本文讨论了 Born 近似与 Rytov 近似的相互关系,并对地面反射、VSP、井间和四周观测系统在异常体速度与背景速度相差5%、10%以及15%的条件下,用这两种近似方法作了重建图像的实验。其结果表明,速度差低于10%时,无论 Born 近似或 Rytov ...本文讨论了 Born 近似与 Rytov 近似的相互关系,并对地面反射、VSP、井间和四周观测系统在异常体速度与背景速度相差5%、10%以及15%的条件下,用这两种近似方法作了重建图像的实验。其结果表明,速度差低于10%时,无论 Born 近似或 Rytov 近似,更射层析均优于透射层析。此时,Rytov 近似的透射层析优势消失,这一结论与传统观点相悖。当速度差大于10%时,Rytov 近似透射层析优于 Born 近似。实验结果还说明,在地面激发、四周观测时,波动理论层析效果最佳,此点与射线理论是一致的。展开更多
In the field of geophysics,although the first-order Rytov approximation is widely used,the higher-order approximation is seldom discussed.From both theo-retical analysis and numerical tests,the accumulated phase error...In the field of geophysics,although the first-order Rytov approximation is widely used,the higher-order approximation is seldom discussed.From both theo-retical analysis and numerical tests,the accumulated phase error introduced in the first-order Rytov approximation cannot be neglected in the presence of strong velocity perturbation.In this paper,we are focused on improving the phase accuracy of forward scattered wavefield,especially for the large-scale and strong velocity pertur-bation case.We develop an equivalent source method which can update the imaginary part of the complex phase iteratively,and the higher-order scattered wavefield can be approximated by multiplying the incident wavefield by the exponent of the imaginary part of the complex phase.Although the convergence of the proposed method has not been proved mathematically,numerical examples demonstrate that our method can produce an improved accuracy for traveltime(phase)prediction,even for strong perturbation media.However,due to the neglect of the real part of the complex phase,the amplitude change of the scattered wavefield cannot be recovered.Furthermore,in the presence of multi-arrivals phenomenon,the equivalent scattering source should be handled carefully due to the multi-directions of the wavefield.Further investigations should be done to improve the applicability of the proposed method.展开更多
文摘本文讨论了 Born 近似与 Rytov 近似的相互关系,并对地面反射、VSP、井间和四周观测系统在异常体速度与背景速度相差5%、10%以及15%的条件下,用这两种近似方法作了重建图像的实验。其结果表明,速度差低于10%时,无论 Born 近似或 Rytov 近似,更射层析均优于透射层析。此时,Rytov 近似的透射层析优势消失,这一结论与传统观点相悖。当速度差大于10%时,Rytov 近似透射层析优于 Born 近似。实验结果还说明,在地面激发、四周观测时,波动理论层析效果最佳,此点与射线理论是一致的。
基金sponsored by the National Natural Science Foundation of China(No.41204086)the Self-governed Innovative Project of China University of Petroleum(No.13CX02041A)+2 种基金the Doctoral Fund of National Ministry of Education(No.20110133120001)the National 863 Project(2011AA060301)the Major National Science and Technology Program(No.2011ZX05006-002)
基金supported by National Natural Science Foundation of China(41604091,41704111,41774126)the great and special project(2016ZX05024-001,2016ZX05006-002).
文摘In the field of geophysics,although the first-order Rytov approximation is widely used,the higher-order approximation is seldom discussed.From both theo-retical analysis and numerical tests,the accumulated phase error introduced in the first-order Rytov approximation cannot be neglected in the presence of strong velocity perturbation.In this paper,we are focused on improving the phase accuracy of forward scattered wavefield,especially for the large-scale and strong velocity pertur-bation case.We develop an equivalent source method which can update the imaginary part of the complex phase iteratively,and the higher-order scattered wavefield can be approximated by multiplying the incident wavefield by the exponent of the imaginary part of the complex phase.Although the convergence of the proposed method has not been proved mathematically,numerical examples demonstrate that our method can produce an improved accuracy for traveltime(phase)prediction,even for strong perturbation media.However,due to the neglect of the real part of the complex phase,the amplitude change of the scattered wavefield cannot be recovered.Furthermore,in the presence of multi-arrivals phenomenon,the equivalent scattering source should be handled carefully due to the multi-directions of the wavefield.Further investigations should be done to improve the applicability of the proposed method.
