• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.1
• /
• pp.114-120
• /
• 2013

Recently, navigation systems based on wireless communication have been applied to the internal structures such as building or ship. If a stable azimuth information is obtained, these systems can effectively guide the direction of the user's progress through the information and then can improve the performance of guidance. Since conventional method which has acquired an azimuth information using geomagnetic and acceleration sensor(azimuth sensor hereafter) is sensitive to the effects of the magnetic field, it has unstable error range according to the surrounding environment. In order to improve these problems, this paper presents a new relative azimuth estimation algorithm using the displacement of a mobile node and its rotation angle based on Wireless communication. For the performance assessment of the proposed algorithm, experiments using rotating arm are performed and the results are confirmed that the proposed system can estimate the relative azimuth without using additional sensors.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.30 no.5
• /
• pp.445-458
• /
• 2012

The objective of GPS control surveying is ultimately to determine coordinate sets of control points within targeted accuracy through a series of observations and network adjustments. To this end, it is of equivalent importance for the accuracy of these coordinates to be realistically represented by using an appropriate method. The accuracy representation can be quantitively made by the variance-covariance matrices of the estimates, of which features are sensitive to the mathematical models used in the adjustment. This paper deals with impact of functional and stochastic modeling techniques into the accuracy representation of the GPS control surveying with a view of gaining background for its standardization. In order to achieve this goal, mathematical theory and procedure of the single-baseline based multi-session adjustment has been rigorously reviewed together with numerical analysis through processing real world data. Based on this study, it was possible to draw a conclusion that weighted-constrained adjustment with the empirical stochastic model was among the best scheme to more realistically describe both of the absolute and relative accuracies of the GPS surveying results.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2006.05a
• /
• pp.852-857
• /
• 2006

하천유량자료는 이수, 치수, 수질관리 등의 목적으로 널리 사용되기 때문에 여러 가지 수문관측 자료 중 가장 중요하다고 할 수 있다. 그러나 우리나라의 유량자료는 여러 가지 한계를 가지고 있어서 수문자료로서 제대로 사용되지 못하고 있는 실정이다. 특히 홍수기 부자측정 방법에 의해 산정된 유량자료는 측정 여건, 방법, 기기 등의 한계로 인해 그 정확도가 더욱 낮다. 홍수기 부자측정 방법에 의한 유량자료의 정확도 향상을 위해서는 현장 유량측정의 정확도를 향상시키는 것이 일차적으로 필요하지만, 측정된 자료를 과학적이고 체계적인 계산과정을 통하여 유량으로 환산하는 것도 매우 중요하다. 국내의 경우 일반적으로 여름에 집중호우가 빈발하고 경사가 급한 산지하천이 많다. 그래서 홍수시 하천의 유속이 매우 빠르고 하천수내에 부유물이 많이 함유되어 있다. 이러한 요인들로 의해 대부분 홍수시 유속계를 이용한 유량측정이 불가하여 대안으로 부자를 이용하여 측정하고 있다. 그 결과 평저수시 유속계 이용시에 비해 측정 및 산정과정에서 매우 큰 오차가 발생하고 있다. 이와 같이 국내의 경우 홍수시 유량측정을 위해 부자에 전적으로 의존하는 현실임에 불구하고 부자를 이용한 유속측정 및 유량산정에 대한 연구는 매우 미흡하였다. 외국의 경우도 부자 측정에 대한 방법론이 ISO 748과 일본수문관측에 간략하게 설명되어 있고 USGS와 WMO에서는 거의 내용을 다루고 있지 않고 있다. 현재 우리나라의 경우는 ISO 748을 일부 참조하고 대부분 일본수문관측 기준에 준해 측정을 하고 있다. 자연하천임을 감안하면, 부자에 의한 유속 측정시 발생할 수 있는 여러 오차들의 경우 적절한 구간의 선택, 충분한 측선수의 확보 등과 같은 측정기준의 개선을 통하여 상당부분 제거가 가능하다. 그러나 부자를 이용해 측정된 성과를 신뢰도 높은 유량으로 산정하기 위해서는 정확한 측정과 더불어 과학적이고 표준화된 유량산정 기준과 절차가 필요하다. 본 연구에서 분석된 결과에 의하면 부자유선 모임, 홍수터 유속 미측정, 기준 흘수 미적용 등과 같은 측정 자체의 문제점을 제외하면, 부자측정 방법에 의한 유량산정시 가장 큰 오차원인은 홍수시 측정된 유속측선의 위치와 홍수 전후로 측정된 횡단면상의 위치가 일치하지 않는 점과, 대부분 두 측정 구간의 평균값을 대푯값으로 사용한다는 점이다. 본 연구는 다년간의 유량 측정 및 검증 경험과 자료를 토대로 현장에서 부자를 이용하여 측정된 측정성과를 정확도 높은 유량자료로 산정하는데 있어서의 문제점을 도출하고, 이로 인해 발생하는 오차를 추정하여 그 개선방안을 제시해 보고자한다. 더불어 보다 정확한 유량 산정을 위한 기준과 범주를 제시하고자 한다.

