• Title/Summary/Keyword: High Altitude Environment

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Analysis on the Impact of Space Environment on LEO Satellite Orbit (우주환경 변화에 따른 저궤도 위성의 궤도변화 분석)

  • Jung, Okchul;Yim, Hyeonjeong;Kim, Hwayeong;Ahn, Sangil
    • Journal of Aerospace System Engineering
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    • v.9 no.2
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    • pp.57-62
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    • 2015
  • The satellite orbit is continuously changing due to space environment. Especially for low earth orbit, atmospheric drag plays an important role in the orbit altitude decay. Recently, solar activities are expected to be high, and relevant events are occurring frequently. In this paper, analysis on the impact of geomagnetic storm on LEO satellite orbit is presented. For this, real flight data of KOMPSAT-2, KOMPSAT-3, and KOMPSAT-5 are analyzed by using the daily decay rate of mean altitude is calculated from the orbit determination. In addition, the relationship between the solar flux and geomagnetic index, which are the metrics for solar activities, is statistically analyzed with respect to the altitude decay. The accuracy of orbit prediction with both the fixed drag coefficient and estimated one is examined with the precise orbit data as a reference. The main results shows that the improved accuracy can be achieved in case of using estimated drag coefficient.

Neutron Dosimetry and Monitoring in the Radiation Environment

  • Nakamura, Takashi
    • Journal of Radiation Protection and Research
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    • v.14 no.2
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    • pp.51-62
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    • 1989
  • The high efficiency moderated-type neutron spectrometer and doseequivalent counter were developed for the measurement of low level environmental neutrons. By using these detectors, the neutron energy spectra and dose equivalent rates due to skyshine effect were measured in the environment surrounding the accelerator facilities and also the altitude variation of cosmic ray neutrons in the aircraft flying over Japan.

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Analysis on Air Quality Characteristics through Air Quality Monitoring Stations in urban Background and High Altitude in 2005~2006 in Seoul (서울시의 2005~2006년 도시배경 및 상층측정망의 대기질 특성 분석)

  • Yoo, Seung-Sung;Jeon, Jae-Sik;Jung, Kweon;Shin, Eun-Sang;Jung, Bu-Jeon;Ryu, Ri-Na;Woo, Jung-Hun;Sunwoo, Young
    • Journal of Environmental Impact Assessment
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    • v.20 no.1
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    • pp.49-59
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    • 2011
  • The results of comparing $PM_{10}$ concentration between 'Namsan' and 'Yongsan-gu' air quality monitoring stations show similar values with averaged concentration in the whole Seoul. The correlation factors in both sites were 0.865, 0.828 in 2005, 2006, respectively. For 'Bukhansan' and 'Gangbuk-gu' air quality monitoring stations, different from the results mentioned above, they showed clear differences as altitude changes. PM10 concentration in 'Bukhansan' monitoring stations was 10 ${\mu}g/m^3$ lower than 'Gangbuk-gu' monitoring station which is located near the ground. Also, averaged PM10 concentration in 'Bukhansan' and 'Gangbuk-gu' monitoring stations was lower than that in the whole Seoul. When comparing $NO_2$ concentration between 'Namsan' and 'Yongsan-gu' monitoring stations, $NO_2$ concentration in 'Namsan' monitoring station was lower than 'Yongsan-gu' monitoring station. For $NO_2$ concentration in 'Bukhansan', 'Gangbuk-gu' and 'the whole Seoul', there were the same pattern in 'Gangbuk-gu' and the 'the whole Seoul' and low values in 'Bukhansan' monitoring station. The correlation factors of $NO_2$ concentration in 'Bukhansan' and 'Gangbukgu' was 0.525, 0.549 in 2005, 2006, respectively, which stands for low correlationship.

Study on the Optimal Location of Low Altitude Air Defense Radar (저고도 방공 레이더 최적 배치에 관한 연구)

  • Baek, Kyung-Hyoek;Lee, Youngwoo;Jang, Hoon
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.2
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    • pp.248-257
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    • 2014
  • As observed in the recent war, suppression of enemy air defense operation is one of the major tactics, simultaneously conducted with high payoff target. Specifically, our air defense operation should be properly constructed, since the operating environment of our forces mostly consists with mountainous terrain, which makes detections of the enemy difficult. The effective arrangements of low altitude air defense radars can be suggested as a way of improving the detection capability of our forces. In this paper, we consider the location problem of low altitude air defense radar, and formulate it as an Integer Programming. Specifically, we surveyed the previous researches on facility location problems and applied two particularly relevant models(MCLP, MEXCLP) to our problem. The terrain factor was represented as demand points in the models. We verified the optimal radar locations for operational situations through simulation model which depicts simple battle field. In the simulation model, the performance of optimal radar locations are measured by the enemy detection rate. With a series of experiments, we may conclude that when locating low altitude air defense radars, it is important to consider the detection probability of radar. We expect that this finding may be helpful to make a more effective air defense plan.

