A Study On The Discernibility Of Transient Electromagnetic Synthetic Aperture Imaging Method

High resolution Transient Electromagnetic Method is now a very hot research in the geophysical prospecting objects. Now the Transient Electromagnetic Method interpretation technology is roughly divided into two categories:one kind is conductivity-depth conversion which is an approximate interpretation method, another kind is layered media inversion.The Thin-sheet theory is a very important approximate interpretation method of TEM from which we can get stratigraphic classification visually according to the features of apparent vertical conductance and its derivative curve. In this paper, based on the basic principle of Thin-sheet theory, we give the definition of apparent vertical conductance and apparent depth, and then calculate its second derivative on depth. The second derivative curve in homogeneous medium is constant to zero, but the second derivative curve produce sharp peak where the medium electrical feature changes. Gathering the peak together from each measuring point can form an image similar to the event in seismic imaging which we called the differential conductance imaging. Compared to traditional methods the differential conductance imaging method reacts more intuitively and clearly on underground electrical distribution especially layered media.More aperture transient electromagnetic physical simulation proves that transient electromagnetic aperture has coherence. The adjacent location echo of the same geological body has coherence, so the transient electromagnetic data can be aperture synthesis imaging. Based on the theory above, in this paper, we use the idea of synthetic aperture radar to correlate the differential conductance signal to improve signal to noise ratio, weak anomalies and thus achieve the goal of improving resolution. At the same time, this approach replace the single point interpretation with multiple coverage processing method of point by point on centering on the measuring point. Adopted the method of cross-correlation and synthetic aperture will greatly enhance the resolution of Airborne Transient Electromagnetic Method.In this paper, we design different theoretical models for numerical simulation and then analyze the synthetic processing data from which we conclude the resolving ability of Airborne Transient Electromagnetic Synthetic Aperture Imaging technology based on different model parameters and different synthetic aperture length. Finally, we use synthetic aperture imaging method dealing with the data of field survey, the results show that synthetic aperture method can effectively improve the transient electromagnetic imaging precision.