基于LTI射线追踪的改进的ART算法
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摘要
CT反演常采用"直线重构模型",即认为射线在震源和接收器之间走直线,这一条件只有在介质基本均匀的情况下近似成立。当介质中存在缺陷,射线行走路径不再是直线而是空间曲线时,若仍然采用"直线重构模型"进行反演,必然引入误差。本文提出了改进的ART算法,并在迭代的过程中利用基于旅行时的线性插值(LTI)射线追踪正演射线的实际行走路径。该算法首先利用概率的方法预判缺陷单元,将预判的缺陷单元与非缺陷单元区别对待,赋予不同的初始波速,在每轮迭代之前利用LTI射线追踪重新计算投影矩阵,并在迭代的过程中给预判的缺陷单元与非缺陷单元赋予不同的松弛因子。计算机模拟实验及混凝土试件实验结果表明,基于LTI射线追踪的改进的ART算法有效提高了计算的精度和图像重建质量,但是相应地增加了反演时间。
Straight line reconstruction model is frequently used in concrete computerized tomography. It assumes the ray travels in a straight line between a sending transducer and a receiving transducer,which is valid for homogeneous medium. When there are defects in the medium,the ray will not travel in a straight line but in a spatial curve,and if still using straight line reconstruction model,error will be brought in. An improved algebraic reconstruction technique (ART)is put forward in the paper,and linear travel time interpolation (LTI)ray tracing is used during the iterations to obtain the real travel paths of rays. Firstly,defect meshes are ascertained by probability and mathematical statistic method,and then defect meshes and normal meshes are provided with different initial wave velocities. Secondly,the projection matrix is anew computed by LTI ray tracing before each iteration. And during each iteration,defect meshes and normal meshes are provided with different relaxation factors. The results of computer simulation and concrete model experiment show that the improved ART based on LTI ray tracing is effective to improve the accuracy of computation and the quality of image reconstruction on concrete,but takes more time.
Straight line reconstruction model is frequently used in concrete computerized tomography. It assumes the ray travels in a straight line between a sending transducer and a receiving transducer,which is valid for homogeneous medium. When there are defects in the medium,the ray will not travel in a straight line but in a spatial curve,and if still using straight line reconstruction model,error will be brought in. An improved algebraic reconstruction technique (ART)is put forward in the paper,and linear travel time interpolation (LTI)ray tracing is used during the iterations to obtain the real travel paths of rays. Firstly,defect meshes are ascertained by probability and mathematical statistic method,and then defect meshes and normal meshes are provided with different initial wave velocities. Secondly,the projection matrix is anew computed by LTI ray tracing before each iteration. And during each iteration,defect meshes and normal meshes are provided with different relaxation factors. The results of computer simulation and concrete model experiment show that the improved ART based on LTI ray tracing is effective to improve the accuracy of computation and the quality of image reconstruction on concrete,but takes more time.
引文
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10Ko HS,Kihm K D.An extended algebraic reconstruction technique(ART)for density-gradient projections:laser speckle photographic tomography[J].experiments in fluids,1999,27(6):542-550.
11Yan Sheng-cun,Li Zhen-zhao,Xue Gui-yu,et al.Discussion on algebraic reconstruction techniques in computerized tomography of dams and its improvement[J].Engineering Journal of Wuhan University,2001,34(4):29-34.[阎生存,李珍照,薛桂玉等.大坝CT中ART算法及其改进探讨[J].武汉大学学报(工学版),2001,34(4):29-34.]
12JGJ/T93-95.Specification for lowstrain dynamic testing of piles[S].[JGJ/T93-95.基桩低应变动力检测规程[S].]
13Huang Liang,Huang Zheng-yu.An improved method of linear interpolation ray tracing[J].Natural Science Journal of Xiangtan University,2002,24(4):105-108.[黄靓,黄政宇.线性插值射线追踪的改进方法[J].湘潭大学自然科学学报,2002,24(4):105-108.]
14Nie Jian-xin,Yang Hui-zhu.Quadratic/linear travel time interpolation of seismic ray-tracing[J].Journal of Tsinghua University(Science and Technology),2003,43(11):1495-1498.[聂建新,杨慧珠.地震波旅行时二次/线性联合插值法[J].清华大学学报(自然科学版),2003,43(11):1495-1498.]
