| Wide field electromagnetic method(WFEM), which is introduced by Academician Jishan He in Central South University, is a new controlled source sounding method in frequency domain. Based on the bipolar source field expression, the accurate wide field apparent resistivity has been calculated. For the observations can be conducted in wide field, not limited to the far field, the exploration depth is increase with the same transceiver distance. Particularly, we only measure one component of the field (electric field component or magnetic field component) of the controlled source and make the measurement of multiple frequencies at the same time. Thereby the relative accuracy and efficiency are increased.The bipolar source field has been obtained by the integral of dipole source field expression along the long grounding wire using a globally adaptive scheme based on Gauss-Kronrod rules, and the wide field apparent resistivity has been calculated by the inverse spline interpolation, then the comparison of cagniard apparent has been carried out. Furthermore the apparent resistivity calculated by the electric field horizontal component and the total electric field were analyzed and compared. Taking quantitative comparison to the bipolar source and dipole source field, the error range of non-dipole effects has been calculated.Based on the one-dimensional forward, using a fast convergence and high accuracy least squares inversion method to make Inversion of the wide field apparent resistivity calculated based on the bipolar source field. As the electrical vertical changes of the geoelectric section can be reflected by the bipolar source wide field resistivity in the transition zone and near, i.e. the near and transition zone correction is unnecessary, then the error caused by correction can be avoided. So the inversion accuracy is improved.The paper has won the support and funding of National natural science foundation project, the basis research of wide field electromagnetic system (40827002). |
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