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

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.223-228
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• 1999

We have investigated the microwave properties of a high-T$_c$. superconducting Josephson junction by Shapiro step measurements. A Josephson junction was fabricated on the bicrystal MgO substrate using pulsed laser deposition method. We have measured Shapiro steps in the I-V characteristics under the irradiation of 1.36 cm wavelength up to 45 K and found inclined current steps above 50 K. In order to understand these results, we introduced an additional resistance connected in series to RSJ model. Using this modified RSJ model, we could explain the inclined current steps as a result of superposition of the junction and an additional resistance above certain temperatures. Also, we presented the received power of the Josephson junction above 50 K.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.1021-1023
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• 2003

We studied field-emission characteristics of CNTs under various pre-treatment with $NH_{3}$ plasma on the substrate. The turn-on electric field is the lowest value and field enhancement factor (${\beta}$) is he highest value in CNTs pre-treated by $NH_3$ plasma (80 W and 5 min). The field-emission property of CNTs grown on the Ta substrate is slightly better than on the W substrate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.616-619
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• 2003

This work presents the design, fabrication and microwave performance of distributed analog phase shifter (DAPS) fabricated on $(Ba,\;Sr)TiO_3$ (BST) thin films for X-band applications. Ferroelectric BST thin films were deposited on MgO substrates by pulsed laser deposition. The DAPS consists of high impedance coplanar waveguide (CPW) and periodically loaded tunable BST interdigitated capacitors (IDC). In order to reduce the insertion loss of DAPS and to remove the alteration of unloaded CPW properties according to an applied dc bias voltage, BST layer under transmission lines were removed by photolithography and RF-ion milling. The measured results are in good agreement with the simulated results at the frequencies of interest. The measured differential phase shift based on BST thin films was $24^{\circ}$ and the insertion loss decreased from 1.1 dB to 0.7 dB with increasing the bias voltage from 0 to 40V at 10 GHz.

• JSTS:Journal of Semiconductor Technology and Science
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• v.5 no.2
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• pp.113-119
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• 2005

4H-SiC planar MESFETs were fabricated using ion-implantation on semi-insulating substrate without recess gate etching. A modified RCA method was used to clean the substrate before each procedure. A thin, thermal oxide layer was grown to passivate the surface and then a thick field oxide was deposited by CVD. The fabricated MESFET showed good contact properties and DC/RF performances. The maximum oscillation frequency of 34 GHz and the cut-off frequency of 9.3 GHz were obtained. The power gain was 10.1 dB and the output power of 1.4 W was obtained for 1 mm-gate length device at 2 GHz. The fabricated MESFETs showed the charge trapping-free characteristics and were characterized by the extracted small-signal equivalent circuit parameters.

• Journal of Magnetics
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• v.14 no.4
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• pp.155-160
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• 2009

This study examined the effects of a decrease in thickness of magnetic alloy flakes on the electromagnetic wave absorption characteristics of nanocrystalline $Fe_{73.5}Cu_1Nb_3Si_{15.5}B_7$ (at.%) alloy flakes/polymer composite sheets available for a quasi-microwave band. The thickness of FeCuNbSiB alloy flakes decreased to 1-2 $\mu$m with increasing milling time up to 24 h, and the composite sheet including alloy flakes milled for 24 h exhibited considerably enhanced power loss properties in the GHz range compared to the sheets having non-milled alloy powders. Although a considerable increase in loss factor upon milling was observed in the narrow frequency range of 4-6 GHz, there was no correlation between the complex permeability and flake thickness. However, the complex permittivity increased with increasing milling time, and there was good agreement between the milling time and the frequency dependences of the complex permittivity and power loss.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.2
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• pp.235-247
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• 2006

Aerosol indirect radiative forcing of climate change is considered the most uncertain forcing of climate change over the industrial period, despite numerous studies demonstrating such modification of cloud properties and several studies quantifying resulting changes in shortwave radiative fluxes. Detection of this effect is made difficult by the large inherent variability in cloud liquid water path (LWP): the dominant controlling influence of LWP on optical depth and albedo masks any aerosol influences. Here we have used ground-based remote sensing of cloud optical depth (${\tau}_c$) by narrowband radiometry and LWP by microwave radiometry to determine the dependence of optical depth on LWP, thereby permitting examination of aerosol influence. The method is limited to complete overcast conditions with liquid-phase single layer clouds, as determined mainly by millimeter wave cloud radar. The results demonstrate substantial (factor of 2) day-to-day variation in cloud drop effective radius at the ARM Southern Great Plains site that is weakly associated with variation in aerosol loading as characterized by light-scattering coefficient at the surface. The substantial scatter suggests the importance of meteorological influences on cloud drop size as well, which should be analyzed in the further intensive studies. Meanwhile, it is notable that the decrease in cloud drop effective radius results in marked increase in cloud albedo.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.430-433
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• 2001

The $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were $1300^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite $SrTiO_{3}$ and ilmenite $MgTiO_{3}$ structures were coexisted in the $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics. The dielectric constant$(\varepsilon_{r})$ was increased with addition of Ce. The temperature coefficient of resonant frequency$(\Gamma_{f})$ was gradually varied from positive value to the negative value with increasing the Ce. The temperature coefficient of resonant frequency of the $0.96MgTiO_{3}-0.04SrTiO_{3}+0.2Ce$ ceramics was near zero, where the dielectric constant, quality factor, and $\Gamma_{f}$ were 20.68, 50,272 and ${-0.5ppm/^{\circ}C}$, respectively.

• Proceedings of the Korean Society of Crop Science Conference
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• 2005.08a
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• pp.75-87
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• 2005

Remote sensing(RS)- and geographic information system(GIS)-based information management to measure and assess agri-environment schemes, and to quantify and map environment indicators for nature and land use, climate change, air, water and energy balance, waste and material flow is in high demand because it is very helpful in assisting decision making activities of farmers, government, researchers, and consumers. The versatility and ability of RS and GIS containing huge soil database to assess agricultural environment spatially and temporally at various spatial scales were investigated. Spectral and microwave observations were carried out to characterize crop variables and soil properties. Multiple sources RS data from ground sensors, airborne sensors, and also satellite sensors were collected and analyzed to extract features and land cover/use for soils, crops, and vegetation for support precision agriculture, soil/land suitability, soil property estimation, crop growth estimation, runoff potential estimation, irrigated and the estimation of flooded areas in paddy rice fields. RS and GIS play essential roles in a management and monitoring information system. Biosphere-atmosphere interection should also be further studied to improve synergistic modeling for environment and sustainability in agri-environment schemes.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.7
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• pp.375-381
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• 2000

In this paper, we described the characterization of High-Tc Superconducting(HTS) microstrip antenna using non-radiating edge feeding technique and reported the microwave properties of HTS antennas with temperature. To do this, we prepared the $YBa_2Cu_3O_{7-x}$ superconducting thin film on MgO substrate using pulse-laser deposition techniques. The HTS microstrip antenna using non-radiating feeding technique was fabricated using chemical wet-etching. Then it was compared with identical antenna patterned with evaporated gold. The diverse measured results have been reported in terms of the input impedance, resonant frequency and return loss. In additional, at around the critical temperature, the effect of kinetic inductance which affect the resonant characteristic of the HTS microstrip antenna was reported.