Mining operation, especially underground coal mining, always has the remarkable risks of ground control. Passive seismic velocity tomography based on simultaneous iterative reconstructive technique (SIRT) inversion ...Mining operation, especially underground coal mining, always has the remarkable risks of ground control. Passive seismic velocity tomography based on simultaneous iterative reconstructive technique (SIRT) inversion is used to deduce the stress redistribution around the longwall mining panel. The mining-induced microseismic events were recorded by mounting an array of receivers on the surface, above the active panel. After processing and filtering the seismic data, the three-dimensional tomography images of the p-wave velocity variations by SIRT passive seismic velocity tomography were provided. To display the velocity changes on coal seam level and subsequently to infer the stress redistribution, these three-dimensional tomograms into the coal seam level were sliced. In addition, the boundary element method (BEM) was used to simulate the stress redistribution. The results show that the inferred stresses from the passive seismic tomograms are conformed to numerical models and theoretical concept of the stress redistribution around the longwall panel. In velocity tomograms, the main zones of the stress redistribution arotmd the panel, including front and side abutment pressures, and gob stress are obvious and also the movement of stress zones along the face advancement is evident. Moreover, the effect of the advance rate of the face on the stress redistribution is demonstrated in tomography images. The research result proves that the SIRT passive seismic velocity tomography has an ultimate potential for monitoring the changes of stress redistribution around the longwall mining panel continuously and subsequently to improve safety of mining operations.展开更多
Sparse-view x-ray computed tomography (CT) imaging is an interesting topic in CT field and can efficiently decrease radiation dose. Compared with spatial reconstruction, a Fourier-based algorithm has advantages in r...Sparse-view x-ray computed tomography (CT) imaging is an interesting topic in CT field and can efficiently decrease radiation dose. Compared with spatial reconstruction, a Fourier-based algorithm has advantages in reconstruction speed and memory usage. A novel Fourier-based iterative reconstruction technique that utilizes non-uniform fast Fourier transform (NUFFF) is presented in this work along with advanced total variation (TV) regularization for a fan sparse-view CT. The proposition of a selective matrix contributes to improve reconstruction quality. The new method employs the NUFFT and its adjoin to iterate back and forth between the Fourier and image space. The performance of the proposed algorithm is demonstrated through a series of digital simulations and experimental phantom studies. Results of the proposed algorithm are compared with those of existing TV-regularized techniques based on compressed sensing method, as well as basic algebraic reconstruction technique. Compared with the existing TV-regularized techniques, the proposed Fourier-based technique significantly improves convergence rate and reduces memory allocation, respectively.展开更多
It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used suc...It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used successfully to improve the image quality. This paper studies the application of iterative algorithms in radar imaging. A discrete model is first derived, and the iterative algorithms are then adapted to radar imaging. Although such algorithms are usually time consuming, this paper shows that, if the algorithms are appropriately simplified, it is possible to realize them even in real time. The efficiency of iterative algorithms is shown through computer simulations.展开更多
层析是电离层三维结构反演的重要技术.增加约束可缓解层析模型的病态问题.然而,迭代层析中,大量无射线穿过的网格易对施加的约束产生与真实意图相违背的约束结果(称负面约束).针对该问题,提出了一种参数平滑的迭代层析方法(iterative to...层析是电离层三维结构反演的重要技术.增加约束可缓解层析模型的病态问题.然而,迭代层析中,大量无射线穿过的网格易对施加的约束产生与真实意图相违背的约束结果(称负面约束).针对该问题,提出了一种参数平滑的迭代层析方法(iterative tomography method via parameters smoothing, ITPS).每次迭代中,先用Chapman函数及最小二乘法拟合及改正每一垂直剖面,获取关于Chapman函数参数的二维图像,然后用移动窗口法平滑各参数图像并以此改正各网格的电子密度.实验表明:ITPS方法可一定程度上减少负面约束并抑制层像的扰动.相对于MART和CMART算法,ITPS方法在垂直剖面、F2层临界频率(f_(o)F_(2))、F_(2)层峰值高度(h_(m)F_(2))、斜电子总含量(Slant Total Electron Content, STEC)及h_(m)F_(2)以上电子密度等方面均具有更佳的表现.相对于精度较高的CMART算法,ITPS方法在f_(o)F_(2)与h_(m)F_(2)的平均优化率分别为7.49%及6.60%,STEC的平均优化率为5.19%,h_(m)F_(2)以上电子密度的平均优化率为11.41%.展开更多
