• 한국수자원학회논문집
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• 제56권8호
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• pp.497-508
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• 2023

수자원의 계절적 편중이 심한 한반도에서 농업용 저수지는 이를 효과적으로 유지 및 관리하기 위한 필수적인 구조물이다. 저수지 모니터링을 위한 수단으로 광학 및 합성개구레이더(Synthetic Aperture Radar, SAR) 위성영상이 활용되고 있으나, 광학영상은 기상현상에 의한 간섭이 심하다는 한계점이 존재하며, SAR 영상은 짙은 식생에서 일어나는 다중 산란 및 노이즈에 의한 오탐지 및 미탐지가 발생하기 쉽다. 이에 본 연구에서는 광학 영상과 SAR 영상의 융합을 통해 저수지 수체 탐지 정확도를 높이고 상호보완적 작용에 대해 정량적으로 분석하고자 하였다. 경기도 이동저수지, 충청남도 천태 저수지를 대상으로, 국내 고해상도 위성인 차세대중형위성 1호, 다목적실용위성 3호 및 3A호, 그리고 유럽우주국의 Sentinel-2 영상 기반 Normalized Difference Water Index (NDWI)와 SAR 탑재 위성인 Sentinel-1 단일 영상에 비지도학습 기법인 K-means 클러스터링 기법을 사용하여 수체를 탐지하고, NDWI-SAR 후방산란계수로 이루어진 2-D grid space에 동일 기법을 활용하여 정확도의 향상 정도를 파악하였다. 전반적인 정확도는 다목적실용위성이 가장 높은 것으로 나타났으며(두 저수지 모두 0.98), 이후 Sentinel-1(두 저수지 모두 0.93), Sentinel-2(이동: 0.83, 천태: 0.97), 차세대중형위성(이동: 0.69, 천태: 0.78) 순서로 감소하였다. 천태저수지에서 2-D K-means 클러스터링 기법을 적용한 결과 차세대중형위성의 수체탐지 정확도는 약 85%의 정밀도 향상과 14%의 재현율 감소와 함께 약 22% 향상되었으며(정확도 약 0.95), 다목적실용위성 및 Sentinel-2의 수체탐지 정밀도는 3-5% 향상되었고, 재현율은 4-7% 감소하였다. 추후 차세대중형위성 5호인 수자원위성 등 고해상도 SAR 위성과 이를 활용할 수 있는 고도화된 영상 융합기술, 수체 탐지 기술이 개발된다면 국내 수자원에 대한 매우 정확한 모니터링이 가능할 것으로 기대된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.642-642
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• 2013

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as high electron mobility, high thermal conductivity and optical transparency. Especially, chemical vapor deposition (CVD) grown graphene has been used as a promising material for high quality and large-scale graphene film. Unfortunately, although CVD-grown graphene has strong advantages, application of the CVD-grown graphene is limited due to ineffective transfer process that delivers the graphene onto a desired substrate by using polymer support layer such as PMMA(polymethyl methacrylate). The transferred CVD-grown graphene has serious drawback due to remaining polymeric residues generated during transfer process, which induces the poor physical and electrical characteristics by a p-doping effect and impurity scattering. To solve such issue incurred during polymer transfer process of CVD-grown graphene, various approaches including thermal annealing, chemical cleaning, mechanical cleaning have been tried but were not successful in getting rid of polymeric residues. On the other hand, lithographical patterning of graphene is an essential step in any form of microelectronic processing and most of conventional lithographic techniques employ photoresist for the definition of graphene patterns on substrates. But, application of photoresist is undesirable because of the presence of residual polymers that contaminate the graphene surface consistent with the effects generated during transfer process. Therefore, in order to fully utilize the excellent properties of CVD-grown graphene, new approach of transfer and patterning techniques which can avoid polymeric residue problem needs to be developed. In this work, we carried out transfer and patterning process simultaneously with no polymeric residue by using a metal etch mask. The patterned thin gold layer was deposited on CVD-grown graphene instead of photoresists in order to make much cleaner and smoother surface and then transferred onto a desired substrate with PMMA, which does not directly contact with graphene surface. We compare the surface properties and patterning morphology of graphene by scanning electron microscopy (SEM), atomic force microscopy(AFM) and Raman spectroscopy. Comparison with the effect of residual polymer and metal on performance of graphene FET will be discussed.

