Study On Collecting And Processing Of Shallow Subsurface TEM Singnal

With the rapid development of economic and city construction, issues of egnineering and environmental geology have attracted great attention recently. The improvement of current TEM method for the area from the surface to 20 meter down is desirable, This is mainly due to the abnormal falling edge of the transmitter current pulse and the transient state of the receiver loop. Most domestic TEM are designed based on foreign technology, key technique has not reached the international leading level. Hence, the development of subsurface TEM measurement that meets domentic demand is very important to the TEM research.Based on NSFC General Project:"Study on TEM based on standard source", study on electricmagnetic wave transmission in homogeneous half-space , the induced current in orebody and the change rate of second induction field. Comparing and annlysing TEM transimiter waves'frequency-domain expression and frequency spectrum, and the effect of transmitter waves with TEM signal.Taking WTEM-1 transmitter as an example, the thesis analyse TEM primary field and secondary field, receiver loops'transient state, construct loops'equivalent model, differential equation and integral equation, put forward"variable structure receiver loop method", derivation element estimating equation and TEM approaching arithmetic. Simulations have been completed to verify that the"variable structure receiver loop method"is feasible. And study this method's disadvantages and countermeasure.This thesis has designed a prototype TEM receiving system using a VHS-ADC high-speed signal processing module. For shallow subsurface exploration, system sampling rate is high, so it is need to solve the problem of data real-time storage. The thesis design the system structure, and complete system modeling, interface, simulation and FPGA code generating and debugging with transmitter, And design the synchronous control module based on the relation between receiver and transmitter. A receive loop has been designed and its material's effection has been discussed.Experiments have been conducted in a outdoor field, including background measurement and metal object measurement embedded in shallow subsurface. Results verify that the developed prototype is capable of performing the TEM measurement, and can provide data for high resolution shallow subsurface imaging.