• Geophysics and Geophysical Exploration
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• v.10 no.2
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• pp.131-137
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• 2007

With consideration of the first arrival picking methodology and inherent errors in picking process, I propose, from the computerization point of view, a practical algorithm for picking and error computation. The proposed picking procedure consists of 2-step; 1) picking the first coherent peak or trough events, 2) derive a line which approximates the record in the interval prior to the pick, and set the intercept time of the line as the first break. The length of fitting interval used in experiment, is few samples less than 1/4 width of the arriving wavelet. A quantitative measure of the error involved in first arrival picking is defined as the time length that needed to determine if an event is the first arrival or not. The time length is expressed as a function of frequency bandwidth of the signal and the S/N ratio. For 3 sets of cross-well seismic data, first breaks are picked twice, by manually, and by the proposed method. And at the same time, the error bound for each trace is computed. Experiment results show that good performance of the proposed picking method, and the usefulness of the quantitative error measure in pick-quality evaluation.

• Tunnel and Underground Space
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• v.29 no.4
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• pp.243-261
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• 2019

Microseismic monitoring technologies have been recognized for its superiority over traditional methods and are used in domestic and overseas underground mines. However, the complex gangway layout of underground mines in Korea and the mixed structure of excavated space and rock masses make it difficult to estimate the microseismic propagation and to determine the arrival time of microseismic wave. In this paper, experimental studies were carried out to determine the source location according to various arrival picking methods and dimensional conditions. The arrival picking methods used were FTC (First Threshold Cross), Picking window, AIC (Akaike Information Criterion), and 2-D and 3-D source generation experiments were performed, respectively, under the 2-D sensor array. In each experiment, source location algorithm used iterative method and genetic algorithm. The iterative method was effective when the sensor array and source generation were the same dimension, but it was not suitable to apply when the source generation was higher dimension. On the other hand, in case of source location using RCGA, the higher dimensional source location could be determined, but it took longer time to calculate. The accuracy of the arrival picking methods differed according to the source location algorithms, but picking window method showed high accuracy in overall.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.36 no.2
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• pp.17-24
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• 2013

This paper is to analyze the picking lead time for picking batch size in a warehouse system and to get minimum picking batch size that is the warehouse system feasible. The warehouse system consists of aisles and racks, which two racks face each other through aisle. The products are picked from the storage locations by batch size. The probability that items are picked in the each row of the rack in the aisle for order picking activity is derived. The picking lead time for picking batch size is the time passed from the first picking location to arrival at starting location in aisle picking all items included in a batch size. The picking lead time for picking batch size in an aisle is analyzed. The picking lead time for picking batch size in the whole warehouse system is obtained. The warehouse system is feasible if all items that customers order are picked from the storage locations for same period. The picking batch size that is the warehouse system feasible is obtained. The problem is analyzed, a solution procedure is developed, and a numerical example is shown to explain the problem.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.120-121
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• 2001

The purpose of this study is to investigate concrete flaw using seismic first arrival and various inversion method. Seismic wave propagation was calculated using finite element method in theoretical modelling and tomogram was made using various inversion methods in theoretical and experimental modelling. Five steps of seismic first arrival were selected from FEM results and these data were used to calculate seismic velocity section. According to the results, exact seismic first arrival picking method was proposed and experimental modelling was conducted.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.193-198
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• 2002

In crosswell ray tomography, the resultant velocity structure could be affected by source static, first-arrival-time picking errors, convergence to a local minimum due to an inappropriate initial velocity model and etc. In the paper, I propose an algorithm that automatically correct the souce static among these error-prone factors. The algorithm automatically corrects source static using the picking times' differences along the source direction. The application of the algorithm to real data produces a quite satisfactory result. Tile algorithm seems to be helpful for users to apply the souce static correction consistently and to acquire accurate velocity structure.

