Diffraction Separation And Imaging In Plane-wave Domain

Seismic data is composed of reflected and diffracted information.In the narrow definition of diffraction,the diffracted wave is the "reflected wave" generated when the curvature of the outer edge of the subsurface reflector or the convex part of the subsurface structure is close to infinity.Diffractions are seismic waves generated by small-scale heterogeneities in the subsurface,and it is often submerged by strong reflections,which reduces the accuracy of the interpreter in identifying and locating scatterers.Therefore,the separation of diffracted and reflected waves is a crucial step to resolve these small-scale diffractors.In order to implement diffraction separation and imaging,this paper starts with the difference between reflection and diffraction in the plane-wave domain,then give the feasibility of diffraction separation and analyzes its dynamic characteristics.So this paper develops two optimized plane-wave domain diffraction separation approach and its application in plane-wave least-squares reverse time migration(PLSRTM).In the first part,the proposed short-time singular spectrum analysis(STSSA)algorithm utilizes the characteristics of the singular spectrum analysis(SSA)to separate linear signals,and by setting up the Hanning window and energy compensation function,it also makes up for the deficiency of SSA in local dip processing and linear signal convergence.In addition,this part has studied the principle and processing effect of the plane-wave destruction(PWD)filter separating diffracted waves in the same plane wave domain,and analyzed the relationship with SSA.In the second part,since there is no clear boundary between reflected and diffracted waves,the energy leakage in the separation leads to the slow convergence of the diffraction wave imaging.In addition,the diffraction separation in the plane-wave domain is the reverse preprocessing of the record.When performing conventional migration imaging,low-frequency noise and other interference will directly affect the imaging conditions,resulting in poor diffraction imaging.This paper take STSSA and PWD as a target constraint for PLSRTM,which greatly improves the imaging quality for diffraction waves.From the tests for models and the processing seismic data our method can effectively improve the resolution of the diffraction imaging and the target constraint enhances the robustness.