具有不规则边界的多层介质非递归合成孔径成像

Shiwei Wu, Keji Yang
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引用次数: 5

摘要

合成孔径聚焦技术(SAFT)由于其横向分辨率的显著提高,在超声无损检测(NDT)中被广泛应用于材料不连续(缺陷)的检测和定形。但对于垂直方向和横向方向均不均匀的不规则多层物体的瞬态位移的研究相对不足。本文提出了一种新的非递归合成孔径成像算法——修正直接傅里叶偏移(M-DFM),以处理这种不规则的多层情况。该算法的推导灵感来自于将Stolt f-k迁移重新表述为一个非平稳滤波器,它可以通过均方根速度扩展到一般的多层情况。实验表明,该算法可以很好地恢复规则多层物体的图像,其精度与最近在平面层状结构中取得成功的相移迁移(PSM)几乎相同。并利用带有凸界面的钢块和侧钻孔的浸没测试数据对算法进行了性能评价,从而考察了该方法提高不规则多层介质中缺陷检测的横向分辨率的能力。此外,该算法提供了一种非递归的方法,通过对滤波后的频谱进行单一的二维傅里叶反变换来恢复图像,而不是通过PSM所需的递归波场外推。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Non-recursive synthetic aperture imaging for multilayered media with irregular boundary
The synthetic aperture focusing technique (SAFT) has been widely used for detection and sizing of material discontinuities (flaws) in ultrasonic nondestructive testing (NDT) because of its significant improvements in lateral resolution. But the efforts of researching on SAFT for irregularly multilayered objects that are inhomogeneous in both the vertical and lateral directions are relatively insufficient. In this paper, a new non-recursive synthetic aperture imaging algorithm, called modified direct Fourier migration (M-DFM), is proposed to deal with such irregularly multilayered situations. The derivation of the algorithm was inspired by reformulating Stolt f-k migration as a nonstationary filter, which could be extended to generally multilayered cases by the root-mean-square velocity. The experiment shows that the proposed algorithm is well suited for restoring images of regularly multilayered objects with almost the same accuracy as phase shift migration (PSM) which has recently succeeded in planar layered structures. And the performance of the proposed algorithm is also evaluated using immersion test data from a steel block with a convex interface and a side drilled hole, in this way investigating the method's capability of improving the lateral resolution of flaws detection in irregularly multilayered media. Furthermore, the proposed algorithm provides a non-recursive means to recover the images by performing a single 2-D inverse Fourier transform on the filtered spectrums rather than by recursive wave field extrapolation needed for PSM.
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