• Title, Summary, Keyword: waveform tomography

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Seismic waveform tomography in the frequency-space domain: selection of the optimal temporal frequency for inversion

  • Yokota Toshiyuki;Matsushima Jun
    • Geophysics and Geophysical Exploration
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    • v.7 no.1
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    • pp.19-24
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    • 2004
  • Frequency-space domain full-wave tomography is a promising technique for delineating detailed subsurface structure with high resolution. However, this method requires criteria for the selection of a set of optimal temporal frequency components, to achieve stability in the sequence of inversion processes together with computational efficiency. We propose a method of selecting optimal temporal frequencies, based on wavenumber continuity. The proposed method is tested numerically and is shown to be able to select an optimal set of frequency components that are sufficient to image the anomalies.

Acoustic 2-D Full-waveform Inversion with Initial Guess Estimated by Traveltime Tomography (주시 토모그래피와 음향 2차원 전파형 역산의 적용성에 관한 연구)

  • Han Hyun Chul;Cho Chang Soo;Suh Jung Hee;Lee Doo Sung
    • Geophysics and Geophysical Exploration
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    • v.1 no.1
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    • pp.49-56
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    • 1998
  • Seismic tomography has been widely used as high resolution subsurface imaging techniques in engineering applications. Although most of the techniques have been using travel time inversion, waveform method is being driven forward owing to the progress of computational environments. Although full-waveform inversion method has been known as the best method in terms of model resolving power without high-frequency restriction and weak scattering approximation, it has practical disadvantage that it is apt to get stuck in local minimum if the initial guess is far from the actual model and it consumes so much time to calculate. In this study, 2-D full-waveform inversion algorithm in acoustic medium is developed, which uses result of traveltime tomography as initial model. From the application on synthetic data, it is proved that this approach can efficiently reduce the problem of conventional approaches: our algorithm shows much faster convergence rate and improvement of model resolution. Result of application on physical modeling data also shows much improvement. It is expected that this algorithm can be applicable to real data.

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Resolution Limits of Cross-Well Seismic Imaging Using Full Waveform Inversion (전파형 역산을 이용한 시추공 영상의 분해능)

  • Cho, Chang-Soo;Lee, Hee-Il;Suh, Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.5 no.1
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    • pp.33-45
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    • 2002
  • It was necessary to devise new techniques to overcome and enhance the resolution limits of traveltime tomography. Waveform inversion has been one of the methods for giving very high resolution result. High resolution image could be acquired because waveform inversion used not only phase but amplitude. But waveform inversion was much time consuming Job because forward and backward modeling was needed at each iteration step. Velocity-stress method was used for effective modeling. Resolution limits of imaging methods such as travel time inversion, acoustic and elastic waveform inversion were investigated with numerical models. it was investigated that Resolution limit of waveform inversion was similar tn resolution limit of migration derived by Schuster. Horizontal resolution limit could be improved with increased coverage by adding VSP data in cross hole that had insufficient coverage. Also, waveform inversion was applied to realistic models to evaluate applicability and using initial guess of travel time tomograms to reduce non-linearity of waveform inversion showed that the better reconstructed image could be acquired.

Reflection travel time tomography using blocky parameterization

  • Kim Wonsik;Hong Soonduk;Shin Changsoo;Yang Seungjin
    • Proceedings of the KSEEG Conference
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    • pp.163-166
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    • 2002
  • Initial velocity model close to real velocity structure of the subsurface governs the quality of image of prestack depth migration. Geophysicists employ velocity estimation tools such as velocity analysis (curvature method, coherency inversion), tomography and waveform inversion. We present a reflection tomography that parameterizes the subsurface into the movable blocks. By interpreting the depth-migrated section or stacked section, we can design an initial constant velocity model having only impedance boundaries. We use shooting-raytracing method that allows us to calculate the Jacobian-matrix efficiently.

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EZTOMO CROSSWELL TOMOGRAPHY SOFTWARE SYSTEM UPDATE (EZTOMO 시추공 토모그래피 소프트웨어 시스템 보완)

  • Lee, Doo-Sung
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.69-72
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    • 2008
  • EZTOMO is a crosswell seismic tomography software system. The system has capability of event picking, raytracing, inversion, error analysis, and visualization of the processing results. Waveform of the first arrival signal has been utilized to select the event of the first motion, and uncertainty measured in estimation of the first breaks has been utilized to improve the inversion process.

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Improved full-waveform inversion of normalised seismic wavefield data (정규화된 탄성파 파동장 자료의 향상된 전파형 역산)

  • Kim, Hee-Joon;Matsuoka, Toshifumi
    • Geophysics and Geophysical Exploration
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    • v.9 no.1
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    • pp.86-92
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    • 2006
  • The full-waveform inversion algorithm using normalised seismic wavefields can avoid potential inversion errors due to source estimation required in conventional full-waveform inversion methods. In this paper, we have modified the inversion scheme to install a weighted smoothness constraint for better resolution, and to implement a staged approach using normalised wavefields in order of increasing frequency instead of inverting all frequency components simultaneously. The newly developed scheme is verified by using a simple two-dimensional fault model. One of the most significant improvements is based on introducing weights in model parameters, which can be derived from integrated sensitivities. The model-parameter weighting matrix is effective in selectively relaxing the smoothness constraint and in reducing artefacts in the reconstructed image. Simultaneous multiple-frequency inversion can almost be replicated by multiple single-frequency inversions. In particular, consecutively ordered single-frequency inversion, in which lower frequencies are used first, is useful for computation efficiency.

