An electromagnetic subsurface profiling system is being developed which incorporates frequencies from 100 Hz to 10 KHz. Forward modeling shows that using a line source in the near-field gives larger anomaly amplitudes than a line source in the far-field or a coil source in the near or far-field. Forward calculations with wave ellipticity using a vertical magnetic dipole as a source indicates that the ellipticity of the magnetic field polarization ellipse is usually a more sensitive parameter than the vertical magnetic field.;Only the ratios of the magnitudes of the total magnetic field and the relative phase in three perpendicular directions is collected from which ellipticity is calculated. High accuracy is obtained by injecting a known calibration signal into the receiving coils to determine coil and system response while taking measurements. A line antenna or a loop antenna may be used for the transmitter and three perpendicular coils are used as receiving antennas.
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