交错网格有限差分正演模拟的联合吸收边界

三维声波方程交错网格有限差分正演模拟中的边界问题一直是热点问题。完全匹配层吸收边界（PML）具有较强且稳定的吸收效果，但必须具有一定的边界厚度才能吸收干净，这就增大了三维正演模拟的模型空间，即增加了运算量； Higdon边界能消除任意角度入射波的边界反射，也具有较强稳定性，但该高阶吸收边界离散化后过于复杂，而低阶时吸收效果不如PML边界。因此，基于对PML吸收层中的平面波传播规律的研究，重新推导PML最外层的Higdon吸收边界条件，得到含PML吸收系数的新的Higdon吸收边界条件。联合吸收边界不仅可使用较小厚度（相对于单纯PML边界）的PML层对分量进行衰减，而且在PML边界外层，能应用新推导的Higdon吸收边界条件对反射波进行匹配吸收。在相同吸收效果下，联合吸收边界大幅度降低了PML厚度，减小了运算量，得到精确的模拟结果。

Joint absorbing boundary in the staggered-grid finite difference forward modeling simulation

The boundary condition is one of the key issues discussed in the simulation of the staggered-grid finite difference of the 3D acoustic equations.The perfectly matched layer absorbing boundary (PML) is stable and effective,but it needs a certain boundary thickness to make perfectly absorption which makes the model bigger and requires a huge computation.Higdon absorbing boundary condition can stably eliminate the incident wave at any angle on the boundary,but it becomes very complex after discretization when the higher order condition used.Based on the plane wave propagation in a PML medium,we obtain a new Higdon absorbing operator in the PML,and then get joint absorbing boundary conditions.In the test of the joint absorbing conditions,it is found that the joint absorbing conditions are effective with a thinner PML layer and smaller computation.