Development of Respiratory Training System Using Individual Characteristic Guiding Waveform (환자고유의 호흡 패턴을 적용한 호흡 연습장치 개발 및 유용성 평가)

  • Kang, Seong-Hee;Yoon, Jai-Woong;Kim, Tae-Ho;Suh, Tae-Suk
    • Progress in Medical Physics
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    • v.23 no.1
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    • pp.1-7
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    • 2012
  • The purpose of this study was to develop the respiratory training system using individual characteristic guiding waveform to reduce the impact of respiratory motion that causes artifact in radiotherapy. In order to evaluate the improvement of respiratory regularity, 5 volunteers were included and their respiratory signals were acquired using the in-house developed belt-type sensor. Respiratory training system needs 10 free breathing cycles of each volunteer to make individual characteristic guiding waveform based on Fourier series and it guides patient's next breathing. For each volunteer, free breathing and guided breathing which uses individual characteristic guiding waveform were performed to acquire the respiratory cycles for 3 min. The root mean square error (RMSE) was computed to analyze improvement of respiratory regularity in period and displacement. It was found that respiratory regularity was improved by using respiratory training system. RMSE of guided breathing decreased up to 40% in displacement and 76% in period compared with free breathing. In conclusion, since the guiding waveform was easy to follow for the volunteers, the respiratory regularity was significantly improved by using in-house developed respiratory training system. So it would be helpful to improve accuracy and efficiency during 4D-RT, 4D-CT.

Evaluation of energy correction algorithm for signals of PET in heavy-ion cancer therapy device

  • Niu, Xiaoyang;Yan, Junwei;Wang, Xiaohui;Yang, Haibo;Ke, Lingyun;Chen, Jinda;Du, Chengming;Zhang, Xiuling;Zhao, Chengxin;Kong, Jie;Su, Hong
    • Nuclear Engineering and Technology
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    • v.52 no.1
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    • pp.101-108
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    • 2020
  • In order to solve the contradiction between requirements of high sampling rate for acquiring accurate energy information of pulses and large amount of data to be processed timely, the method with an algorithm to correct errors caused by reducing the sampling rate is normally used in front-end read-out system, which is conductive to extract accurate energy information from digitized waveform of pulse. The functions and effects of algorithms, which mainly include polynomial fitting with different fitting times, double exponential function fitting under different sampling modes, and integral area algorithm, are analyzed and evaluated, and some meaningful results is presented in this paper. The algorithm described in the paper has been used preliminarily in a prototype system of Positron Emission Tomography (PET) for heavy-ion cancer therapy facility.

Algorithm Study for Diagnosis the Breast Cancer Using LMA and FDTD (LMA와 FDTD를 이용한 유방암 진단용 알고리즘 연구)

  • Seo, Min-Gyeong;Kim, Tae-Hong;Mun, Ji-Yeon;Jeon, Soon-Ik;Pack, Jeong-Ki
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.22 no.12
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    • pp.1124-1131
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    • 2011
  • In this paper, image reconstruction algorithm for breast cancer detection using MT(Microwave Tomography) was investigated. The breast cancer detection system under development uses 16 transmit/receive antennas. The signal waveform was a sinusoidal wave at 900 MHz. To solve the 2D inverse scattering problem, we used the 2D FDTD (Finite Difference Time Domain) method for forward calculation and LMA(Levenberg-Marquardt Algorithm) for optimization. The result of the image reconstruction using the numerical phantom by MRI(Magnetic Resonance Imaging) obtained from real patient of breast cancer showed that we can detect the position of the tumor accurately.

Ultrasonic Image Reconstruction using Mode-Converted Rayleigh Wave (파형 변환된 레이리파를 이용한 초음파영상복원)

  • Suh Dong-Man
    • Proceedings of the Acoustical Society of Korea Conference
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    • pp.403-408
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    • 1999
  • In this paper, ultrasonic tomography by the Mode-Converted Rayleigh wave (MCRW) in the back-scattered direction is presented. When a beam with a short pulse and narrow beam width enters a reflector with smooth surface, in general, two major arrivals can be observed in the output waveform: the specular reflection and the radiation of the MCRW from the reflector surface. The time-delay between the two waves is relatively large and thus can be measured easily. This large time-delay is due to the fact that the MCRW is slower than incident wave. In our method, this large time- delay is used for ultrasonic image reconstruction. To effectively detect the MCRW, the arrayed-receiving transducers are circularly arranged around the transmitter. In addition, a deconvolution method is employed to remove specular echo signals for reconstructing the MCRW image.

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