• Korean Journal of Agricultural and Forest Meteorology
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• v.14 no.4
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• pp.269-276
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• 2012

The objective of this short communication is to introduce several evaluation methods to crop model users because the evaluation of crop model performance is an important step to develop or select crop model. In this paper, mean error, mean absolute error, index of agreement, root mean square error, efficiency of model, accuracy factor and bias factor were explained and compared in terms of dimension and observed number. Efficiency of model and index of agreement are dimensionless and independent of number of observation. Relative root mean square, accuracy factor and bias factor are dimensionless and not independent of number of observation. Mean error and mean absolute error are affected by dimension and number of observation.

• The Korean Journal of Applied Statistics
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• v.16 no.1
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• pp.1-14
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• 2003

In this study, we suggest the method of small area estimation based on the Economically Active Population Survey (EAPS) data in producing unemployment statistics for the local self-government areas (LSGAs) within large areas. The small area estimators considered are design-based indirect estimators such as the synthetic and composite estimators. The jackknife mean square error was used as a measure of accuracy of such small area estimators. The total unemployed and jackknife mean square errors of the 10 LSGAs within the large area of ChoongBuk region are derived from the estimation procedure suggested in this study, using EAPS data of December 2000. The reliability of small area estimators was assessed using the relative bias values and relative root mean square errors of these estimators. We find that under the current Korean EAPS system, the composite estimator turns out to be much more stable than other estimators.

• Journal of the Korean Data and Information Science Society
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• v.20 no.2
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• pp.349-356
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• 2009

In this study, we suggest the estimation method of the relative risk for the unemployment statistics of a small area such as si, gun, gu in Korea. The considered method are the usual pooled estimator, weighted estimator with the inverse of log-variance as weights, and the Jackknife estimator. And we compare with the efficiency of the three estimators by estimating the bias and mean square errors using real data from the 2002 Economically Active Population Survey of Gyeonggi-do. We compute the unemployed rate of male and female in small areas, and then estimate the common relative risk for the unemployed rate between male and female. Also, the stability and reliability of the three estimators for the common relative risk was evaluated using the RB(relative bias) and the RRMSE(relative root mean square error) of these estimators. Finally, the Jackknife estimator turned out to be much more efficient than the other estimators.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.142-146
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• 2007

본 연구에서는 강우강도식의 매개변수를 보다 효율적으로 산정하기 위해서 유전자알고리즘을 적용한 매개변수 산정법을 제시하였으며, 지속기간의 장, 단기간에 따른 매개변수의 변화를 고려하기 위하여 다목적 유전자알고리즘을 적용하여 매개변수를 추정한 후 기존의 강우강도식에 의한 결과와 비교해 보았다. 매개변수는 지점빈도해석을 통해 산정된 확률강우량을 사용하여 추정하였고, 유전자 알고리즘의 목적함수로는 Nash & Sutcliffe Index, Root Mean Square Error(RMSE), Relative Root Mean Square Error(RRMSE), 결정계수, 평균들을 사용하여 가장 효율적인 형태의 목적함수를 구성하였다. 그 결과 기존의 매개변수 추정 방법들에 비해 유전자알고리즘을 이용한 경우에 더 정확한 강우량값을 산정할 수 있었고, 특히 다목적 유전자 알고리즘을 사용할 경우 장기간과 단기간에 걸쳐서 동시에 정확도를 향상시킬 수 있는 매개변수를 추정할 수 있는 것으로 나타났다.

• Transactions of Materials Processing
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• v.29 no.5
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• pp.282-289
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• 2020

Flexible roll forming is an advanced sheet-metal-forming process that allows the production of parts with various cross-sections. During the flexible process, material is subjected to three-dimensional deformation such as transverse bending, inhomogeneous elongations, or contraction. Because of the effects of process variables on the quality of the roll-formed products, the approaches used to investigate the roll-forming process have been largely dependent on experience and trial- and-error methods. Web-warping is one of the major shape defects encountered in flexible roll forming. In this study, an SVR model was developed to predict the web-warping during the flexible roll forming process. In the development of the SVR model, three process parameters, namely the forming-roll speed condition, leveling-roll height, and bend angle were considered as the model inputs, and the web-warping height was used as the response variable for three blank shapes; rectangular, concave, and convex shape. MATLAB software was used to train the SVR model and optimize three hyperparameters (λ, ε, and γ). To evaluate the SVR model performance, the statistical analysis was carried out based on the three indicators: the root-mean-square error, mean absolute error, and relative root-mean-square error.

