Conductivity-depth Identification Research Of Time-domain Helicopter Electromagnetic Three-dimensional Anomalies

It is well known that mineral resources is the material basis of human survivaland development. The resources such as coal and mine ore is rich, but per capita isless. With the rapid development of economy, the reserves of mineral resources is less.Some old ore reserves are almost depleted. New mine is needed. Therefore, theapplication of geophysical need to progress quickly. Time-domain helicopterelectromagnetic method stand out at home and broad recently. The development ofthis method is rapid. Time-domain helicopter electromagnetic method applywidely.This method is rapid and economic, which have great exploration depth,high explanation precision and resolution. It is one of the effective methods formineral resources exploration and is especially suitable for looking for new minessurrounding the old mining area and deep prospecting in China.With the wide application of time-domain helicopter electromagnetic method, itneeds to improve airborne electromagnetic data processing and interpretation urgently.The data of airborne time-domain electromagnetic measurement is large. Conductivity-depth imaging need a lot of time. Three-dimensional inversion are still difficult.Faced with these problems, the thesis is in the support of national natural sciencefoundation project “research about the3D geological identify technology based on thefull waveform aviation time-domain electromagnetic detection”. Based on the theoryof time-domain helicopter electromagnetic method and relevant knowledge, the majorresearches are as follows:1、 We use time-domain three-dimensional finite difference method andsubdivision the3D earth. Deducing the expressing of the initial field and iterationfield, which is under time-domain helicopter loop source. We confirm the initialtime and compute the electromagnetic response of time-domain helicopter loopsource.2、According to the actual parameter of time-domain helicopter electromagneticresponse detection, computing multiple sets of anomalies. Building the panel pool of3D anomalies model. We classify the profile curve of3D anomalies upright model.There are three kinds: one peak, double peaks and multiple peaks. The method ofMaxime Claprood have been to studied to extract seven attributes.3、We use the sample data. The dependent variable is conductivity and depth ofthree-dimensional anomaly. The independent variable is seven attributes. We build theregression equation. We diagnose the sample data, there is no outliers. But defaultvalues exist and delete them. From variance inflation factor, eigenvalue, conditionindex and variance proportion, we diagnose multicollinearity. We findmulticollinearity among the independent variables. If multiple collinearity exist, theregression equation is not stable. Fitting effect is bad. Therefore, we use threemethods, for example, stepwise regression, ridge regression and principal componentregression, to build the regression equation. Then we obtain the optimal regressionequation about conductivity and depth.4、 Based on the theory of time-domain electromagnetic, we analyze theregression equation about conductivity and depth.Compare with the foreign literature,we take the regression equation is right. We choose principal component regression asthe optimal regression equation about conductivity. Three method regressions are good. We use ring to equivalent to anomaly. The results show: In sand tankexperiments, the relative error of circular ring is less than10.48%, the relative errorof square ring is less than15%;The relative error is less than15.28%of helicopterflight experiments in Tongbai. Therefore, the optimal regression equation ofconductivity parameters is effective.Therefore, multiple linear regression is entirely feasible to estimate conductivityand depth of anomalies. It is an efficient, accurate and rapid method, which lay afoundation for HTEM flight in field measurement of mass data of rapid detection andidentification.