Study On Flight Parameter Calibration Method Of Airborne Electromagnetic System Based On Wire-loop

In the process of the fixed-wing airborne system detection,we make a definition of the stationary flight state,of which the flight speed is the same and the track is in accordance with designed line without any disturb from the outside environment such as the wind direction,wind speed,and air flow.However,during the actual flight,the aircraft is in the non-stationary flight state in most cases.Compared with the stationary flight state,the position and attitude of the receiving coil are changed.The position parameters and attitude parameters are collectively referred to as the flight parameters of the airborne electromagnetic system.According to the basic principle of the fixed-wing time domain airborne electromagnetic method,the change of flight parameters will change the electromagnetic response of the secondary field.Conventionally,if the measured electromagnetic response is processed and interpreted according to the ideal state of stationary flight state,it will cause larger errors.In view of the above problems,the flight parameters in the actual detection process are obtained from the measured electromagnetic responses through the appropriate methods,then the flight errors and measurement errors of the fixed-wing airborne electromagnetic system are determined.Furthermore,the measurement values of the flight parameters are corrected,it is of great significance to improve the system detection accuracy and data interpretation accuracy.A flight parameter calibration method of airborne electromagnetic system based on wire-loop is proposed.The main research contents are as follows:1)Based on the principle of fixed-wing time domain airborne electromagnetic method,it is deduced that the mutual inductance between the wire-loop and the receiving coil with attitude changes at any position,then the three-component electromagnetic response forward calculation formula based on the wire-loop is deduced.2)The wire-loop model is used to study the relationship between flight parameters and electromagnetic responses.The effects of the former are analyzed from three aspects: single change of the position parameter,single change of the attitude parameter,and the combination change of the flight parameters,which provides the theoretical basis of the solution of the flight parameters.3)The formula for calculating the electromagnetic response is a multivariate function of the flight parameters.All of them are non-linear and difficult to solve directly.Using the idea of the inversion in geophysics,combined with the application of fish-swarm algorithm in optimization problems,the problem of solving the actual flight parameters is transformed into the minimum optimization problem.According to different corrected flight parameters,the corresponding optimization objective function is constructed and solved.And the effectiveness of the algorithm is verified.The noise data is used to verify the noise immunity of the algorithm.The relative error of the solution of flight parameters is less than 5%.4)In order to verify the actual effect of the flight parameter correction algorithm,the wire-loop experimental data of fixed-wing airborne electromagnetic system in Yueyang,Hunan province was selected to correct the flight parameters.The relative error of the corrected electromagnetic response is less than 5%.Before the field application,pre-processing methods for the measured data were studied,including oversampling,targeted noise reduction by SNR ratings and time constant correction,etc.5)In order to facilitate the theoretical calculation and data processing,a wire-loop electromagnetic response numerical calculation module,an actual measurement data preprocessing module,a flight parameter correction module,etc.are designed through MATLAB GUI,then all the modules are integrated into a set of software.