• Title, Summary, Keyword: X-band

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Wind Retrieval from X-band SAR Image Using Numerical Ocean Scattering Model

  • Kim, Duk-Jin
    • Korean Journal of Remote Sensing
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    • v.25 no.3
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    • pp.243-253
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    • 2009
  • For the last 14 years, space-borne satellite SAR system such as RADARSAT-1, ERS-2, and ENVISAT ASAR have provided a continuous observation over the ocean. However, the data acquired from those systems were limited to C-band frequency until the advent of the first spacebome German X-band SAR system TerraSAR-X in 2007. Korea is also planning to launch the nation's first X-band SAR satellite (KOMPSAT-5) in 2010. It is timely and necessary to develop X-band models for estimating geophysical parameters from these X-band SAR systems. In this study, X-band wind retrieval model was investigated and developed based on numerical ocean scattering model (radar backscattering model and hydrodynamic interaction model). Although these models have not yet been tested and validated for broad ranges of wind conditions, the estimated wind speeds from TerraSAR-X data show generally good agreement with in-situ measurements.

POTENTIAL OF MULTI-BAND SAR DATA FOR CLASSIFYING FOREST COVER TYPE

  • Shin, Jung-Il;Yoon, Jong-Suk;Kang, Sung-Jin;Lee, Kyu-Sung
    • Proceedings of the KSRS Conference
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    • pp.258-261
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    • 2007
  • Although there have been lack of studies using X-band SAR data particularly for forestry application as compared to C-, and L-band SAR data, it has a potential to distinguish tree species because most signals are backscattered on the top of canopy. This study aimed to compare signal characteristics of multi-band SAR data including X-band for classifying tree species. The data used for the study are SIR-C/X-SAR data (X-, C-, L-band) obtained on Oct. 3, 1994 over the forest area near Seoul, S. Korea. Thirty ground sample plots were collected per each tree species. Initial comparison of backscattering coefficients among three SAR bands shows that X-band data showed better separation of tree species than C- and L-band SAR data irrespective of polarization. The weak penetrating in canopy layer might be possible source of information for X-band data to be useful for the classification of forest species and cover type mapping.

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Automatic Detection and Analysis of Rip Currents at Haeundae Beach using X-band Marine Radar (항해용 X-band 레이다를 이용한 해운대해수욕장 이안류 자동탐지 및 특성 분석)

  • Oh, Chanyeong;Ahn, Kyungmo;Cheon, Se-Hyeon
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.6
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    • pp.485-492
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    • 2019
  • The observation system has been developed to investigate the rip currents at Haeundae beach using X-band marine radar. X-band radar system can observe shape, size, and velocity of rip currents, which is difficult to obtain through field observation by conventional device. Algorithms which automatically detect locations, shapes, and magnitudes of rip currents were developed using time averaged X-band radar sea clutter images. X-band sea clutter images are transformed through 3D FFT into 2D wave number spectrum and frequency spectrum. Rip current velocities were estimated using differences in wave-number spectra and wave frequency spectra due to Doppler shift. The algorithm was verified by drift experiments. At Haeundae beach, the radar system exactly located the rip currents and found to be sustained for 1-2 days at fixed locations.

Soil Moisture Measurement of Bare and Vegetated Surfaces by X-band Radars

  • Oh, Yi-Sok;Kwon, Soon-Gu;Hwang, Ji-Hwan
    • Journal of electromagnetic engineering and science
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    • v.10 no.4
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    • pp.212-218
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    • 2010
  • The radar backscatter from various earth surfaces is sensitive to the frequency of the incident wave. This study examined the radar sensitivities for surface parameters such as soil moisture content and surface roughness of both bare and vegetated surfaces at X-band. Because L-band frequencies are often used for sensing the surface parameters, the sensitivities of X-band are also compared with those of the L-band. The sensitivities of the X-band radar backscatter were examined with respect to soil moisture content and surface roughness of rough bare soil surfaces. These sensitivities were also examined using the same parameters for vegetated surfaces for various vegetation densities and incidence angles. Use of the X-band radar for soil moisture detection was as effective as L-band radar for bare soil surfaces. For vegetated surfaces, the soil moisture could be detected using an X-band radar at lower incidence angles, where the upper limit of the incidence angles was dependent on vegetation density.

Dual Polarized Array Antenna for S/X Band Active Phased Array Radar Application

  • Han, Min-Seok;Kim, Ju-Man;Park, Dae-Sung;Kim, Hyoung-Joo;Choi, Jae-Hoon
    • Journal of electromagnetic engineering and science
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    • v.10 no.4
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    • pp.309-315
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    • 2010
  • A dual-band dual-polarized microstrip antenna array for an advanced multi-function radio function concept (AMRFC) radar application operating at S and X-bands is proposed. Two stacked planar arrays with three different thin substrates (RT/Duroid 5880 substrates with $\varepsilon_r$=2.2 and three different thicknesses of 0.253 mm, 0.508 mm and 0.762 mm) are integrated to provide simultaneous operation at S band (3~3.3 GHz) and X band (9~11 GHz). To allow similar scan ranges for both bands, the S-band elements are selected as perforated patches to enable the placement of the X-band elements within them. Square patches are used as the radiating elements for the X-band. Good agreement exists between the simulated and the measured results. The measured impedance bandwidth (VSWR$\leq$2) of the prototype array reaches 9.5 % and 25 % for the S- and X-bands, respectively. The measured isolation between the two orthogonal polarizations for both bands is better than 15 dB. The measured cross-polarization level is ${\leq}-21$ dB for the S-band and ${\leq}-20$ dB for the X-band.

