• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.258-262
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• 2004

The uncertainty of the detector-based candela scale is limited by the area measurement uncertainty of radiometric apertures. The apertures were fabricated with a diamond-turning machine which trimmed the edge of the apertures as sharply as a knife edge. The positions of the apertures were controlled by a digital feedback algorithm to scan the laser spot with the beam waist less than 5 ${\mu}{\textrm}{m}$. The knife edge scan yielded a set of coordinates on the edges of the aperture. The areas of the apertures were obtained by fitting the coordinates to the ellipses. The relative standard uncertainty of the measurement was estimated to be 8${\times}$10$^{-5}$.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.22-25
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• 2008

Aperture synthesis with platform motion has been presented as a useful tool to achieve the high spatial resolution imaging. Using a motion induced synthetic aperture radiometer (MISAR), a passive microwave image can be achieved with a small number of antennas. Moreover, the MISAR is capable of imaging better than the case without motion, using the same configuration of antenna array. With a platform motion, visibility can be sampled more efficiently, and as a result the imaging performance of the MISAR shows higher quality than the case without platform motion. In this paper, the advantage of MISAR is demonstrated experimentally. Using a laboratory model of inteferometric radiometer, the point source images are obtained under the condition with platform motion and without platform motion. In the experimental results, the point source response of the MISAR shows better quality of sidelobe level and beam efficiency than the case without platform motion.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.6
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• pp.940-953
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• 2006

The major source of carbon monoxide (CO) at the Earth's surface is the incomplete combustion of biomass and fossil fuels. Because the global lifetime of CO is about two months, it can be used as a tracer for pollution from anthropogenic activities and biomass hurtling. In this paper, we introduced the principle and algorithm of the Measurement of Pollution in the Troposphere (MOPITT) instrument for global CO monitoring. The MOPITT instrument, which was launched on the Satellite Terra in 1999, measures CO column and mixing ratio based on gas correlation radiometry. CO levels can be determined by a retrieval algorithm based on the maximum likelihood method minimizing the difference between observed and modeled radiances. MOPITT level 2 data (HDF format) can be downloaded through the Earth Observing System (EOS) data gateway of NASA. ASCII files of CO parameters can be extracted from HDF files, and then temporal and spatial distributions can be obtained. Finally, we showed an example of CO monitoring in April 2000. The locations of forest fires and distribution of MOPITT CO clearly indicated that not only anthropogenic emissions but also forest fires play an important role in CO levels and global CO distribution. Our introduction to MOPITT and the example of MOPITT data interpretation would be helpful for scientists who want to use the EOS data.

• Archives of Craniofacial Surgery
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• v.16 no.1
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• pp.1-10
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• 2015

Facial symmetry is an important component of attractiveness. However, functional symmetry is favorable to aesthetic symmetry. In addition, fluctuating asymmetry is more natural and common, even if patients find such asymmetry to be noticeable. However, fluctuating asymmetry remains difficult to define. Several studies have shown that a certain level of asymmetry could generate an unfavorable image. A natural profile is favorable to perfect mirror-image profile, and images with canting and differences less than $3^{\circ}-4^{\circ}$ and 3-4 mm, respectively, are generally not recognized as asymmetry. In this study, a questionnaire survey among 434 medical students was used to evaluate photos of Asian women. The students preferred original images over mirror images. Facial asymmetry was noticed when the canting and difference were more than $3^{\circ}$ and 3 mm, respectively. When a certain level of asymmetry is recognizable, correcting it can help to improve social life and human relationships. Prior to any operation, the anatomical component for noticeable asymmetry should be understood, which can be divided into hard tissues and soft tissue. For diagnosis, two-and three-dimensional (3D) photogrammetry and radiometry are used, including photography, laser scanner, cephalometry, and 3D computed tomography.

• Proceedings of the Korean Society of Computer Information Conference
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• 2020.07a
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• pp.667-668
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• 2020

최근에는 범죄예방과 시설물 안전 및 출입관리, 화제예방 등 다양한 목적으로 감시카메라(CCTV)가 널리 보급되어 공공기관이나 상업시설 등 어느 곳에서나 찾을 수 있다. 이렇듯 많은곳에서 저마다의 이유로 사용되고 있는 감시카메라지만, 가장 흔하게 사용되는 이유는 범죄예방에 있다. 시설 내·외부에 감시카메라를 설치하여 도난사건 등을 사전에 방지하고 사후 증거확보에 유용하게 쓰일 수 있기 때문인데 문제는 감시카메라를 통해 사건을 사전에 방지하기 위해서는 실시간으로 사람이 카메라 영상을 지켜보고 있어야 한다. 하지만 사람이 항상 감시할수있을수는 없기 때문에 예방보다는 사후 증거확보를 위해 사용되는 실정이다. 즉 대부분의 감시카메라가 본래의 역할에 절반밖에 하지 못하고 있다는 것이다. 본 과제는 이러한 문제점을 해결하기 위해 감시카메라 자체의 기능을 추가하여 감시카메라가 인력을 필요로 하지않고 스스로 본래의 역할을 다할수있게 할 것이다.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.386-397
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• 2012

