• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.1
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• pp.63-73
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• 2014

Recently, researches on DBRN(DataBase Referenced Navigation) system are being carried out to replace GNSS(Global Navigation Satellite System), as weaknesses of GNSS were found that are caused by the intentional interference and the jamming of the satellite signal. This paper describes the gravity gradient modeling and the construction of EKF(Extended Kalman Filter) based GGRN(Gravity Gradient Referenced Navigation). To analyze the performance of GGRN, fourteen flight trajectories were made for simulations over whole South Korea. During the simulations, we considered the errors in both DB(DataBase) and sensor as well as the flight altitudes. Accurate performances were found, when errors in the DB and the sensor are small and they located at lower altitude. For comparative evaluation, the traditional TRN(Terrain Referenced Navigation) was also developed and performances were analyzed relative to those from the GGRN. In fact, most of GGRN performed better in low altitude, but both of precise gravity gradient DB and gradiometer were required to obtain similar level of precisions at the high altitude. In the future, additional tests and evaluations on the GGRN need to be performed to investigate on more factors such as DB resolution, flight speed, and the update rate.

• Korean Journal of Applied Biomechanics
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• v.18 no.4
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• pp.77-87
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• 2008

This study is to formulate strategy for subject who are selected as national team in horizontal bars event in apparatus gymnastics. For this, skill training program was applied to players for 8 weeks. Then it was analyzed by using 3D motion Analysis system to seek the difference between before and after using the program. There were decisive demerit element K's first try for Tkatchev stretched movement from low elevation and crooked body while elevating. Not only, the location of his center of mass is far and low and there was some concern in his landing due to bended his hip-joint, but also, it exposed weak point in retro-action followed technique. Thus, to overcome that weak point, the subject repeated practices on following; when preparing for Tkatchev stretched movement at downward for big spin, make sure extend shoulder angle faster, make sure Tap movement is short and concise using hip-joint angular while delaying Tap timing for folding the body, and moreover, while backlashing the body, used shoulder joint angle wide to pull up the body. As a result, the speed of vertical upward did rut increase when separation from the bar. However, height of elevation increased that the leg would rut hit the horizontal bar even straight up the hip-joint. Therefore, the movement itself provided magnificent motion and even helped decrease the demerits.

• Tunnel and Underground Space
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• v.26 no.1
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• pp.24-31
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• 2016

Recently, many studies have been conducted to use fixed-wing and rotary-wing unmanned aerial vehicles (UAVs, Drones) for topographic surveying in open-pit mines. Because the fixed-wing and rotary-wing UAVs have different characteristics such as flight height, speed, time and performance of mounted cameras, their results of topographic surveying at a same site need to be compared. This study selected a construction site in Yangsan-si, Gyeongsangnam-do, Korea as a study area and compared the topographic surveying results from a fixed-wing UAV (SenseFly eBee) and a popular rotary-wing UAV (DJI Phantom2 Vision+). As results of data processing for aerial photos taken from eBee and Phantom2 Vision+, orthomosaic images and digital surface models with about 4 cm grid spacing could be generated. Comparisons of the X, Y, Z-coordinates of 7 ground control points measured by differential global positioning system and those determined by eBee and Phantom2 Vision+ revealed that the root mean squared errors of X, Y, Z-coordinates were around 10 cm, respectively.

• Korean Journal of Remote Sensing
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• v.37 no.6_3
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• pp.2035-2046
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• 2021

Glacier movement speed is the most basic measurement for glacial dynamics research and is a very important indicator in predicting sea level rise due to climate change. In this study, the two-dimensional velocity measurements of Campbell Glacier located in Terra Nova Bay in East Antarctica were observed through the SAR offset tracking technique. For this purpose, domestic KOMPSAT-5 SAR satellite images taken on July 9, 2021 and August 6, 2021 were acquired. The Multi-kernel SAR offset tracking proposed through previous studies is a technique to obtain the optimal result that satisfies both resolution and precision. However, since offset tracking is repeatedly performed according to the size of the kernel, intensive computational power and time are required. Therefore, in this study, we strategically proposed a coarse-to-fine offset tracking approach. Through coarse-to-fine SAR offset tracking, it is possible to obtain a result with improved observation precision (especially, about 4 times in azimuth direction) while maintaining resolution compared to general offset tracking results. Using this proposed technique, a two-dimensional velocity measurements of Campbell Glacier were generated. As a result of analyzing the two-dimensional movement velocity image, it was observed that the grounding line of Campbell Glacier exists at approximately latitude -74.56N. The flow velocity of Campbell Glacier Tongue analyzed in this study (185-237 m/yr) increased compared to that of 1988-1989 (140-240 m/yr). And compared to the flow velocity (181-268 m/yr) in 2010-2012, the movement speed near the ground line was similar, but it was confirmed that the movement speed at the end of the Campbell Glacier Tongue decreased. However, there is a possibility that this is an error that occurs because the study result of this study is an annual rate of glacier movement that occurred for 28 days. For accurate comparison, it will be necessary to expand the data in time series and accurately calculate the annual rate. Through this study, the two-dimensional velocity measurements of the glacier were observed for the first time using the KOMPSAT-5 satellite image, a domestic X-band SAR satellite. It was confirmed that the coarse-to-fine SAR offset tracking approach of the KOMPSAT-5 SAR image is very useful for observing the two-dimensional velocity of glacier movements.

