• Title, Summary, Keyword: Migration velocity

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Measurement of vertical migration speed of Sound Scattering Layer using an bottom mooring type Acoustic Doppler Current Profiler (해저설치형 음향도플러유향유속계를 이용한 음향산란층의 연직이동속도 측정)

  • Jo, Hyeon-Jeong;Lee, Kyoung-Hoon
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.46 no.4
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    • pp.449-457
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    • 2010
  • This study shows that the vertical migration speed of sound scattering layers (SSLs), which is distributed in near Funka Bay, were measured by 3D velocity components acquired from a bottom moorng ADCP. While the bottom mooring type has a problem to measure the velocity vectors of sound scattering layer distributed near to surface, both the continuous vertical migration patterns and variability of backscatterers were routinely investigated as well. In addition, the velocity vectors were compared with the vertical migration velocity estimated from echograms of Mean Volume Backscattering Strength, and estimated to produce observational bias due to SSLs which is composed of backscatterers such as euphausiids, nekton, and fishes have swimming ability.

Improvement of Reverse-time Migration using Modified Receiver Aperture (수진기 배열 변경에 의한 역시간 구조보정 영상 개선 연구)

  • Cheong Soon-Hong;Shin Chang-Soo
    • Geophysics and Geophysical Exploration
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    • v.6 no.3
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    • pp.153-159
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    • 2003
  • Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.

Data Processing for a GPR survey of Fourcade glacier (Fourcade 빙하지역의 GPR 자료처리)

  • Kim, Ki-Young;Hong, Myung-Ho;Lee, Joo-Han;Hong, Jong-Kuk;Jin, Young-Keun;Shon, Ho-Woong
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.139-144
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    • 2007
  • To delineate subglacial and englacial images of the western Fourcade Glacier in Antarctica, GPR data were acquired along a 470 m profile in November 2006. Signature deconvolution, migration velocity analysis, and finite difference depth migration were effective in increasing vertical resolution, obtaining the velocity function, and yielding clear depth images of the mixed-phase single-channel data, respectively. The source signature was extracted through stacking reflection signals from the basement. The deconvolution successfully compressed the source signatures to increase temporal resolution and attenuated reverberations. Medium velocities were analyzed with 112 diffraction events by the constant-velocity migration method based on the Stolt algorithm. Finally, depth migration based on the finite difference algorithm provided clear englacial and subglacial images in the laterally-varying velocity field.

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Weighted Kirchhoff Prestack Depth Migration using Smooth Background Model (Smooth Background Model(SBM)을 이용한 가중 키리히호프 중합전 심도구조보정)

  • Ko, Seung-Won;Yang, Seung-Jin;Shin, Chang-Su
    • Geophysics and Geophysical Exploration
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    • v.4 no.3
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    • pp.84-88
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    • 2001
  • For the elastic migation, the velocity errors between the initial velocity model and true velocity model seriously affect the migrated images. The assumption of an initial velocity model, thus, is one of the critical factor for the successful migration. In case of applying the layered earth model as an initial velocity model, the layer boundary having large velocity contrast can not be defined well with conventional traveltime calculation algolithms and we have the difficulties for expressing the characteristics of the real subsurface. Smooth Background Model (SBM) we have applied as an initial velocity model in our study is characterized to be linearly varying the velocity with the depth, which can express the velocity variation in the subsurface properly. Thus it can properly be applied to traveltime calculation algolithms such as Vidale's method. In this study, Kirchhoff operator for prestack migration was used and the absolute amplitude obtained by modeling was applied as a weighted value to consider the true amplitude for initial model. Initial velocity model for migration was determined by using stacking velocity and we applied this model to real data.

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MIGRATION OF ELASTIC CAPSULE IN A CHANNEL FLOW (채널 유동 내 유연한 캡슐 움직임에 대한 수치해석)

  • Shin, S.J.;Sung, H.J.
    • 한국전산유체공학회:학술대회논문집
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    • pp.504-507
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    • 2011
  • The inertial migration of a two-dimensional elastic capsule in a channel flow was studied over the Reynolds number range $1{\leq}Re{\leq}100$. The lateral migration velocity, slip velocity, and the deformation and inclination angle of the capsule were investigated by varying the lateral position, Reynolds number, capsule-to-channel size ratio(${\lambda}$), membrane stretching coefficient(${\Phi}$), and membrane bending coefficient(${\gamma}$). During the initial transient motion, the lateral migration velocity increased with increasing Re and ${\lambda}$ but decreased with increases in ${\Phi}$, ${\gamma}$ and the lateral distance from the wall. The initial behavior of the capsule was influenced by variation in the initial lateral position ($y_0$), but the equilibrium position of the capsule was not affected by such variation. The balance between the wall effect and the shear gradient effect determined the equilibrium position. As Re increased, the equilibrium position initially shifted closer to the wall and then moved towards the channel center. A peak in the equilibrium position was observed near Re=30 for ${\gamma}=0.1$, and the peak shifted to higher Re as ${\gamma}$ increased. Depending on the lateral migration velocity, the equilibrium position moved toward the centerline for larger ${\gamma}$ but moved toward the wall for larger ${\Phi}$ and ${\gamma}$.

