Tae-Kuk Kim

Analysis of the spectral surface radiance by using the surface BRDF and the atmospheric transmission effects

The spectral radiance received by a remote sensor is consisted of the self-emitted component directly from the target surface, the reflected component of the solar irradiance at the target surface, and the scattered component by the atmosphere without ever reaching the object surface. The self-emitted radiance from a surface can be calculated by using the temperature and optical characteristics of the surface together with the spectral atmospheric transmittance. The reflected radiance can be calculated by using the BRDF model. MODTRAN4 is used to model the scattered radiance by the atmosphere, and the solar radiation including the direct and diffuse solar energy components. In this paper, the infrared signatures received by a remote sensor are computed by using the spectral transmittances obtained for different sensor positions and for different surface materials.

Estimation of the Properties for a Charring Material Using the RPSO Algorithm

Fire characteristics can be analyzed more realistically by using more accurate properties related to the fire dynamics and one way to acquire these fire properties is to use one of the inverse property estimation techniques. In this study two optimization algorithms which are frequently applied for the inverse heat transfer problems are selected to demonstrate the procedure of obtaining pyrolysis properties of charring material with relatively simple thermal decomposition. Thermal decomposition is occurred at the surface of the charring material heated by receiving the radiative energy from external heat sources and in this process the heat transfer through the charring material is simplified by an unsteady 1-dimensional problem. The basic genetic algorithm(GA) and repulsive particle swarm optimization(RPSO) algorithm are used to find the eight properties of a charring material; thermal conductivity(virgin, char), specific heat(virgin, char), char density, heat of pyrolysis, pre-exponential factor and activation energy by using the surface temperature and mass loss rate history data which are obtained from the calculated experiments. Results show that the RPSO algorithm has better performance in estimating the eight pyrolysis properties than the basic GA for problems considered in this study.

Narrow band radiative solutions within a cubical enclosure filled with real gas mixtures

Radiative transfer by nongray gas mixtures with nonuniform concentration and temperature profiles is studied by using the statistical narrow-band model and the ray-tracing method with the sufficiently accurate T60 quadrature set. Transmittances through the nonhomogeneous gas mixtures are calculated by using the Curtis-Godson approximation. Three different cases with different temperature and concentration profiles are considered to obtain benchmark solutions for the radiative transfer by nongray gas mixtures. The solutions obtained from this study are verified and found to be very well matched with the previous solutions for uniform gas mixtures. The results presented in this paper can be used as benchmark solutions in developing various solution methods for radiative transfer by nongray gas mixtures.

Study on spectral transmission characteristics of the reflected and self-emitted radiations through the atmosphere

This paper is a part of developing a software that predicts spectral radiance from ground objects by considering spectral surface properties. The material surface properties are essential for determining the reflected radiance by solar energy and the self-emitted radiance from the object surface. We considered the composite heat transfer modes including conduction, convection and spectral solar irradiation for objects within a scene to calculate the surface temperature distribution. The software developed in this study could be used to model the thermal energy balance to obtain the temperature distribution over the object by considering the direct and diffuse solar irradiances and by assuming the conduction within the object as one-dimensional heat transfer into the depth. MODTRAN is used to model the spectral solar irradiation including the direct and diffuse solar energy components. Resulting spectral radiance in the MWIR (3~5 mum) region and LWIR (8~12 mum) regions arrived at the sensor are shown to be strongly dependent on the spectral surface properties of the objects.

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

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.

Spot size converter integrated semiconductor optical amplifier

Spot size converter (SSC)-SOA consists of a slightly tensile bulk 0.2 /spl mu/m thick InGaAsP (/spl lambda/=1.55 /spl mu/m) active layer and 0.1 /spl mu/m thick InGaAsP (/spl lambda/=1.3 /spl mu/m) waveguides, which were grown by selective area growth (SAG) using MOCVD to implement SSC. The total device length is 1500 /spl mu/m. The thickness enhancement factor was greater than 3 by using SiO/sub 2/ mask. The SAG method with lateral tapering technique provided a typical beam divergences of 8/spl deg//spl times/15/spl deg/. To reduce facet reflectivity, window regions of 20 /spl mu/m length were introduced and the waveguides were tilted by 7/spl deg/. Both facets were antireflection coated to minimize the reflection from the cleaved facet. The gain measurement was done by coupling lensed fibers to both sides. To obtain the higher coupling efficiency in SOA module, taper lensed fiber with AR coating were used. Larger than 22 dB of the fiber to fiber gain was obtained for -20 dBm input power and 150 mA at 1540 nm.

