• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.38-42
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• 2003

In this paper, a radar scattering model for forest canopies has been developed based on an empirical rough surface scattering model and the radiative transfer theory. Leaves in the forest canopy are modeled by rectangular resistive sheets, brunches and trunks are modeled by cylinder, which sizes and orientations are randomly distributed. The scattering model has been verified with the measurement data of JPL/AirSAR system.

• Journal of The Korean Astronomical Society
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• v.49 no.1
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• pp.1-8
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• 2016

The aim of this study is to describe the physical processes taking place in the solar photosphere. Based on 3D hydrodynamic simulations including a detailed radiation transfer scheme, we investigate thermodynamic structures and radiation fields in solar surface convection. As a starting model, the initial stratification in the outer envelope calculated using the solar calibrations in the context of the standard stellar theory. When the numerical fluid becomes thermally relaxed, the thermodynamic structure of the steady-state turbulent flow was explicitly collected. Particularly, a non-grey radiative transfer incorporating the opacity distribution function was considered in our calculations. In addition, we evaluate the classical approximations that are usually adopted in the onedimensional stellar structure models. We numerically reconfirm that radiation fields are well represented by the asymptotic characteristics of the Eddington approximation (the diffusion limit and the streaming limit). However, this classical approximation underestimates radiation energy in the shallow layers near the surface, which implies that a reliable treatment of the non-grey line opacities is crucial for the accurate description of the photospheric convection phenomenon.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.66.1-66.1
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• 2014

Radiative transfer programs to simulate the 3-micron auroral $CH_4$ emissions of Jupiter have been developed. The formalism of the radiative transfer calculations including the thermal, fluorescent, and auroral emissions of the $CH_4$ bands for an atmospheric layer having an optical depth of ${\tau}_v$ is given by: ${\mu}dI_v/d{\tau}_v=I_v-{\varpi}_v{^*}J_v(1-{\varpi}_v{^*})B_v-{\varpi}{^*}F_{ov}{e}{x}{p}(-{\tau}_v/{\mu}_o)4{\pi}-hv{\varpi}{^*}V/4{\pi}$ where ${\varpi}_v{^*}$ is the single scattering albedo of $CH_4$ consisting of Einstein A coefficient and collisional deexcitation rate. Other terms are usual radiative transfer parameters appearing in textbooks including the terms for scattered ${\varpi}_v{^*}J_v$, thermal $(1-{\varpi}_v{^*})B_v$, and attenuated solar radiations $F_{ov}$ at the certain atmospheric layer. For auroral excitations, we include V, which is the number of excited states per $cm^3$ persec by auroral particle bombardments. We apply this formalism to the high-resolution spectra of the auroral regions observed with GNIRS/Gemini North, and will present preliminary results for the 3 micron auroral processes of Jupiter.

• Proceedings of the KSRS Conference
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• 1998.09a
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• pp.180-185
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• 1998

Microwave polarimetric backscattering from a various types of grassland canopies has been analyzed by using the first-order radiative transfer theory in this paper. Leaves in the grassland are modeled by rectangular resistive sheets, which sizes (widths and lengths) and orientations (elevation and azimuth angles) are randomly distributed. Surface roughness and soil moisture of the ground plane under the grass canopy is considered in this computation. The backscattering coefficients of grasslands are computed for different radar parameters (angles, frequencies and Polarizations) as well as different canopy Parameters (size and orientation distributions of leaves, canopy depth, moisture contents of leaves and soil, rms height and correlation length of soil surface). A radar system for 15GHz has been fabricated and used for measurement of the scattering coefficient from a grass canopy. The computation result obtained by the scattering model for the grass canopy is compared with the measurements.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.962-967
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• 2011

Radiative properties of alumina particles which is the main element of the plume from booster and kick motor used for increasing thrust and insertion into the orbit is analyzed. In order to derive the wavelength integrated (i.e., gray) emissivity, emission term in radiative transfer equation is rearranged to be able to tie up with the parameters induced from fundamental particle scattering Mie theory. Result shows that derived gray emissivity with optical properties increases with temperature rising.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.310-313
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• 2007

