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超声实验表明,采用适当的扫描图形及近似的方法,地球物理绕射层析成象技术能够成功地为与周围介质只有4％速度差异的微弱非均匀介质成象。实验是在微机控制的水槽中进行的。采用宽频带检波器测量由物体产生的散射波场。根据图象重构中的畸变情况,比较了Born和Rytov两种近似方法,结果表明,只要由物体引起的相位变化能得到精确的测量及很好的解释,Rytov近似法要比Born近似法的适用范围广一些。文中对扫描图形,如井间、垂直地震剖面及反射等也作了评价,井间的图形在垂直方向有较好的分辨能力。反射法描述物体较近的一边要比较远的一边效果好一些。垂直地震剖面图形在图象重构中产生严重的人为畸变。在我们使用的图象重构的算法中没有考虑由于吸收造成的水下声波的衰减,可能会给结果带来误差。
Ultrasound experiments show that geophysical diffraction tomography can successfully image weakly inhomogeneous media with a difference of only 4% from the surrounding medium using appropriate scanning patterns and approximations. The experiment was carried out in a computer-controlled sink. A wideband detector is used to measure the scattered wave field generated by the object. According to the distortion in the image reconstruction, two approximations of Born and Rytov are compared. The results show that the Rytov approximation is better than the Born approximation as long as the phase change caused by the object can be accurately measured and well explained A wider range. In this paper, the scanning patterns, such as crosswell, vertical seismic profile and reflection are also evaluated. The cross-well pattern has good resolution in the vertical direction. Reflex method to describe the object closer to the side of the effect is better. Vertical seismic profiles generate serious human-induced distortions in image reconstruction. The algorithm for image reconstruction we use does not account for the attenuation of underwater sound waves due to absorption, which can cause errors in the results.