Preface

Transient electromagnetic (TEM) method has been widely used in the exploration of mineral resources, environmental and engineering purposes, geological hazard survey, and other areas for its unique advantages. It has attracted much attention from geophysicists and geologists. With more and more mature or developing method from seismic being applied in TEM, the migration imaging of TEM data has become a hot research area in electromagnetic exploration. People are increasingly interested in methods such as pseudo-seismic inversion and interpretation, electromagnetic migration, or combination of migration and inversion. From the viewpoint of wave field, these methods not only expand and enrich research on TEM, but they also extract more meaningful information from the survey data that are more useful for imaging the underground targets but cannot be obtained via the conventional TEM method. With enhancing the requirements of geophysicists in the resource exploration (deep mine and blind orebodies, etc.) and engineering survey (precise exploration), research and development of the multiple coverage technique for TEM method becomes necessary and practically significant. In addition, the multi-component array observation techniques can get abundant geoelectrical information and the technical research has also drawn attention. It is the direction and tendency for modern instruments to develop multi-component and multi-channel array transient EM systems that have strong anti-interference ability, high-power, timely data processing functions, versatile and intelligent. The development of high sensitivity, high performance and resolution, three-component sensors is also important part of the development of transient electromagnetic instruments. On the basis of previous researches, the authors successively worked together with more than 20 graduate students to study pseudo-seismic interpretation of TEM data. We proposed the optimization algorithms for transformation from transient EM field to wave field and applied the regularization for the calculation of the inverse transformation, and successfully extracted virtual seismic wavelets. Experiments shown that using multi-aperture radiation field source we can obtain stronger magnetic field a single-aperture radiation field source. From observations of the primary field, we also find that multi-aperture field significantly improves the