Research On Detection Resolution Of3-D Anomaly’s ATEM Response By Central Loop

With the development of national economy, our lives are closely related to the mineralresources. The distribution of mineral resources is relative concentration, more and morepoverty, difficult in exploitation and the low utilization rate of mineral. Therefore, study andexplore new detection technology that will provide significant resources for the development ofnational economy needs protection, which is suitable for the special environment of China.Airborne electromagnetic time–domain (ATEM) method has been widely used in areas such asexploration, hydrological mapping, environmental monitoring, which has the advantage of fast,efficiency and deep exploration.ATEM is on the basis of the development of ground Transient Electromagnetic method.Their theoretical research is based on the uniform half-space or layered model of the earth, andon the foundation of forward modeling to calculate the approximate inverse one-dimensionaland two-dimensional. Using Finite Difference Numerical Calculation method and non-uniformmesh of Yee, calculate the Airborne Time Domain electromagnetic response of3-D anomaly bythe way of center loop. Taking advantage of the weighted multiple linear regression method, setup a regression equation of three-dimensional anomaly which is in different depth. Researchon detection resolution of3-D anomaly’s ATEM response by central loop, which obtain thefollowing results:1. Combine the basic theory of electromagnetic and the classification of3-D non-uniformYee mesh. Deduce that the Central Loop of the initial field and the computing process ofiteration field, which is under the center loop of3-D anomaly of ATEM.2. Have researched the impact of the altitude, shutdown time, emission current and theemission wave in ATEM response. At the same time period and the calculation of modelparameters, we can know that:The higher altitude, the greater of the rate of change of the electromagnetic responsewhose altitude is0m, which is relative to the surface. When the launching waves are different,the shape of the curve of the3-D ATEM response is different. On the basis of step wave, usingconvolution, we can calculate the airborne time domain electromagnetic response of trapezoidwave, half-sine and triangle wave quickly. However, after shutdown the current, the ATEMresponse of the trapezoid wave is the maximum, and the response of triangular-wave is the minimum. When the shutdown time of the trapezoid wave is200μs, the electromagneticresponse of switch-off-time is the maximum, and the response of off-time is the minimum. Andyet, when the shutdown time of the trapezoid wave is50μs, the response of switch-off-time isthe minimum, and whose response of off-time is the maximum. In addition, the size of theemission current is proportional to the electromagnetic response of airborne time domain by3-D anomalies.3. When the conductivity of anomaly and background is200and the size of finiteconductor is70m×70m×70m, the maximum detection depth is180m. If reasonably increasefront-end magnification of the receiver, you can effectively enhance the exploration depth.However, when has a same time channel, the lower of the depth, the greater the resolution ofthe electromagnetic response. When the buried deep is135m, we can detect the minimumelectrical conductivity ratio of3-Danomaly and surrounding rock is1.5. And, when has a sametime channel and surrounding rock conductivity is unchanged, the greater the ratio of σ0σh, theeasier to detect anomalous bodies. Only change the depth of the anomaly, the lower the depth,the ratio ε1ε0of anomalies and inhomogeneous half-space is lager. If the ratio of σ0σhis greater,the ratio of ε1ε0is greater. In addition, unchanged the background conductivity, when σ0σhratiois greater, the ratio of ε1ε0is bigger, which can also detect the response of abnormal much moreeasily.4. Take advantage of high-order statistics theory and weighted multi-linear regression,extract seven attributes of the depth-related characteristics by3-D and found the stepwiseregression equation of the depth of3-D anomaly.5. Have given the accuracy of depth’s stepwise regression equation of3-D anomaly. Themodel accuracy of the depth stepwise regression equation is from0.0155%to12.34%. And, thesum of squares of residuals (SSR) by the3-D anomaly model is1.2122×10~3.The checkingaccuracy of depth regression equation is between24.61%and40.26%. The more intense ofdividing depth is, the smaller the relative error of the depth stepwise regression equation is. Inaddition, there is higher precision.The research on detection resolution of ATEM response by central loop and theestablishment of depth stepwise regression equation have provided the theoretical basis andtechnical guidance for the recognition of conductance, size and dip of ATEM of3-D anomalies.