• 로봇학회논문지
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• 제15권1호
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• pp.32-38
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• 2020

This paper describes a method for tracking attitude and position of underwater robots. Underwater work with underwater robots is subject to differences in work efficiency depending on the skill of the operator and the utilization of additional sensors. Therefore, this study developed an underwater robot that can operate autonomously and maintain a certain attitude when working underwater to reduce difference of work efficiency. The developed underwater robot uses 8 thrusters to control 6 degrees of freedom motion, IMU (Inertial Measurement Unit), DVL (Doppler Velocity Log) and PS (Pressure Sensor) to measure attitude and position. In addition, the thruster allocation algorithm was designed to follow the control desired value using 8 thrusters, and the motion control experiments were performed in the engineering water basin using the thruster allocation method.

• Journal of Positioning, Navigation, and Timing
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• 제5권2호
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• pp.97-107
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• 2016

Military Autonomous Underwater Vehicle (AUV) is utilized to search a mine under the sea. This paper presents design and performance verification of real-time hybrid navigation system for AUV. The navigation system uses Doppler Velocity Log (DVL) integration method to correct INS error in underwater. When the AUV is floated on the water, the accumulated error of navigation algorithm is corrected using position/velocity of GPS. The navigation algorithm is verified using 6 Degree Of Freedom (DOF) simulation, Program In the Loop Simulation (PILS). Finally, the experiments are performed in real sea environment to prove the reliability of real-time hybrid navigation algorithm.

• International Journal of Ocean System Engineering
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• 제1권2호
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• pp.102-109
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• 2011

This paper describes the implementation of a precise underwater navigation solution using a multiple sensor fusion technique based on USBL, GPS, DVL and AHRS measurements for the operation of a remotely operated mine disposal vehicle (MDV). The estimation of accurate 6DOF positions and attitudes is the key factor in executing dangerous and complicated missions. To implement the precise underwater navigation, two strategies are chosen in this paper. Firstly, the sensor frame alignment to the body frame is conducted to enhance the performance of a standalone dead-reckoning algorithm. Secondly, absolute position data measured by USBL is fused to prevent cumulative integration error. The heading alignment error is identified by comparing the measured absolute positions with the DR algorithm results. The performance of the developed approach is evaluated with the experimental data acquired by MDV in the South-sea trial.

• 제어로봇시스템학회논문지
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• 제19권9호
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• pp.774-781
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• 2013

The purpose of this paper is to design a DVL-RPM based VKF (Velocity Kalman Filter) design for a performance improvement underwater integrated navigation system. The proposed approach relies on a VKF, augmented by a altitude from Echo-sounder based switching architecture to yield robust performance, even when DVL (Doppler Velocity Log) exceeds the measurement range and the measured value is unable to be valid. The proposed approach relies on two parts: 1) Indirect feedback navigation Kalman filter design, 2) VKF design. To evaluate proposed method, we compare the results of the VKF aided navigation system with simulation result from a PINS (Pure Inertial Navigation System) and conventional INS-DVL method. Simulations illustrate the effectiveness of the underwater navigation system assisted by the additional DVL-RPM based VKF in underwater environment.

• 한국해양공학회지
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• 제27권2호
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• pp.93-99
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• 2013

This paper describes a robust algorithm for an integrated underwater navigation system based on VKF (velocity Kalman filter). The proposed approach relies on a VKF, augmented by the altitude from an echo-sounder-based switching architecture to yield robust performance, even when DVL (Doppler velocity log) exceeds the measurement range and the measured value cannot be valid. The proposed approach relies on three parts: 1) PINS (pure inertial navigation system), 2) VKF design, and 3) VKF-aided integrated navigation filter design. To evaluate the proposed method, we compare the results of the VKF-aided navigation system with the simulation result from a PINS and conventional INS-DVL method.

• 한국ITS학회 논문지
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• 제9권2호
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• pp.60-67
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• 2010

최근에, LED를 사용한 WPAN 응용 기술에 많은 연구가 진행되고 있다. 하지만, LED를 이용한 가시광 통신은 통신을 수행하는데 약점을 가지고 있다. 시스템 성능을 저하시키는 요인으로 통신 환경에서 다른 물체에 의한 전파 지연으로 발생하는 다중 경로 페이딩을 들 수 있다. 따라서 본 논문에서 OFDM 기술은 다중 경로 페이딩과 분산을 줄이고, 고속 데이터 전송을 제공하기 위해서 적용하였다. 게다가, 광잡음에 의한 정보 손실을 줄이기 위해서 채널코딩으로써 터보 부호화 기술을 사용하였다. OFDM과 터보 부호화를 적용하므로써, 약 4 [dB] 정도의 성능향상을 보임을 알 수 있었다. 또한, 도플러 효과가 일어난다고 가정하였을 경우, 시스템 성능이 저하됨을 시뮬레이션을 통해 알 수 있었다.