• Journal of Aerospace System Engineering
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• v.16 no.4
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• pp.60-67
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• 2022

An Electro-Optical Tracking System (EOTS) is an electric optical system with EO/IR cameras, laser sensors, and an IMU. The EOTS calculates coordinates of targets, using attitude and acceleration measured by the IMU. In particular for an armed aircraft, the performance of the weapon system depends on how quickly and accurately it acquires the target coordinates. The IMU should be operated after alignment is complete, to meet the coordinate accuracy required by the weapon system so the initial stabilization time of the IMU should be reduced, by quickly measuring the attitude and acceleration. Alignment is the process of determining the initial attitude by resolving the attitude error of the IMU, and the IMU of mission equipment such as an airborne EOTS, uses velocity matching based on the velocity from GPS/INS for aircraft navigation. In this paper, a method is presented to improve the transfer alignment performance of the airborne EOTS, by maneuvering aircraft and the mission equipment. First, the performance factor of the alignment was identified, as a heading error through the velocity matching model and simulation results. Then acceleration maneuvers and attitude changes were necessary, to correct the error. As a result of flight tests applied to an EOTS on a OOO aircraft system, the transfer alignment performance was improved as the duration time was decreased, by more than five times when the aircraft accelerated by more than 0.2g and the EOTS was moving until 6.7deg/s.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• v.10 no.2
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• pp.201-211
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• 1999

Objectives：This study investigated the characteristics of detained delinquent adolescents and variables related to the repeated crime during 6 months after release. Methods：The socio-demographic and crime-related characteristics of 73 detained adolescents were evaluated by semi-structured interviews and police records, and the psychological characteristics of them measured by the MMPI. We also compared the characteristics between subjects with and without repeated crime during 6 months after release. Results：1) Most of detained adolescents had families with low socioeconomic status(77%) and broken families(48%). Sixty-six percent of them were dropped out of school. The most frequent crime pattern was theft(49%), and with accomplice(77%). Seventy-five percent of total subjects had the records of previous conviction. Of the previous convictions, seventy-eight percent was same with the present crimes. 2) Subjects with repeated crime during 6 months after release were younger and had higher T-score on Pa scale of MMPI than the subjects without repeated crime. More adolescents with repeated crime had broken families than those without repeated crime. They also showed the crime-related characteristics of higher percent of theft among crime patterns, higher incidence of previous conviction, younger age of the first crime, and shorter crime-free duration from the last to present crime. Conclusion：These results of present study suggest that the development and the persistence of adolescent delinquency would be resulted from interaction of factors of individual, family, school, and community. By the comparison between subjects with and without repeated crime, it was found that familial dysfunction, younger age at first crime, presence of previous conviction might be the risk factors for repeated delinquency. To prevent repeated crime of delinquent adolescents more effectively, early therapeutic intervention and the development of programs to help adaptation in school and community would be essential.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.1
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• pp.46-53
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• 2017

This paper shows a length of wirecutter using an analysis based on Rotorcraft's control input and taxiing speed. In case of selecting an inappropriate length of wirecutter which applies to rotorcraft for safety, this causes a collision between blade and wirecuter, or an accident by wire. We review the control input which was used in development stage, and establish the conditions of control input which are needed in taxiing. Based on these conditions, we review the collision possibility between blade and wirecutter through analysis in case of 20, 40, 60 kts taxiing speed. Following, this result is verified by comparison with that of a simulation test in rotorcarft. Finally, in case of high collision possibility, we presented the downsize length to avoid the collision and increment of non-protective area in flight, simultaneously.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.10
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• pp.946-951
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• 2011

This paper presents the simulation results of GBAS availability and requirement (with respected to Vertical Protection Level) using simulated data at CAT I, CAT II/III DH point (Decision Height), which are generated using Jeju international GNSS reference position, aircraft horizontal velocity and reference/aircraft GNSS antenna performance index and so on. Two kinds of protection levels are presented, one is from a hypothesis (H0) and other is from a alternative hypothesis (H1). These protection levels are compared with AL (Alert Limit), and we analyse the GBAS availability and requirement for CAT I and CAT II/III at the airport.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.5
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• pp.335-342
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• 2020

Tailless aircraft designed for stealth efficiency uses spoilers instead of rudders for the directional control. When the spoiler is rapidly deployed, highly nonlinear and unsteady aerodynamic characteristics can be generated, resulting in adverse effects on aircraft flight performance. This paper investigates the aerodynamic characteristics of an airfoil with moving spoiler using dynamic mesh CFD technique. The effects of spoiler operation speed, mounting location, and deployment scheduling are analyzed to reduce the adverse effects of the spoiler's dynamic operation. The results shows that the adverse effects of dynamic spoiler can be reduced by appropriate selection of the spoiler mounting location and deployment scheduling.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.9
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• pp.856-861
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• 2010

In this work, experiments on hybrid sounding rocket were conducted to investigate the aerodynamic characteristics and analyze longitudinal static stability. Tests were performed on 1/10 scale models of sounding rocket through Mach number ranging from 1.75 to 2.5 and for angle of attack from $0^{\circ}$ to $6^{\circ}$. Aerodynamic forces and moments were measured by means of a 4 component internal balance. With measured forces and moments, static stability characteristics of rocket were calculated. Tests were made for three models with different length to determine the effect of body length. The visualization of shock waves was carried out by Schlieren optical system to observe variations of shock waves with Mach number and angle of attack.