Study on Infrared Image Generation for Different Surface Conditions with Different Sensor Resolutions

This paper is a foundation work in developing a software for generating infrared images from a scene with various objects. The spectral radiance receiv ed by a remote sensor is consisted of the self-emitted, reflected and scattered components. In general, the self-emitted component is the most important part for generating Infrared signatures from the object. In this paper, the infrared image generation considering various surface temperature and optical surface property of a flat plate is demonstrated in MWIR(3~5μm) and LWIR(8~12μm) regions for different spatial resolutions of the images. Resulting spectral radiance values in the MWIR(3~5μm) and LWIR(8~12μm) regions arrived at the infrared sensor are compared numerically and graphically by recognizing that they are strongly dependent on the surface conditions such as the surface tempera ture and the surface emissivity. And these infrared images are also shown to be strongly dependent on the resolutions of the infrared imaging devices as well. This study reveals that the surface conditions are more dependent on the radiance level from the surface while the resolution of the imaging device is more responsible for identifying the shape of object.

Study on the spectral transmission characteristics of MWIR through the atmosphere

This paper is a part of developing a software that predicts surface emitted radiance from ground objects by considering solar irradiation and atmospheric convection. The radiance emitted from a surface can be calculated by using the temperature and optical characteristics of the surface together with the spectral atmospheric transmittance. The thermal modeling is essential for identifying objects on the scenes obtained from the satellites. And the temperature distribution on the object is used to obtain their infrared images in contrast to the background. We considered the composite heat transfer modes including conduction, convection and spectral solar radiation for objects within a scene to calculate the surface temperature distribution. The software developed in this study could be used to model the thermal energy balance to obtain the temperature distribution over the object by considering the direct and diffuse solar irradiances and by assuming the conduction within the object as one-dimensional heat transfer into the depth. LOWTRAN7 are used to model the spectral solar radiation including the direct and diffuse solar energy components. The object considered is assumed to be consisted of several different materials with different properties, such as conductivity, absorptivity, density, and specific heat etc. Resulting spectral radiances in the MWIR region arrived at the sensor are shown to be strongly dependent on the spectral surface properties of the objects.

Study on inverse estimation of radiative properties from directional radiances by using statistical RPSO algorithm

Infrared signals are widely used to discriminate objects against the background. Prediction of infrared signal from an object surface is essential in evaluating the detectability of the object. Appropriate and easy method of procurement of the radiative properties such as the surface emissivity, bidirectional reflectivity is important in estimating infrared signals. Direct measurement can be a good choice but a costly and time consuming way of obtaining the radiative properties for surfaces coated with many different newly developed paints. Especially measurement of the bidirectional reflectivity usually expressed by the bidirectional reflectance distribution function (BRDF) is the most costly job. In this paper we are presenting an inverse estimation method of the radiative properties by using the directional radiances from the surface of concern. The inverse estimation method used in this study is the statistical repulsive particle swarm optimization (RPSO) algorithm which uses the randomly picked directional radiance data emitted and reflected from the surface. In this paper, we test the proposed inverse method by considering the radiation from a steel plate surface coated with different paints at a clear sunny day condition. For convenience, the directional radiance data from the steel plate within a spectral band of concern are obtained from the simulation using the commercial software, RadthermIR, instead of the field measurement. A widely used BRDF model called as the Sandford-Robertson(S-R) model is considered and the RPSO process is then used to find the best fitted model parameters for the S-R model. The results obtained from this study show an excellent agreement with the reference property data used for the simulation for directional radiances. The proposed process can be a useful way of obtaining the radiative properties from field measured directional radiance data for surfaces coated with or without various kinds of paints of unknown radiative properties.

Study on inverse estimation of radiative reflection properties in mid-wavelength infrared region by using the repulsive particle swarm optimization algorithm.

In this study, we develop software that estimates radiative properties of painted surfaces in the mid-wavelength infrared (MWIR) region inversely from the measured temperature and radiance variations with time by applying the repulsive particle swarm optimization algorithm. In this study the radiance in the MWIR region and surface temperature are obtained from a commercial software considering winter weather, and these results are used to estimate radiative reflection properties. Surface radiative reflection properties for three different paints are estimated by using the predetermined radiance in the MWIR region and surface temperature. This finding suggests that the process for obtaining surface radiative properties proposed in this study could be a useful way to obtain infrared signatures from objects with various surface coatings of unknown radiative properties.