• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1097-1107
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• 2015

General VTOL aircraft uses gas turbine engine which has high power to weight ratio. However, in the VTOL UAV in small sector, the gas turbine as a prime mover is not adequate because of the limitation of the high fuel consumption ratio of the gas turbine. In this research, The Series Hybrid-Electric Propulsion System(SHEPS) has been proposed and technology survey & comparison analysis has conducted to constitute propulsion system for engine, electric motor and battery. To achieve this object a 65kg-class P-UAV from "Company I" was used. And to estimate the validity of power control algorithm and developed power management control, Matlab/simulink$^{(R)}$ has been used for the simulation. As a result, the developed algorithm worked comparatively well and the research has predicted that SHEPS was satisfied enough for 7 hour of endurance for mission profile.

• Atmosphere
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• v.27 no.3
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• pp.359-370
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• 2017

In this study, the oceanic Total Precipitable Water (TPW) retrieval algorithm at 16 km altitude of High Altitude Long Endurance Unmanned Aerial Vehicle (HALE UAV) is described. Empirical equation based on Wentz method (1995) that uses the 18.7 and 22.235 GHz channels is developed using the simulated brightness temperature and SeeBor training dataset. To do radiative simulation, Satellite Data Simulator Unit (SDSU) Radiative Transfer Model (RTM) is used. The data of 60% (523) and 40% (349) in the SeeBor training dataset are used to develop and validate the TPW retrieval algorithm, respectively. The range of coefficients for the TPW retrieval at the altitude of 3~18 km with 3 km interval were 153.69~199.87 (${\alpha}$), 54.330~58.468 (${\beta}$), and 84.519~93.484 (${\gamma}$). The bias and RMSE at each altitude were found to be about $-0.81kg\;m^{-2}$ and $2.17kg\;m^{-2}$, respectively. Correlation coefficients were more than 0.9. Radiosonde observation has been generally operated over land. To validate the accuracy of the oceanic TPW retrieval algorithm, observation data from the Korea Meteorological Administration (KMA) Gisang 1 research vessel about six clear sky cases representing spring, autumn, and summer season is used. Difference between retrieved and observed TPW at 16 km altitude were in the range of $0.53{\sim}1.87kg\;m^{-2}$, which is reasonable for most applications. Difference in TPW between retrieval and observation at each altitude (3~15 km) is also presented. Differences of TPW at altitudes more than 6 km were $0.3{\sim}1.9kg\;m^{-2}$. Retrieved TPW at 3 km altitude was smaller than upper level with a difference of $-0.25{\sim}0.75kg\;m^{-2}$ compared to the observed TPW.

• Journal of the Korean Institute of Gas
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• v.22 no.2
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• pp.59-66
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• 2018

Using hydrogen fuel is expected to be suitable as a reciprocating internal combustion engine with heightened interest in HALE(High Altitude Long Endurance) UAV(Unmanned Aerial Vehicle). Hydrogen is hightest energy density per mass so it can continue to charge for long periods of time and have positive part of the environmental effects. However, it is estimated that there is less research on hydrogen fuel engine currently applied, and many studies need to be done. Depending on the operation, there are factors that result in supercooling due to reduced radiation or reduce cooling performance due to low air density. Therefore, the experiment was to change the temperature of the cooling water and investigate the effect on engine combustions. The limitation of the stable operation range due to backfire is dominated by the excess air ratio rather than the effect of the cooling water temperature change. When the cooling water temperature increases, the volumetric efficiency decreases and the torque decreases. As the cooling water temperature decreases, the heat loss was increased and consequently the thermal efficiency was decreased.

• Korean Journal of Remote Sensing
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• v.36 no.2_2
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• pp.263-275
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• 2020

In this study, DEMs (Digital elevation model) based on LIDAR, TanDEM-X and UAV (Unmanned Aerial Vehicle) are used to analyze topographic change of Gomso tidal flat during a few years. DEM from LIDAR data was observed at 2011 by KHOA (Korean hydrographic and oceanographic agency) and DEM based on TanDEM-X data was generated at Lee and Ryu (2017). UAV data was observed at KM and KH area of Gomso tidal flat. KM area was surveyed at MAY and AUG 2019, and KH area was surveyed at APR 2018 and MAY 2019. During research period, 2011 to AUG 2019, elevation of KM area is decreased 0.24 m in average, and Chenier is retreat to landward about 130 m. In KH area, elevation is increased 0.16 m in average during research period, 2011 to MAY 2019. It is expected that multi-platform remotely sensed data can help to study accurate topographic change of tidal flat.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.2
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• pp.257-264
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• 2020

Vectorization is currently the main method in feature collection (extraction) during digital mapping using UAV-Photogrammetry. However, this method is time consuming and prone to gross elevation errors when extracted from a DSM (Digital Surface Model), because three-dimensional feature coordinates are vectorized separately: plane information from an orthophoto and height from a DSM. Consequently, the demand for stereo plotting method capable of acquiring three- dimensional spatial information simultaneously is increasing. However, this method requires an expensive equipment, a Digital Photogrammetry Workstation (DPW), and the technology itself is still incomplete. In this paper, we evaluated the accuracy of low-cost stereo plotting system, Menci's StereoCAD, by analyzing its three-dimensional spatial information acquisition. Images were taken with a FC 6310 camera mounted on a Phantom4 pro at a 90 m altitude with a Ground Sample Distance (GSD) of 3 cm. The accuracy analysis was performed by comparing differences in coordinates between the results from the ground survey and the stereo plotting at check points, and also at the corner points by layers. The results showed that the Root Mean Square Error (RMSE) at check points was 0.048 m for horizontal and 0.078 m for vertical coordinates, respectively, and for different layers, it ranged from 0.104 m to 0.127 m for horizontal and 0.086 m to 0.092 m for vertical coordinates, respectively. In conclusion, the results showed 1: 1,000 digital topographic map can be generated using a stereo plotting system with UAV images.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.4
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• pp.223-233
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• 2018

