• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.3
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• pp.185-193
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• 1994

Conventional ultrasonic flaw detection system uses a large amplitude narrow pulse to excite a transducer. However, these systems are limited in pulse energy. An excessively large amplitude causes a dielectric breakage of the transducer, and an excessively long pulse causes decrease of the resolution. Using the pulse compression, a long pulse of pseudorandom signal can be used without sacrificing resolution by signal correlation. In the present work, the pulse compression technique was implemented into an ultrasonic system. Golay code was used as a pseudorandom signal in this system, since pair sum of autocorrelations has no sidelobe. The equivalent input pulse of the Golay code was derived to analyze the pulse compression system. Throughout the experiment, the pulse compression technique has demonstrated for its improved SNR(signal to noise ratio) by reducing the system's white noise. And the experimental data also indicated that the SNR enhancement was propotional to the square root of the code length used. The technique seems to perform particularly well with highly energy-absorbent materials such as polymers, plastics and rubbers.

• Journal of Korea Water Resources Association
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• v.37 no.7
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• pp.581-587
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• 2004

An experimental watershed was selected and sustainable yield was evaluated. The study area(3.89$\textrm{km}^2$) was located in Kyungpook Sangju Yangchon-dong. The visual MODFLOW was verified by comparing the observed and estimated groundwater table. The analysis of the observed and estimated groundwater table from 19 March 2003 to 18 March 2004 showed that the average error was 0.0009m, the error sum of squares 7.245$m^2$, absolute mean error 0.094 m, root mean square error 0.141m, and the model efficiency was 92%. The normal, 10- and 30- year drought frequency years were selected and sustainable yield was evaluated in these periods. Ratios of sustainable yield to the annual infiltration were 14.5% for the normal year(1992), 15.1% for the 10-year(1994), and 15.2% for the 30-year drought frequency year(1982). The results of this study can be used as a basic information for groundwater development and management planning considering regional characteristics.

• Journal of the Korean Association of Geographic Information Studies
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• v.3 no.2
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• pp.11-23
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• 2000

The subjects of this study are to examine and to apply the methods of making 1 : 10,000 scale digital maps using Russian's 2 m resolution satellite images of Alternative and 8 m resolution stereo satellite images of MK-4 for the Kyoha area of Paju-city where aerial-photo surveying is not possible. A digital elevation model (DEM) was calculated from MK-4 images. With this DEM, the Alternative images were orthorectified. Ground control points (GCP) were acquired from GPS surveyings and were used to perform geometric corrections on Alternative images. From field investigation, thematic attributes are digitized on the monitor. RMS errors of the planar and vertical positions are estimated to ${\pm}0.4$ m and ${\pm}15$ m, respectively. The planar accuracy is better than an accuracy required by NGIS (national GIS) programs. Local information from field investigation was added and the resulting maps should be good as base maps for, such as, regional and urban plannings.

• Journal of the Korean Data and Information Science Society
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• v.20 no.2
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• pp.293-299
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• 2009

In this article, we consider linear models such as regression, ARIMA (autoregressive integrated moving average), and regression+ARIMA (regression with ARIMA errors) for predicting hourly ozone concentration level in two areas of Daegu. Based on RASE(root average squared error), it is shown that the ARIMA is the best model in one area and that the regression+ARIMA model is the best in the other area. We further analyze the residuals from the optimal models, so that we might predict the ozone warning days where at least one of the hourly ozone concentration levels is over 120 ppb. Based on the training data in the years from 2000 to 2003, it is found that 35 ppb is a good cutoff value of residulas for predicting the ozone warning days. In on area of Daegu, our method predicts correctly one of two ozone warning days of 2004 as well as all of the remaining 364 non-warning days. In the other area, our methods predicts correctly all of one ozone warning days and 365 non-warning days of 2004.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.5
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• pp.493-504
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• 2008

