Feasibility Research On The Integrated MRS-TEM Method In Groundwater Exploration

Since 1946 discovered the Nuclear Magnetic Resonance phenomenon, along with the science and technology development, the Nuclear Magnetic Resonance phenomenon entered the application and the phase of exploitation by the fundamental research experiment. It widely applies to domains of physics, chemistry, biology, medicine and so on, and also has obtained the widespread application in the geophysics. Magnetic resonance sounding (MRS) is the new method for underground water investigation in recent decades, and the only geophysical method currently used to direct investigation of groundwater. MRS technology is cutting-edge technology in today's world and the new domains that using to investigate groundwater. It has the characteristics of novel principle and quantificational results, and has acquired obvious achievement in application.Transient Electromagnetic method (TEM) is a branch of the electric method for exploration with the quick development and good geological effect in recent years. With the digital and intellectual development of Transient Electromagnetic instruments, the use of forward computation and inversion of digital model computer, the improvement of explanation level, TEM can resolve a large range of geology problems which almost includes every field of geophysical exploration: ore exploration, constitution exploration, hydrogeology and engineering geology investigation, environment survey supervising and archaeology and so on. It is the method based on electrical discrepancy of the target,so it can measure the position of underground inhomogeneous substance and estimate its scale and electricity capability.This paper expounds the principle of MRS and TEM technology for investigating groundwater and the development of instrument for groundwater investigation in domestic and aboard. According to the comparison of the principles and characteristics about the two methods, necessity for groundwater investigation based on MRS combined with TEM is expatiated. Based on the research of the theory and examples using the two methods together, the feasibility in application of the integrated MRS-TDEM method for groundwater exploration is proved. This paper is the preparation for application of the integrated MRS-TDEM method, with the only loop line just as the transmitter loop and the receiver loop. The two methods are combined for rational allocation to achieve both the advantages and get good geological effects. This paper firstly solves functional transformation of the MRS or TEM, and research how to select the mode of the two functions. Here the SPDT switch with high voltage tolerance is used to select the mode of TEM in integrated instrument, and measure every test point in the observation area, then change to the MRS mode, lay the loop line to detect the MRS signal. This can play the advantages of both the modes, and improve the efficiency and precision.Secondly, the form and the circuit design of transmitter/receiver loop are researched in the paper. The transmitter/receiver loop line is the same one with time-sharing in the MRS mode, the emission current is up to 450A,and the voltage may 400V, but the receive signal of MRS is only in nV level. So the relay must be connected after energy in the transmitter loop line has consumed. In this case transmitter and receiver must be separated by the switch with high voltage tolerance, and can shut off in high speed. The STC89C54 is used as the Controller to generate control signal of the relay, also two efficiency diodes with two pros and cons connects in parallel fashion,and the high voltage vacuum relay are used to realize fast shut off of the transmitter and the receiver's cut and the isolation successfully. It has realized the launch and the receive cut in the same loop line with time-sharing.When the integrated MRS-TDEM instrument works in the TEM mode, there are two forms of the same loop as the antenna, one is the loop all time on line and the other is the loop with time-sharing. Limiter protection circuit and the synchronization control signal are designed to protect the whole system in the same loop line for transmitter and receiver all time on line. While with the mode of the same loop line with time-sharing, the switch circuit is designed to separate the transmitter and receiver. The control signals of the synchronization Generated by MSP430 and the relay of LRL-102PCZ-10KV are used to realize the cut and the isolation, which can make the system to lose fewer data.The research work also gives a design of the experimental prototype transmitter for groundwater base on the MRS-TEM method using MSP430,which can realize to transmit MRS wave,TEM wave and control signals of the synchronization.In order to test the system based on the control of protected circuit or the relay control model, the experiment and field results are showed in the paper. The transmitter, receiver and control system have been tested, and various contrastive experiments have been done in order to check the system performance. Finally, some suggestions in further design and research are given.