• Ocean and Polar Research
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• 제25권1호
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• pp.9-20
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• 2003

A solar radiation model was used to investigate the UV radiation at the surface offing Sejong Station in West Antarctica. The results calculated by this model were compared with the values measured by UV-Biometer and UV-A meter during 1999-2000. In this study, the parameterization of solar radiative transfer process was based on Chou and Lee(1996). The total ozone amounts measured by Breve. Ozone Spectrophotometer and the aerosol amounts by Nakajima et al.(1996) was used as the input data of the solar radiative transfer model. And the surface albedo is assumed to be 0.20 in summer and 0.85 in winter. The sensitivity test of solar radiative transfer model was done with the variation of total ozone, aerosol amount, and surface albedo. When the cosine of solar zenith angle is 0.3, Erythemal UV-B radiation decreased 73% with the 200% increase of total ozone from 100 DU to 300 DU, but the decrease of UV-A radiation is about 1%. Also, for the same solar zenith angle, UV-A radiation was decreased 31.0% with the variation of aerosol optical thickness from 0.0 to 0.3 and Erythemal UV-B radiation was decreased only 6.1%. The increase of Erythemal W-B radiation with the variation of surface albedo was twice that of UV-A increase. The surface Erythemal UV-B and UV-A radiation calculated by solar raditive transfer model were compared with the measured values fer the relatively clear day at King Sejong Station in West Antarctica. The model calculated Erythemal UV-B radiation at the surface coincide well with the measured values except for cloudy days. But the difference between the model calculated UV-A radiation and the measured value at the surface was large because of cloud scattering effect. So, the cloud property data is needed to calculate the UV radiation more exactly at King Sejong Station in West Antarctica.

• Journal of Astronomy and Space Sciences
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• 제18권3호
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• pp.239-248
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• 2001

2002년에 발사 예정인 과학 위성 1호의 주 탑재체로 원자외선 분광기가 실릴 예정이다. 원자외선 분광기는 영상과 분광의 기능을 함께 수행하게 되는데, 광학 부품 중 포물 원통 만가경의 경우 천문 관측용으로는 제작된 바가 없어 제작과 이에 관련된 측정 방법을 새로이 고안하여 제작시험이 이루어 겼다. 관측 목표로부터 도출된 사양 중에서 성능과 가장 밀접한 관계가 있는 형상오차의 경우 ~ $lambda/cm$의 한계를 만족하였으며, 산란장과 연관된 표면 거칠기의 경우 새로이 고안된 비구면 pitch polishing의 방법으로 $R_{q}$의 값이 1 nm 이하로 감소하였으며, 이로써 전체 파장 영역에서 0.02, 즉 2% 미만의 빛이 산란됨을 간접적으로 확인하였다.

• 대한화장품학회지
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• 제42권1호
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• pp.45-55
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• 2016

빛은 피부에서 개개인마다 상이한 반사, 흡수 및 산란 등의 광학적 거동을 보여준다. 특히, 피부에서 빛의 반사는 분광반사율이라는 물리량 측정을 통해 개인의 피부 밝기지표로 널리 활용되어 왔다. 따라서 피부에서 빛의 반사 거동 연구는 개인 맞춤형 화장품, 특히 메이크업 제품 개발에 있어 좀 더 효율적인 처방 개선에 기여하거나 새로운 평가법에 활용될 수 있다. 본 연구에서는 Kubelka-Munk 모델을 이용하여 개인의 피부 특성에 따른 빛의 분광반사율 거동에 대해 다각적인 분석을 수행하였다. 또한, 상기 모델과 기존에 알려진 문헌 정보를 이용하여 개인의 피부 분광반사율에 영향을 줄 수 있는 피부 두께 및 헤모글로빈 등의 다양한 파라미터들에 대한 기여도 분석을 수행하였다. 이를 통해, 일반적인 여성의 피부에서의 분광반사율 이론치를 계산하였고, 분광반사율 실측을 통해 이론치와 실측치 간의 유사성을 확인하였다. Kubelka-Munk 모델을 이용한 피부 분광반사율 연구는 향후 새로운 개인 맞춤형 메이크업 화장품 개발에 유용하게 이용될 수 있을 것으로 사료된다.

