• 제목/요약/키워드: polarimetry

검색결과 69건 처리시간 0.025초

The polarimetric study of (331471) 1984QY1: an asteroid in comet-like orbit

  • Kim, Jooyeon;Ishiguro, Masateru;Bach, Yoonsoo P.;Kuroda, Daisuke;Naito, Hiroyuki;Kim, Yoonyoung;Kwon, Yuna G.;Imai, Masataka;Kuramoto, Kiyoshi;Watanabe, Makoto
    • 천문학회보
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    • 제42권2호
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    • pp.50.2-50.2
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    • 2017
  • Spatial distribution of atmosphereless bodies in the solar system provides an important clue as to their origins, namely asteroids from Mainbelt or comets from outer solar system. It is, however, difficult to distinguish asteroids and dormant comets due to their similar appearances. In this study, we conducted a unique observation to differentiate asteroids and dormant comets in terms of 'polarimetry'. We observed (331471) 1984 QY1 (hereafter QY1) at large phase angles using the Multi-Spectral Imager (MSI) on the 1.6-m Pirka Telescope from UT 2016 May 25 to June 24. QY1 is a dormant comet candidate in terms of the dynamical properties (i.e. the Tisserand parameter with respect to Jupiter, TJ = 2.68). We analyzed the polarization degree of QY1 as a function of phase angle and found its maximum polarization degree, $Pmax=8.68{\pm}0.28%$ and $8.72{\pm}0.38%$, in RC-and V-band, respectively, around the phase angle of ${\alpha}=100^{\circ}$. In addition, we obtained the geometric albedo, $pV=0.16{\pm}0.02$ by means of an empirical slope-albedo law. The polarimetric properties and the albedo value we acquired are similar to those of S-type asteroids rather than cometary nuclei. In this presentation, we introduce our observation and findings. In addition, we further discuss a dynamical transportation process from Mainbelt to the current orbit.

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다편광 SAR 자료를 이용한 조간대 표면 퇴적물에서의 마이크로파 산란 특성 연구 (A study on microwave scattering characteristics in intertidal flats using polarimetric SAR)

  • 박상은;김덕진;문우일
    • 한국지구물리탐사학회:학술대회논문집
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    • 한국지구물리탐사학회 2006년도 공동학술대회 논문집
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    • pp.271-276
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    • 2006
  • 이 논문에서는 다편광 Synthetic Aperture Radar (PolSAR) 관측값을 이용하여 남해안 여자만의 조간대 표면 퇴적물에 대한 지구물리학적 특성에 대한 연구를 실시하였다. 원격 탐사를 이용한 조간대 지역의 연구는 종래의 야외 조사를 통한 연구 방법의 한계를 보완할 수 있으며 특히 다편광 SAR 자료는 주 야 및 기상 상태와 관계 없이 지구 표면의 지구물리학적 정보를 정량적으로 획득 할 수 있다. 이 연구를 위하여 사용된 여자만 지역의 다편광 AIRSAR 자료는 2000 년 9 월 30 일 NASA/JPL PACRIM-II 프로젝트를 통해 획득되었다. AIRSAR 자료의 다편광 정보를 이용한 마이크로파의 산란모델을 바탕으로 조간대 지역의 표면퇴적물에서의 마이크로파 산란 특성을 연구하였다.

