oa New Art for Crosshole Electromagnetic Tomography

Crosshole Electromagnetic Tomography (CEMT) is a powerful geophysical exploration technique. Two new ray EM tomography strategies are proposed in this paper, one is named Average Multi-Frequency Absorption Tomography (AMFAT) and another DuaI-Frcquency Conductivity Tomography (DFCT). In AMFAT, the absorption tomography is done using the average of the data of different frequencies. The averaged data should be that measured at same configuration. In DFCT, the conductivity tomography is done using the following equation $$ E_1 - E_2 = 20 ¥log ( ¥sqrt{f_1 / f_2 } ) + 8.6859 ¥sqrt{¥pi ¥mu } ( ¥sqrt{f_1} - ¥sqrt{f_2} ) ¥int{ ¥hat{¥sigma} (r) dr} $$ where $E_1$, $E_2$ are electric field intensities (unit: dB) measured at same geometry configuration in far field, $f_1$, $f_2$ are frequencies, $¥hat{¥sigma} = ¥sqrt{¥sigma}$, $¥hat{¥sigma }$ is the conductivity of the rnedia detected. DFCT is suitable for the medium with high conductivity and AMFAT is suitable for the medium with low conductivity. AMFAT can increase the S/N ratio. DFCT can markedly eliminate the image distortion rising from the approximation of the directional factor of dipole antenna used by that of a half wave-length dipole antenna.