• Journal of Biomedical Engineering Research
• /
• v.23 no.5
• /
• pp.413-418
• /
• 2002

The purpose of this study was to design a single frequency BIA(Bioelectrical Impedance Analyzer) which can measure body impedance when patient is sitting on the toilet and to develope a prediction equation for designed BIA. For the purpose of this study, we acquired body impedances with designed BIA from 181 subjects composed of healthy Korean by attaching electrodes to suitable positions(wrist and thigh) for toilet measurement. We computed an appropriate FFM(Fat Free Mass) for Korean using modified-Siri equation to the same subjects instead of Siri equation which nay cause accuracy problems in hydrodensitometry when it applied to Korean. We used this FFM as reference value and developed a Korean FFM prediction equation based on body impedance index, body weight and sex. Correlation coefficient between prediction value and reference value of FFM was extremely high (r = 0.977) and SEE(Standard Error of Estimation) was low 2.47kg.(p<0.05) For comparison between existing electrode-attaching method and our method for toilet measurement, we acquired body impedance with designed BIA from same subjects attaching electrodes on existing positions (wrist and ankle) and made FFM prediction equation for BIA. Correlation coeffient between predicted value and reference value was 0.978 and SEE was 2.43kg(p<0.05). It means that the developed system has not significant differences with existing method. In conclusion bioelectrical impedance analyzer and the FFM prediction equation developed in this paper are evaluated to he adequate to compute FFM of Korean.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.8
• /
• pp.31-37
• /
• 2016

Ranging is divided into a synchronous scheme and an asynchronous scheme according to the presence of global synchronization between nodes. In general, the asynchronous ranging is preferred over synchronous ranging because it does not require an expensive high-precision oscillator for the global synchronization. On the other hand, in a conventional asynchronous ranging scheme, the packets, which are generated by all nodes in a positioning system of a large-scale infrastructure and need to be sent for localization by reference nodes, are considerable, which cause an increase in network traffic as the number of nodes increases. The traffic congestion lowers the throughput of the network leading to a considerable loss of energy. To solve this problem, this paper proposes a ranging scheme, in which virtual transmission slots randomly and discretely selected by a plurality of nodes are used to reduce the overheads needed in synchronizing the nodes, and the ranging is performed asynchronously based on the virtual transmission slots, thereby decreasing the network traffic. In addition, a performance test proved that the proposed ranging scheme was stronger than the TWR and SDS-TWR on an error range, even though the intensity of traffic was very low.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.28 no.1
• /
• pp.98-106
• /
• 2024

Due to advancements in construction technology and analytical tools, an increasing number of cable-stayed bridges have been designed and constructed in recent years. A cable is a structural element that primarily transmits the main load of a cable-stayed bridge and plays the most crucial role in reflecting the overall condition of the entire bridge system. In this study, a vision-based method was applied to estimate the tension of the stay cables located at a long distance. To measure the response of a cable using a vision-based method, it is necessary to install feature points or targets on the cable. However, depending on the location of the point to be measured, there may be no feature points in the cable, and there may also be limitations in installing the target on the cable. Hence, it is necessary to find a way to measure cable response that overcomes the limitations of existing vision-based methods. This study proposes a method for measuring cable responses by utilizing the characteristics of cable shape. The proposed method involved extracting the cable shape from the acquired image and determining the center of the extracted cable shape to measure the cable response. The extracted natural frequencies of the vibration mode were obtained using the measured responses, and the tension was estimated by applying them to the vibration method. To verify the reliability of the vision-based method, cable images were obtained from the Hwatae Bridge in service under ambient vibration conditions. The reliability of the method proposed in this study was confirmed by applying it to the vibration method using a vision-based approach, resulting in estimated tensions with an error of less than 1% compared to tensions estimated using an accelerometer.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2007.12a
• /
• pp.98-99
• /
• 2007

It is necessary to use satellite radio navigation system as well as satellite radio navigation augmentation system such as differential Global Positioning System to achieve the positioning accuracy and reliability requested by International Maritime Organization in port and coastal area. Especially, position accuracy of DGPS user is effected by accuracy of pseudorange correction broadcasted from DGPS reference station. This paper shows pseudorange correction calculation algorithm adopting a non-common error estimation filter in order to improve accuracy of pseudorange correction. Finally, this paper verifies that the pseudorange correction calculated by adopting a non-common error estimation filter satisfies performance specifications of RTCM.

