• Proceedings of the KSRS Conference
• /
• 2004.10a
• /
• pp.389-392
• /
• 2004

Classification of Earth natural components within a full polarimetric SAR image is one of the most important applications of radar polarimetry in remote sensing. In this paper, the unsupervised classification algorithms based on the combined use of the polarimetric processing technique such as the target decomposition and statistical complex Wishart classification method are evaluated and applied to vegetated terrain in Jeju volcanic island.

• Korean Journal of Remote Sensing
• /
• v.26 no.1
• /
• pp.1-7
• /
• 2010

This paper proposes a new decomposition technique for polarimetric synthetic aperture radar (SAR) images. This new decomposition technique is based on the degree of polarization (DoP) and co-polarized phase-difference (CPD) of the measured polarimetric backscattering coefficients. This decomposition technique is compared with the existing three- and four-component decomposition techniques with the ALOS PALSAR full polarimetric L-band data acquired in 2009. It is shown that the new decomposition technique is better or comparable to the existing techniques for the study areas such as sea, bare soil, forest, and urban area.

• Korean Journal of Remote Sensing
• /
• v.33 no.1
• /
• pp.47-60
• /
• 2017

The permafrost active layer plays an important role in permafrost dynamics. Ecological patterns, processes, and water and ice contents in the active layer are spatially and temporally complex depending on landscape heterogeneity and local-scale variations in hydrological processes. Although there has been emerging interest in the application of optical remote sensing techniques to permafrost environments, optical sensors are significantly limited in accessing information on near surface geo-cryological conditions. The primary objective of this study was to investigate capability of L-band SAR data for monitoring spatio-temporal variability of permafrost ecosystems and underlying soil conditions. This study exploits information from different polarimetric SAR observables in relation to permafrost environmental conditions. Experimental results show that each polarimetric radar observable conveys different information on permafrost environments. In the case of the dual-pol mode, the radar observables consist of two backscattering powers and one correlation coefficient between polarimetric channels. Among them, the dual-pol scattering powers are highly sensitive to freeze/thaw transition and can discriminate grasslands or ponds in thermokarst area from other permafrost ecosystems. However, it is difficult to identify the ground conditions with dual-pol observables. Additional backscattering powers and correlation coefficients obtained from quad-pol mode help understanding seasonal variations ofradar scattering and assessing geo-cryological information on soil layers. In particular, co-pol coherences atHV-basis and circular-basis were found to be very usefultools for mapping and monitoring near surface soil properties.

• Proceedings of the KSRS Conference
• /
• 2008.10a
• /
• pp.29-32
• /
• 2008

In this paper, we propose one unsupervised classification technique using the degree of polarization (DoP) and the co-polarized phase-difference (CPD) statistics, instead of the entropy and alpha. It is shown that the DoP is closely related to the entropy, and the CPD to the alpha. The DoP explains the feature how much the effect of multiple reflections is contained. Hence, the DoP could be used as an important factor for classifying classes. The CPD can also be computed from the measured Mueller matrix elements. For the smooth surface scattering, the CPD is about $0^{\circ}$, and for dihedral-type scattering, the CPD is about $180^{\circ}$. A DoP-CPD diagram with appropriate boundaries between six different classes is developed based on the SAR image. The classification results are compared with the existing Entropy-alpha diagram as well as the IPL-AirSAR polarimetric data. The technique may have capability to classify an SAR image into six major classes; a bare surface, a village, a crown-layer short vegetation canopy, a trunk-layer short vegetation canopy, a crown-layer forest, and a trunk-dominated forest. Based on the DoP and CPD analysis, a simple three-component decomposition technique was also proposed.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.51.2-51.2
• /
• 2018

Polarimetry is a powerful technique to investigate the physical properties of surface materials on airless bodies in the solar system. It is known that the degree of linear polarization changes as a function of the phase angle (the angle between Sun-target-Observer). Especially, the dependency of the polarization degree at large phase angle allows us to obtain information related to the particle size and porosity, which is difficult to be determined via other observation techniques (i.e., photometry and spectroscopy). However, despite the advantage, only a few asteroids were observed with polarimetric devices at large phase angles. Here, we present our new polarimetric research of Near-Earth Asteroids (NEAs) observed at the large phase angles. Among the NEAs, we focus on S- and Q-type asteroids, which include: (331471) 1984 QY1, (90075) 2002 VU94, and (66391) 1999 KW4. The observation was conducted using the Pirka 1.6-m Telescope at the Nayoro Observatory of Hokkaido University at the phase angles ${\alpha}{\sim}100degree$, which provides us the maximum polarization degrees of these objects. Considering the observational results together with two objects ((1566) Icarus and (4179) Toutatis) in reference papers [1], [2], we will discuss the implication of the regolith size on their surfaces.

