• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.314-327
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• 2009

Weather launch criteria of launch at Oenarodo Space Center is important for the successful launch operation. In particular, most of the launch failure occurs during the period of separation from the launch pad, thus meteorological condition is critical at this phase. In earlier days, the weather launch criteria adopted wind and forecast data for the launch operation. Nevertheless, the control of position and stability require other meteorological components such as vertical wind shear, lightning, temperature and visibility, because the launch vehicle is moving mostly vertically. We analyze these meteorological components by using the observed data at KMA at neighboring Oenarodo to determine the weather launch criteria. These criteria need further refinements through long-term observation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.5
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• pp.393-400
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• 2017

A virtual simulation test program to carry out the handling qualities of unmanned Rotorcraft has developed by using the MATLAB GUIDE(Graphic User Interface Development Environment). The handling quality evaluation program based on ADS-33E contributes to design the flight control system and to evaluate handling qualities. In addition, Linear Quadratic Tracker with Integrator(LQTI) attitude controller based on Linear Quadratic Regulator(LQR) for to rotorcraft BO-105C and the effects of the handling qualities is analyzed change to weight matrices of the Q and R.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.82-82
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• 2023

홍수기 하천에서 유량측정은 예산, 인력, 안전 및 측정 시 편의성 등의 이유로 측정에 제한이 많다. 특히, 태풍 등으로 인한 호우사상 발생 시 위와 같은 문제로 홍수량 측정에 어려움이 따른다. 이러한 문제점을 개선하기 위해 Lee et al.(2021)은 드론과 전자파표면유속계의 기능을 융합한 DSVM(Dron and Surface Veloctity Meter using doppler radar) 측정방법을 개발하였다. 전자파표면유속계 측정의 제한 요소인 진동을 감소시키기 위해 댐퍼플레이트를 개발하였고 금강의 지류인 봉황천에 현장 적용을 통해 DSVM 측정방법의 실용성을 확인하였다. 기존 연구에서 DSVM 방법은 드론의 각 측선 이동을 위한 조종과 전자파표면유속계 측정의 제어를 측정자가 수행하였는데 본 연구에서는 통합 드론측정시스템(IDMS, Integrated Drone Measurement System) 개발을 통해 측정자의 조종 의존도를 줄임과 동시에 안전하고 정확한 유량측정을 위해 노력하였다. 기존 댐퍼플레이트의 상하 진동 흡수 기능뿐만 아니라 전자파표면유속계의 흔들림 현상 등 자세 제어 기능을 보완하기 3축 모터를 적용한 방수짐벌을 개발하여 측정 정확도를 향상시켰다. 미션컴퓨터 개발로 측정지점의 측정 임무정보를 DB화하여 각 측선별 헤딩, 고도, 이동 등 자동항법 기능과 기체의 안정화 이후 전자파표면유속계를 자동으로 제어하여 측정을 실시하는 기능을 구현하였다. 또한 통합 GCS(Ground Control System)를 통해 비행 및 측정에 대한 모든 정보를 확인하고 컨트롤 할 수 있게 하였다. 2022년 금산군(제원대교), 무주군(취수장), 경주시(서천교) 지점에서 홍수기 유량측정에 도입하여 중간단면적법, 지표유속법을 적용하여 통합드론측정시스템의 실용성을 검증 완료하였다. 2023년 현장에 18대의 통합 드론측정시스템을 도입하여 홍수기 유량측정에 활용할 계획이다.

• Journal of Aerospace System Engineering
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• v.17 no.5
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• pp.63-75
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• 2023

The antenna radiation pattern was simulated by arranging the mounted antennae of the transport drone in 5 locations where radio interference was expected to be low, and they could be mounted. Depending on the mounting location, the probability that the link margin was less than 0 dB was (5.41 - 26.92) %. When two antennae were mounted and one was selected, the probability was (0.11 - 3.3) %. Among the arrangements, placing one antenna in the upper part of the front and one in the lower part of the rear showed the lowest link fail probability. In this case, it was analyzed that if the attitude roll and pitch of the aircraft were limited, link fail would not occur at an operating distance of 12 km or less. An antenna selection formula for this case was derived, and a method of reducing frequent alternation of antennae was applied to maintain a stable link.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.6
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• pp.455-466
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• 2020

In this study, we built a thermal model for SNIPE 6U nano-satellite which has scientific mission for measuring science data in near Earth space environment and described thermal design based on the thermal model. And the validity of the thermal design was verified through the on-orbit thermal analysis. The thermal design was carried out mainly on the passive thermal control techniques such as surface finishes, insulators, and thermal conductors in consideration of the characteristics of the nano-satellite. However, the components with narrow operating temperature range and directly exposed to the orbital thermal environments, such as a battery and thrusters, are accomodated with heaters to satisfy the temperature requirements. On-orbit thermal analysis conditions are based on the basic orbital conditions of the satellite, and thermal analysis was performed for Normal mode, Launch & Early Orbit Phase (LEOP), Safehold mode, and Maneuver mode which are classified by the power consumption and the attitude of the satellite according to the mission scenario. The analysis results for each mode confirmed that every component satisfies the temperature requirement. In addition, the heater capacity and duty cycle of the battery and thruster were calculated through the analysis results of the Safehold mode.

