Application Of TEM In Detection Of Anomalous Body In The Shallow Water

With the development of many years,transient electromagnetic method(TEM)has been applied in many fields.TEM widely used in engineering exploration,mineral resources,groundwater exploration,archaeology and environmental geological hazard exploration.Several methods have been developed among TEM,such as airborne Transient Electromagnetic(ATEM),ground-airborne transient electromagnetic method,marine transient electromagnetic method and mine transient electromagnetic method(MTEM)and others.With the continuous development of exploration field,TEM has to face increasingly complex environment and topography,and exploration targets.It is an important application area to explore on water.Detection of small anomalous bodies in shallow water is difficult by TEM.At present,there are few research about detection of TEM in the shallow water in China.This paper studies the effect of TEM through 3D modeling of TEM and field experiment,to study from theory and practice.TEM forward modeling methods mainly include finite element method,finite volume method,finite difference time domain and integral equation method.What's more,the finite element method is more flexible in modeling complex models,and it is simpler and more operable when constructing the model.In this paper,we carry out the three-dimensional forward modeling for low resistance small-scale anomaly in shallow water area by using the finite difference time domain method.Meanwhile,the characteristic of electromagnetic response of anomalous body is researched,the definition of apparent resistivity is completed,and also the distribution of different time fields is studied.That is,based on the forward modeling,the theory of transient electromagnetic application in shallow water is studied and its feasibility is verified.In this paper,field experiment had been carried out on the basis of theory.After searching and comparing,the test site was designed in Miyun Reservoir in Beijing.This experiment used the latest independent research and development of split-type transient electromagnetic instruments which made by Institute of Electronics of the Chinese Academy of Sciences.Cross scan lines were used to scan the target area and complete the data collection on the water.In the data processing process,we recalibrated the measuring line measuring point.Defined of apparent resistivity and data interpretation.At the end of this paper,we summarize the shortcomings and mistakes in this study,and point out the direction of future development.