| Since Nuclear Magnetic Resonance (NMR) was discovered in 1946, it has been applied intothe field of geology, physics, chemistry, biology, medicine and so on. In the field of geology, it isemployed by Surface Nuclear Magnetic Resonance (SNMR), proton magnetometer, NMRspectrometer, core tester, NMR logging.et. It also almost 30 years since a former Soviet Russiascientist group in which A G Semenov been researched on the instrument of detectinggroundwater and Hydroscope was invented. In the 30 years, they get ahead in the groundwaterdetecting by the use of SNMR method, and can estimate the aquifer in a certain extent. A seriesof SNMR equipments such as Hydroscope NUMIS etc were developed, which are tools fordetecting groundwater.However, SNMR technology is a new geophysical method. It is not perfect which limited itapplied in more aspects effectively. Geophysicist should study the limitations and try to breakthem, so that SNMR be improved further.The precision of detecting is the one of main limitations of SNMR method. Just onedimensional detecting theory is used by SNMR instruments at present. It means that groundwateris assumed to be horizontal layer aquifer, and geophysicists get the information of the aquifer.Strictly speaking, groundwater is always three dimensional configurations, so that the suppositioncannot be satisfied completely. The error can not still be ignored if we detect 3-D configurationgroundwater by use of 1-D theory, which restricted the more application of SNMR method also.In this paper, in order to breach the limitations, it is need to research on how to enhance theprecision of SNMR method and study the signal of complex configurable groundwater. In term ofgeophysics, it named SNMR three dimensional forward, and it is why choose this project as mymaster paper.In this paper, the magnetism of nucleus is introduced at first. SNMR signal expression isfinally obtained by Bloch equation and reciprocity theorem. This content is particular introducedin chapter two.The excitation magnetic field of SNMR method generated by transmitter loop is studied inchapter three. For the purpose of simplification, we assume transmitter and receiver wire areloops, and the ground medium is uniformity in electricity. The electromagnetic fields of a loopwhich transmit a Lamor frequency current are studied in Chapter three. The celerity computationof magnetic field expression is main difficulty, because a product of two Bessel function iscontained in the expression. Bessel function is resisting characterized by surge intense andattenuation slowly, and the characters are enhanced by the product of two Bessel function, thismake the integral of the expression be quite difficult. This problem is solved by the computemethod of HuaJun at last. The expression is computed rapidly and accurately by use of themethod.A method of how to calculate the SNMR signal expression is introduced in section one ofchapter four. Two grid methods are given and their advantages and disadvantages are analyzed.The transmitted magnetic field component perpendicular to the geomagnetic field, tipped angle, three dimensional kernel functions are computed in section 2,3,4 of chapter four. The distributionin underground and the influence from other parameters are gotten in these sections too. The 1-Dsignal is computed by use of method of this paper in section 5, by the comparison of the resultsand the results of NUMIS software, and we can come to the conclusions that the numerationmethod used by this paper is accurate. Based on the conclusion, some 3-D forward groundwatermodels are calculated in section 6. First, 3-D models are constructed base on actual groundwatertypes. Then, the response of SNMR signals are computed in the case of the models withinvariation parameters, such as groundwater content, depth and so on. Some characters of theresponse are acquired.According to the front and direction of SNMR study at home and abroad, the responsesignals of some groundwater models are computed and discussed while separate transmitter andreceiver be used in chapter 5. To begin with, the response signals of one level aquifer withindifferent radius of transmitter and receiver loops are computed. Then, the response signals ofsurvey points which lay on an underground river model in different position are computed.Finally, the capability of groundwater detecting using separated receiver and transmitter isachieved, by the analyses of that response signal.To sum up, in view of the existing situation of 1-D detecting of SNMR fieldwork, the workof theory study of 2-D of SNMR is just at first stage and it is hardly reported about theresearches on 3-D forward, we went deeply into the study of 3-D forward.Innovations of this paper are follows:1. The computation problem of expression of excitated magnetic field is solved by use ofmethod of HuaJun.2. Program of three dimensional forward is achieved by use of grids of column formreference frame and Cartesian frame on that foundation. The program work fast and can get aexact result, and have comparative efficiency with NUMIS.3. Nineteen models are constructed base on actual groundwater types, and response of thatmodels while coinciding receiver and transmitter is computed by the program, and some materialresults are got by analyses of that response.4. At last, we did some work on the separated receiver and transmitter, response of anaquifer while radiuses of loops are different is computed. Response of a survey line whichconsists of five SNMR point and lay on a underground river model is computed too. Thecharacters of SNMR response while separated loops are acquired, which is helpful to developtheory and method of SNMR for separated loops.Finally, we should point out that, although we did much work on three dimensional forward,some result computed in this paper cannot fit the practice completely because of some hypotheticprecondition in the beginning of this paper. The tentative are: 1. receiver and transmitter wire arecircular loops; 2. there is no topographty and ground medium have uniform electricity. So, futurestudy should be tried to solve the problems, so that we can settle the problems of 3-D forward ofSNMR completely.
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