• 한국광학회지
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• 제31권5호
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• pp.218-222
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• 2020

본 연구에서는 편광 유지 광섬유 기반의 고출력 이터븀 첨가 광섬유 증폭기를 이용하여 고품질의 2 kW급 출력을 갖는 파장제어 빔 결합 레이저를 구현하였다. 파장제어 빔 결합을 위하여 광섬유 증폭기의 발진 파장은 각각 1062 nm, 1063 nm, 1064 nm, 1065 nm, 1066 nm로서 서로 다른 값을 갖는다. 협대역 광섬유 레이저 증폭 시 발생하는 유도 브릴루앙 산란 비선형 효과를 완화하기 위해 시드 광원은 유사이진난수 신호(pseudo-random bit sequence, PRBS)를 이용하여 위상 변조된 5 GHz의 협대역 선폭을 갖도록 하였으며 전송광섬유는 30 ㎛ 코어 크기를 가지는 대면적 편광 유지 광섬유를 이용하였다. 파장제어 빔 결합으로 얻은 레이저의 최대 출력은 2.3 kW이며 빔 품질(M²)은 1.74이었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.363-363
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• 2008

The development of dry etching process for sapphire wafer with plasma has been key issues for the opto-electric devices. The challenges are increasing control and obtaining low plasma induced-damage because an unwanted scattering of radiation is caused by the spatial disorder of pattern and variation of surface roughness. The plasma-induced damages during plasma etching process can be classified as impurity contamination of residual etch products or bonding disruption in lattice due to charged particle bombardment. Therefor, fine pattern technology with low damaged etching process and high etch rate are urgently needed. Until now, there are a lot of reports on the etching of sapphire wafer with using $Cl_2$/Ar, $BCl_3$/Ar, HBr/Ar and so on [1]. However, the etch behavior of sapphire wafer have investigated with variation of only one parameter while other parameters are fixed. In this study, we investigated the effect of pressure and other parameters on the etch rate and the selectivity. We selected $BCl_3$ as an etch ant because $BCl_3$ plasmas are widely used in etching process of oxide materials. In plasma, the $BCl_3$ molecule can be dissociated into B radical, $B^+$ ion, Cl radical and $Cl^+$ ion. However, the $BCl_3$ molecule can be dissociated into B radical or $B^+$ ion easier than Cl radical or $Cl^+$ ion. First, we evaluated the etch behaviors of sapphire wafer in $BCl_3$/additive gases (Ar, $N_2,Cl_2$) gases. The behavior of etch rate of sapphire substrate was monitored as a function of additive gas ratio to $BCl_3$ based plasma, total flow rate, r.f. power, d.c. bias under different pressures of 5 mTorr, 10 mTorr, 20 mTorr and 30 mTorr. The etch rates of sapphire wafer, $SiO_2$ and PR were measured with using alpha step surface profiler. In order to understand the changes of radicals, volume density of Cl, B radical and BCl molecule were investigated with optical emission spectroscopy (OES). The chemical states of $Al_2O_3$ thin films were studied with energy dispersive X-ray (EDX) and depth profile anlysis of auger electron spectroscopy (AES). The enhancement of sapphire substrate can be explained by the reactive ion etching mechanism with the competition of the formation of volatile $AlCl_3$, $Al_2Cl_6$ or $BOCl_3$ and the sputter effect by energetic ions.

• 한국의학물리학회지:의학물리
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• 제16권2호
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• pp.104-109
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• 2005

암치료에 사용되고 있는 광역학 치료는 환자에게 광민감제를 투여하고 다이오드 레이저(630 nm)를 조사하여 생성되는 단일상태 산소와 자유 라디칼에 의해 암조직을 괴사시키는 치료방법이다. 현재 광역학 치료의 문제점은 부피가 큰 종양이나 고형암에서는 빛이 종양전체를 투과할 수 없으므로 광역학 치료의 효과가 떨어지는 것이다. 따라서 이 문제를 해결하기 위하여 간질성 광역학 치료법을 개발하고자 한다. 생체조직내의 정확한 광선량 측정이 간질성광역학치료의 효과에 매우 중요한 영향을 주므로, 실험 연구에 사용된 계수는 실제 생체조직의 광학 계수이다. 생체조직 대부분은 가시광선영역에서 큰 산란계수를 가지며, 투과 깊이에 많은 영향을 미치는 것으로 확인되었다. 가시영역에서의 인체조직의 투과깊이는 약 $15\~20mm$이었다. 몬테칼로 시뮬레이션(Monte Carlo simulation)을 이용하여 생체조직내의 광전파, 광선량, 에너지율, 투과깊이를 잘 측정할 수 있음을 알았다. 그리고 이 시뮬레이션 결과를 가지고 고형암에 간질성 광역학 치료를 하여 치료효과를 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.493-493
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• 2014

