• Title/Summary/Keyword: LOWTRAN

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Study on the LOWTRAN7 Simulation of the Atmospheric Radiative Transfer Using CAGEX Data. (CAGEX 관측자료를 이용한 LOWTRAN7의 대기 복사전달 모의에 대한 조사)

  • 장광미;권태영;박경윤
    • Korean Journal of Remote Sensing
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    • v.13 no.2
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    • pp.99-120
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    • 1997
  • Solar radiation is scattered and absorbed atmospheric compositions in the atmosphere before it reaches the surface and, then after reflected at the surface, until it reaches the satellite sensor. Therefore, consideration of the radiative transfer through the atmosphere is essential for the quantitave analysis of the satellite sensed data, specially at shortwave region. This study examined a feasibility of using radiative transfer code for estimating the atmospheric effects on satellite remote sensing data. To do this, the flux simulated by LOWTRAN7 is compared with CAGEX data in shortwave region. The CAGEX (CERES/ARM/GEWEX Experiment) data provides a dataset of (1) atmospheric soundings, aerosol optical depth and albedo, (2) ARM(Aerosol Radiation Measurement) radiation flux measured by pyrgeometers, pyrheliometer and shadow pyranometer and (3) broadband shortwave flux simulated by Fu-Liou's radiative transfer code. To simulate aerosol effect using the radiative transfer model, the aerosol optical characteristics were extracted from observed aerosol column optical depth, Spinhirne's experimental vertical distribution of scattering coefficient and D'Almeida's statistical atmospheric aerosols radiative characteristics. Simulation of LOWTRAN7 are performed on 31 sample of completely clear days. LOWTRAN's result and CAGEX data are compared on upward, downward direct, downward diffuse solar flux at the surface and upward solar flux at the top of the atmosphere(TOA). The standard errors in LOWTRAN7 simulation of the above components are within 5% except for the downward diffuse solar flux at the surface(6.9%). The results show that a large part of error in LOWTRAN7 flux simulation appeared in the diffuse component due to scattering mainly by atmispheric aerosol. For improving the accuracy of radiative transfer simulation by model, there is a need to provide better information about the radiative charateristrics of atmospheric aerosols.

Radiometric Characteristics of KOMPSAT EOC Data Assessed by Simulating the Sensor Received Radiance

  • Kim, Jeong-Hyun;Lee, Kyu-Sung;Kim, Du-Ra
    • Korean Journal of Remote Sensing
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    • v.18 no.5
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    • pp.281-289
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    • 2002
  • Although EOC data have been frequently used in several applications since the launch of the KOMPSAT-1 satellite in 1999, its radiometric characteristics are not clear due to the inherent limitations of the on-board calibration system. The radiometric characteristics of remotely sensed imagery can be measured by the sensitivity of radiant flux coming from various surface features on the earth. The objective of this study is to analyze the radiometric characteristics of EOC data by simulating the sensor- received radiance. Initially, spectral reflectance values of reference targets were measured on the ground by using a portable spectre-radiometer at the EOC spectrum. A radiative transfer model, LOWTRAN, then simulated the sensor-received radiance values of the same reference target. By correlating the digital number (DN) extracted from the EOC image to the corresponding radiance values simulated from LOWTRAN, we could find the radiometric calibration coefficients for EOC image. The radiometric gain coefficients of EOC are very similar to those of other panchromatic optical sensors.

Study on Modeling the Spectral Solar Radiation Absorption Characteristics in Determining the surface Temperature of a Ground Object (지상물체의 표면온도 계산을 위한 파장별 태양복사 흡수특성 모델링 연구)

  • Choi, Jun-Hyuk;Gil, Tae-Jun;Kim, Tae-Kuk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.1
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    • pp.33-39
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    • 2007
  • This paper is aimed at the development of a software that predicts the surface temperature profiles of three-dimensional objects on the ground by considering the spectral solar radiation through the atmosphere. The spectral solar radiation through the atmosphere is modeled by using the well-known LOWTRAN7 code which analyzes the detailed spectral transmission characteristics by considering the atmospheric gas layers. In this paper, the transient temperature distribution over a cylinder is calculated by using the semi-implicit method. The spectral radiative surface properties such as the absorptivity and emissivity of the objects are used to model the effects of the solar irradiation and the surface emission. Both the detailed spectral modeling and the simple total modeling for the solar radiation absorption show fairly good agreement with each other by showing less than 3% difference in surface temperature.

