逆时偏移成像方法是时域电磁法中最直观的一种方法，由于矿井下环境复杂，电磁干扰严重，影响着矿井下成像的分辨率。因此，提高逆时偏移成像分辨率对逆时偏移方法具有十分重要的意义。
    针对低频噪声导致逆时偏移成像分辨率低的问题，提出一种基于波场分离的时域伪谱逆时偏移成像方法。将时域伪谱算法引入逆时偏移成像过程中，研究二维时域伪谱算法的稳定性条件，确定激励源为Ricker子波，选取PML作为边界条件。在逆时偏移波场延拓时，采用波场分离的方法提取所需的波场，在有效路径上进行波场互相关，通过坡印廷矢量判断源波场与接收波场的夹角，在使用成像条件时乘以权重系数来压制大角度成像产生的噪声，在成像后，对成像剖面采用拉普拉斯滤波提高成像分辨率。建立圆形、矩形空洞模型，对比基于波场分离的时域伪谱逆时偏移成像算法与基于时域伪谱逆时偏移成像算法的成像效果。建立矿井富水区含水陷落柱、含水断层以及采空区积水模型，采用波场分离的时域伪谱成像算法对矿井富水区三种典型模型进行成像。
    富水区三种典型模型的xoz面与xoy面成像图与原始模型相比，三种模型的相对误差平均值分别为：4.9％、4.98％以及5.6％，整体平均误差为5.16％，所得xoz面与xoy面成像结果图中其形状、位置和范围与原始模型基本吻合。成像结果表明，基于波场分离的时域伪谱逆时偏移成像算法解决了时域伪谱逆时偏移成像算法中成像分辨率低的问题，理论上能够对富水区的几种典型模型实现高分辨成像。
 

    The reverse time migration imaging method is the most intuitive method in the time domain electromagnetic method. Due to the complex underground environment and serious electromagnetic interference, it affects the resolution of underground imaging. Therefore, improving the imaging resolution of reverse time migration is of great significance to the reverse time migration method.
    Aiming at the problem that low frequency noise causes low resolution of reverse time migration imaging, a time-domain pseudospectral reverse time migration imaging method based on wavefield separation is proposed. The time-domain pseudo-spectrum algorithm is introduced into the reverse time migration imaging process, the stability conditions of the two-dimensional time-domain pseudo-spectrum algorithm are studied, the excitation source is determined to be the Ricker wavelet, and PML is selected as the boundary condition. In reverse time migration wavefield continuation, the wavefield separation method is used to extract the required wavefield, and the wavefield cross-correlation is performed on the effective path, and the angle between the source wavefield and the received wavefield is judged by the Poynting vector When using imaging conditions, multiply the weight coefficient to suppress the noise generated by large-angle imaging. After imaging, Laplacian filtering is used to improve the imaging resolution of the imaging section. Establish circular and rectangular cavity models, and compare the imaging effects of time-domain pseudo-spectrum reverse-time migration imaging algorithm based on wavefield separation and time-domain pseudo-spectrum reverse-time migration imaging algorithm. Establish water-bearing subsidence columns, water-bearing faults, and old-gap water models in the water-rich area of the mine, and use the time-domain pseudospectral imaging algorithm with wave field separation to image three typical models of the water-rich area of the mine.
    Compared with the original model of the xoz surface and xoy surface imaging images of the three typical models in the rich water area, the relative errors of the three models are respectively: 4.9%, 4.98% and 5.6%, and the overall average error is 5.16%. The obtained xoz The shape, position and range of the surface and xoy surface imaging results are basically consistent with the original model. The imaging results show that the time-domain pseudospectral reverse-time migration imaging algorithm based on wavefield separation solves the problem of low resolution in reverse-time migration imaging, and can theoretically achieve high-resolution imaging of several typical models in the water-rich area.
 

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