The manufacturing cost of thin-film photovoltics can potentially be lowered by minimizing the amount of a semiconductor material used to fabricate devices. Thin-film solar cells are typically only a few micrometers thick, whereas crystalline silicon (c-Si) wafer solar cells are $180{\sim}300\mu}m$ thick. As such, thin-film layers do not fully absorb incident light and their energy conversion efficiency is lower compared with that of c-Si wafer solar cells. Therefore, effective light trapping is required to realize commercially viable thin-film cells, particularly for indirect-band-gap semiconductors such as c-Si. An emerging method for light trapping in thin film solar cells is the use of metallic nanostructures that support surface plasmons. Plasmon-enhanced light absorption is shown to increase the cell photocurrent in many types of solar cells, specifically, in c-Si thin-film solar cells and in poly-Si thin film solar cell. By proper engineering of these structures, light can be concentrated and coupled into a thin semiconductor layer to increase light absorption. In many cases, silver (Ag) nanoparticles (NP) are formed either on the front surface or on the rear surface on the cells. In case of poly-Si thin film solar cells, Ag NPs are formed on the rear surface of the cells due to longer wavelengths are not perfectly absorbed in the active layer on the first path. In our cells, shorter wavelengths typically 300~500 nm are also not effectively absorbed. For this reason, a new concept of plasmonic nanostructure which is NPs formed both the front - and the rear - surface is worth testing. In this simulation Al NPs were located onto glass because Al has much lower parasitic absorption than other metal NPs. In case of Ag NP, it features parasitic absorption in the optical frequency range. On the other hand, Al NP, which is non-resonant metal NP, is characterized with a higher density of conduction electrons, resulting in highly negative dielectric permittivity. It makes them more suitable for the forward scattering configuration. In addition to this, Ag NP is located on the rear surface of the cell. Ag NPs showed good performance enhancement when they are located on the rear surface of our cells. In this simulation, Al NPs are located on glass and Ag NP is located on the rear Si surface. The structure for the simulation is shown in figure 1. Figure 2 shows FDTD-simulated absorption graphs of the proposed and reference structures. In the simulation, the front of the cell has Al NPs with 70 nm radius and 12.5% coverage; and the rear of the cell has Ag NPs with 157 nm in radius and 41.5% coverage. Such a structure shows better light absorption in 300~550 nm than that of the reference cell without any NPs and the structure with Ag NP on rear only. Therefore, it can be expected that enhanced light absorption of the structure with Al NP on front at 300~550 nm can contribute to the photocurrent enhancement.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2008년도 제33회 펄프종이기술 국제세미나
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• pp.47-70
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• 2008

Cost efficiency is today the primary requirement in the paper and board industry. This has led therefore, to a greater preponderance of products with specifically designed functionality to take account of current industry needs. Continually increasing machine coating speeds together with these new coating colour components have put more emphasis on the importance of the correct rheology and water retention of the coating colours to achieve good runnability and end product quality. In the coating process, some penetration of the aqueous phase, to the base paper or board must occur to anchor the pre-coating to the base or the topcoat to the pre-coat. The aqueous phase acts as a vehicle not only for the binder, but also for the other components. If this water or material penetration is not controlled, there will be excessive material shift from the coating colour to the base, before immobilization of the coating colour will stop this migration. This can result in poor machine runnability, unstable system and uneven coating layer, impacting print quality. The performance of rheology modifiers or thickeners on the coating color have tended to be evaluated by the term, "water retention". This simple term is not sufficient to explain their performance changes during coating. In this paper we are introducing a new concept of "material retention", which takes note of the total composition of the coating colour material and therefore goes beyond the concept of only water retention. Controlled material retention leads to a more uniform z-directional distribution of coating colour components. The changes that can be made to z-directional uniformity will have positive effects on print quality as measured by surface strength, ink setting properties, print gloss, mottling tendency. Optical properties, such as light scattering, whiteness and light fastness delivery should also be improved. Additionally, controlled material retention minimizes changes to the coating colour with time in re-circulation giving less fluctuation in quality in the machine direction since it more closely resembles fresh coating for longer periods. Use of the material retention concept enables paper and board producers to have more stable runnability (i.e. lower process costs), improved end product quality (i.e. better performance of used chemicals) and/or optimized use of coating colour components (i.e. lower total formulation cost)