• Geophysics and Geophysical Exploration
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• v.23 no.4
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• pp.243-252
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• 2020

To share an understanding of trajectory measurement in surveys using borehole, this tutorial summarizes the relevant mathematical principles of the borehole deviation survey based on coordinate transform. For uncased or open holes, calculations of the azimuth-deviation-tool face rotation using three-component accelerometer and magnetometer measurements are summarized. For the steel-cased holes, calculations are based on the time-derivative formula of the coordinate transform matrix; yaw-pitch-roll angles through time are mathematically determined by integrating the threecomponent angular velocity measurements from the gyroscope while also removing the Earth's rotation effect. Sensor and data fusion to increase the accuracy of borehole deviation survey is explained with an example of the method. These principles of borehole deviation surveys can be adapted for attitude estimation in air-borne surveys or for positioning in tunnels where global positioning system (GPS) signals cannot be accessed. Information on the optimization filter that must be incorporated in sensor fusion is introduced to help future research.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.9
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• pp.854-864
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• 2016

The use of small drone platform has become a popular topic in these days but its application for SAR operation has been little known due to the burden of the payload implementation. Drone platforms are distinguished from the conventional UAV system by the increased vulnerability to the turbulences, control-errors and poor motion stability. Consequently, sophisticated motion compensation may be required to guarantee the successful acquisition of high quality SAR imagery. Extremely limited power and mass budgets may prevent the use of additional hardwares for motion compensation and the difficulty of SAR focusing is further aggravated. In this paper, we have carried out a feasibility study of mico-SAR drone operation. We present the image acquisition results from the preliminary flight tests and a quality assessment is followed on the experimental SAR images. The in-flight motion errors derived from the unique drone movements are investigated and attempts have been made to compensate for the geometrical and phase errors caused by motions against the nominal trajectory. Finally, the successful operation of drone SAR system is validated through the focussed SAR images taken over test sites.

• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1479-1488
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• 2022

Accidents in which oil spills occur intermittently in the ocean due to ship collisions and sinkings. In order to prepare prompt countermeasures when such an accident occurs, it is necessary to accurately identify the current status of spilled oil. To this end, the Coast Guard patrols the target area with a fixed-wing airplane or helicopter and checks it with the naked eye or video, but it was difficult to determine the area contaminated by the spilled oil and its exact location on the map. Accordingly, this study develops a technology for direct ortho-rectification by automatically geo-referencing aerial images collected by the Coast Guard without individual ground reference points to identify the current status of spilled oil. First, meta information required for georeferencing is extracted from a visualized screen of sensor information such as video by optical character recognition (OCR). Based on the extracted information, the external orientation parameters of the image are determined. Images are individually orthorectified using the determined the external orientation parameters. The accuracy of individual orthoimages generated through this method was evaluated to be about tens of meters up to 100 m. The accuracy level was reasonably acceptable considering the inherent errors of the position and attitude sensors, the inaccuracies in the internal orientation parameters such as camera focal length, without using no ground control points. It is judged to be an appropriate level for identifying the current status of spilled oil contaminated areas in the sea. In the future, if real-time transmission of images captured during flight becomes possible, individual orthoimages can be generated in real time through the proposed individual orthorectification technology. Based on this, it can be effectively used to quickly identify the current status of spilled oil contamination and establish countermeasures.

• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1125-1139
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• 2022

In an unmanned aerial vehicles (UAVs) system, a physical offset can be existed between the global positioning system/inertial measurement unit (GPS/IMU) sensor and the observation sensor such as a hyperspectral sensor, and a lidar sensor. As a result of the physical offset, a misalignment between each image can be occurred along with a flight direction. In particular, in a case of multi-sensor system, an observation sensor has to be replaced regularly to equip another observation sensor, and then, a high cost should be paid to acquire a calibration parameter. In this study, we establish a precise sensor model equation to apply for a multiple sensor in common and propose an independent physical offset estimation method. The proposed method consists of 3 steps. Firstly, we define an appropriate rotation matrix for our system, and an initial sensor model equation for direct-georeferencing. Next, an observation equation for the physical offset estimation is established by extracting a corresponding point between a ground control point and the observed data from a sensor. Finally, the physical offset is estimated based on the observed data, and the precise sensor model equation is established by applying the estimated parameters to the initial sensor model equation. 4 region's datasets(Jeon-ju, Incheon, Alaska, Norway) with a different latitude, longitude were compared to analyze the effects of the calibration parameter. We confirmed that a misalignment between images were adjusted after applying for the physical offset in the sensor model equation. An absolute position accuracy was analyzed in the Incheon dataset, compared to a ground control point. For the hyperspectral image, root mean square error (RMSE) for X, Y direction was calculated for 0.12 m, and for the point cloud, RMSE was calculated for 0.03 m. Furthermore, a relative position accuracy for a specific point between the adjusted point cloud and the hyperspectral images were also analyzed for 0.07 m, so we confirmed that a precise data mapping is available for an observation without a ground control point through the proposed estimation method, and we also confirmed a possibility of multi-sensor fusion. From this study, we expect that a flexible multi-sensor platform system can be operated through the independent parameter estimation method with an economic cost saving.