In recent years, to develop the elastic wave CT technology, still a developing geophysical prospecting approach, considerable progresses have been made in theory, data acquisition, instrument, equipment, and software, etc. As an advanced technology, it has been applied widely in the quality detection of concrete cutoff wall (Leng 1999, Duan et al. 2000, Xue et al. 2002). Most application examples have shown, with elastic wave CT technology, one can distinctly find the defects, e. g., cave and unconsolidated body within the wall. However, this technology is related to the inverse problem of imaging reconstruction where the precision of imaging directly affects the quality of detection results. Thus, it is of great significance to analyze the factors that influence the resolution and to probe into the relationship of them. In general, the resolution is influenced by inversion algorithm, recording geometry, source frequency, the shape and property of object, etc. Some scholars have involved in the research of imaging resolution of elastic wave CT and have got encouraging results (Zhu et al. 1994, Cao et al. 1995, Chen 1996, Pei et al. 2002). Based on the analysis of the factors that affect the resolution (Wang 1993, Yang et al. 1993, Yang 1997, Wang 1998) together with the characteristics of concrete cutoff wall and common defect types, we have designed various models with low velocity object, i. e., unconsolidated part or crack, inside. We have adopted curving ray tracing method for forward modeling and inversion so as to determine the relations between imaging precision and those affecting factors. At last, the measures to improve the imaging resolution are put forward.
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