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PAGAN I: MULTI-FREQUENCY POLARIMETRY OF AGN JETS WITH KVN

  • KIM, JAE-YOUNG;TRIPPE, SASCHA;SOHN, BONG WON;OH, JUNGHWAN;PARK, JONG-HO;LEE, SANG-SUNG;LEE, TAESEOK;KIM, DAEWON
    • 천문학회지
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    • 제48권5호
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    • pp.285-298
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    • 2015
  • Active Galactic Nuclei (AGN) with bright radio jets offer the opportunity to study the structure of and physical conditions in relativistic outflows. For such studies, multi-frequency polarimetric very long baseline interferometric (VLBI) observations are important as they directly probe particle densities, magnetic field geometries, and several other parameters. We present results from first-epoch data obtained by the Korean VLBI Network (KVN) within the frame of the Plasma Physics of Active Galactic Nuclei (PAGaN) project. We observed seven radio-bright nearby AGN at frequencies of 22, 43, 86, and 129 GHz in dual polarization mode. Our observations constrain apparent brightness temperatures of jet components and radio cores in our sample to > 108.01 K and > 109.86 K, respectively. Degrees of linear polarization mL are relatively low overall: less than 10%. This indicates suppression of polarization by strong turbulence in the jets. We found an exceptionally high degree of polarization in a jet component of BL Lac at 43 GHz, with mL ~ 40%. Assuming a transverse shock front propagating downstream along the jet, the shock front being almost parallel to the line of sight can explain the high degree of polarization.

Revealing the Powering Mechanism of Lyman Alpha Blob via Polarization

  • Kim, Eunchong;Yang, Yujin;Zabludoff, Ann;Smith, Paul;Jannuzi, Buell;Lee, Myung Gyoon
    • 천문학회보
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    • 제43권1호
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    • pp.35.4-36
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    • 2018
  • $Ly{\alpha}$ blobs are mysterious, giant (~100 kpc), glowing gas clouds in the distant universe. They occupy the dark matter halos that will evolve into the richest groups and clusters today. The blob's gas may be the proto-intracluster medium and their embedded galaxies are considered as the progenitors of massive cluster galaxies. Yet we do not know why $Ly{\alpha}$ blobs glow. There are evidences of kinematic measurements to exclude shocks and winds from AGN or starbursts as a power source, suggesting that photoionizing radiation or scattering of $Ly{\alpha}$ photons might be responsible. Polarization mapping can discriminate between these photo-ionization and scattering. Previous results of imaging polarimetry for $Ly{\alpha}$ nebulae are roughly consistent with scattering models. However the polarization morphologies in those of previous results are all different, motivating our polarimetric survey of $Ly{\alpha}$ nebulae for the statisticallymeaningful sample. As initial results of our survey, we present the total polarization map of the LABd05 which has the spatial offset between the peak of $Ly{\alpha}$ surface brightness and an obscured AGN. We detect the significant polarization in this target with the radially increasing polarization gradient, suggesting that scattering plays major role within this nebula. The polarization pattern is more aligned with the $Ly{\alpha}$ peak rather than the AGN (the potential energy source), indicating that the $Ly{\alpha}$ photons are originated from the region near the peak of $Ly{\alpha}$ intensity.

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북한 학술지에 실린 태양 연구 활동 분석 (ANALYSIS OF SOLAR RESEARCH ACTIVITIES PUBLISHED IN NORTH KOREAN JOURNALS)

  • 김수진;양홍진;정종균;임인성
    • 천문학논총
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    • 제36권2호
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    • pp.37-45
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    • 2021
  • We have analyzed 42 research papers regarding on the solar astronomy written by North Korea scientists to investigate the current status of astronomical activities in North Korea. The papers are surveyed from the 'Bulletin of Astronomy', the 'Physics', the 'Bulletin of Academy of Science', and the 'Natural Science' in North Korea, and SCI journals. In addition, we refer to the presentation material announced in the 2015 IAU by director of Pyongyang Astronomical Observatory (PAO) and the 2013 OAD/IAU reports. We have analyzed the papers statistically according to three criteria such as research subject, research field, and research members. The main research subjects are the sunspot (28%), observation system (21%), and space environments (19%). The research fields are distributed with data analysis (50%), numerical method (29%), and instrument development (21%). There have been 25 and 9 researchers in the solar astronomy and space environment, respectively since 1995. North Korea's solar research activities were also investigated in three area: instrument, solar physics, and international research linkage. PAO has operated two of sunspot telescope and solar horizontal telescope for spectroscopy and polarimetry, but there is no specific information on solar radio telescopes. North Korea has cooperated in solar research with Europe and China. We expect that the results of this study will be used as useful resource in supporting astronomical cooperation between South and North Korea in the future.