In this study was classified the cadastral control points and parcel boundary points into 40m, 100m by flight altitude of UAV (Unmanned Aerial Vehicle) which compared the coordinates extracted from the orthophoto with the parcel boundary point coordinates by GNSS (Global Navigation Satellite System) ground survey. As a results of this study, first, in the spatial resolution analysis that the average error of the orthoimage by flight altitude were 0.024m at 40m, and 0.034m at 100m which were higher 40m than 100m for spatial resolution of orthophotos and position accuracy. Second, in order to analyze the accuracy of image recognition by airmark of flight altitude that was divided into three cases of nothing, green, and red of RMSE (Root Mean Square Error) were X=0.039m, Y=0.019m and Z=0.055m, the highest accuracy. Third, the result of the comparison between orthophotos and field survey results that showed the total RMSE error of the cadastral control points were X=0.029m, Y=0.028m, H=0.051m, and the parcel boundary points were X=0.041m, Y=0.030m. In conclusion, based on the results of this study, it is expected that if the average error of flight altitude is limited to less than 0.05m in the legal regulations related to orthophotos for cadastral surveying, it will be an economical and efficient method for cadastral survey as well as spatial information acquisition.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.2
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• pp.111-118
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• 2016

This paper presents an X-band (9.375 GHz) $1{\times}2$ array microstrip antenna which is capable of active beam compensation for installation of an unmanned aerial vehicle (UAV). First of all, a basic $1{\times}2$ array microstrip antenna incorporated with wilkinson power divider was designed and performance of the array antenna was verified. Next, to verify beam steering performance of the designed array microstrip antenna, we fabricated a phase shifter, and the wilkinson power divider as module structure and measured characteristics of beam steering according to phase shifting. The main lobe is 0.6 dBi at $0^{\circ}$, and the side lobe decreased 18.8 dB. The reliable radiation pattern was achieved. Finally, an active beam steering microstrip array antenna attached with the phase shifter and the power divider on the back side of the antenna was designed and fabricated to install wing of UAV for compactness. The maximum gain is 0.1 dBi. Therefore, we obtained a basic antenna technology for compensating beam error according to wing deformation of an UAV installed array antennas.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.167-179
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• 2021

In order to characterize the mixing process of confluence for understanding the impacts of a river on the other river, it has been crucial to analyze the spatial mixing patterns for main streams depending on various inflow conditions of tributaries. However, most conventional studies have mostly relied upon hydraulic or water quality numerical models for understanding mixing pattern analysis of confluences, due to the difficulties to acquire a wide spatial range of in-situ data for characterizing mixing process. In this study, backscatters (or SNR) measured from ADCPs were particularly used to track sediment mixing assuming that it could be a surrogate to estimate the suspended sediment concentration. Raw backscatter data were corrected by considering the beam spreading and absorption by water. Also, an optical Laser diffraction instrument (LISST) was used to verify the method of acoustic backscatter and to collect the particle size distribution of main stream and tributary. In addition, image-based spatial distributions of sediment mixture in the confluence were monitored in various flow conditions by using an unmanned aerial vehicle (UAV), which were compared with the spatial distribution of acoustic backscatter. As results, we found that when acoustic backscatter by ADCPs were well processed, they could be proper indicators to identify the spatial patterns of the three-dimensional mixing process between two rivers. For this study, flow and sediment mixing characteristics were investigated in the confluence between Nakdong and Nam river.

• Korean Journal of Remote Sensing
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• v.33 no.5_2
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• pp.677-687
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• 2017

In this paper, we propose the use of hierarchical classification for winter crop mapping based on satellite imagery. A hierarchical classification is a classifier that maps input data into defined subsumptive output categories. This classification method can reduce mixed pixel effects and improve classification performance. The methodology are illustrated focus on winter cropsin Gimje city, Jeonbuk with Landsat-8 imagery. First, agriculture fields were extracted from Landsat-8 imagery using Smart Farm Map. And then winter crop fields were extracted from agriculture fields using temporal Normalized Difference Vegetation Index (NDVI). Finally, winter crop fields were then classified into wheat, barley, IRG, whole crop barley and mixed crop fields using signature from Unmanned Aerial Vehicle (UAV). The results indicate that hierarchical classifier could effectively identify winter crop fields with an overall classification accuracy of 98.99%. Thus, it is expected that the proposed classification method would be effectively used for crop mapping.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1035-1047
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• 2015

Wind tunnel experiment and computational analysis have been carried out to evaluate the performance of propeller for scale electric-powered HALE UAV, named EAV-2H+. Performance curves are measured for three propellers and their adequacy for EAV-2H+ installation is examined through consideration of operating conditions. Decline in performance coefficients is observed in low rpm region. Also, the effect of transition tape on propeller performance is measured and analyzed. The computational performance analyses are carried out by using commercial CFD program. The thrust and power coefficient from computations show good agreement with experimental results. Performance coefficients are compared and the influence of measurement device which contributes to discrepancy of the results is examined. Transition SST model is confirmed to yield the tendency of performance decline in low rpm range, similar to experimental observation. The decrease in aerodynamic performance of blade element due to low Reynolds number is identified to cause the decline in propeller performance. Analyses for high altitude conditions confirms degradation in propeller performance.