Study Of Data Acquisition Design And Data Correction Research For Semi-airborne Transient Electromagnetics

The research on the semi-airborne transient electromagnetics(SATEM)with grounded long wire source is still in its infancy.Although there have been many successful application cases of SATEM system in karst tunnel survey and mineral exploration,but there are relatively few researches on the data acquisition design,that is design of effective detection areas and observation areas for this method.At the same time,data processing and interpretation mostly follow the data processing and interpretation schemes of other traditional electromagnetic methods,and there is a lack of supporting data correction processing systems for SATEM,The above-mentioned shortcomings greatly limits the development and application of this method.Therefore,this article has carried out relevant research work on the three issues of effective detection area analysis,exploration area design and data correction processing of SATEM.First,in order to recognize and understand the effective detection area of SATEM,this paper conducts calculation and research on the footprint and sensitivity of SATEM based on the strategy of footprint and sensitivity analysis in aviation electromagnetics.Based on Maxwell's equations and the assumption of finite conductive medium,the expression of the underground electromagnetic response in the time domain of the uniform half-space model under the long wire source and the vertical magnetic dipole source is derived,and the Hz contribution distribution of the receiving point from underground induced current field is calculated by using the Green tensor integral function.In addition,based on the underground induced electric field under the equivalent magnetic source of the long wire source and the receiving coil,the sensitivity distribution is obtained by the method of time-discrete to obtain approximate convolution integral,and the same receiving is analyzed and compared distribution of Hz contribution under different decay time.The results show that the distribution of sensitivity and Hz contribution is basically the same in the overall characteristics.As the receiving time goes backward,the area with the largest contribution(sensitivity)gradually moves closer to and below the receiving point,and the increase of the offset contributes to Hz.The distribution shape has little effect,but the contribution of the area near the source gradually decreases,and the footprint volume gradually expands.The change of the receiving point relative to the source position will distort the distribution shape of the footprint;the main effective detection area(sensitive area)of SATEM)is the area between the source and the receiving point,and it is much larger than that of the aviation electromagnetic method,revealing the large volume effect of this method.At the same time,the numerical simulation results for the main contribution area reveal that the response after 0.5ms mainly comes from the area below and near the receiving point.The above results can guide the data processing and interpretation of SATEM.Second,when the SATEM is currently applied,the design of the exploration area is mostly based on the experience of other electromagnetic exploration methods.This article is based on the principle that the transient electromagnetic secondary field decays quickly in high resistance and slow in low resistance.Based on the difference between the uniform half-space model and the H-model multi-channel map in the representation of the underground medium distribution,the attenuation rate function is proposed to indicate the attenuation rate of the secondary field numerically,and the standard attenuation rate is determined to divide the observation area,and the best fit is used The elliptic curve fits the regional boundary;a large number of numerical simulations are used to determine the model parameters that have a greater impact on the boundary distribution:the length of the emission source and the buried depth of the abnormal body.Finally,the boundary equation of the SATEM region is summarized and divided suitable and unsuitable observation areas,to a certain extent guide the design of SATEM field exploration areasThird,in order to study and propose a data correction processing system for SATEM,this article aims at the characteristics of the measured data of SATEM,and performs(1)antenna noise removal on the exploration data:select ?-trimmed filter as De-noising processing,and proposes Haar wavelet decomposition to automatically identify the main effective data segment to protect it from being affected in the de-noising process;(2)Motion noise removal:In view of the temporal discontinuity of pure secondary field exploration data,compare Analyzing the denoising effects of wavelet decomposition and polynomial fitting,the results show that single-period polynomial fitting denoising can achieve excellent motion noise removal effect after removing the main valid data using Haar wavelet strategy;(3)Data attitude correction processing:based on receiving The principle of the deflection of the local coordinate system of the coil is derived,and the z-component data attitude correction formula is derived to perform attitude correction processing on the exploration data;(4)Data quality evaluation and screening:use the average energy ratio of the main effective data segment and the remaining data segment to evaluate the data quality,and Set the average energy ratio threshold to filter the data;finally,integrate the above-mentioned SATEM exploration data denoising and correction processing scheme,combined with data superposition and time window integration and other data processing procedures,and finally form the data for SATEM Correction processing system.Finally,this article is based on the Longwan No.2 tunnel project in Guangxi Zhuang Autonomous Region,After data acquisition design and data acquisition work,the SATEM data correction processing system and apparent resistivity imaging successfully obtained the underground apparent resistivity distribution of the work area.After a joint comparison and verification with geological data,the feasibility and effectiveness of the above results in SATEM field exploration experiments are proved.The research in this paper integrates theoretical derivation,numerical calculation,data correction processing work and field experimental application verification work,to a certain extent,expands and enriches the SATEM theory system,and initially forms data correction processing for actual measured data.The system provides a foundation for the follow-up research,development,popularization and application of the SATEM.