非分裂完全匹配层边界存储时间域全波形反演

正演波场的储存或重建是制约时间域全波形反演的关键问题，以计算代替存储的常规分裂完全匹配层（PML）边界存储策略可有效减少存储量。但常规分裂PML边界条件所需变量个数多、计算存储量大以及编程复杂。为此，采用非分裂复频移完全匹配层（CFS-NPML）有效边界存储策略重建正演波场实现时间域全波形反演。研究表明：CFS-NPML所需变量个数少，在边界吸收层网格点较少时吸收效果优于常规PML边界条件，波场重建过程中所需存储量少于常规PML边界条件。数值试验表明，该存储策略得到的重建波场与正向传播波场几乎无差别，其全波形反演结果与常规保存波场反演法一致；正演过程中引入并行计算技术未显著增加波场重建导致的额外正演时间。

Time-domain full waveform inversion with CFS-NPML boundary storage

The forward-modeling wavefield storage or reconstruction is a key question in the time-domain full waveform inversion.The strategy of storage replaced by computation based on conventional splitting perfect matched layer (SPML) boundary conditions can effectively reduce the amount of storage.However,conventional SPML boundary conditions require a large number of variables,a large amount of memory,and complex programming.In this paper,an effective boundary storage strategy based on the complex frequency shifted non-splitting perfect matched layer (CFS-NPML) is proposed to reconstruct the forward-modeling wavefield to realize the time-domain full waveform inversion.According to our study,fewer variables in CFS-NPML are needed; the absorption effect is better than conventional SPML boundary conditions when grid points of the boundary absorption layer are less.So less storage capacity is needed than that of conventional SPML boundary conditions in the wavefield reconstruction process.Numerical experiments show that there is almost no difference between the forward-modeling wavefield and the reconstructed wavefield obtained with this storage strategy.The velocity obtained by the full waveform inversion with this storage strategy is consistent with that obtained by the conventional storage wavefield inversion.The wavefield reconstruction does not significantly increase the computer time consuming thanks to parallel computation introduction.