• Title, Summary, Keyword: techniques: interferometric

Search Result 50, Processing Time 0.039 seconds

INTERFEROMETRIC MONITORING OF GAMMA–RAY BRIGHT ACTIVE GALACTIC NUCLEI II: FREQUENCY PHASE TRANSFER

  • ALGABA, JUAN-CARLOS;ZHAO, GUANG-YAO;LEE, SANG-SUNG;BYUN, DO-YOUNG;KANG, SIN-CHEOL;KIM, DAE-WON;KIM, JAE-YOUNG;KIM, JEONG-SOOK;KIM, SOON-WOOK;KINO, MOTOKI;MIYAZAKI, ATSUSHI;PARK, JONG-HO;TRIPPE, SASCHA;WAJIMA, KIYOAKI
    • Journal of The Korean Astronomical Society
    • /
    • v.48 no.5
    • /
    • pp.237-255
    • /
    • 2015
  • The Interferometric Monitoring of Gamma–ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma–ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence time at the higher frequencies of this program (86 and 129 GHz) and image additional sources that were not detected using standard techniques. We find that this method is applicable to the iMOGABA program even under non–optimal weather conditions.

The high accurate monitoring technique of land deformation by using satellite image - PSInSAR -

  • Mizuno Toshimi;Kuzuoka Shigeki
    • 한국지구물리탐사학회:학술대회논문집
    • /
    • /
    • pp.305-312
    • /
    • 2003
  • Remote sensing can provide invisible information in addition to acquire wide-view image data from space. Synthetic Aperture Radar (SAR) transmits microwave to the earth from a satellite and collects the reflected echo from the surface. Interferometric processing of SAR data can detect the subtle land deformation. The information of the surface movement by SAR is useful to monitor the volcanic activity, extended subsidence of urbanized area and the prediction of the earthquake caused by crustal deformation, and it complements the conventional levelling and GPS technique. PSInSAR (Permanent Scatterers Interferometric SAR) is one of interferometric techniques to be applied to practical projects in Japan. In this paper, the projects of land deformation monitoring are shown after the explanations of the PSInSAR principle. Tokai earthquake risk assessment is the first example. PSInSAR detects the subduction of crustal deformation of the adjacent area of new assumed epicenter region of the Tokai Earthquake. The extended subsidence of the urbanized area was implemented by using Japanese satellite data i.e. JERS that has so much data the surrounding of Japan as the archive. We examine the relationship between the geological structure and settlement at Nohbi basin including Nagoya city.

  • PDF

Assessment of DEM Generated by Stereo C-band and X-band SAR images using Radargrammetry (Radargrammetry를 이용한 C-밴드 및 X-밴드 SAR 위성영상의 DEM 생성 평가)

  • Song, Yeong Sun;Kim, Gi Hong
    • Journal of Korean Society for Geospatial Information Science
    • /
    • v.21 no.4
    • /
    • pp.109-116
    • /
    • 2013
  • To extract the 3D geometric information from SAR(Synthetic Aperture Radar) images, two different techniques, interferometric SAR and radargrammetry, have been widely used. InSAR is most widely used for the generation of precise DEM(Digital Elevation Model) until now. But, Interferometric SAR requires severe temporal correlation over areas covered with vegetation and high relief areas. Because radargrammetry is less sensible to temporal correlation, it can provide better results than interferometric SAR in certain, especially X-band SAR. In this paper, we assess the properties of DEMs generated by radargrammetry using stereo C-band RADARSAT-1 images and X-band TerraSAR-X images.

VLBI MEASUREMENT OF WEAK SOURCES WITH IMPROVED SENSITIVITY

  • SHU, FENGCHUN;JIANG, WU
    • Publications of The Korean Astronomical Society
    • /
    • v.30 no.2
    • /
    • pp.651-653
    • /
    • 2015
  • Compared with traditional analog system, the Chinese VLBI Data Acquisition System (CDAS) is a digital one with better bandpass and wider bandwidth which allow weaker sources to be detected and measured by VLBI techniques. After optimizing and verifying the performance of CDAS in wide bandwidth observing mode, we performed an experiment by observing 85 weak sources along the ecliptic with Chinese VLBI stations located at Shanghai, Kunming and Urumqi. The capability of CDAS has been demonstrated for the detection of weak sources with improved sensitivity.

EHT data processing and BH shadow imaging techniques

  • Cho, Ilje
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.44 no.1
    • /
    • pp.59.2-59.2
    • /
    • 2019
  • Event Horizon Telescope (EHT) aims to resolve the innermost region to the super massive black hole (SMBH) with its extremely high angular resolution (~20-25 uas) and enhanced sensitivity (down to 1-10 mJy) in concert with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm wavelength. This has a great importance as the first observational probe of the black hole shadow which has been theoretically predicted as a ring-like emission affected by the general relativistic effect under a strong gravitational field of SMBH. During the 2017 April 5-11, four nights of EHT observing campaign were carried out towards its primary targets, M87 and $SgrA{\ast}$. To robustly ensure the data processing, independent pipelines for various radio data calibration softwares (e.g., AIPS, HOPS, CASA) have been developed and cross-compared each other. The EHT has also been developing newer interferometric imaging techniques (e.g., eht-imaging-library, SMILI, dynamical imaging), as well as using an established method (CLEAN). With these, the EHT has designed various strategies which will be adopted for convincing imaging results. In this talk, I review how the robustness of EHT data processing and imaging will be validated so that the results can be ensured against well known uncertainties or biases in the interferometric data calibration and imaging.

