In order to improve the country’s economic development speed and adapt to therapid development of science and technology, in recent years, a variety ofelectromagnetic technology have get an unprecedented rapid development.Electromagnetic method has a widely application, include oil and mineral resourcesexploration, groundwater exploration, geothermal exploration and Engineering survey.etc. However, electromagnetic method still has some problems in the practicalapplication, the most important problem is how to improve the quality of the datecollected in the wild. In the practical application, electromagnetic method mostlyobserves on the ground, it can also observe in the underground mining roadway. Thetransmitting and receiving of the electromagnetic method in the underground miningroadway are all in the roadway. Compared to observing on the ground, observing inthe underground mining roadway suffers the less electromagnetic interference, and itsreceiver is more close to targets, so it can gets the stronger signal. This paper’s mainresearch contents is the3D forward of frequency domain electromagnetic method inroadway, forward is the basis of inversion, then getting reliable and stable forward canensure the correctness of the inversion results.This paper starts from Maxwell equations that electromagnetic method satisfies,and adopts the method to separating the total field into the primary field (backgroundfield) and the secondary field. The calculation of the primary field considering thereflection of the roadway, it starts from the derivation of the electromagnetic responsetheory formulas which the source is horizontal electric dipole, then pointing along thewire direction to get the theory formulas which the source is long earthing conductor,and the best Hankel filter coefficients are obtained by simulating some typical models.The secondary field’s calculation uses the staggered-grid finite difference method toderiving the expression of the magnetic field component and electric field component.Then the calculation of the secondary field is transformed to the solution of linearequations systems, the secondary field value is zero in each boundary are introducedin this paper. The reason to use staggered-grid finite difference method is it can notonly apply a very flexible grid for the discretization of the model, but also accord withright helical code. We can get a large scale system of linear equations after thecalculation of the secondary field using the staggered-grid finite difference method, then we use the BICGSTAB method to solve it, finally accomplished the frequencydomain electromagnetic method’s3D forward in roadway.In the last part of this paper, after the three dimensional numerical simulation ofsome typical geoelectric model, we analyzed its response to verify the correctness ofthe3D forward modeling algorithm. |