复波场的实部和虚部对同时源波形反演的影响

高精度的成像需要准确的速度场信息，波形反演被认为是目前具有最高分辨率的速度反演方法之一.计算效率是目前全波形反演需要考虑的一个主要问题.为了很好地解决计算效率的问题，本文引入了一种高效的无串扰同时源反演方法，并详细介绍了其原理与计算流程.同时，基于此多震源同时反演方法，本文拓展出实波场反演、虚波场反演及复波场反演的三种反演策略，进而分析复波场的实部和虚部对全波形反演的影响.实验表明，相比于复波场全波形反演，无论是实波场反演还是虚波场反演，反演分辨率有所降低；相比于实波场反演，虚波场反演对初始模型的依赖性较小，目标函数的非线性较弱；最后，通过使用组合反演策略，即初始阶段采用虚波场反演，中后期阶段采用复波场反演，不仅可以降低反演的非线性，而且能够保证高精度建模.

The influence of the real and imaginary parts of complex wavefield on simultaneous source waveform inversion

High-precision subsurface imaging requires accurate velocity field information. Currently, waveform inversion is considered as one of the most effective methods to produce high-resolution velocity models. However, low computational efficiency is a major issue that obstructs full-waveform inversion from large-scale computation. To solve this problem, we introduce an efficient simultaneous source inversion method without crosstalk and describe its detailed principle and calculation process. Meanwhile, based on the multi-source simultaneous inversion method, we also develop three inversion strategies, real wavefield inversion, imaginary wavefield inversion, and complex wavefield inversions, to analysize the influence of real and imaginary parts of complex wavefield on waveform inversion. Experiments show that compared with complex wavefield inversion, the resolution of both real wavefield inversion and imaginary wavefield inversion is reduced. While compared with real wavefield inversion, imaginary wavefield inversion is less dependent on the initial model, indicating the weak nonlinearity of phase inversion. Thus, taking advantage of a combined inversion strategy (imaginary wavefield inversion in the initial stage and complex wavefield inversion in the middle and late stages) not only decreases the inversion nonlinearity, but also ensures the high precision of modeling.