Research Of Calculation And Application Of All-time Apparent Resistivity Calculation For Large Fixed Loop Transient Electromagnetic Methods

The transient electromagnetic method is a kind of artificial source in the time domain onthe basis of the principle of electromagnetic induction electromagnetic detection method. Thismethod to the low resistivity anomalies body has a higher sensitivity; carry a rich spectrumcomponent of the pulse waveform time excitation can cover the frequency band of detectionrequired, greatly improving the work efficiency. Especially large fixed loop, as a method oftransient electromagnetic detection method most commonly used, have an unparalleledadvantage, this method has a strong ability to adapt, so the method in geological exploration,the project, geothermal environment exploration has been an extremely wide range ofapplications.However, to receive the actual measurement of the relative position when placedbetween the wireframe and launch wireframe is inaccurate, resulting in measurement error,making data processing more difficult. And usually calmed down, the Central loop method ofapparent resistivity calculated mostly using the formula of the late central loop methodapproximate calculation, but this method of calculation by the boundary effect, and when notsatisfied with advanced conditions, the apparent resistivity values calculated distortionTherefore, the method is simple but there are large errors and limitations, the general effect.To find a method than the Central loop method of the late method of calculating the apparentresistivity to more accurately reflect the method of calculation of interpretation of thegeological body ground is very important to study the region of apparent resistivitycalculation for the production practice has a certain practical significance.In this paper, The region of all-time apparent resistivity proposed by Spies et al, use ofthe Raiche released large fixed loop device response formula, each side will launch thewireframe(line source)seen as the electric dipole integrals, line box any point electromagneticfields as these horizontal electric dipole made of electromagnetic fields in the cumulative. Bythis method analysis large fixed loop device of the secondary field response attenuationcharacteristics for the homogeneous half space.Since the apparent resistivity response of an implicit function, so using the method ofspline difference, use the response value to calculate the all-time apparent resistivity of large fixed loop region. But generally calculated apparent resistivity appears the solution is notunique situation, using the points sooner or later, variety judgment to arrive at aco-understanding here. And the preparation of the corresponding computer program, thecalculation of the homogeneous half-space and layered media model, Verified the correctnessof the calculation method.Finally, The all-time apparent resistivity method and loop method were used forprocessing the measured data, by contrast, all-time apparent resistivity than the central loopmethod apparent resistivity method could better reflect the geological body geoelectricalcharacteristics in the early and mid-term, and more better to eliminate border effects. So thisstudy has some practical value.