Horizontal Components Response And Its Application Of Magnetic Sources Transient Electromagnetic Method

After the development of several decades, transient electromagnetic (TEM) method has become an important geophysical exploration method in finding mineral resources, as well as in engineering, environmental and hydrological services. In real TEM exploration, vertical-component of transient electromagnetic field is usually adopted. Most of the modern TEM equipment can acquire 3-component data synchronously, because of the absence of the interpretation theory and software, the horizontal data cannot be used, vast useful information is wasted unnecessarily. Multi-component, multi-method inversion can apply the known information as much as possible. The most true geoelectric section can be expected if multi-component, multi-method inversion is applied. The horizontal-component study can be useful to multi-component inversion, at least we can get some qualitative description of the 3-D objects under the surface, we can speedup the 3-D inversion by using the constraint conditions got from the horizontal-component study. In this dissertation, the study was focused on the horizontal-component responses of the magnetic sources TEM. The main results of the study are as below:It can be known that the horizontal-component is more sensitive to the conductive objects than the vertical-component from the respective expressions for the components. The exciting-field distribution of the rectangle transmitter loop was calculated and analyzed. The locations relation among the target object, the transmitter source and the receiver coil has important influence on the observed results. The non-exciting-angle and non-response-angle positions must be avoided when horizontal-component data are observed. A new hypothesis was introduced to the traditional"smoke ring"theory, that the"smoke ring"would diffuse downwards with the same shape of the transmitter loop and co-axial with the loop in uniform half-space or horizontally stratified medium. The formulas for calculating the magnetic field response with rectangle"smoke ring"were provided. The horizontal-component response was calculated using the formulas forementioned, this may be the foundation to the horizontal-component interpretation. When conduct time domain finite difference method (FDTD) program, the Mur boundary conditions were used to every truncation side, and the exciting source was transformed into initial conditions by using the accurate expressions of the components of TEM field in uniform half-space. The horizontal-component responses were simulated for half-space and for a 3-D conductive object in half-space. The figures tell us how the horizontal-component fields propagate under the surface of the earth. The results show that: the TEM wave travel slower in conductive objects than in resistive objects, so the TEM method has higher resolution for conductive objects exploration; for the same 3-D object, the two horizontal components have different resolutions and different anomalous characteristics, the component parallel to the long side of the 3-D object has clearer show to the transverse boundary.For fixed-loop source TEM, the pure anomalous data can be obtained using the data observed in field detract the standard response data which can be computed by applying"smoke ring"theory or conducting FDTD program. The pure anomalous data is easily to be interpreted. At last, a real case was demonstrated. The 3-component data was used to get more useful geological information. The results show the horizontal-component is helpful for the accomplishment of the geological task.