Low-frequency transient (time domain) electromagnetic fields propagating in a marine environment

✍ Scribed by Marius Birsan

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 146 KB
• Volume: 17
• Category: Article
• ISSN: 0894-3370
• DOI: 10.1002/jnm.537

✦ Synopsis

Abstract

The propagation of electromagnetic waves in seawater is quite different from the propagation in free air. Both the velocity of propagation and the attenuation of the wave reveal a strong dependency on frequency. When using electromagnetic methods for underwater purposes, the low‐frequency bands are preferable since high‐frequency components are attenuated very quickly. Consider a transmitted electromagnetic pulse travelling outward from a submerged electric dipole. Such a pulse contains many frequency components. Since the different components travel with different velocity, the shape of the pulse will become more and more distorted as it travels from the source. In seawater, the distance of propagation is very limited to encourage practical applications. However, when the environment contains several electrically different media, the electromagnetic wave can propagate along the boundaries to a much longer distance and this property makes them valuable tools in geophysical prospecting and radio communication. The purpose of this study is twofold: first the paper outlines a technique that generalizes the solution of Maxwell's equations to an arbitrary number of layers; the second goal is to investigate the propagation of low‐frequency transient electromagnetic fields in a marine environment modelled as a layered media. The frequency‐domain formula for the travelling field of a horizontal electric dipole excited by a current pulse is Fourier transformed to obtain the solution for the field in time domain. Possible application to remote sensing in the ocean is considered. © Crown Copyright 2004. Reproduced with the permission & Her Majesty's Stationary Office. Published by John Wiley & Sons, Ltd.