A Study on Prediction of Surface Temperature and Reduction of Infrared Emission from a Naval Ship by Considering Emissivity of Funnel in the Mid-Latitude Meterological Conditions (중위도 기상조건에서 함정의 연돌 방사율을 고려한 적외선 복사량 예측 및 감소방안 연구)

  • Gil, Tae-Jun;Choi, Jun-Hyuk;Cho, Yong-Jin;Kim, Tae-Kuk
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.1 s.151
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    • pp.40-47
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    • 2007
  • This study is focused on developing a software that predicts the temperature distribution and infrared Emission from 30 objects considering the solar radiation through the atmosphere. The solar radiation through the atmosphere is modeled by using the well-known LOWTRAN7 code. Surface temperature information is essential for generating the infrared scene of the object. Predictions of the transient surface temperature and the infrared emission from a naval ship by using the software developed here show fairly good results by representing the typical temperature and emitted radiance distributions expected for the naval ship considered in mid latitude. Emissivity of each material is appeared to be an important parameter for recognizing the target in Infrared band region. The numerical results also show that the low emissivity surface on the heat source can be helpful in reducing the IR image contrast as compared to the background sea.

STUDY ON THERMAL MODELING METHODS OF A CYLINDRICAL GROUND OBJECT CONSIDERING THE SPECTRAL SOLAR RADIATION THROUGH THE ATMOSPHERE

  • Choi Jun-Hyuk;Choi Mi-Na;Gil Tae-Jun;Kim Tae-Kuk
    • Proceedings of the KSRS Conference
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    • 2005.10a
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    • pp.205-208
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    • 2005
  • This research is aimed at the development of a software that predicts the surface temperature profiles of three-dimensional objects on the ground considering the spectral solar radiation through the atmosphere. The thermal modelling is essential for identifying the objects on the scenes obtained from the satellites. And the temperature distribution on the objects is necessary to obtain their infrared images in contrast to the background. We developed a software that could be used to model the thermal problems of the ground objects irradiated by the spectral solar radiation. This software can be used to handle the conduction within the object as a one-dimensional mode into the depth or as a three-dimensional mode through the media. LOWTRAN7 is used to model the spectral solar radiation including the direct and diffuse solar radiances. In this paper, temperature distributions on the objects obtained by using the one-dimensional and the three-dimensional thermal models are compared with each other to examine the applicability of the relatively easy-to-apply one-dimensional model.

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DEVELOPMENT OF DAYTIME OBSERVATION MODEL FOR STAR SENSOR AND CENTROIDING PERFORMANCE ANALYSIS (주간 별 센서 관측 모델 개발 및 중심찾기 성능 분석)

  • Nah, Ja-Kyoung;Yi, Yu;Kim, Yong-Ha
    • Journal of Astronomy and Space Sciences
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    • v.22 no.3
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    • pp.273-282
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    • 2005
  • A star sensor daytime observation model is developed in order to test the performance of the star sensor useful for daylight application. The centroid errors of the star sensor in the day time application are computed by using the model. The standard atmospheric model (LOWTRAN7) is utilized to calculate the physical quantities of the daylight atmospheric environments where the star sensor is immersed. This observation model takes the separation angles between the sun and star, the centroid algorithm and the various system specifications of the star sensor into the account. The developed star sensor model will provide more realistic measurement errors in estimating the performance of the attitude determination from the vector observations.

