• 제어로봇시스템학회논문지
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• 제15권1호
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• pp.54-60
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• 2009

In this paper, a precision landing approach is implemented based on real-time image processing. A full-scale landmark for automatic landing is used. canny edge detection method is applied to identify the outside quadrilateral while circular hough transform is used for the recognition of inside circle. Position information on the ground landmark is uplinked to the unmanned helicopter via ground control computer in real time so that the unmanned helicopter control the air vehicle for accurate landing approach. Ground test and a couple of flight tests for autonomous landing approach show that the image processing and automatic landing operation system have good performance for the landing approach phase at the altitude of $20m{\sim}1m$ above ground level.

• 한국습지학회지
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• 제4권1호
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• pp.33-41
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• 2002

Investigated was the ground-walking Coleoptera at the moor and adjacent forest at 800 m and rice paddies at lower level of 50 m in altitude. There were 5 species belonging to 5 genera and 2 families, 4 species belonging to 4 genera and 3 families, and 17 species belonging to 11 genera and 2 families respectively. Diplous depressus (Gebler) was the dominant species at the moor and forest in distinctive numbers, while Pheropsophus javanus (Dejean) was the one at the paddies. Three investigated sites supported independently their ground-walking Coleoptera groups. The moor group seemed to fail in establishing the resident Coleoptera community. The fact may imply to be related a kind of the pioneer species in early dry succession that D. depressus was found in a considerable range between forest and moor. The Coleoptera groups of moor and forest was different from that of paddies in species structure.

• Journal of Biosystems Engineering
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• 제25권3호
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• pp.233-240
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• 2000

A commercially available Doppler radar was modified and evaluated for on-board monitoring of ground speed. The radar output was corrected for pitch angle of aircraft based on the output of an electrolytic tilt sensor. The effects of aircraft speed, height and mounting angle on error in the ground speed were evaluated. The speed error decreased with an increase of the mounting angle since the radar contact angle with respect to the ground approached to the mounting angle. The error increased with an increase of the nominal aircraft speed. The altitude insignificantly affected the speed error. The Doppler radar provided acceptable percent errors within 5% in most measurements. The error can be reduced within ${\pm}$1.5% by increasing the mounting angle ($43^{\circ}$). The error of -3.8% at the mounting angle of $29^{\circ}$could be reduced by adjusting the mounting angle with respect to the radar contact angle.

• 한국군사과학기술학회지
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• 제24권6호
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• pp.602-609
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• 2021

Aircraft radar has special function which is ranging from aircraft to ground of antenna boresight. Because ranging information is used to calibrate altitude of aircraft or to drop a conventional bomb, the measuring have to be precise and robust. Therefore, we propose a simple and efficient method using monopulse radar for ground ranging. Proposed method calculates balancing weight according to linearity of monopulse ratio and mixes two ranging measurements in proportional to the weight. By exploiting balancing weight, radar is able to react to various environment as monopulse ratio contains characteristics of clutter environment. As a result, robust ranging information can be achieved. We use DEM(Digital Elevation Model) in order to simulate heterogeneous environment. In experimental result, it is shown that proposed method shows better accuracy and precision in any environment.

• 한국환경과학회지
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• 제27권11호
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• pp.1155-1167
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• 2018

We developed a small sensor observation system (SSOS) at a relatively low cost to observe the atmospheric boundary layer. The accuracy of the SSOS sensor was compared with that of the automatic weather system (AWS) and meteorological tower at the Korea Meteorological Administration (KMA). Comparisons between SSOS sensors and KMA sensors were carried out by dividing into ground and lower atmosphere. As a result of comparing the raw data of the SSOS sensor with the raw data of AWS and the observation tower by applying the root-mean-square-error to the error, the corresponding values were within the error tolerance range (KMA meteorological reference point: humidity ${\pm}5%$, atmospheric pressure ${\pm}0.5hPa$, temperature ${\pm}0.5^{\circ}C$. In the case of humidity, even if the altitude changed, it tends to be underestimated. In the case of temperature, when the altitude rose to 40 m above the ground, the value changed from underestimation to overestimation. However, it can be confirmed that the errors are within the KMA's permissible range after correction.