Space-Based Augmentation System (SBAS), which is one of the GPS augmentation systems, is a Wide-Area Differential GPS that provides differential GPS corrections and integrity data. In this study, we did performance analysis of kinematic SBAS surveying by conducting Real-Time Kinematic (RTK), DGPS, standalone, and SBAS surveys. Considering static survey results as truth, 2-D Root Mean Square (RMS) error and 3-D RMS error were computed to evaluate the positioning accuracy of each survey method. As a result, the 3-D positioning error of RTK was 13.1cm, DGPS 126.0cm, standalone (L1/L2) 135.7cm, standalone (C/A) 428.9cm, and SBAS 109.2cm. The results showed that the positioning accuracy of SBAS was comparable to that of DGPS.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.35 no.6
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• pp.441-452
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• 2017

Drones are increasingly being used to investigate disaster damage because they can quickly capture images in the air. It is necessary to extract the damaged area by registering the drones and the existing ortho-images in order to investigate the disaster damage. In this process, we might be faced the problem of registering two images with different time and spatial resolution. In order to solve this problem, we propose a new methodology that performs initial image transformation using line pairs extracted from images and association matrix, and final registration of images using linear features to refine the initial transformed result. The applicability of the newly proposed methodology in this study was evaluated through experiments using artifacts and the natural terrain areas. Experimental results showed that the root mean square error of artifacts and the natural terrain was 1.29 pixels and 4.12 pixels, respectively, and relatively high accuracy was obtained in the region with artifacts extracted a lot of linear information.

• Journal of Korea Water Resources Association
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• v.33 no.2
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• pp.263-276
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• 2000

This paper is to derive the probable rainfall depths and the probable rainfall intensity formulas for Inchon Metropolitan district. The annual maximum rainfall data from 10 min. to 6 hours have been collected from the Inchon weather station. Eleven types of probability distribution are considered to estimate probable rainfall depths for 12 different storm durations at the Inchon Metropolitan district. Three tests including Chi-square, Kolmogorov-Smimov and Cramer Von Mises with the graphical analysis are adopted to select the best probability distribution. The probable rainfall intensity formulas are then determined by the least squares method using the trial and error approach. Five types of Talbot type, Sherman type, Japanese type, Unified type I, and Unified type II are considered to determine the best type for the Inchon rainfall intensity. The root mean squared errors are computed to compare the accuracy from the derived formulas. It has been suggested that the probable rainfall intensities having Unified type I for the short term duration should be the most reliable formulas by considering the root mean squared errors and the difference between computed probable rainfall depth and estimated probable rainfall depth.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.701-705
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• 2006

강우자료는 수문 모델링 작업에서 가장 기초적인 수문학적 입력자료로 시간과 공간에 따른 변동성이 크므로 규명하기 복잡한 수문현상 중의 하나이다. 산악지역이 많은 우리나라의 지형학적 특성과 태풍, 장마 및 특히, 최근의 게릴라성 집중호우 등으로 인하여 이러한 변동성이 더욱 커지고 있는 실정이다. 장기간 실측된 수문기상 기초 자료가 부족한 우리나라의 실정상 홍수예보 및 수공구조물 설계를 위해 정확한 강우량 자료의 취득이 선행돼야 한다. 따라서 적절한 장소에 수문관측소 설치 및 관리를 통해 양호한 강우량 자료를 획득해야 하지만, 현장 여건상 등의 이유로 미계측 및 결측, 이상자료가 발생하고 있다. 따라서 이러한 미계측 혹은 결측지점의 우량을 추정할 수 있는 방법을 비교, 분석하여 적절한 보정과정을 수행할 필요가 있다. 그간의 연구에서는 미계측 지점 혹은 산악지역에서의 점 강우량 보정방법에 대한 연구가 진행되었지만, 본 연구에서는 '도시홍수재해관리기술연구사업단'에서 운영 중인 도시하천 유역 특히 소배수구역에서의 결측 자료에 대해 여러 추정 방법을 비교, 분석하여 적절한 방안을 찾고자 한다. 이를 위하여 중랑천 유역의 3개 소배수 구역(월계1 배수구역, 군자 배수구역, 어린이대공원 배수구역)에 설치된 3개 우량관측소와 건설교통부 관할 우량관측소 2개소의 우량자료를 사용하였다. 본 연구에서는 결측치 보간을 위하여 널리 이용되고 있는 산술평균법(Arithmetic Average method), 역거리법(Reciprocal Distance Squared method), 거리고도비율법(Ratio of Distance and Elevation method), 인근관측소와의 관계식 이용, 크리깅방법(Simple Kriging method)을 비교, 검토 적용하였다. 중랑천 유역의 소배수구역을 대상으로 연중 발생하는 큰 호우사상에 대해 임의의 강우관측소를 결측지점으로 가정하고 주변의 강우관측소로부터 각각의 방법을 이용해 가중치들을 산정하여 결측지점의 강우량 값을 보정하고자 하였다. 또한 각각의 방법을 이용하여 얻어진 결과에 대해 실측값과 보정값의 오차정도를 평균절대오차법(Mean Absolute Error)과 제곱평균제곱근오차법(Root Mean Squared Error)에 의해 산정하여 보정 방법간의 효율성을 검토하고자 하였다.