Observation and Analysis of the Long and Short Wave Radiation According to Different Altitudes and Locations in Daegu During Summer (대구지역의 고도와 위치에 따른 하절기 장·단파복사 관측과 해석)

  • Choi, Dong-Ho;Lee, Bu-Yong;Oh, Ho-Yeop
    • Journal of the Korean Solar Energy Society
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    • v.32 no.4
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    • pp.71-81
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    • 2012
  • This study for the understanding of the radiation environment according to the altitude in urban area in the summer observes the long and short wave radiation environment at the 4 urban areas with different height and the 1 suburban area. The results of this study are as follows. (1) When the altitude was high, the more short wave radiation was observed. (2) As the altitude was high, the temperature of atmosphere got lower. And because of that the downward long wave radiation was also lower. This general trend was confirmed through the study. (3) Through the observation of long wave radiation, the upper atmosphere of suburban area had the atmosphere characteristic which the temperature was rising and decreasing faster. Therefore, the difference radiation characteristics between the urban and suburban area were confirmed. (4) The result of the ratio of short wave radiation to long wave radiation(short wave radiation/long wave radiation) according to the altitude and location, the value was increased when the distance was far from the artificiality structure or a heat source, and the urban effect became smaller. Thus, it is expected that the ratio will be an evaluation index for evaluating urbanization effect.

Hemato-Biochemical Indices of Hanwoo Cattle Raised at Different Altitudes (서로 다른 고도에서 사육된 비육한우의 혈액-혈청 지수)

  • Ji, Joong-Ryong;Alam, Md. Rafiqul;Na, Chong-Sam;Kim, Nam-Soo
    • Journal of Veterinary Clinics
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    • v.28 no.2
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    • pp.219-224
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    • 2011
  • The health status of three groups of Hanwoo steers (n=157) aged 2-3 years, raised at three different altitudes (600 m, n=50; 200-400 m, n=58; plane land, n=49) and environment with more or less similar management have been evaluated through hematological, biochemical and globulin examinations in order to determine the optimum environment suitable for raising cattle while at the same time minimizing the risk of disease. Five mL of blood samples from each animal were collected by jugular veinipuncture and 2 mL was transferred to a tube containing EDTA for complete blood count (CBC) and 3 mL in lithium heparin for chemistry screening (CS) and immunoassay. Among the CBC parameters a significantly higher white blood cell count (tWBC), total red blood cell count (tRBC), hemoglobin (Hb) and packed cell volume (PCV) were noticed in the high altitude groups, whereas those were lower in the plane land group. In the CS parameters higher levels of aspartate aminotransferase (AST), creatinine, lactate dehydrogenase (LDH) and total bilirubin (TBL) were found in the plane land group, whereas those were lower in the high altitude groups. The total protein (significantly) and globulins were higher in the 600 m group. The results of this study revealed that the overall health status of the Hanwoo cattle based on the hemato-biochemical indices was superior in the highest altitude and inferior in the plane land group but all the parameters were within the reference range in all the groups. Therefore, for recommendation of a suitable environment at an appropriate altitude for raising cattle there need to be further studied along with the hemato-biochemical parameters; considering, breeding, feeding, management, marketing, waste disposal and other factors.

Study on Starting Pressure of Supersonic Exhaust Diffusers to Simulate high Altitude Environment (고고도 모사용 초음속 디퓨져의 시동압력에 대한 연구)

  • Yoon, Sang-Kyu;Yeom, Hyo-Won;Kim, Jin-Kon;Sung, Hong-Gye;Kim, Yong-Wook;Oh, Seung-Hyup
    • Journal of the Korean Society of Propulsion Engineers
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    • v.12 no.4
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    • pp.16-23
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    • 2008
  • Theoretical and numerical approaches were conducted in order to study supersonic exhaust diffusers to simulate high altitude performance of rockets on the ground. A physical model of concern includes a rocket motor, vacuum chamber, and diffuser, which have axisymmetric configurations. An analysis was conducted to investigate operation characteristics of supersonic exhaust diffusers from a flow-development point of view. Emphasis was placed on theoretical formulation to predict the starting pressure of diffusers, the effect of the vacuum chamber size, and the minimum starting pressure of the rocket motor to start the diffuser.

