Shallow Sounding of Crustal Regions Using Electromagnetic Surface Waves

摘要

A specific physical interpretation of the effect of relative permittivities epsilon and conductivities sigma upon the amplitude and phase of propagating electromagnetic surface waves is given, where epsilon and sigma characterize the layered material regions of a planetary lithosphere. The interpretation is made possible by the availability of simple formulas for the fields of vertical and horizontal unit electric dipoles near interfaces between regions of matter; the earth's lithosphere at its interface with salt water is used an an example. The ranges of epsilon, sigma frequency f, and radial distance tho over which the formulas apply are shown to be quite broad. The E1 rho component (the radial electric field in region 1, characterized by complex wave number k1 and adjoined at a planar interface to region 2, characterized by k2, where (abs.val.k1)sq >>(abs.val.k2)sq) is discussed in detail. The attenuation of 20 log(abs.val.E1 rho) as a function of rho and rho/delta sq, where delta is the skin depth, is illustrated for conductivity ratios sigma 2/sigma 1 = 0.1 to 0.001, over a range of f from 1 Hz to 100,000 Hz. A specific experiment is proposed for testing a specialized insulated antenna for seafloor use in shallow coastal waters at 1 kHz.