• Title/Summary/Keyword: 다중반사

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An Investigation of Multi-path Propagation Characteristics Considering Slope of the Ground (지면의 경사를 고려한 다중경로 전파특성 분석)

  • Chae, Gyoo-Soo;Lim, Joong-Soo;Kim, Min-Nyun
    • Proceedings of the KAIS Fall Conference
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    • 2007.11a
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    • pp.201-204
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    • 2007
  • 본 논문에서 디지털지도를 이용하여 다중경로 전파의 특성을 연구하였다. 일반적으로 목표물에서의 전계의 세기는 직접파와 지면 반사파의 합으로 구해진다. 이 논문에서는 수직면의 장애물인 고압선, 철탑, 산악지형의 경사면 등에 의한 반사파를 고려하여 전체 전계를 계산 하였다. 그리고 지면 반사의 경우, 지면의 경사를 고려하여 목표물에서의 전체 전계의 정확도를 향상시켰다.

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Underwater Acoustic Channel Bandwidth and its Effects on BFSK/BPSK Performance (수중음향채널의 대역에 따른 BFSK/BPSK 전송 성능)

  • 박지현;윤종락;박규칠
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.8 no.6
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    • pp.1243-1249
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    • 2004
  • In this paper, the multipath effect on underwater acoustic channel bandwidth and BFSK and BPSK bit error dependancy on channel bandwidth are analyzed. The multipath is modeled as a discrete multipath and a continuous multipath and the channel bandwidth is expressed as a function of multipath delay spread constant. Bit error characteristics on the channel bandwidth and the criteria of the multipath delay spread constant are found through the numerical simulation. The transmission bit rate of less than 100bps in the water tank which has a channel bandwidth of 100Hz, is a consistent result with the numerical simulation.

Computation of Wave Propagation over Multi-Step Topography by Partition Matrix Method (분할행렬법에 의한 다중 계단지형에서의 파랑변형 계산)

  • Seo, Seung-Nam
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.4B
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    • pp.377-384
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    • 2009
  • In order to reduce computing time significantly for a large matrix in EFEM of linear waves propagation over ripple beds, each of which is approximated to a multi-step topography, a partition method is presented to calculate reflection coefficients. By use of 10 evanescent modes in the model, the most accurate numerical solutions have been obtained up to date, which show different behaviors of computed reflection coefficient in some cases against the existing results. Both computing time and memory of the present partition model for solving a large matrix are still so much demanding that it is needed to develop an efficient method.

Derivation and Evaluation of Surface Reflectance from UAV Multispectral Image for Monitoring Forest Vegetation (산림 식생 모니터링을 위한 무인기 다중분광영상의 반사율 산출 및 평가)

  • Lee, Hwa-Seon;Seo, Won-Woo;Woo, Choongshik;Lee, Kyu-Sung
    • Korean Journal of Remote Sensing
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    • v.35 no.6_2
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    • pp.1149-1160
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    • 2019
  • In this study, two radiometric correction methods deriving reflectance from UAV multispectral image for monitoring forest vegetation were applied and evaluated. Multispectral images were obtained from a small multispectral camera having 5 spectral bands. Reflectance were derived by applying the two methods: (1) the direct method using downwelling irradiance measurement and (2) the empirical line correction method by linking a set of field reflectance measured simultaneous with the image capture. Field reflectance were obtained using a spectroradiometer during the flight and used for building the linear equation for the empirical method and for the validation of image reflectance derived. Although both methods provided the high correlations between field reflectance and image-derived reflectance, their distributions were somewhat different. While the direct method provided rather stable and consistent distribution of reflectance all over the entire image area, the empirical method showed very unstable and inconsistent reflectance distribution. The direct method would be more appropriate for relatively wide area that requires more time to acquire image and may vary in downwelling irradiance and atmospheric conditions.

Improvement of Hologram Dencity using a Micro-Mirror Surface (마이크로 미러 표면을 이용한 홀로그램 저장 밀도의 향상)

  • 양병춘
    • Proceedings of the Optical Society of Korea Conference
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    • 1998.08a
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    • pp.92-93
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    • 1998
  • 폴리 실리톤으로 제작된 마이크로 미러의 표면에서 반사되는 스펙클을 이용하여 홀 로그램을 기록하였다. 마이크로 미러에서 반사되는 스펙클 패턴은 다중모드 광섬유에서 관 측할 수 있는 스펙클과 거의 비슷한 형태로 보이며 이를 이용하여 홀로그램의 기록밀도를 향상시킬수 있음을 보였다.

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Simulation of Reflective Boundaries Using the Sponge Layer in Boussinesq Wave Propagation Model (Boussinesq 파랑전파모델에서 스펀지층을 이용한 반사경계의 모의)

  • Chun, In-Sik
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.19 no.5
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    • pp.429-435
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    • 2007
  • The present study proposed a method fer simulating reflective boundary conditions in Boussinesq wave propagation model by lining lateral boundaries like breakwaters and seawalls with artificial sponge layers. In order to find out the reflective characteristics of sponge layers, 1D numerical experiments were performed varying the relative sponge width (sponge width/wave length). The results showed that the reflection coefficient can be effectively realized from no reflection to full reflection simply by adjusting the relative sponge width. Based on the results, a multiple regression formula was proposed to delineate the relationship among the reflection coefficient and other dimensionless variables. Finally, the reflective sponge layer was applied to a semi-infinite breakwater, demonstrating that it can also be successfully employed in 2D applications.

