Research On Reverse Time Migration From Badain Jaran Desert Sand Dune Structure Ground Penetrating Radar Data

Formed sand dunes have wind sedimentry structure in Badan Jaran desert,which are important records of changing of wind-energy environment.Ground-Penetrating Radar(GPR)can detect at high resolution internal structure of sand dunes,and reveal the changing of wind directions and climate in this region.Due to have affect on the diffraction waves and reflections,they have difficult to reflect with high resolution the characteristic of internal structure of sand dunes from GPR sections.The process of migration for GPR data can improve image authenticity.Reverse Time Migration(RTM)can better adapt to topographic relief and the medium of laterally variable velocity,which is higher accuracy migration method.Due to have influence on rugged topographic relief and inclined bedding,the sand dunes GPR data in Badain Jaran desert have problems as following:(1)The electromagnetic propagation direction was caused by rugged topographic surface,and they have some problems of topographic correction distortion at rugged topographic relief;(2)The anisotropic feature of electromagnetic propagation velocity which was caused by tilted calcium bedding.It is difficult to adapt the change of electromagnetic wave variable velocity in isotropic medium and need to study the migration method in anisotropic medium.The existing method of GPR RTM with topographic surface using Cartesian coordinate in isotropic medium cannot well improve the precision of migration imaging for GPR data.In this thesis,based on the GPR migration method before,we would study contents as following:(1)We would improve the GPR RTM with topographic surface using Cartesian coordinate in isotropic medium,and developed the GPR RTM with topographic surface using curvilinear coordinate in anisotropic medium which can adapt to rugged topographic relief in Badain Jaran desert;(2)The sand dune numerical models were designed and used the forward modeling method with topographic relief using curvilinear coordinate in anisotropic medium to simulate zero-offset GPR section,and realize RTM imaging using curvilinear coordinate in isotropic medium and anisotropic medium,which can analyze anisotropic electromagnetic velocity can affect the accuracy of migration imaging.(3)We would design sand tank physical experimental model,and analyzed the advantage of GPR RTM with topographic surface using curvilinear coordinate in anisotropic medium can process the topographic relief and tilt slabby medium.(4)We used migration method to process GPR data in Badain Jaran desert,and analyzed the advantage of GPR RTM section with topographic surface using curvilinear coordinate can better reflect the internal structure of sand dunes.Based on the result of RTM imaging,we would reveal the sand dunes bending structure and wind direction.In this topic,based on the difficult problem of traditional GPR RTM imaging with topographic surface using Cartesian coordinate in isotropic medium when we process the GPR data migration imaging in Badain Jaran desert.We would develop the GPR RTM with topographic surface using curvilinear coordinate in anisotropic medium,which can eliminate the staircase grid's effect in Cartesian coordinate and solve the problems of electromagnetic propagation direction and velocity anisotropic.The result of real GPR data RTM sections have shown that the GPR RTM method with topographic surface using curvilinear coordinate in anisotropic medium can better reflect the internal structure of sand dunes,and provide the new evidences for researching the wind sedimentary sand dunes structure.