy - Office of Naval Research (Contract N00014-83-K-0258)National Aeronautics and Space Administration (Contract NAG 5-725)International Business Machines, Inc.Lincoln Laborator