• Geophysics and Geophysical Exploration
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• v.7 no.3
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• pp.157-163
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• 2004

In this study, a travel-time tomography software was developed under the MS Windows system and GUI environment for user. The software supports following features: (1) supporting various data input format (2) flexible treatment of shot and receiver coordinate coding (3) flexible first arrival picking and modification (4) easy modification of intermediate tomogram. It is expected that the effort of the user can be minimized in each data processing step.

• Geophysics and Geophysical Exploration
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• v.12 no.3
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• pp.233-238
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• 2009

An inversion method regulated by the error in the measurement of the first arrival time was developed, and we conducted a feasibility study by applying the method to a real cross-well seismic data. The inversion is a two-step regulation process; 1) derive the measurement error bound based on the resolution of the velocity image want to derive, and exclude the records whose picking error is larger than the error bound, 2) set the travel time residual to zero if the residual is less than the measurement error. This process prevents the trivial residuals are accumulated and contribute to the velocity-model update. Comparison of two velocity images, one by using all records and another by using the regulate inversion method, shows that the later velocity image exhibits less numerical artefacts, and it also indicates that, according to the Fermat's principle, the latter image is a more feasible velocity model.

• The Journal of Engineering Geology
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• v.29 no.2
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• pp.153-162
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• 2019

Rapid variations in the geometry (i.e., thickness) of the refractor and low velocities affect greatly the imaging of the reflectors of land seismic data. Conventional solutions to obtain the weathering models utilizes first break picking method, which requires time consuming steps and causes the human error in picking the first arrivals. A new interferometric approach (interferometric refraction statics, IRS) which utilizes the first arrival signal (S/N enhanced by refraction convolution stack) instead of first break picking, is tested in this study to the synthetic data from the velocity structure provided by surface geophysics (refraction, MASW) and borehole geophysics (tomography, SPS logging) for the Cheongju granitic bodies. The results of IRS approach are found to be better than the ones from conventional first break picking in terms of continuities and horizontal resolution of the reflectors. The unresolved long-wavelength statics in brute stack are much removed by IRS weathering correction and the overlying refractors (the base of shallow weathering zone) are incidentally delineated in the refraction convolution stack.

• Geophysics and Geophysical Exploration
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• v.18 no.2
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• pp.64-73
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• 2015

Recently, hydraulic fracturing is used in various fields and microseismic monitoring is one of the best methods for judging where hydraulic fractures exist and how they are developing. When locating microseismic events using single vertical well data, distances from the vertical array and depths from the surface are generally decided using time differences between compressional (P) wave and shear (S) wave arrivals and azimuths are calculated using P wave hodogram analysis. However, in field data, it is sometimes hard to acquire P wave data which has smaller amplitude than S wave because microseismic data often have very low signal to noise (S/N) ratio. To overcome this problem, in this study, we developed a grid search algorithm which can find event location using all combinations of arrival times recorded at receivers. In addition, we introduced and analyzed the method which calculates azimuths using S wave. The tests of synthetic data show the inversion method using all combinations of arrival times and receivers can locate events without considering the origin time even using only single phase. In addition, the method can locate events with higher accuracy and has lower sensitivity on first arrival picking errors than conventional method. The method which calculates azimuths using S wave can provide reliable results when the dip between event and receiver is relatively small. However, this method shows the limitation when dip is greater than about $20^{\circ}$ in our model test.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.299-307
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• 2007

Slowness time coherence (STC) technique has been applied to 3-receiver slim hole sonic log using 3 NX sized concrete model holes of different physical properties. We analyzed the effects of different source center frequencies on the wave forms, their amplitude spectra, and their STC results. We could determine the sonic velocity of each mode accurately by the application of STC method with the semblance projection and efficient selection of center frequency. Theoretical model and experimental model hole studies indicate that 4-receiver condition is the most ideal for STC in near surface slim hole sonic log. The result also indicates that favorable STC result can be obtained from three-receiver sonic log provided with the help of the first arrival picking method.