Research On Full Domain Apparent Resistivity Definition Of Large Loop Transient Electromagnetic Method

Currently, a large loop transient electromagnetic method has been widely used in manyareas. But its data processing and interpretation, inversion level are not high enough, stillstaying in the one-dimensional stage. When working in the field, usually, we measure morethan one point in the center area of the transmitter loop, so that the induction electromotiveforce will be affected by measuring points’ location. Without considering the location ofmeasuring points, the formula of apparent resistivity, calculated in later period, can notreally response to electric model. Therefore, a method, which can continuously andintuitively given change of underground media information and is not restricted by heightand offset, has great help to the transient electromagnetic in engineering investigation,mineral exploration, tunnel advanced prediction and all kinds of geological disasters in coal.It has been discussed in the article that the research on large loop source transientelectromagnetic component definition technology and full domain apparent resistivity.Starting with the Maxwell’s equations which the electromagnetic field satisfies, we havederived the expression of the large frequency domain electromagnetic loop source device,given out the relationship expression between frequency domain electromagnetic field andexpression of electromagnetic field in time domain. Based on calculation on the center pointof large loop source in both frequency domain and time domain, we conducted non-centralpoints’ forward calculation. We have calculated the response of the homogeneous halfspace, two layers and three layers of horizontal homogeneous medium in both frequencydomain and time domain. And then, we verified the accuracy and summarized the variation.Large loop source transient electromagnetic full domain apparent resistivity definitiontechnology achieved good effects in the interpretation of the theoretical model. Then weused this technique processing the data of a certain mining area in Guangdong. Weintercepted a part of the data of the entire mine for processing and interpretation, andachieved good effects. Finally, we delineated the scope of the exception.