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Improvement of Reverse-time Migration using Homogenization of Acoustic Impedance (음향 임피던스 균질화를 이용한 거꿀시간 참반사보정 성능개선)

  • Lee, Gang Hoon;Pyun, Sukjoon;Park, Yunhui;Cheong, Snons
    • Geophysics and Geophysical Exploration
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    • v.19 no.2
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    • pp.76-83
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    • 2016
  • Migration image can be distorted due to reflected waves in the source and receiver wavefields when discontinuities of input velocity model exist in seismic imaging. To remove reflected waves coming from layer interfaces, it is a common practice to smooth the velocity model for migration. If the velocity model is smoothed, however, the subsurface image can be distorted because the velocity changes around interfaces. In this paper, we attempt to minimize the distortion by reducing reflection energy in the source and receiver wavefields through acoustic impedance homogenization. To make acoustic impedance constant, we define fake density model and use it for migration. When the acoustic impedance is constant over all layers, the reflection coefficient at normal incidence becomes zero and the minimized reflection energy results in the improvement of migration result. To verify our algorithm, we implement the reverse-time migration using cell-based finite-difference method. Through numerical examples, we can note that the migration image is improved at the layer interfaces with high velocity contrast, and it shows the marked improvement particularly in the shallow part.

Visualization and Velocity Measurement of Migrating Cells in Microchannels with Various Width (다양한 크기의 마이크로 채널 내에서 이동하는 세포의 가시화 및 이동 속도 측정)

  • Lee, Seung-Youl;Kim, Myung-Jun;Chae, Sang-Min;Jin, Song-Wan
    • Journal of the Korean Society of Visualization
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    • v.9 no.1
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    • pp.29-35
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    • 2011
  • In this paper, we applied various microfluidic chambers to visualize cell migration and measured the migration velocity in microchannels. Migration speed of B16 cell in a large channel was similar with that of wound healing experiment. However, the speed decreased gradually as the cell move inside of the channel. It is expected that this phenomenon is due to the shortage of oxygen or nutrition, whichare essential for cell growth. In the case of cell in the small channel whose size is smaller than the cell, its speed was slower than that in a larger channel.

Hydraulic Model Experiment for Field Application of Iceharbor-type Precast Fishway (조립식 아이스하버식 어도의 현장 적용을 위한 수리모형실험)

  • Kim, Jae-Ok;Park, Sang-Hyun;Cho, Jae-Won;Hwang , Jong-Seo;Jo , Guk-Hyun;Joh , Seong-Ju
    • Journal of The Korean Society of Agricultural Engineers
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    • v.46 no.2
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    • pp.3-14
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    • 2004
  • This study was conducted to assess the possibility of the field application of the iceharbor-type precast fishway. When overflow depth of weir is 4.0 cm in model fishway, upper part velocities appear appropriate for upstream migration of fish and the lowest overflow wall (right line) in lower part has shown velocity distribution more or less inadequate for upstream migration. Except that right line, left and middle line revealed that velocities are appropriate for upstream migration of fish. Therefore, we concluded that this fishway owing to be not broad growth width of overflow velocities according to increasing discharges can correspond to variation of water level. Also We consider that various velocities in fishway were effective, because slow velocity line can guide flow for upstream migration. For low flow, the arrangement of different crest level or each overflow part (higher left, middle and lower right, or lower left, middle and higher right) was more effactive than unform crert level. Hole plays an important role as migration pass during drought and flood flow. Therefore, We concluded that this fishway can cope with water depth variation by various overflow wall height change and raise the field applicability with better performance hydraulically and structurally.

Prestack Reverse Time Migration for Seismic Reflection data in Block 5, Jeju Basin (제주분지 제 5광구 탄성파자료의 중합전 역시간 구조보정)

  • Ko, Chin-Surk;Jang, Seong-Hyung
    • Economic and Environmental Geology
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    • v.43 no.4
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    • pp.349-358
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    • 2010
  • For imaging complex subsurface structures such as salt dome, faults, thrust belt, and folds, seismic prestack reverse-time migration in depth domain is widely used, which is performed by the cross-correlation of shot-domain wavefield extrapolation with receiver-domain wavefield extrapolation. We apply the prestack reverse-time migration, which had been developed at KIGAM, to the seismic field data set of Block 5 in Jeju basin of Korea continental shelf in order to improve subsurface syncline stratigraphy image of the deep structures under the shot point 8km at the surface. We performed basic data processing for improving S/N ratio in the shot gathers, and constructed a velocity model from stack velocity which was calculated by the iterative velocity spectrum. The syncline structure of the stack image appears as disconnected interfaces due to the diffractions, but the result of the prestack migration shows that the syncline image is improved as seismic energy is concentrated on the geological interfaces.