The Calculation of the Energy Band Gaps of Zincblende InAs1-X NX on Temperature and Composition (온도 및 조성비 변화에 따른 질화물계 화합물 반도체 InAs1-X NX의 에너지 밴드갭 계산)

  • Chung, Ho-Yong;Kim, Dae-Ik
    • The Journal of the Korea institute of electronic communication sciences
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    • v.11 no.12
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    • pp.1165-1174
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    • 2016
  • The energy band gaps and the bowing parameters of zincblende InAs1-xN are determined by using an empirical pseudopotential method(EPM) within the improved virtual crystal approximation(VCA), which includes the disorder effect. The direct-band-gap bowing parameter calculated by using the EPM is 4.1eV for InAs1-xNx ($0{\leq}x{\leq}0.05$). The dependences of the band gaps of N-dilute InAs1-xNx on the temperature and composition are calculated by modifying the band anti-crossing(BAC) model. The calculation results are consistent with experimental values, and the coupling parameter CMN of InAs1-xNx is found to be equal to 1.8 by fitting the EPM data.

Investigation of Micro-vibration Isolation Performance of SMA Mesh Washer Isolator for Vibration Isolation of X-band Antenna (SMA 메쉬 와셔 진동 절연기를 적용한 X-band 안테나의 미소진동 절연성능 검토)

  • Jeon, Su-Hyeon;Kwon, Sung-Choel;Kim, Dae-Kwan;Oh, Hyun-Ung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.11
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    • pp.988-995
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    • 2014
  • Two axis gimbal type X-band antenna system has been widely used to effectively transmit the real time image data from the observation satellite to the ground station. The micro-vibration generated by stepping motor actuation and imperfect intermeshed gear configuration of the antenna is one of the sources to degrade the image quality. To guarantee a high quality image of high resolution observation satellite, micro-vibration isolation of X-band antenna is required. In this paper, the X-band antenna vibration isolation system using pseudoelastic SMA(Shape Memory Alloy) mesh washer has been newly suggested. The basic characteristics of the SMA mesh washer isolator proposed in this study has been measured through static load tests and its effectiveness has been demonstrated by the micro-vibration isolation test of the X-band antenna.

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
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    • v.21 no.4
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    • pp.109-116
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    • 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.

Two-dimensional As1-xPx binary compounds: Highly tunable electronic structure and optical properties

  • Hu, Tao;Xu, Ben;Hong, Jisang
    • Current Applied Physics
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    • v.17 no.2
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    • pp.186-191
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    • 2017
  • We explored a two-dimensional (2D) binary compound consisting of arsenic and phosphorus by means of density functional theory (DFT) calculations. The geometry, electronic structure, and optical properties of monolayer, few-layer and bulk $As_{1-x}P_x$ compounds with different composition ratio were investigated. We can achieve a more continuous tuning in band gap by change the composition and thickness. The band gap of $As_{1-x}P_x$ monolayer was almost the same as that of phosphorene monolayer, regardless of the As concentration. However, the band gaps of few-layer systems decrease significantly. In the case of few-layer systems, they can possess various band gap values those the pristine phosphorus system cannot reach. The direct-indirect band gap transition occurred at a certain threshold when the As concentration continuously increased. The more concentration of As was, the faster band gap decreased. The band gaps of their bulk systems were in the range of 0.3-0.4 eV, which is very close to that of bulk phosphorus and this was not sensitive to the composition and topological arrangement. The dielectric function calculations revealed that the optical properties of the arsenic phosphide systems were highly tunable by changing the composition and thickness. Overall, we propose that the tunable electronic and optical properties of the $As_{1-x}P_x$ binary compounds make them great candidates for application in the field of electronics and optoelectronics.

The Calculation of the Energy Band Gaps and Optical Constants of Zincblende InyGa1-yAs1-xNx on Composition (조성비 변화에 따른 질화물계 화합물 반도체 InyGa1-yAs1-xNx의 에너지 밴드갭과 광학상수 계산)

  • Chung, Ho-Yong;Kim, Dae-Ik
    • The Journal of the Korea institute of electronic communication sciences
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    • v.14 no.5
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    • pp.877-886
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    • 2019
  • The energy band gaps and optical constants of zincblende $In_yGa_{1-y}As_{1-x}N_x$ on the variation of temperature and composition are determined by using band anticrossing method. The energy band gaps are decreasing continuously in $In_yGa_{1-y}As_{1-x}N_x$ ($0{\leq}x{\leq}0.05$, $0{\leq}y{\leq}1.0$, 300K) and the bowing parameter is calculated as 0.522eV. The calculation results of energy band gaps are consistent with those of other studies. A refractive index n and a high-frequency dielectric constant ${\varepsilon}$ are calculated by a proposed modeling equation using the results of energy band gaps.