A Study of the Distribution of Extremely Low Frequency (ELF) Electromagnetic Fields in the Ocean Near A Shoreline.

摘要

Measurements of extremely low frequency (ELF) noise in the sea were made to determine the distribution of underwater electromagnetic fields near a shoreline as a function of depth below the sea surface. The source of this noise is predominantly atmospheric noise from thunderstorm activity,which occurs almost continuously over the surface of the earth. The atmospheric noise penetrating into the sea is at first found to be attenuated with depth by the skin depth effect of the sea water. However,as one approaches the ocean bottom the level of ELF noise appears to increase in some cases,suggesting the possibility that contributions of ELF energy are entering the sea from the ocean bottom. In this study, a modified wedge model of the ocean is used to represent the ocean near a shoreline,and the ELF electromagnetic fields are described for various regions of the model:the deep ocean,the shallow ocean,and the coastal waters. This model is intended to help establish guidelines for the design of future measurements of underwater ELF fields. Experimental data obtained by the author and others are discussed and evaluated,and proposal is made for further work. (Author)