15Zhao Gai-shan,Hao Shou-lin,Yang Er-hao,et al.Seismic ray tracing algorithm based on the Iinear traveltime interpolation[J].Geophysical Prospecting for Petroleum,1998,37(2):14-25.[赵改善,郝守玲,杨尔皓等.基于旅行时线性插值的地震射线追踪算法[J].石油物探,1998,37(2):14-25.]
2Koshovyi V V,Nazarchuk Z T.Estimating the predefective state of a material using methods of ultrasonic computerized tomography[J].Materials Science,2001,37(2):279-293.
3Smith Brian J,Adhami Reza R.Enhanced localized computerized tomography employing the discrete wavelet transform[J].Circuits,Systems,and Signal Processing,2000,19(5):399-409.
4Huang Zheng-yu,Huang Liang,Miao Lun.Study on computerized tomography of ultrasonic attenuation for concrete[J].Journal of Railway Science and Engineering,2004,1(2):35-38.[黄政宇,黄靓,缪仑.混凝土超声波幅值衰减层析成像研究[J].铁道科学与工程学报,2004,1(2):35-38.]
5Zhao Ming-jie,Xu Rong.Ultrasonic tomography technology and its applications in undamage test of bridge foundation piles[J].Journal of Chongqing Jiaotong University,2001,20(2):73-77.[赵明阶,徐蓉.超声波CT成像技术及其在大型桥梁基桩无损检测中的应用[J].重庆交通学院学报,2001,20(2):73-77.]
6Pantazopoulos J S,Tzafestas S G.An efficient algorithmfor ray tracing[J].Journal of Intelligent and Robotic Systems,2000,28(1):171-180.
7Grunberg Marc,Genaud Stephane,Mongenet Catherine.Seismic ray-tracing and Earth mesh modeling on various parallel architectures[J].Journal of Supercomputing,2004,29(1):27-44.
8Rathore S K,Kishore N N,Munshi P.An improved method for ray tracing through curved inhomogeneities in composite materials[J].Journal of Nondestructive Evaluation,2003,22(1):1-9.
9Zhang Po,Liu Hong,Li You-ming.The situation and progress of ray tracing method research[J].Progress in Geophysics,2000,15(1):36-45.[张钋,刘洪,李幼铭.射线追踪方法的发展现状[J].地球物理学进展,2000,15(1):36-45.]
10Ko HS,Kihm K D.An extended algebraic reconstruction technique(ART)for density-gradient projections:laser speckle photographic tomography[J].experiments in fluids,1999,27(6):542-550.
11Yan Sheng-cun,Li Zhen-zhao,Xue Gui-yu,et al.Discussion on algebraic reconstruction techniques in computerized tomography of dams and its improvement[J].Engineering Journal of Wuhan University,2001,34(4):29-34.[阎生存,李珍照,薛桂玉等.大坝CT中ART算法及其改进探讨[J].武汉大学学报(工学版),2001,34(4):29-34.]
12JGJ/T93-95.Specification for lowstrain dynamic testing of piles[S].[JGJ/T93-95.基桩低应变动力检测规程[S].]
13Huang Liang,Huang Zheng-yu.An improved method of linear interpolation ray tracing[J].Natural Science Journal of Xiangtan University,2002,24(4):105-108.[黄靓,黄政宇.线性插值射线追踪的改进方法[J].湘潭大学自然科学学报,2002,24(4):105-108.]
14Nie Jian-xin,Yang Hui-zhu.Quadratic/linear travel time interpolation of seismic ray-tracing[J].Journal of Tsinghua University(Science and Technology),2003,43(11):1495-1498.[聂建新,杨慧珠.地震波旅行时二次/线性联合插值法[J].清华大学学报(自然科学版),2003,43(11):1495-1498.]
15Zhao Gai-shan,Hao Shou-lin,Yang Er-hao,et al.Seismic ray tracing algorithm based on the Iinear traveltime interpolation[J].Geophysical Prospecting for Petroleum,1998,37(2):14-25.[赵改善,郝守玲,杨尔皓等.基于旅行时线性插值的地震射线追踪算法[J].石油物探,1998,37(2):14-25.]
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