• Journal of Korea Water Resources Association
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• v.39 no.8 s.169
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• pp.677-690
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• 2006

The LH-OAT (Latin Hypercube One factor At a Time) method for sensitivity analysis and SCE-UA (Shuffled Complex Evolution at University of Arizona) optimization method were applied for the automatic calibration of SWAT model in Bocheong-cheon watershed. The LH-OAT method which combines the advantages of global and local sensitivity analysis effectively identified the sensitivity ranking for the parameters of SWAT model over feasible parameter space. Use of this information allows us to select the calibrated parameters for the automatic calibration process. The performance of the automatic calibration of SWAT model using SCE-UA method depends on the length of calibration period, the number of calibrated parameters, and the selection of statistical error criteria. The performance of SWAT model in terms of RMSE (Root Mean Square Error), NSEF (Nash-Sutcliffe Model Efficiency), RMAE (Relative Mean Absolute Error), and NMSE (Normalized Mean Square Error) becomes better as the calibration period and the number of parameters defined in the automatic calibration process increase. However, NAE (Normalized Average Error) and SDR (Standard Deviation Ratio) were not improved although the calibration period and the number of calibrated parameters are increased. The result suggests that there are complex interactions among the calibration data, the calibrated parameters, and the model error criteria and a need for further study to understand these complex interactions at various representative watersheds.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.301-301
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• 2016

국내의 경우 수공구조물을 설계하기 위해서는 빈도해석을 통해 설계수문량을 산정한다. 일반적으로 실무에서는 지점빈도해석을 수행하게 되는데 설계빈도보다 대부분 짧은 기간의 자료를 이용하여 산정한다. 지역빈도해석은 이러한 자료기간이 가지는 문제점을 극복하기 위하여 확률수문량의 정확도와 신뢰도를 향상시키는 기법이다. 스케일 모델은 지속기간별로 관측된 강우자료를 이용하여 재현기간에 대한 지속기간의 함수로 표현이 가능하며, 이를 통해 강우의 IDF곡선을 제시할 수 있는 수학적 모델이다. 대상지역의 강우관측소에서 관측된 강우자료가 일단위이면, 기준지속기간이 24시간이 되며, 기준지속기간에 대한 확률강우량으로부터 임의의 지속기간에 대한 확률강우량을 스케일 모델을 이용하여 추정할 수 있다. 따라서 짧은 자료를 보유한 지역이거나 미계측 지역에 대한 확률강우량을 추정을 위해 지역빈도해석과 지역 스케일 모델을 이용하여 확률강우량을 추정하여 지점빈도해석과 비교하고자 한다. 본 연구를 위해 한강유역의 강우 관측소를 이용하였으며, 군집분석 중 k-means방법을 적용하여 수문학적 동질성을 확보한 후 지역을 구분하였다. 구분된 지역은 지점 및 지역빈도해석을 수행한 후 상대평균제곱근오차(relative root mean square error, RRMSE)를 비교하여 정확도를 판단하였고, 정확도가 높은 빈도해석에 지역 스케일 모델을 적용하여 미계측 지점에 대한 임의의 시간에 대한 확률강우량을 추정하고자 한다.

• Food Engineering Progress
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• v.14 no.1
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• pp.75-79
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• 2010

Partial least square regression (PLSR) was executed on curve data of force-deformation from back extrusion test and sensory data for commercial instant noodles. Sensory attributes considered were hardness (A), springiness (B), roughness (C), adhesiveness to teeth (D), and thickness (E). Eight and two kinds of fried and non-fried instant noodles respectively were used in the tests. Changes in weighted regression coefficients were characterized as three stages: compaction, yielding, and extrusion. Correlation coefficients appeared in the order of E>D>A>B>C, root mean square error of prediction D>C>E>B>A, and relative ability of prediction D>C>E>B>A. Overall, 'D' was the best in the correlation and prediction. 'A' with poor prediction ability but high correlation was considered good when determining the order of magnitude.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.315-324
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• 2003

Stream flow data was analyzed for determining the lowflow which is the standard for river maintenance flow. Lowflow quantiles were estimated based on the parametric and nonparametric methods and two methods were compared by Monte Carlo simulation study. As the results of the parametric method, three probability distributions such as gamma-2, lognormal-2 and Weibull-2, are selected as appropriate models for stream flow data of 13 stations in Han River Basins. According to simulation results, relative bias (RBIAS) and relative root mean square error (RRMSE) of the lowflow quantiles are the smallest when the applied and population models are the same. The fame statistical properties from the nonparametric models are good within the interpolation range. Among 7 bandwidth selectors used in this study, the RRMSEs of the Park and Marron method (PM) are the smallest while those of the Shoaler and Jones method (SJ) are the largest.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.39 no.3
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• pp.123-132
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• 2021

To determine 3D(three-dimensional) positions using a stereo-camera in close-range photogrammetry, camera calibration to determine not only the interior orientation parameters of each camera but also the relative orientation parameters between the cameras must be preceded. As time passes after performing camera calibration, in the case of non-metric cameras, the interior and relative orientation parameters may change due to internal instability or external factors. In this study, to evaluate the stability of the stereo-camera, not only the stability of two single cameras and a stereo-camera were analyzed, but also the three-dimensional position accuracy was evaluated using checkpoints. As a result of evaluating the stability of two single cameras through three camera calibration experiments over four months, the root mean square error was ±0.001mm, and the root mean square error of the stereo-camera was ±0.012mm ~ ±0.025mm, respectively. In addition, as the results of distance accuracy using the checkpoint were ±1mm, the interior and relative orientation parameters of the stereo-camera were considered stable over that period.