Determination of the Apparent Resistivity of the Earth from ElectromagneticSounding with Magnetic Dipoles

摘要

Electromagnetic sounding techniques operating at very low frequencies (110 Hz-56kHz) have a great potential to investigate the shallow subsurface between 0-50 m. In this report, frequency domain techniques are considered. These techniques make use of electric-current carrying loops which generate a electromagnetic field. Before applying an inverse method to the field data, the authors first search for a global information of the subsurface. In this report, the apparent resistivity is obtained by fitting the analytical expression for a homogeneous half-space to the field data using both the amplitude and the phase information of the data. This procedure to obtain the apparent resistivity is implemented using a non-linear optimization scheme. In this paper only two setups are used: the source and receiver loops are either in a horizontal or in a vertical position. Using different frequencies, different offsets and different source-receiver setups, a global resistivity distribution in the subsurface is obtained. (Copyright (c) Laboratory of electromatic Research 1995.)