김석환 교수

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750 and 1750-2800) will range from an all-sky survey (limit m AB ~20-21) to an ultra-deep survey of 4 square degrees (limit m AB ~26). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (m AB ~20-25) and sky coverage (100 to 2 square degrees) over the 1350-2800 b

In order to investigate the origin of the far-UV (FUV) flux from the early-type galaxies, the Galaxy Evolution Explorer is collecting the UV data for the elliptical-rich clusters at moderate redshifts (z<0.2) where the dominant FUV source is predicted to be hot horizontal-branch (HB) stars and their post-HB progeny. Here we present our first result for the early-type galaxies in A2670 at z=0.076. Compared to NGC 1399, a nearby giant elliptical galaxy in the Fornax Cluster, it appears that the re

The <i>Precessions</i> process for producing aspheric and other optical surfaces is undergoing rapid development. In this paper, we summarise the considerable success achieved in controlling the repeatability of the process on both the 200mm and 600mm machines, and illustrate this with examples of aspherics that have been produced. We particularly describe our approach to fine form-control. This has required the development of various strategies to moderate the volumetric removal rates, in order

Contributions of the JEM-EUSO Collaboration to the 32nd International Cosmic Ray Conference, Beijing, August, 2011.

Computer controlled polishing of large optics has required complex and expensive tooling, which is impractical at the smaller scale. This paper describes the simulation of a simple aspheric polishing regime using a large active lap, and its embodiment in a new generalized aspheric polishing machine for instrumentation optics.

Contrary to the academic interests of other existing studies elsewhere, this study deals with how the alignment algorithms such as sensitivity or Differential Wavefront Sampling (DWS) can be better used under effects from field, compensator positioning and environmental errors unavoidable from the shop-floor alignment work. First, the influences of aforementioned errors to the alignment state estimation was investigated with the algorithms. The environmental error was then found to be the domina

This paper outlines recent progress in a novel active fabrication technique for severely aspheric optics. The underlying technology has been initially developed at the Optical Science Laboratory (OSL), at University College London, and has been incorporated in the OSL full-size active lap, used for polishing large astronomical optics. Optical Generics Limited (OGL) and OSL are currently collaborating to further develop the technology. A prototype OGLP-400 computer controlled polishing machine ha

Earth-Sun-Heliosphere Interactions Experiments(EARTHSHINE) 미션의 주 탑재체인 Albedo Monitor and Radiometer(Amon-Ra) 광학계는 최초로 제1 라그랑제 지점(Lagrange point 1) 주위의 혜일로(Halo) 궤도에 위치하여 태양 복사 활동 및 지구 반사율 변화를 1% 정확도 이내로 측정함으로서 현존하는 지구 반사율 추이의 모순을 해결할 수 있는 과학적 측정 자료를 제시하는데 그 목적을 가지고 있다. 이에 이미 개발된 광학 성능 검증용 Amon-Ra 광학계의 가시광채널 시험 모델 및 광선 추적 기법을 이용한 통합적 광선 추적 end-to-end 과학 임무 성능 평가 수치 모사 기법을 확립하였으며, 개발된 기법을 이용하여 실제 제작된 Amon-Ra 광학계를 제1라그랑제 지점에 위치시키고 태양과 지구 밝기를 다양하게 변화시킨 후 광학계에 입사되는 에너지 복사량을 수치 모사로 측정하였다. 관측된 지구 및 태양

Contrary to the academic interests of other existing studies elsewhere, this study deals with how thealignment algorithms such as sensitivity or Differential Wavefront Sampling (DWS) can be better usedunder effects from field, compensator positioning and environmental errors unavoidable from the shop-flooralignment work. First, the influences of aforementioned errors to the alignment state estimation wasinvestigated with the algorithms. The environmental error was then found to be the dominant f

Continuous and accurate ceilometer measurements can provide the sky-condition such as cloud base height (CBH), cloud vertical structure (CVS), and cloud cover at around the sites of meteorological stations. In this study, ceilometer measurement data over a period of 3 years (January 2017 to December 2019) were analyzed to compare the characteristics of CBH at inland and coastal stations sharing the same climate characteristics in Korea. The annual averaged frequency of cloud occurrence between 0

After Geostationary Ocean Color Imager (GOCI) was launched at June 27th, 2010, it is operated to observe the Korean peninsula on the geostationary orbit as one of the three main payloads in COMS satellite. Generally, the performance indicators are Ground Sample Distance (GSD), Modulation Transfer Function (MTF), and Signal to Noise Ratio (SNR) that verify the optical performance of payload. Most of all, the MTF performance is widely used since it is closely related to reliability and accuracy of

The LAser raDAR (LADAR) system designed in this study shows a ghost pattern around the object image when operated. The system contains 4 wedge prisms, each with different rotational directions and speeds. Therefore, an efficient and thorough analysis method was established. Ray path analysis was performed, and categorized, for every instantaneous case sampled using a backward ray tracing method. The rays' flux and directions were accumulated according to their path histories. This backward ray t