In this study, a new technique for atmospheric transmittance estimated from ALOS PRISM data is developed. It is based on satellite's observing radiances of different view angles and assumes that the cause of difference in radiances is the different view angles. The ALOS PRISM has three independent optical systems for viewing forward and backward and producing a stereoscopic image along the satellite's track. This stereo pair data can be used to estimate the transmittance according to the radiative transfer theory. This derived transmittance will be validated by the AERONET data and compared with the MODTRAN4 simulation results. Results show that the higher the land cover albedo, the better the derived transmittance compared to the AERONET data. Besides, this technique also shows the transmittance retrieval will be underestimated for the low land cover albedo.

• Journal of The Korean Astronomical Society
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• v.47 no.5
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• pp.187-193
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• 2014

Recent cosmological observations indicate that the reionized universe may have started at around z = 6, where a significant suppression around $Ly{\alpha}$ has been observed from the neutral intergalactic medium. The associated neutral hydrogen column density is expected to exceed $10^{21}cm^{-2}$, where it is very important to use the accurate scattering cross section known as the Kramers-Heisenberg formula that is obtained from the fully quantum mechanical time-dependent second order perturbation theory. We present the Kramers-Heisenberg formula and compare it with the formula introduced in a heuristic way by Peebles (1993) considering the hydrogen atom as a two-level atom, from which we find a deviation by a factor of two in the red wing region far from the line center. Adopting a representative set of cosmological parameters, we compute the Gunn-Peterson optical depths and absorption profiles. Our results are quantitatively compared with previous work by Madau & Rees (2000), who adopted the Peebles approximation in their radiative transfer problems. We find deviations up to 5 per cent in the Gunn-Peterson transmission coefficient for an accelerated expanding universe in the red off-resonance wing part with the rest wavelength ${\Delta}{\lambda}{\sim}10{\AA}$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.8
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• pp.563-569
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• 2008

Radiative, heating is suitable for outdoor heating system in windy and cold seasons. Optimal design of the reflector is very important to maximize heat transfer to a specific target area in the open space. The geometrical optical theory can be applied to analyze efficiency of the reflector. Commercial ray tracing computer programs are available only for limited geometries of the reflector. Alternatively, it may be designed and analyzed through an approximated simple lens theory. Two types of reflectors are analyzed using either of these methods. The key issue in this paper is to propose a new illumination experimental method for determination of the radiative efficiency. Optical light source and illuminometer are employed. The calculated efficiency of the reflector is compared with experimental one for checking the reliability. The relative errors between the experimental and analytical results are less than 5%, which proves the validity of this method. Based on these methodologies, a practical reflector and heating lamp unit is developed.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.3 no.2
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• pp.40-45
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• 1992

A simple emission model applicable for low scattering (scattering << absorption) anisotropic layer is developed and applied to the interpretation of measurements of microwave emission from row crops. The vegetation layer of row crops is modeled as a random slab embedded with small spheroid with major axis aligend paralel to the crop-row direction. The total emission is given in a simple algebraic form based on the zero-order radiative transfer theory. The single scattering albedo for spheroid and its polarimetric phase function are presented. The effects of layer azimuthal dependence on emission are accounted for by using an anisotropic albedo in the zero-order transfer theory. The developed emission theory favorably compares with the brightness temperature measured over soybeans canopy.

• Korean Journal of Optics and Photonics
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• v.30 no.1
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• pp.1-7
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• 2019

MANPADS (man-portable air defense system) is a counterweapon system against enemy aircraft, tracking the MWIR (mid-wavelength of infrared) signature of the plume. Under foggy conditions, however, multiple scattering phenomenon caused by the particles affects the MWIR transmittance, and the MANPADS detection performance. Therefore, in this study we analyzed the lock-on range of MANPADS with varying fog conditions and plume characteristics. To analyze the optical extinction properties and transmittance in fog, Mie scattering theory and analytic solution of the radiative-transfer equation are utilized. In addition, we used flare signature as an alternative MWIR light source. We confirmed that the lock-on range could be noticeably reduced under conditions of mist, and proportional to the flare temperature.