• Journal of The Korean Astronomical Society
• /
• v.55 no.4
• /
• pp.87-97
• /
• 2022

Polarimetric measurements of the lunar surface from lunar orbit soon will be available via Wide-Field Polarimetric Camera (PolCam) onboard the Korea Pathfinder Lunar Orbiter (KPLO), which is planned to be launched in mid 2022. To provide calibration data for the PolCam, we are conducting speckle polarimetric measurements of the nearside of the Moon from the Earth's ground. It appears that speckle imaging of the Moon for scientific purposes has not been attempted before, and there is need for a procedure to create a "lucky image" from a number of observed speckle images. As a first step of obtaining calibration data for the PolCam from the ground, we search for the best sharpness measure for lunar surfaces. We then calculate the minimum number of speckle images and the number of images to be shift-and-added for higher resolution (sharpness) and signal-to-noise ratio.

• Journal of The Korean Astronomical Society
• /
• v.56 no.2
• /
• pp.293-299
• /
• 2023

The Wide-Angle Polarimetric Camera (PolCam) is installed on the Korea's lunar orbiter, Danuri, which launched on August 5, 2022. The mission objectives of PolCam are to construct photometric maps at a wavelength of 336 nm and polarization maps at 461 and 748 nm, with a phase angle range of 0°-135° and a spatial resolution of less than 100 m. PolCam is an imager using the push-broom method and has two cameras, Cam 1 and Cam 2, with a viewing angle of 45° to the right and left of the spacecraft's direction of orbit. We conducted performance tests in a laboratory setting before installing PolCam's flight model on the spacecraft. We analyzed the CCD's dark current, flat-field frame, spot size, and light flux. The dark current was obtained during thermal / vacuum test with various temperatures and the flat-field frame data was also obtained with an integrating sphere and tungsten light bulb. We describe the calibration method and results in this study.

• Journal of The Korean Astronomical Society
• /
• v.44 no.4
• /
• pp.135-142
• /
• 2011

A $200'{\times}200'$ region around 30 Doradus in the Large Magellanic Cloud (LMC) is observed and analyzed in the near-infrared. We obtain polarimetry data in the J, H, and Ks bands using the SIRIUS polarimeter SIRPOL at the Infrared Survey Facility 1.4 m telescope. We measure the Stokes parameters of 2562 point-like sources to derive the degree of polarization and the polarization position angles. We discuss the statistics of the groups classified by color-magnitude diagram and proper motions of the sources, in order to separate the Galactic foreground sources from those present in the LMC. We notice that groups classified by the proper motion data show a tendency towards different polarimetric properties.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.453-455
• /
• 2015

In this paper we introduce the Plasma Physics of Active Galactic Nuclei project, which is an ongoing experiment with Korean VLBI Network (KVN) and KVN and VERA Array (KaVA) to study multi-frequency polarimetric properties on parsec scales of active galaxies. The goal of the project is to improve our understanding of fundamental jet physics, especially evolution of the relativistic outflow coupled with the large-scale magnetic field. We selected six radio-loud AGN as our targets. So far we (i) detected resolved emissions regions at 86 and 129 GHz on VLBI scales, (ii) constructed 2D spectral index maps of the outflows, and (iii) found polarizations at 22 and 43 GHz for a few targets. Here we present spectral index distributions of 3C 120 between 22 and 43 GHz and a linear polarization map of BL Lac at 43 GHz obtained with KVN.

• Journal of The Korean Astronomical Society
• /
• v.48 no.5
• /
• pp.285-298
• /
• 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 > 10^8.01 K and > 10^9.86 K, respectively. Degrees of linear polarization m_L 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 m_L ~ 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.