Study On Conductivity Depth Imaging Of Fixed-wing Time-domain Electromagnetic Data Based On Iterative Lookup Tables

Fixed-wing airborne time-domain electromagnetic method is a kind of geophysical exploration based on the law of electromagnetic.It has advantages such as greater investigation depth,high efficiency and low cost,which can be widely used in oil and gas exploration and other fields.As the attitude and height of the aircraft change during a flight survey,the collected data and corresponding conductivity-depth imaging results can be affected.In this paper,relying on the National Natural Science Foundation "fixed-wing time domain airborne electromagnetic inversion method to detect the overall study," research the electromagnetic response changed with the flight height and the pitch of the receiver coil.As the detection system cannot obtain the pitch,so an improved conductivity-depth imaging algorithm with consideration of height and pitch is developed herein based on an iterative lookup table,the main contents are as follows:AEM-based detection theory,the three-component one-dimensional forward calculation method is deduced with arbitrary attitude of receiver coil.The influence of flight height variation on the electromagnetic response is studied.The influence of the roll,pitch and yaw angles on electromagnetic response characteristics are studied.It is difficult for the conventional airborne electromagnetic system to obtain the pitch information,and pitch is considered into the conductivity depth imaging.The CDI algorithm with two-component lookup table with pitch is studied.The Bx-Bz-?-pitch tables under different height are established with forward calculation.According to the measured flight height,the corresponding table is found,and the apparent conductivity(?)is calculated by interpolation of the two-component table method,and the imaging depth is obtained according to the diffusion formula.Ultimately achieve the CDI algorithm with consideration of pitch.In the case of the height is inaccuracy,the flight height and pitch are considered as the parameters into the CDI algorithm.The CDI algorithm with the height and pitch is studied.Through the forward calculation,the Bx-Bz-?-height table of each time channel under fixed pitch attitude angle and the Bx-Bz-?-pitch table of each time channel under fixed height are established.According to the measured electromagnetic response in the two data tables iterative calculation,the iteration is ended until the conductivity,height and pitch all meet the accuracy requirements,then output the apparent conductivity,flight height and pitch attitude angle information.The depth of each layer is calculated by using the diffusion formula,and the imaging depth is calculated with the average apparent conductivity.Finally,an iterative lookup conductivity depth imaging algorithm with flight height and pitch is realized.The simulation results show that the depth of the iterative method is better than the imaging results without consideration of the flight height and pitch attitude angle error,and even if the accurate flight height information is obtained,the depth of the iterative method is improved about 10%.Finally,this paper studied the parameters accuracy of iterative lookup table CDI algorithm and system auxiliary.Studied the accuracy requirements with iterative lookup table CDI for system auxiliary parameters.Calculated the error between auxiliary parameters and iterative lookup table CDI algorithm.The simulation results verified that the height error between auxiliary parameters and iterative lookup table CDI algorithm is 20% while the pitch error is 10%.