All-time Secondary Electromagnetic Field Extraction In High Resolution Transient Electromagnetic System For Subsurface Imaging

With the developing of social economic and city construction, and more attention for the engineering and environmental geology, shallow subsurface investigation and evaluation has become the key subject of current research. Transient electromagnetic exploration (TEM) is an important method for environment and engineering, mainly applied in ground water investigation, ground solid waste and poison detecting, archaeology, soil engineering studies and detecting city ground piping, etc.Recently, high resolution shallow subsurface sounding is a popular electromagnetic research orient. Removing primary field and transient process from the measured all-time TEM(ATTEM)signals is the key technology for high resolution shallow subsurface sounding. Based on all-time transient electromagnetic response of nonmagnetic conductive sphere under tilting step signal, this dissertation, which depends on China Geology Investigation Project "Portable area TEM instrument advancement and demonstration" and National Natural Science Foundation "Research on high resolution shallow subsurface all time TEM system and key technology" and "Research on near area magnetic source TEM system and experiment " and National Science and Technology the tenth Five Plan "Strong field source TEM technology perfecting and advancement", mainly discusses on removing transient process from the measured all-time TEM signals and gaining the secondary field. The achievements are obtained as following:1. Research on primary induction voltage and its transient process under the tilting step impulse, and discuss all time transient response characterization of secondary induction voltage and its transient process based on nonmagnetic conductive sphere model. Analyze the all time transient response relation between the primary field and secondary field while the transient process exists in receiver coil.2.Research all time transient electromagnetic response affected by primary induction voltage and its transient process, and analyze all time transient response changing with the receive coil electrical parameters, also demonstrate to gain all time secondary field by removing primary field and reduce earliest sampling time in order to achieve smaller exploration depth.3. According to combine measured parameters and theoretical computation, research on all time secondary field extraction at line 4 Mountain Tiger Zhoushan Zhejiang Province and Changchun Geology Palace room 327, and prove further that removing the primary field can improve the resolution and precision of shallow subsurface sounding and it can eliminate high resistivity shallow layer during apparent resistivity reversion.4. It is put forward to adopt three-point exponential approximation nonlinear smooth filter and logarithm equal-interval based on geometry average approximation after researching on improving later signal noise ratio of transient electromagnetic signal. Develop a set of software for data process and inversion based on "smoke coil" theory one dimensional fast inversion method.5. The exploration results, using self-made ATTEM instrument Changchun Caijia alive faultage and zhoushan Liandao Engineering Zhejiang Province, prove further that removing primary field can improve resolution of shallow subsurface sounding. Main innovation in this dissertation:1.It is proposed firstly removing primary field from measured all time transient electromagnetic response while considering transient process of receiver coil and extract all time secondary field and improve resolution and precision of shallow subsurface exploration.2.To the end of equally compression sampling, it is put forward firstly to process data using three-point exponential approximation nonlinear smooth filter and logarithm equal-interval in order to enhance later signal noise ratio of transient electromagnetic signal. 3. From the point of inversion method and measurement system, break through only measuring attenuation part of transient response in the routine time-domain electromagnetic...