2-d And3-d Forward Modeling And The Response Analysis Of The Fixed-wingairborne Time-domain Transient Electromagnetic Method

According to the situation of development on the fixed-wing airbornetime-domain transient electromagnetic method at home and abroad and the basictheory of electromagnetic field,, the forward numerical simulation of airborneelectromagneticwas realized, and abnormal posture have been discussed. The mainresults are as follows:(1)one-dimensional medium model:based on the basic principle ofelectromagnetic field, analyzing the fixed-wing airborne time-domain transientelectromagnetic calculation method of the electromagnetic response characteristicsof one-dimensional medium model, the disturbing factors such as the resistivity,dielectric constant, flying height, size of cap rock resistivity，emission waveformswhich maybe affect geoelectric model electromagnetic response are analysed. andstudying of the depth of investigation and low resistivity thin layer.It providesservices for the system design parameters and it also provides the research foundationfor one dimensional inversion method.(2) two-dimensional medium model: In order to study the2-d forward modelingof three dimensional field source, A finite difference frequency domain-wavenumber domain method has been studied, the2.5D forward modeling of the fixedwing airborne transient electromagnetic was realized, the response results arecontrasted in the different wave Numbers. the range of suitable wave numberareanalyzed.In order to improve the operation efficiency, the cubic spline interpolationwas used to quickly calculate the frequency response, The equations are solved byusing theLU analytic method., among other measures. and the correctness of thealgorithm is verified by the model, analyzed the different characters ofelectromagnetic response of the syncline model and prismatic abnormal body model.(3) three-dimensional medium model:staggered grid subdivision for computingarea and the Finite Difference Method (FDM) was adopted to realize the fixed-wingairborne transient electromagnetic three-dimensional forward numerical simulation;And using Jacobi iteration as a preconditioning the matrix of the preconditioning conjugate gradient method was adopted in the process of solving large-scale sparsematrix linear equations, increasing the precision of the numerical simulation andimproving the iterative speed; the calculation precision of different number offrequency points were compared with the results of the three dimensional numericalsolution and analytical solution of the layered model.the disturbing factors such asflying height, cover thickness,the target body resistivity size,the target body burieddepth, the distance between the target body, which maybe affect geoelectric modelelectromagnetic response are analysed and discussing response law of complexmedium model. establishes the basis of further the inversion processing,interpretationand system design.(4) the coil attitude: Analyzed the five kinds of abnormal posture and the effectsof different abnormal posture on the record data were simulated, the formula ofelectromagnetic response is deduced about an arbitrary revolution the receiver coilaround a rotation angle.the disturbing factors such as tilting posture change oftransmitter coil,flying height fluctuation which maybe affect the electromagneticresponse are simulated by three-dimensional model. Under the influence of all sorts ofattitude,the size of relative error of respond to change was analyzed. it laid a solidfoundation for the theoretical analysis of aviation transient electromagnetic posturecorrection.it offers theory foundations for the error analysis of the measured data ofproduction and has established the foundation for the reasonable inversioninterpretation. All these are of practical significance for improving the system designrequirements.Finite Difference Method (FDM) was adopted to realize three-dimensionalforward numerical simulation; and the response characteristics of the several specificmodel was obtained, analyzing the abnormal situation of attitude,it has certainreferential value to the system design and proper inversion interpretation.