| Acoustic tomography is widely used in medical detection,resource exploration,nondestructive testing of engineering buildings,and internal imaging of the earth because it has no harm to the measured object.With the development of computer and detection technology,the accuracy of inversion and the resolution of imaging have been the focus of attention in the field of acoustic tomography.By studying the characteristics of tomographic inversion about direct waves and reflected waves,we combine the direct waves with reflected waves to invert the model in order to increase the effective information of inversion and improve the quality of imaging.Firstly,this paper briefly introduces the applications of acoustic tomography and the significance of improving the image resolution,and discusses the history and current situation of tomography about direct waves,reflected waves and multi-type waves.Basing on the mathematic and physical principles of acoustic tomography,this paper introduces the solution to obtain the travel time and the paths by ray tracing,and illustrates the damping least squares method of the inversion process.Secondly,the multi-scale progressive mesh models are used to inverse to calculate the velocity by direct waves.At the same time,the reflected waves is used to invert the velocity and the reflector depth.Furthermore,this paper illustrates the effects and the characteristics of the two waves and analyzes the influencing factors of single wave imaging quality.Finally,based on the limitation of single wave inversion and the practical application,this paper also combines the direct waves with reflected waves to invert the velocity and the reflector depth of the model.The derivative weights are adjusted to improve the convergence rates because of the different derivative sensitivity.For the case of horizontal and inclined reflections,the inversion of calculation is performed to certify the direct waves and reflected waves joint inversion can improve the image quality. |
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