Research On The Interpretation Methods Of Double Combined Electrical Sources Time-domain Ground-airborne Electromagnetic Data

The time-domain surface-to-air electromagnetic measurement system is composed of ground transmitting system and air receiving system.Compared with the time-domain ground electromagnetic system,it has the advantages of fast,efficiency and adapting to complex terrain.Compared with the time-domain air electromagnetic system,it has higher signal-to-noise ratio,better spatial resolution,deeper detection depth and higher security.Time-domain surface-to-air electromagnetic method combines the advantages of ground system and air system,and at the same time overcomes the disadvantages of both.It has become a key research in the field of transient electromagnetic method in recent years,which has provided a new method for goaf and coal mine storage detection in China.However,there are still several problems as follows: first,the terrain of the detection area is complex,so it is necessary to lay the transmitting source according to the terrain.Secondly,time-domain surface-to-air electromagnetic data has a large dynamic range,and the late data amplitude is small,so it is easy to be drowned in noise.In the flight detection,electromagnetic data will be disturbed by various noises,which will reduce data quality.In addition,the previous inversions of ground-air data in time-domain adopt LOTEM method,which requires repeated iterations which is slow and has large near source error.Therefore,an intelligent algorithm is needed to calculate the apparent resistivity and improve the inversion accuracy.In view of the above problems,the improved processing method of time-domain surface-to-air electromagnetic data based on double combined sources is studied.The main researches are as follows:(1)Based on the theory of electric dipole source developed by Nabighian,we have deduced the calculation formula of layered earth based on double combined sources,verified the algorithm with uniform and layered half-space model,and analyzed the characteristics of time-domain ground-air electromagnetic data with different models.(2)In the improved interpretation methods of time-domain surface-to-air electromagnetic data based on dual sources,lots of the problems such as electromagnetic signal loss and decay curve distortion problem are solved through characteristics analyses of time-domain electromagnetic signal and electromagnetic noise and the adoption of adaptive variable Bayesian Kalman noise suppression method.Combining time-domain attenuation characteristics of electromagnetic data,exponential fitting method and Bayesian Kalman filter,the electromagnetic noise is eliminated.(3)The formulas for calculating apparent resistivity and apparent depth of double combined sources are derived.An improved apparent resistivity calculation method is proposed to solve the problem of large errors in near-source area and layered models based on simulated annealing algorithm.(4)According to the fact that the transmitting current is slanted step off,the primary field in the coil is removed.The filtering method and simulated annealing method have been applied to the experimental data in Shanxi and Inner Mongolia,and have a good denoising effect which has improved interpretation accuracy efficiently.