The stability and structure of bluff-body stabilized hydrogen flames were investigated numerically and experimentally. The velocity of coflowing air was varied from subsonic velocity to a supersonic velocity of Mach 1.8. OH PLIF images and Schlieren images were used for analysis. Flame regimes were used to classify the characteristic flame modes according to the variation of the fuel-air velocity ratio, into jet-like flame, central-jet-dominated flame, and recirculation zone flame. Stability curves were drawn to find the blowout regimes and to show the improvement in flame stability with increasing lip thickness of the fuel tube, which acts as a bluff-body. These curves collapse to a single line when the blowout curves are normalized by the size of the bluff-body. The variation of flame length with the increase in air flow rate was also investigated. In the subsonic coflow condition, the flame length decreased significantly, but in the supersonic coflow condition, the flame length increased slowly and finally reached a near-constant value. This phenomenon is attributed to the air-entrainment of subsonic flow and the compressibility effect of supersonic flow. The closed-tip recirculation zone flames in supersonic coflow had a reacting core in the partially premixed zone, where the fuel jet lost its momentum due to the high-pressure zone and followed the recirculation zone; this behavior resulted in the long characteristic time for the fuel-air mixing.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.216-219
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• 2004

In this study, the concept and techniques to generate the level lA, lB and 2A image products have been reviewed. In particular, radiometric and geometric corrections and bands registration used to generate level lA, lB and 2A products have been focused in this study. Radiometric correction is performed to take into account radiometric gain and offset calculated by compensating the detector response non-uniformity. And, in order to compensate satellite altitude, attitude, skew effects, earth rotation and earth curvature, some geometric parameters for geometric corrections are computed and applied. Bands registration process using the matching function between a geometry, which is called 'reference geometry', and another one which is corresponds to the image to be registered is applied to images in case of multi-spectral imaging mode. In order to generate level-lA image products, a simple radiometric processing is applied to a level-0 image. Level-lB image has the same radiometry correction as a level-lA image, but is also issued from some geometric corrections in order to compensate skew effects, Earth rotation effects and spectral misregistration. Level-2A image is generated using some geo-referencing parameters computed by ephemeris data, orbit attitudes and sensor angles. Level lA image is tested by visual analysis. The difference between distances calculated level 1 B image and distances of real coordinate is tested. Level 2A image is tested Using checking points.

• Korean Journal of Optics and Photonics
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• v.23 no.5
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• pp.179-188
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• 2012

Lenses with an ultra wide angle of view are usually called fisheye lenses since a fish can see an ultra wide panoramic view under water. As the angle of view for these kinds of lenses reaches a wide angle, the illumination on an image sensor is reduced by a rapid drop. In this paper, we discuss the causes and the ways to correct for a rapid drop. First, it is treated for the sign convention of directional cosine vectors and normal vectors on the curved surface by means of analytic geometry. And, from the fundamental discussion for these vectors, the rapid illumination drop is numerically analyzed for various kinds of causes by utilizing geometrical optics and radiometry as well as Fresnel equations derived from electromagnetic boundary conditions. As a result, we are able to get the full understanding for the rapid illumination drop and to propose ways to correct effects due to an wide angle of view.

• Imaging Science in Dentistry
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• v.37 no.3
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• pp.149-156
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• 2007

Purpose: The purpose of this study was to measure the absorbed dose and to calculate the effective dose for periapical radiography done by portable intraoral x-ray machines. Materials and Methods: 14 full mouth, upper posterior and lower posterior periapical radiographs were taken by wall-type 1 and portable type 3 intraoral x-ray machines. Thermoluminescent dosemeters were placed at 23 sites at the layers of the tissue-equivalent ART woman phantom for dosimetry. Average tissue absorbed dose and radiation weighted dose were calculated for each major anatomical site. Effective dose was calculated using 2005 ICRP tissue weighted factors. Results: On 14 full mouth periapical radiographs, the effective dose for wall-type x-ray machine was 30 Sv; for portable x-ray machines were 30 Sv, 22 Sv, 36 Sv. On upper posterior radiograph, the effective dose for wall-type x-ray machine was 4 Sv; for portable x-ray machines doses were 4 Sv, 3 Sv, 5 Sv. On lower posterior radiograph, the effective dose for wall type x-ray machine was 5 Sv; for portable x-ray machines doses were 4 Sv, 4 Sv, 5 Sv. Conclusion: Effective doses for periapical radiographs performed by portable intraoral x-ray machines were similar to doses for periapical radiographs taken by wall type intraoral x-ray machines.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.443-448
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• 2004

We realized the national standard of the candela, one of the SI units, by using two photometers with the spectral responsivity measured in reference to the absolute cryogenic radiometer. The external apertures of the photometers were fabricated using a diamond turning machine, and measured in terms of area with uncertainty of 0.05 %(k = 1). The candela is realized using a 1 kW FEL lamp and the characterized photometers on an optical bench. The uncertainty is budgeted to be 0.25 %(k = 1) considering the uncertainty of the spectral responsivity and the response uniformity of the detectors, the area of the external apertures, the color temperature of the lamp, and the positioning reproducibility of the photometers and the lamp. We verified the realized scale by comparing with the scale of National Institute of Standards and Technology, USA. They coincided with each other within 0.1%.