  • PDF

SUBSIDENCE AT DUK-PO AREA REVEALED BY DINSAR AND INTERFEROGRAM STACKING

  • Hong, Sang-Hoon;Kim, Sang-Wan;Won, Joong-Sun
    • Proceedings of the KSRS Conference
    • /
    • /
    • pp.308-311
    • /
    • 2002
  • Radar interferometric phase is sensitive to both ground topography and coherent surface displacement. The basic tactics of differential interferometric synthetic aperture radar (DInSAR) technique are to separate the two effects. Applications of DInSAR to Duk-Po area in Busan were studied. In the study area, an abrupt subsidence, possibly caused by sub-way construction, was observed by JERS-1 SAR interferometry. Differential interferograms were generated using twenty-three JERS-1 SAR data acquired between April 24, 1992, and August 7, 1998. Because the area is relatively flat with little topographic relief the topographic effects were not removed. A phase filtering and interferogram techniques were applied to increase fringe clarity as well as to decrease decorrelation error. The stacking improves the quality of interferograms especially when the displacement is discontinuous. The interferograms clearly show the evidence of subsidence along Duk-Po subway railroad. These results demonstrate that the interferogram stacking technique can improve the detectability of radar interferometry to an abrupt displacement and DInSAR is useful to geological engineering applications.

  • PDF

SIMULATION OF COSMIC MICROWAVE BACKGROUND POLARIZATION FIELDS FOR AMiBA EXPERIMENT

  • PARK CHAN-GYUNG;PARK CHANGBOM
    • Journal of The Korean Astronomical Society
    • /
    • v.35 no.2
    • /
    • pp.67-73
    • /
    • 2002
  • We have made a topological study of cosmic microwave background (CMB) polarization maps by simulating the AMiBA experiment results. A ACDM CMB sky is adopted to make mock interferometric observations designed for the AMiBA experiment. CMB polarization fields are reconstructed from the AMiBA mock visibility data using the maximum entropy method. We have also considered effects of Galactic foregrounds on the CMB polarization fields. The genus statistic is calculated from the simulated Q and U polarization maps, where Q and U are Stokes parameters. Our study shows that the Galactic foreground emission, even at low Galactic latitude, is expected to have small effects on the CMB polarization field. Increasing survey area and integration time is essential to detect non-Gaussian signals of cosmological origin through genus measurement.

SPATIO-SPECTRAL MAXIMUM ENTROPY METHOD: II. SOLAR MICROWAVE IMAGING SPECTROSCOPY

  • Bong, Su-Chan;Lee, Jeong-Woo;Gary Dale E.;Yun Hong-Sik;Chae Jong-Chul
    • Journal of The Korean Astronomical Society
    • /
    • v.38 no.4
    • /
    • pp.445-462
    • /
    • 2005
  • In a companion paper, we have presented so-called Spatio-Spectral Maximum Entropy Method (SSMEM) particularly designed for Fourier-Transform imaging over a wide spectral range. The SSMEM allows simultaneous acquisition of both spectral and spatial information and we consider it most suitable for imaging spectroscopy of solar microwave emission. In this paper, we run the SSMEM for a realistic model of solar microwave radiation and a model array resembling the Owens Valley Solar Array in order to identify and resolve possible issues in the application of the SSMEM to solar microwave imaging spectroscopy. We mainly concern ourselves with issues as to how the frequency dependent noise in the data and frequency-dependent variations of source size and background flux will affect the result of imaging spectroscopy under the SSMEM. We also test the capability of the SSMEM against other conventional techniques, CLEAN and MEM.

VLBI STUDIES OF Sgr A*

  • SHEN ZHI-QIANG
    • Journal of The Korean Astronomical Society
    • /
    • v.38 no.2
    • /
    • pp.261-266
    • /
    • 2005
  • This paper reviews the progress in the VLBI (Very Long Baseline Interferometry) studies of Sgr A$\ast$, the best known supermassive black hole candidates with a dark mass concentration of $4 {\times} 10^6 M_{\bigodot}$ at the center of the Milky Way. The emphasis is on the importance of the millimeter and sub-millimeter VLBI observations in the detection of Sgr A$\ast$'s intrinsic structure and search for the structural variation.

THE LONG BASELINE ARRAY

  • EDWARDS, PHILIP G.;PHILLIPS, CHRIS
    • Publications of The Korean Astronomical Society
    • /
    • v.30 no.2
    • /
    • pp.659-661
    • /
    • 2015
  • The Long Baseline Array is an array of radio telescopes using the technique of Very Long Baseline Interferometry to achieve milli-arcsecond-scale angular resolution. The core telescopes are located in Australia, with telescopes in New Zealand and South Africa also participating regularly. In this paper the capabilities of the Long Baseline Array are described, and examples of the science undertaken with the array are given.