Development of Poynting vector direction method for electromagnetic pulses in the earth

We detected electromagnetic (EM) pulses in the earth whose waveforms were quite different from those generated by lightning discharges. In order to confirm their propagation directions (up- or down-ward), we conducted comparative measurements of phase and amplitude between waveforms of horizontal magnetic fields of the EM pulses detected on the ground and at the depth of 95 m in a borehole. Clear differences in the phase and the amplitude seemed to suggest that some of them were up propagating modes and others were down propagations. We, however, found that the decision by this method was wrong, because EM pulses measured at the 95 m-depth in the borehole represented ellipsoidal polarizations whereas those simultaneously detected on the ground were linear polarizations. We concluded that EM pulses of this kind were artificial ones having propagated along the ground surface. For determining propagation directions of unknown EM pulses, we have to obtain their propagating directions from analysis of strict Poynting vector of EM pulses using field values detected by tri-axial electric dipole antennas and tri-axial magnetic search coils. In the present paper, we introduce the measuring method of Poynting vector of EM pulses in the earth.