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最小二乘偏移能够压制不规则地震数据偏移时产生的偏移假象,但存在计算量巨大、收敛速度缓慢等问题。为了快速地压制偏移噪音,发展了基于奇异值谱约束的叠前平面波最小二乘逆时偏移方法(Plane-wave prestack least-squares reverse time migration,PLSRTM)。一方面,通过奇异值谱分析(Singular spectrum analysis,SSA)方法对角度域共成像点道集(Take-Off Angle Domain Common-Image Gathers,TADCIGs)进行预处理,以压制偏移假象,同时引入随机奇异值分解减小SSA的计算量。另一方面,由于偏移速度不准确时叠加成像结果不能有效地压制偏移噪音,将相邻角度平面波偏移结果的差异作为正则化约束加入误差泛函,以改善这一问题。对Marmousi模型数据的成像测试结果表明该方法能够快速压制平面波道集及不规则地震数据偏移产生的偏移假象,改善PLSRTM的成像质量;当偏移速度不准确时,该方法能够得到偏移噪音更少、构造更加连续的成像结果。
Least Squares Offset can suppress the offset artifacts caused by irregular seismic data migration, but there is a huge computational complexity and slow convergence speed. In order to suppress the offset noise rapidly, Plane-wave prestack least-squares reverse time migration (PLSRTM) is developed based on the singular value spectrum constraint. On the one hand, the Take-Off Angle Domain Common-Image Gathers (TADCIGs) were preprocessed by singular spectrum analysis (SSA) to suppress the migration artifacts and introduced random Singular value decomposition reduces the computational complexity of SSA. On the other hand, because the inaccurate migration velocity can not effectively suppress the offset noise, the difference of the offset results of the adjacent angular plane waves can be added as the regularization constraint to the error function to improve this problem. The test results of the Marmousi model data show that this method can quickly suppress the offset artifacts caused by the offset of the plane channel set and the irregular seismic data and improve the imaging quality of the PLSRTM. When the migration velocity is not accurate, the method can obtain the offset Less noise, resulting in more continuous imaging results.