SAR(Synthetic Aperture Radar) 위성 개발현황 및 향후 HRWS(High Resolution Wide Swath) SAR 위성 개발전략 (Current Trends of the Synthetic Aperture Radar (SAR) Satellite Development and Future Strategy for the High Resolution Wide Swath (HRWS) SAR Satellite Development)

  • 고웅대;서인호;이주영;정현재
    • 우주기술과 응용
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    • 제1권3호
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    • pp.337-355
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    • 2021
  • 본 논문은 SAR 위성 기술의 현황을 조사하여 향후 우리나라 HRWS SAR (High Resolution Wide Swath Synthetic Aperture Radar) 위성을 개발하기 위한 전략을 제안하기 위해 만들어졌다. 현황조사를 통해, 최신 SAR 기술 동향은 SAR 위성 영상을 보다 적극적으로 활용하기 위해 DBF(Digital Beam-Forming), SCORE(SCan-On-REceive), DPCA(Displaced Phase Center Antenna), 간섭계, 그리고 편파 기술을 사용하는 것이라는 것을 알 수 있었다. 이와 같은 최신 SAR 기술 동향 및 해외 HRWS SAR 개발 사례를 기반으로, 수년 내로 발사가 예정된 KOMPSAT-6(KOrea Multi-Purpose SATellite-6)를 사용하여 DPCA 및 SCORE 기술을 개발하고, 결국에는 전지구를 일주일 간격으로 관측할 수 있는 HRWS SAR 위성을 개발하는 것을 향후 우리나라 HRWS SAR 위성 개발을 위한 전략으로 제안하였다.

이중 편파 Sentinel-1 SAR 영상의 편파 지표를 활용한 인공지능 기반 선박 탐지 (Exploitation of Dual-polarimetric Index of Sentinel-1 SAR Data in Vessel Detection Utilizing Machine Learning)

  • 송주영;김덕진;김준우;이성뢰
    • 대한원격탐사학회지
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    • 제38권5_2호
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    • pp.737-746
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    • 2022
  • 전천후 자료 취득이 가능한 SAR 영상을 기반으로 한 선박 탐지와 인공지능 기반 탐지 알고리즘과 함께 사용하는 것은 안정적인 선박 모니터링에 효과적이다. 기존의 SAR 영상에서는 인공지능 기반 선박 탐지 알고리즘에 진폭 영상만을 주로 사용하였으며, 물체의 산란 특성을 구분할 수 있는 다중 편파 SAR 영상의 편파 지표는 사용되지 않았다. 이에, 본 연구에서는 이중 편파 Sentinel-1 SAR 영상으로부터 고유값 분해를 통해 취득한 4개의 편파 지표인 H, p1, DoP, DPRVI와 방사 보정을 통해 취득한 2개 편파의 산란계수인 γ0, VV, γ0, VH를 이용하여 총 6개의 밴드를 가진 SAR 영상 52장의 데이터베이스를 구축하고, 이와 상응하는 시간에 취득한 선박의 실시간 위치 및 속도 정보인 AIS 자료를 사용하여 학습자료를 추출하였다. 구축된 밴드 조합에 대해 선박탐지 정확도를 평가한 결과, 이중 편파 지표를 진폭과 함께 사용한 경우 진폭 값만을 사용했을 때에 비해 개선된 탐지 정확도를 보였다.