• 천문학회보
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• 제35권1호
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• pp.29.2-29.2
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• 2010

The Extreme ultraviolet Imaging Spectrometer (EIS) on board Hinode provide us with excellent imaging spectroscopic data with very good spatial and spectral resolutions, which can be used for detecting Doppler flows in transition region and coronal lines as well as diagnosing plasma properties such as temperature, density, and non-thermal velocity. In this study we have made an EUV-imaging spectroscopic study of the source region of a partial halo coronal mass ejection (CME) that occurred on 2007 July 9 in NOAA 10961. Dopplergrams are obtained before and after the CME eruption using 12 EIS spectral lines (Log T= 4.9~7.2). Major results are summarized as follows. First, it is noted that either red shifts disappeared or blue shifts newly appeared for all spectral lines lower than Log T =6.0. Second, there were significant intensity increases for all wavelengths. Third, there were no significant variations in non-thermal motions for all wavelengths. We found one interesting bright point that newly appeared after the CME eruption. We discuss the implication on the results in terms of the CME eruption.

• 한국습지학회지
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• 제21권3호
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• pp.207-214
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• 2019

본 실험연구는 자유수면을 이루는 환형수조에서 초음파 유속계를 이용하여 흐름특성을 분석하였다. 여기서 점착성 유사의 응집을 방해하지 않도록 설계된 실린더의 회전에 따라 흐름이 형성되도록 하였다. 종방향 유속에 대한 내부 실린더의 영향은 이동 경계 근처에서 가장 높았고 외측 벽쪽으로는 감소했다. 종방향 저유속에서 난류 운동에너지는 바닥근처 지점에서 가장 크게 나타났지만 종방향 유속이 증가함에 따라 위쪽으로 이동하였다. 멱법칙으로 산정된 종방향 유속은 바닥 마찰길이를 고려한 대수분포형태인 로그법칙으로 예측한 값보다 실측치와 잘 일치하였다. 레이놀즈 응력 방법으로 산정한 평균마찰속도는 종방향 유속이 증가할 때 로그법칙과 멱법칙으로 계산된 값보다 작게 나타났다.

• 제어로봇시스템학회논문지
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• 제19권8호
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• pp.702-708
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• 2013

Underwater TRN (Underwater Terrain Referenced Navigation) estimates an underwater vehicle state by measuring a distance between the vehicle and undersea terrain, and comparing it with the known terrain database. TRN belongs to absolute navigation methods, which are used to compensate a drift error of dead reckoning measurements such as IMU (Inertial Measurement Unit) or DVL (Doppler Velocity Log). However, underwater TRN is different to other absolute methods such as USBL (Ultra-Short Baseline) and LBL (Long Baseline), because TRN is independent of the external environment. As a magnetic-field-based navigation, TRN is a kind of geophysical navigation. This paper develops an EKF (Extended Kalman Filter) formulation for underwater TRN. A filter propagation part is composed by an inertial navigation system, and a filter update is executed with echo-sounder measurement. For large-initial-error cases, an adaptive EKF approach is also presented, to keep the filter be stable. At the end, simulation studies are given to verify the performance of the proposed TRN filter. With simplified sensor and terrain database models, the simulation results show that the underwater TRN could support conventional underwater navigation methods.

• 천문학회지
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• 제42권6호
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• pp.145-153
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• 2009

We present measurements of diffuse interstellar $H_2$ absorption lines in the continuum spectra of 10 early-type stars. The data were observed with the Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) of the ORFEUS telescope on board the ORFEUS-SPAS I and II space-shuttle missions in 1993 and 1996, respectively. The spectra extend from the interstellar cutoff at 912 $\AA$ to about 1200 $\AA$ with a resolution of ~ 3000 and statistical signal-to-noise ratios between 10 and 65. Adopting Doppler broadening velocities from high-resolution optical observations, we obtain the $H_2$ column densities of rotational levels J" = 0 through 5 for each line of sight. The kinetic temperatures derived from J" = 0 and 1 states show a small variation around the mean value of 80 K, except for the component toward HD 219188, which has a temperature of 211 K. Based on a synthetic interstellar cloud model described in our previous work, we derive the incident UV intensity IUV and the hydrogen density $n_H$ of the observed components to be -0.4 $\leq$ log $I_{UV}\leq2.2$ and $6.3{\leq}n_H2500cm^{-3}$, respectively.