Holistic Inversion Of Fixed-wing Time Domain Electromagnetic Data

Fixed-wing time-domain electromagnetic method is a kind of geophysicalexploration which based on the law of electromagnetic. It has advantages such asgreater investigation depth, and high efficiency, which can be widely used in oil andgas exploration, and other fields, especially in forest, swamp and desert. Thetransmitting coil of fixed-wing time-domain electromagnetic system is mounted on anaircraft and the receiving is towed behind the aircraft. Traditionally, the forward ismainly to calculate electromagnetic response when the bird flies straight and levelly.However, during the survey of the fixed-wing time-domain electromagnetic system，the changing of transmitter and receiver coil and attitude bird swing, which introducethe system parameters error to the survey data including the direction of transmittermagnetic moment, the component and position of receiver coils, as well as thehorizontal distances between transmitter loop and the receiver coils etc., consequentlyaffect the inversion results. The data processing and inversion theory start relativelylate, and have a certain gap compared with foreign countries. In recent years, moreand more attention has been paid to the airborne electromagnetic, domestic scholarshave done a lot of research in data inversion theory. But traditional data processingmethods take correction and inversion individually, the effect of system parametersare not considered in the process of inversion.To solve the above problem, this article relies on the National Natural ScienceFoundation "the holistic inversion of fixed-wing time-domain electromagnetic" andNational major research equipment projects sub-topics "study of the ATEM systemdata processing and explanation software technology ".We put forward a quasi-twodimensional holistic inversion method with correction of the fixed-wing oftime-domain airborne electromagnetic data, realized a quasi-two dimensional holisticinversion method with "correction-inversion" at the same time on a line majorfindings and content are as follows.(1)Based on the forward modeling of the fix-wing time-domain electromagnetic and the layered earth, the expression of three-component electromagnetic response isderived. Meanwhile, we obtained calculation expression with arbitrary attitude of thetransmitter loop and the receiver coils. The electromagnetic response in respect to thebird rotation and swing is studied. The variation of the electromagnetic response whenin-line swing angle and the pitch of the transmitter and receiver coil coexist isanalyzed. The correction of attitude and bird swing of the fixed-wing airborneelectromagnetic is conducted. By contrast with the theoretical model the inversionresults of a quasi-two-dimensional layered earth model show the accuracy of themethod.(2)In view of the traditional fixed-wing airborne electromagnetic complex dataprocessing and inversion method ’-inversion-correction, then correction-inversion...’The swing angle and the receiving coil pitch attitude angle as the parameters of themodel, participate in the inversion. And introduced the model parameters verticalroughness and prior information according to Tikhonov regularization inversiontheory. Then the iterative inversion equations are derived.1D inversion of fixed-wingairborne electromagnetic data with correction is realized. The1D inversion withcorrection results are compared with single-site Marquart inversion for the syntheticdata. The results verify the effectiveness of the algorithm. In the inversion iteration,regularization factor is selected by a linear search method automatically, and theJaccobin matrix is calculated by the variable step size difference accumulatingalgorithm.(3) Based on one-dimensional inversion algorithm we have constructed the datamisfit of survey line by integrating observation data, and introduced the modelparameters spatial roughness and prior information. Then the iterative inversionequations are derived. Solutions of large sparse matrix of whole survey line data isobtained by using ultra relaxation conjugate gradient algorithm. Quasi2D holisticinversion of fixed-wing airborne electromagnetic data is realized. And then introducedthe swing angle and the receiving coil pitch attitude angle as the parameters of themodel. At the same time, constrained the adjacent point’s correction parameters bythe continuity in time2D holistic inversion of fixed-wing airborne electromagneticdata with correction is realized. The2D holistic inversion with correction results arecompared with2D holistic inversion for the synthetic data. The results verify theeffectiveness of the algorithm.(4)The detection capabilities of the thin layer of the geological structure of the fixed-wing time-domain airborne electromagnetic system was studied. Calculated theelectromagnetic response while changing the thickness and depth of the electricallyconductive film and with or without a group of typical high and low resistance modelof rock conductivity. Used the relative error of apparent resistivity the result ofconductivity-depth imaging. Analyzed the detection capabilities of the thin layer ofthe geological structure according to the error. Given the resolution limit of highresistivity thin layer and low resistivity thin layer under different conditions.Meanwhile, the use of quasi-two-dimensional holistic inversion algorithm forinversion model data on the limiting resolution, and the results were compared withCDI results and Occam’s results, proved that the quasi-two-dimensional holisticinversion algorithm has better ability to differentiate abnormal of thin layer.Finally through the system noise,the influence of the inversion resolution wasanalyzed, concluded that quasi-two-dimensional holistic inversion algorithm withcorrection is equally applicable to the field data, and verified the practicability of thealgorithm.The main innovation lies as follow:(1)I derived the calculation expression with arbitrary attitude of the transmitterloop and the receiver coils. The electromagnetic response in respect to the birdrotation and swing is studied. This study laid a foundation for the correction ofattitude of the transmitter loop and the receiver coils.(2)1D holistic inversion of fixed-wing airborne electromagnetic data I proposedcan solve electromagnetic complex data processing and inversion method"inversion-correction, then...correction-inversion...".And introduced the swing angleand the receiving coil pitch attitude angle as the parameters of the model.(3)I have constructed the data misfit of survey line by integrating observationdata, proposed the quasi2D inversion of fixed-wing airborne electromagneticdata,and the inversion of all survey line data at the same time is realized. The quasi2D holistic inversion of fixed-wing airborne electromagnetic data was proposed, andthe accuracy of fixed-wing airborne electromagnetic data inversion results can beimproved.