편광을 통한 수화한 소행성 연구 (Study of Hydrated Asteroids via Polarimetry: Correlation between Polarimetric Properties and the Degree of Aqueous Alteration of Hydrated asteroids)

  • 김주연
    • 천문학회보
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    • 제46권1호
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    • pp.46.1-46.1
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    • 2021
  • Hydrated asteroids get widespread attention for the evolution of water in the Solar System, especially thanks to the recent successes of the Hayabusa2 and OSIRIS-REx space missions. The target asteroids of these missions are believed to be fragments that have experienced aqueous alteration in their parent bodies [3]. Although hydrated asteroids have been studied well via spectroscopy, focusing on the 0.7 um or the 2.7 um absorption bands [2, 3, 4], polarimetric properties of these asteroids have rarely been investigated. In this study, we conducted a polarimetric observation of 18 C-complex main-belt asteroids with the 1.6-m Pirka telescope at the Nayoro Observatory of Hokkaido University, Japan. We used a polarimetric imaging mode of the Multi-Spectral Imager (MSI) with the standard Rc-band filter (the central wavelength at 0.64 um) [5]. As a result, we found that all of these hydrated asteroids indicate deep negative branches of their polarimetric profiles. Accordingly, the hydrated asteroids have the polarization minima (Pmin), whose values are significantly lower than any other taxonomic types of asteroids (including C-group asteroids). Because Pmin depends on albedo, particle size, and porosity of the surface materials [1], we suspect that hydrated asteroids are distinctive from other asteroids in terms of these physical properties. In this presentation, we introduce our polarimetric observation and findings. We discuss why hydrated asteroids indicate such low Pmin values, comparing Pmin with spectral features at 0.7 um and 2.7 um based on the observation results.

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Polarimetry of solar system small bodies using the Seoul National University 61cm telescope and TRIPOL

  • Jin, Sunho;Ishiguro, Masateru;Kwon, Yuna Grace;Geem, Jooyeon;Bach, Yoonsoo P.;Seo, Jinguk;Sasago, Hiroshi;Sato, Shuji
    • 천문학회보
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    • 제44권1호
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    • pp.64.2-64.2
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    • 2019
  • It is known that lights scattered by comets and asteroids are partially polarized. From polarimetric observations of those objects, we can investigate physical properties, such as albedos, sizes of cometary dust particles and regolith of asteroids. Since the polarization degrees of those objects highly depend on their phase angles (Sun-object-observer's angles), long-term monitoring observations are required. Moreover, comets show unforeseeable activations (i.e., outbursts) which need follow-up observations to understand the mechanism. In order to realize such monitoring and transient observations, we installed the Triple-Range Imager and POLarimeter (TRIPOL) on the 61cm telescope of Seoul National University (Hereafter, SNU) Gwanak campus. With this combination, we can obtain g', r', i' bands photopolarimetric images simultaneously with $8.0^{\prime}{\times}8.0^{\prime}$ field of view and pixel resolution of 0.94" pixel-1. Here, we make a presentation regarding the photometric and polarimetric performances of TRIPOL on the SNU 61cm telescope. In addition, we introduce initial polarimetric results of asteroid and comets with the instruments. First, we determine the limiting magnitudes (defined as magnitudes for S/N=5) of $15.17{\pm}0.06$ (g'-band), $15.68{\pm}0.01$ (r'-band), $16.24{\pm}0.03$ (I'-band), respectively, with total 240-seconds exposure (four 60-seconds exposure images, each was taken at different rotation angle for the half-wave plate). Second, we found that the instrumental polarization is negligibly small, ($-0.32{\pm}0.04%$ in the g', $-0.36{\pm}0.05%$ in the r' and $-0.21{\pm}0.04%$ in the i'-bands), while the polarization efficiencies are large enough to maximize the performance (i.e., $97.52{\pm}0.03%$ in the g', $98.83{\pm}0.02%$ in the r' and $99.15{\pm}0.02%$ in the i'-bands). With the instruments, we made observations of three Jupiter-family comets, 21P/Giacobini-Zinner, 38P/Stephan-Oterma, and 46P/Wirtanen and plan to observe one near-Earth asteroid, (433) Eros, on a trial basis. Especially for comets, we discriminate signals from dust and gas to eliminate gas contamination, which are known to change observed degree of linear polarization, using multi-band images. We confirm that the phase angle dependency of these comets are consistent with previous observations, probably because polarimetric property of Jupiter-family comets are broadly homogeneous unlike asteroids. We will also describe future observation plans using TRIPOL and SNU 61cm telescope.

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