A Study on the Nozzle Flow in the Sub-scale High-Altitude Test (축소형 고공환경모사 시험에서의 노즐 유동에 관한 연구)

  • Choi, Jiseon;Lee, Seongmin;Lee, Heejune;Ko, Youngsung;Kim, Seonjin;Lee, Jungmin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.1011-1015
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    • 2017
  • In this study, numerical and experimental studies on the nozzle flow in a sub-scale cold flow test were conducted to simulate high altitude condition. In the theoretical calculation, the temperature of the nozzle outlet is calculated to be lower than the liquefaction point, and the fluid exists at the phase change point. Also, numerical analysis result is higher than theory calculation but lower than liquefaction temperature. As a result of cold flow test, it was confirmed that the temperature was much higher than theory and analysis. This is because it assumed that it is adiabatic in the theoretical calculation, but the experiment in the actual environment is not the adiabatic but the heat exchange with the outside exists.

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An Experimental Study on Startup Characteristics of a Center Body Diffuser for High Altitude Simulation (고공환경 모사용 Center Body Diffuser의 시동 특성에 관한 실험적 연구)

  • Yeon, Hae In;You, Isang;Kim, Wan Chan;Im, Ji Nyeong;Ko, Young Sung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.2
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    • pp.93-102
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    • 2016
  • An experimental study has been conducted to verify the startup characteristic of a Center Body Diffuser (CBD) for simulating a low pressure environment when at high altitudes. Vacuum chamber pressure and startup characteristics of the CBD were investigated according to various geometries of the center body structure by a cold gas flow test. The test results show that the startup pressure is lowest when the center body contraction angle is approximately $15^{\circ}$. The startup characteristic of the CBDs significantly improves when the diffuser inlet length ($L_d/D_d$) is decreasing and the divergence length ($L_s$) is increasing. Additionally, it is possible to simulate various high altitude, low pressure conditions for various rocket engines that have different nozzle expansion ratios by adjusting the center body's position inside the diffuser.

An Ultra-narrow Bandwidth Filter for Daytime Wind Measurement of Direct Detection Rayleigh Lidar

  • Han, Fei;Liu, Hengjia;Sun, Dongsong;Han, Yuli;Zhou, Anran;Zhang, Nannan;Chu, Jiaqi;Zheng, Jun;Jiang, Shan;Wang, Yuanzu
    • Current Optics and Photonics
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    • v.4 no.1
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    • pp.69-80
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    • 2020
  • A Rayleigh Lidar used for wind detection works by transmitting laser pulses to the atmosphere and receiving backscattering signals from molecules. Because of the weak backscattering signals, a lidar usually uses a high sensitivity photomultiplier as detector and photon counting technology for signal collection. The capturing of returned extremely weak backscattering signals requires the lidar to work on dark background with a long time accumulation to get high signal-to-noise ratio (SNR). Because of the strong solar background during the day, the SNR of lidar during daytime is much lower than that during nighttime, the altitude and accuracy of detection are also restricted greatly. Therefore this article describes an ultra-narrow bandwidth filter (UNBF) that has been developed on 354.7 nm wavelength of laser. The UNBF is used for suppressing the strong solar background that degrades the performance of Rayleigh wind lidar during daytime. The optical structure of UNBF consists of an interference filter (IF), a low resolution Fabry-Perot interferometer (FPI) and a high resolution FPI. The parameters of each optical component of the UNBF are presented in this article. The transmission curve of the aligned UNBF is measured with a tunable laser. Contrasting the result of with-UNBF and with-IF shows that the solar background received by a Licel transient recorder decreases by 50~100 times and that the SNR with-UNBF was improved by 3 times in the altitude range (35 km to 40 km) compared to with-IF at 10:26 to 10:38 on August 29, 2018. By the SNR comparison at four different times of one day, the ratio-values are larger than 1 over the altitude range (25~50 km) in general, the results illustrate that the SNR with-UNBF is better than that with-IF for Rayleigh Lidar during daytime and they demonstrate the effective improvements of solar background restriction of UNBF.