• The Korean Journal of Financial Management
• /
• v.10 no.2
• /
• pp.137-159
• /
• 1993

본 연구에서는 우리나라의 금융자산, 특히 회사채와 주식이 인플레이션과 관련하여 어떠한 행태를 보이는가를 실증적으로 살펴본다. 1976년부터 1992년까지의 기간중 채권 및 주식수익률에 피서가설이 성립하는가의 여부, 주식수익률과 기대인플레이션과 관련된 Fama의 허구성가설 및 Geske & Roll의 역인과성가설 등을 공적분관계검정 및 VAR모형의 예측오차 분산분해등을 통하여 포괄적으로 결정한다. 이를 위하여 본 연구는 다음과 같은 순서로 진행하였다. 첫째, 단순정태회귀분석을 통하여 우리나라 금융시장에서 주식이나 채권이 기대된 인플레이션이나 예상치 못했던 인플레이션에 대해 얼마나 인플레이션방어수단으로 유효한지를 살펴보았다. 우선, 회사채수익률의 경우 피서가설의 성립을 기각하기 어려웠다. 반면, 주식의 경우에는 피서가설이 성립될 수 없음은 물론이고, 대부분의 선진국가들처럼 기대인플레이션에 주식수익률이 만대방향으로 반응하는 것으로 나타났다. 주식수익률을 설명하는 변수에 예상되는 산업생산증가나 통화량증가를 나타내는 변수들을 추가하여도 주식수익률과 기대인플레이션간의 부의 관계는 여전히 유의적인 것으로 남아있었다. 따라서 파마의 주식수익률과 기대인플레이션간의 허위관계가설은 우리나라 주식시장에서는 적용되지 않는 것으로 나타났다. 둘째, 단순정태분석에서 활용된 여러 회귀식들이 가성적회귀관계(假性的回歸關係)를 나타내는 경우를 확인하기 위하여 공적분관계가 형성되는지를 검정하였다. 그 결과, 회사채수익률과 인플레이션은 공적분관계가설이 기각되지 않았으나, 주식수익률과 기대인플레이션간에는 공적분관계가 나타나지 않았다. 공적분관계에 입각하여 오차수정모형을 추정한 결과, 회사채수익률의 변화는 단기적인 인플레이션의 동태를 예측하는데 있어서 도움을 주지만, 기대인플레이션 및 예상산업생산증가률의 변화는 주식실질수익률의 단기적 동해예측에 개별적으로는 도움이 되지 못하였다. 마지막으로 여러 변수들의 관계를 사전적으로 설정하지 않고 VAR 모형의 오차분해를 통하여 인과관제를 분석한 결과, 주식수익률과 기대인플레이션이 허구적(虛構的)인 관계가 아님을 시사하고 있다. 그러나, 주식수익률변동은 예상산업생산증가에 의하여 어느정도 설명이 가능하고 대부분의 경제변수에 대하여는 외생적인 성격을 강하게 보여주고 있어서, 기대인플레이션과의 인과관계에 있어서도 선행적인 위치를 지지하고 있다.

• Journal of Advanced Navigation Technology
• /
• v.22 no.3
• /
• pp.220-227
• /
• 2018

The most widely used method for constructing an inertial navigation system (INS)/global navigation satellite system (GNSS) coupling system is to construct an integrated navigation system using a Kalman filter. However, depending on the trajectory, non-observable state variables may be generated. In this case, the state variables are not estimated. To solve this problem, a integrated navigation system is constructed and then an observability analysis is performed. In this paper, a 24th order position-matched Kalman filter is defined to design an INS/GNSS integrated navigation system for vehicles moving with a large pitch angle change. To verify the appropriateness of the error state variables applied to the Kalman filter, an observability analysis was performed. The trajectory was divided into five segments, and the piece-wise constant system (PWCS) was assumed for each segment, and the results were analytically analyzed. The analytical results and the simulation results confirm that the error state parameters of the Kalman filter are well-designed to the estimation side.

• Journal of the Institute of Convergence Signal Processing
• /
• v.13 no.4
• /
• pp.166-172
• /
• 2012

The standard wave height measurement system is usually based on spectrum analysis for measuring wave height. The spectrum analysis is complicated because of the FFT, and the FFT is not for real time processing since it requires the saved data segments. In this paper, we carried out the performance evaluation of real-time and simpler wave height measurement system using the kalman filter and inertial sensors. The kalman filter theory is complicated, but its algorithm is simpler than the FFT and the kalman filter is used to estimate wave height by integrating acceleration data. But the accumulated error is occurred when the acceleration data is integrated. We developed the algorithm using the wind wave characteristic to decrease the accumulated error. In this paper, the performance evaluation of the wave height measurement system is carried out for various wind wave conditions. Through the experiments, we verified that it shows high measurement performance with the 3.5% margin of error in wind wave condition.