Investigation of the Effects of UAV Nozzle Configurations on Aircraft Lock-on Range (무인항공기의 노즐 형상 변화가 Lock-on Range에 미치는 영향에 관한 연구)

  • Kim, Min-Jun;Kang, Dong-Woo;Myong, Rho-Shin;Kim, Won-Cheol
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.43 no.3
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    • pp.204-212
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    • 2015
  • The infrared lock-on range of target aircraft plays a critical role in determining the aircraft survivability. In this investigation, the effects of various UAV engine nozzle configurations on the aircraft lock-on range were theoretically analyzed. A virtual subsonic aircraft was proposed first, based on the mission requirement and the engine performance analysis, and convergent-type nozzles were then designed. After determining thermal flow field and nozzle surface temperature distribution with the CFD code, an additional analysis was conducted to predict the IR signature. Also, atmospheric transmissivity for various latitude and seasons was calculated, using the LOWTRAN code. Finally, the lock-on and lethal envelopes were calculated for different nozzle configurations, assuming the sensor threshold of the given IR guided missile. It was shown that the maximum 55.3% reduction in lock-on range is possible for deformed nozzles with the high aspect ratio.

Star Detectability Analysis of Daytime Star Sensor (주간 활용 별센서의 별 감지가능성 분석)

  • Nah, Ja-Kyoung;Yi, Yu;Kim, Yong-Ha
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.9
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    • pp.89-96
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    • 2005
  • This paper discusses the daytime atmospheric conditions and the possibility of daytime star detection with the purpose of practical use of the star sensor for daylight navigation. In order to estimate the daytime atmospheric data, we use the standard atmospheric model (LOWTRAN 7), from which atmospheric transmittance and radiance from background sky are calculated. Assuming the star sensor with an optical filter to reduce background radiation, different separation angles between the star sensor and the sun are set up to express the effect of the solar radiation. As considerations of field of view (FOV) of the star sensor, the variation of the sky background radiation and the star density of the detectable star are analyzed. In addition, the integration time to achieve a required signal-to-noise ratio and the number of the radiation-caused electrons of the charge coupled detector(CCD) working as the limit to daylight application of the star sensor are calculated.

Investigation of Aircraft Plume IR Signature for Various Nozzle Configurations and Atmospheric Conditions (노즐형상 및 대기조건에 따른 항공기의 플룸 IR 신호 연구)

  • Kang, Dong-Woo;Kim, In-Deok;Myong, Rho-Shin;Kim, Won-Cheol
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.1
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    • pp.10-19
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    • 2014
  • Nozzle configurations and atmospheric conditions play a significant role in the infrared signature level of aircraft propulsion system. Various convergent nozzles of an unmanned aircraft under different atmospheric conditions are considered. An analysis of thermal flow field and nozzle surface temperature distribution is conducted using a compressible CFD code. It is shown that the IR level in rear direction is considerably reduced in deformed nozzles, whereas the IR level in adjacent azimuth angles is increased in aspect ratios around 6 due to the plume spreading effect caused by high aspect ratio of nozzles. In addition, an analysis of atmospheric transmissivity for various seasons and observation distance is conducted using the LOWTRAN 7 code and subsequently plume IR signature is calculated by considering atmospheric effects. It is shown that the IR signature is reduced significantly in summer season and near the band of carbon dioxide in case of relatively close distance.

A MODEL FOR MUV AIRGLOW FROM THE UPPER ATOMOSPHERE ABOVE THE KOREAN PENINSULA (한반도 상공 고층대기의 중간 자외선 대기광 모델)

  • MOON BONG-KON;KIM YONG HA;YI YU;KIM JHOON
    • Journal of The Korean Astronomical Society
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    • v.34 no.1
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    • pp.35-40
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    • 2001
  • For the planned experiments of Korea Sounding Rocket-III (KSR-III), we have constructed a model of MUV dayglow in the mid-latitude. The model computes relative intensities of individual emission lines in the Vegard-Kaplan and 2PG band systems of $N_2$ in the wavelength range of 2500-3500${\AA}$. In addition to the emission lines, solar scattered continuum was computed by an extended LOWTRAN7 code, in which we have included solar scattering in altitudes higher than 100 km by using MSIS90 thermosphere model. Ratios among vibrational bands of VK and 2PG system, were computed from the observed MUV dayglow spectra of Cleary et al. (1995). The model provides MUV dayglow intensitiy profiles with a wavelength resolution of 3.13${\AA}$ as a function of altitude. The computed intensity profiles have been utilized in designing the KSR-III airglow photometers.

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