文摘Mining operation, especially underground coal mining, always has the remarkable risks of ground control. Passive seismic velocity tomography based on simultaneous iterative reconstructive technique (SIRT) inversion is used to deduce the stress redistribution around the longwall mining panel. The mining-induced microseismic events were recorded by mounting an array of receivers on the surface, above the active panel. After processing and filtering the seismic data, the three-dimensional tomography images of the p-wave velocity variations by SIRT passive seismic velocity tomography were provided. To display the velocity changes on coal seam level and subsequently to infer the stress redistribution, these three-dimensional tomograms into the coal seam level were sliced. In addition, the boundary element method (BEM) was used to simulate the stress redistribution. The results show that the inferred stresses from the passive seismic tomograms are conformed to numerical models and theoretical concept of the stress redistribution around the longwall panel. In velocity tomograms, the main zones of the stress redistribution arotmd the panel, including front and side abutment pressures, and gob stress are obvious and also the movement of stress zones along the face advancement is evident. Moreover, the effect of the advance rate of the face on the stress redistribution is demonstrated in tomography images. The research result proves that the SIRT passive seismic velocity tomography has an ultimate potential for monitoring the changes of stress redistribution around the longwall mining panel continuously and subsequently to improve safety of mining operations.
基金Projected supported by the National High Technology Research and Development Program of China(Grant No.2012AA011603)the National Natura Science Foundation of China(Grant No.61372172)
文摘Sparse-view x-ray computed tomography (CT) imaging is an interesting topic in CT field and can efficiently decrease radiation dose. Compared with spatial reconstruction, a Fourier-based algorithm has advantages in reconstruction speed and memory usage. A novel Fourier-based iterative reconstruction technique that utilizes non-uniform fast Fourier transform (NUFFF) is presented in this work along with advanced total variation (TV) regularization for a fan sparse-view CT. The proposition of a selective matrix contributes to improve reconstruction quality. The new method employs the NUFFT and its adjoin to iterate back and forth between the Fourier and image space. The performance of the proposed algorithm is demonstrated through a series of digital simulations and experimental phantom studies. Results of the proposed algorithm are compared with those of existing TV-regularized techniques based on compressed sensing method, as well as basic algebraic reconstruction technique. Compared with the existing TV-regularized techniques, the proposed Fourier-based technique significantly improves convergence rate and reduces memory allocation, respectively.
文摘It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used successfully to improve the image quality. This paper studies the application of iterative algorithms in radar imaging. A discrete model is first derived, and the iterative algorithms are then adapted to radar imaging. Although such algorithms are usually time consuming, this paper shows that, if the algorithms are appropriately simplified, it is possible to realize them even in real time. The efficiency of iterative algorithms is shown through computer simulations.
文摘层析是电离层三维结构反演的重要技术.增加约束可缓解层析模型的病态问题.然而,迭代层析中,大量无射线穿过的网格易对施加的约束产生与真实意图相违背的约束结果(称负面约束).针对该问题,提出了一种参数平滑的迭代层析方法(iterative tomography method via parameters smoothing, ITPS).每次迭代中,先用Chapman函数及最小二乘法拟合及改正每一垂直剖面,获取关于Chapman函数参数的二维图像,然后用移动窗口法平滑各参数图像并以此改正各网格的电子密度.实验表明:ITPS方法可一定程度上减少负面约束并抑制层像的扰动.相对于MART和CMART算法,ITPS方法在垂直剖面、F2层临界频率(f_(o)F_(2))、F_(2)层峰值高度(h_(m)F_(2))、斜电子总含量(Slant Total Electron Content, STEC)及h_(m)F_(2)以上电子密度等方面均具有更佳的表现.相对于精度较高的CMART算法,ITPS方法在f_(o)F_(2)与h_(m)F_(2)的平均优化率分别为7.49%及6.60%,STEC的平均优化率为5.19%,h_(m)F_(2)以上电子密度的平均优化率为11.41%.