• Journal of Korea Water Resources Association
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• v.44 no.7
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• pp.537-551
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• 2011

Based on optimal input data combination selected in the earlier study, Neuro-Fuzzy flood forecasting model linked Takagi-Sugeno fuzzy inference theory with neural network in Wangsukcheon and Gabcheon is established. The established model was applied to Wangsukcheon and Gabcheon and water levels for lead time of 0.5 hr, 1 hr, 1.5 hr, 2.0 hr, 2.5 hr, 3.0 hr are forecasted. For the verification of the model, the comparisons between forecasting floods and observation data are presented. The forecasted results have shown good agreements with observed data. Additionally to evaluate quantitatively for applicability of the model, various statistical errors such as Root Mean Square Error are calculated. As a result of the flood forecasting can be simulated successfully without large errors in all statistical error. This study can greatly contribute to the construction of a high accuracy flood information system that secure lead time in medium and small streams.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1136-1140
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• 2009

지상강우 관측망을 이용한 강우량 측정의 대안으로서 사용되는 기상 레이더를 활용한 강우량 추정의 경우, Z-R 방정식을 이용하여 반사도를 강우량으로 환산하는 방법을 일반적으로 사용한다. 이때 발생하는 각종 오차는 레이더 장비가 가지는 기계적인 오차뿐만 아니라 Z-R 방정식이 가지는 오차 등이 있으며, 이를 보정하기 위해서 레이더를 활용하여 추정된 강우량에 지상강우량계와 레이더강우량과의 비율인 G/R비를 보정하는 방법을 일반적으로 사용한다. 본 연구에서는 이와 같이 레이더 강우량을 보정하기 위해서 사용되는 G/R비를 산정하는데 미치는 지형적인 효과를 고려하기 위해서 광덕산 레이더 유효범위 100km 내(군사분계선 이북 미포함)의 지역에 대하여 군집분석을 실시하여 크게 산악지역과 평야지역으로 구분하고, 각각 구분된 지역에 대하여 G/R 비를 산정하여 초기추정 레이더 강우량에 곱하는 mean-field bias 보정을 실시하였다. 광덕산 레이더 기상관측소의 유효범위 100km 내의 2007년, 2008년 홍수기(6/21${\sim}$9/20)기간 동안 94개 Automatic Weather Station(AWS)지점에 대하여 크게 산악지역과 평야지역으로 지역화 시키는 방법은 비계층적 군집분석 기법 중 fuzzy-c mean 방법을 적용하였다. 또한 광덕산 레이더 반사도 기본 자료는 차폐영역으로 생기는 반사도 데이터 누락을 보완하기 위하여 0도와 1.5도 sweep 합성 10분단위 uf 자료를 사용하였으며, AWS와 보정이 이루어지는 레이더 격자의 크기는 최대 4km${\times}$4km로 선정하였다. 본 연구에 있어서 검증방법은 지역을 구분하기 전과 후를 AWS 실측 관측값과 절대상대오차, 평균제곱근 오차로써 비교하였다.