• Current Optics and Photonics
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• 제8권4호
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• pp.382-390
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• 2024

Laser propagation through atmospheric disturbances is vital for applications such as laser optical communication, satellite laser ranging (SLR), laser guide stars (LGS) for adaptive optics (AO), and laser energy transmission systems. Beam degradation, including energy loss and pointing errors caused by atmospheric turbulence, requires thorough numerical analysis. This paper investigates the impact of laser beam parameters on ground-to-space laser propagation up to an altitude of 100 km using vertical atmospheric disturbance profiles from the Geochang SLR Observatory in South Korea. The analysis is confined to 100 km since sodium LGS forms at this altitude, and beyond this point, beam propagation can be considered free space due to the absence of optical disturbances. Focusing on a 100-watt class laser, this study examines parameters such as laser wavelengths, beam size (diameter), beam jitter, and beam quality (M²). Findings reveal that jitter, with an influence exceeding 70%, is the most critical parameter for long-exposure radius and pointing error. Conversely, M², with an influence over 45%, is most significant for short-exposure radius and scintillation.

• 대한공간정보학회지
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• 제16권4호
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• pp.79-87
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• 2008

위성측량이나 기존의 항공측량에 비해 경제적이면서 기상영향을 덜 받는 저고도 고해상 영상의 취득과 항공사진측량의 많은 수요를 충족하기 위해 신속한 맵핑을 위한 UAV(Unmanned Aerial Vehicle) 기술 개발이 요구되고 있으며, 특히 효율적인 지형보정에 관한 연구가 중요한 이슈로 부각되고 있다. 그러나, 민간분야 활용을 위한 UAV의 높은 잠재력에 비해 최근까지 직접 지형보정과 같은 사진측량측면에서의 기술개발은 초기 단계에 머물고 있으며, 지속적인 연구와 추가적인 기술개발 노력이 필요하다. 본 연구에서는 최소한의 지상기준점 정보를 이용하여 간편한 부등각사상변환식과 부등각사상변환의 블록조정에 의해 자동으로 저고도 UAV 영상을 기하보정하는 기법을 제안하였으며, 상용 프로그램 처리결과와 비교를 통하여 UAV 정지영상 기하모형식으로서의 적용가능성을 평가하였다.

• 한국항공우주학회지
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• 제42권6호
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• pp.468-477
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• 2014

본 연구에서는 태양광 고고도 무인항공기가 어떻게 태양광 에너지만을 이용해서 지상에서 이륙, 상승비행을 하여 임무고도인 18 km 지점까지 도달할 수 있는지에 관한 연구를 수행하였다. 주익면적 $35.98m^2$와 가로세로비 25의 글라이더 형태의 항공기가 기준 항공기 형상으로 사용되었다. 미국 나사의 공개 프로그램인 OpenVSP와 XFLR5을 사용하여 형상변수 및 양력계수와 항력계수를 계산하였으며, 태양광으로부터의 가용에너지와 상승비행에 필요한 에너지 균형을 통해 항공기의 상승비행을 예측하였다. 각 고도에서 비행속도를 최소화하여 최소시간 상승비행이 가능하도록 하였고 이륙시간에 따른 임무고도 도달까지의 총소요시간과 소모되는 에너지량을 예측하였다. 또한 편서풍과 비행속도에 의한 항공기의 이동거리를 계산하였다.

• 한국항행학회논문지
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• 제19권3호
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• pp.244-249
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• 2015

본 연구는 지구의 높은 고도에서 핵폭발로 발생된 HEMP (high-altitude electromagnetic pulse)가 발생 즉시 지면에 도달하면서 OFDM (orthogonal frequency division multiplexing) 시스템에 미치는 영향을 분석한다. HEMP가 미치는 영향은 BER (bit error rate) 특성으로 확인한다. 시스템의 Q-factor로 인해 간섭 영향의 지속시간이 변화가 발생한다. Q값이 작으면, 간섭으로부터의 회복이 빠르고, Q값이 크면 영향을 받는 지속시간이 길어져 회복이 300~600%까지 늦어짐을 확인하였다.

• 한국추진공학회지
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• 제12권4호
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• pp.16-23
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• 2008

고고도에서 작동하는 로켓의 작동 환경을 지상에서 모사하기 위한 초음속 디퓨져의 연구를 위하여 이론적 접근과 수치적 접근을 수행하였다. 물리적 모델은 축대칭 형상을 갖는 디퓨져, 진공챔버, 로켓모터로 구성하였으며, 유동 발달 측면에서 초음속 디퓨져 작동특성에 관한 연구를 수행하였다. 본 논문은 디퓨져의 시동압력 예측모델, 진공챔버 크기의 효과, 디퓨져 시동을 위한 로켓모터의 최소 시동압력에 대한 연구내용을 수록하였다