The Numerical Simulation Of Time Domain Airborne Electromagnetic Of Magnetic And Conductive Body In Sea

Airborne electromagnetic method(AEM)is a geophysical detection method that studies the distribution of electrical properties of subsurface media based on the distributional difference of electrical properties of subsurface media.An aircraft is used as a flight carrier to transmit the high-power EM signal by transmitter device and receive the primary field propagated through the air and the second field induced by underground medium.With the emphasis on the detection of underwater targets in different countries,AEM has been used by domestic scholars and experts to detect underwater targets due to its characteristics and advantages,such as super power,high flexibility,high efficiency and low detection cost.In this thesis,the geoelectric model of the magnetic and conductive body in sea is established.The three-dimensional airborne electromagnetic numerical simulation is realized based on the integral equation method.The airborne electromagnetic response characteristics of the magnetic and conductive body in sea are studied.Through the numerical simulation in this thesis,the main conclusions are as follows.(1)The airborne electromagnetic attenuation of the seawater background model becomes slower and its response becomes larger but the growth rate decreases when the thickness of the seawater becomes larger in the background portion.(2)The airborne electromagnetic response of the magnetic and conductive body in sea becomes larger but its growth rate decreases,and the peak of the scattering field(abnormal field)is delayed when the conductivity or magnetic permeability of the magnetic and conductive body increases.(3)The magnetic induction Bz response curve shows an "M" double-peak shape along a route perpendicular to the long columnar magnetic and conductive body.The induced electromotive force dBz/dt response curve exhibits a "W" double valley shape in the early stage of attenuation and changes from "W" double valley to "M" double peak in the late stage with the permeability of the magnetic good conductor increasing.(4)The airborne electromagnetic response curve of the magnetic and conductive body in sea changes from "M" double peak to "?" shaped single peak,and the response range becomes wider and the response peak becomes larger when the extension of the magnetic and conductive body in the X direction increases.(5)The scattering field(abnormal field)can highlight the abnormal value of the magnetic and conductive body in the early stage of attenuation,and the relative field,from that the scattering field divide by the response of the seawater background model,can emphasize the abnormal value in the late stage.These conclusions will play a certain guiding role in the identification and location of underwater targets by airborne electromagnetic method,and also lay a theoretical foundation for three-dimensional inversion.