NDVI signature for mountain forest in accordance with topographic effects using QuickBird multi-spectral data (QuickBird 다중분광자료를 이용한 산림 지형효과의 NDVI 특성)

  • Hong, Min-Gee;Park, Soon-Chul;Kim, Gwang-Deuk;Yoon, Chang-Yeol;Kim, Choen
    • Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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    • 2010.06a
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    • pp.117-118
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    • 2010
  • 위성 주사 및 촬영자료는 지표면의 반사광을 다중분광 형태로 주사하여 기록된다. 그리나 각 밴드에 기록된 지표복사체의 반사치는 피복체의 분광특성만을 나타내기 보다는 태양고도 및 방위, 그리고 지형 등에 따른 방향성 영향이 포함되기 때문에 산림의 관리 및 이용을 위한 기초자료로 식생지수를 추정할 때에 오차의 범위를 넘어 오류가 발생한다. 따라서 동일 방향성 조건의 수종에 따른 고유 정규식생지수(Normalized Difference Vegetation Index, 이하 NDVI) 값을 구하기 위해서는 지형효과에 대한 보정이 필요하다. 본 연구에서는 QuickBird 다중분광(MS)자료 기반의 NDVI값을 사면향별로 분석하여 산림 NDVI의 방향성을 증명하였다.

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Regeneration of Plausible Lighting using a Specular Sphere in Augmented Reality (증강현실에서의 반사구를 활용한 사실적 조명 생성)

  • Lee, Seok-Jun;Jung, Soon-Ki
    • Journal of the Korea Computer Graphics Society
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    • v.17 no.3
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    • pp.21-31
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    • 2011
  • This paper presents a practical method to estimate the directions of light sources in real environment, using a mirror sphere placed on a set of known natural features in augmented reality. For the stable result of static lighting, we take the multiple images around the sphere and estimate the principal light directions of the vector clusters for each light source in realtime. We also estimate the moving illuminant for changes of the scene illumination, and augment the virtual objects onto the real image with the proper highlighting and shadows. The proposed method of this paper can be applied to augmented reality visualization without any previous information respecting the environmental illuminations.

Study of Scattering Mechanism in Oyster Farm by using AIRSAR Polarimetric Data (AIRSAR 다중편파 자료를 이용한 굴 양식장 산란현상 연구)

  • Lee Seung-Kuk;Hong Sang-Hoon;Won Joong-Sun
    • Korean Journal of Remote Sensing
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    • v.21 no.4
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    • pp.303-316
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    • 2005
  • Strong radar returns were observed in oyster sea farms, and coherent interferometric pairs were successfully constructed. Tide height in coastal area is possible to be measured by using interferometric phase and intensity of SAR data. This SAR application technique for measuring the tide height in the near coastal zone can be further improved when applied to double bounce dominant areas. In this paper, we investigate the characteristics of polarimetric signature in the oyster farm structures. Laboratory experiments were carried out using Ku-band according to the target scale. Radar returns from vertical poles are stronger than those from horizontal Pole by 10.5 dB. Single bounce components were as strong as double bounce components and more sensitive to antenna look direction. Double bounce components show quasi-linear relation with the height of vertical poles, which implies double bounce is more useful to determine water level than total power. A L-band NASA/IPL airborne SAR (AIRSAR) image was classified into single-, double-bounce, and volume scattering components. It is observed that oyster farms are not always characterized by double bounced scattering. Double bounce is a main scattering mechanism in oyster farms standing above seawater, while single bounce is stronger than double bounce when bottom tidal flats are exposed to air. Ratios of the normalized single to double bounce components in the former and latter cases were 0.46 and 5.62, respectively. It is necessary to use double bounce dominant sea farms for tide height measurement by DInSAR technique.

효율적인 무반사 특성을 갖는 주기적인 실리콘 계층 나노구조 제작 연구

  • Lee, Su-Hyeon;Im, Jeong-U;Gwan, Sang-U;Kim, Jeong-Tae;Yu, Jae-Su
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.312.2-312.2
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    • 2014
  • 실리콘은 광센서, 태양전지, 발광다이오드 등 광소자 응용 분야에서 널리 사용되고 있는 물질이다. 그러나 실리콘의 높은 굴절율(n~3.5)은 표면에서 약 30% 이상의 Fresnel 반사를 발생시켜 소자의 효율을 감소시키는 원인이 된다. 따라서, 반사손실을 줄이기 위해서는 실리콘 표면에 효율적인 무반사 코팅을 필요로 한다. 기존의 단일 혹은 다중 박막을 이용한 무반사 코팅 기술은 물질간 열팽창계수의 불일치, 접착력 문제, 박막 두께 조절 및 적합한 굴절율을 갖는 물질 선택 어려움 등의 단점을 지니고 있다. 최근, 이러한 무반사 코팅 기술의 대안으로 곤충 눈 구조를 모방한 나노크기의 서브파장 격자구조 (subwavelength gratings, SWGs)에 대한 연구가 활발히 이루어지고 있다. 이러한 SWGs 구조는 공기와 반도체 표면 사이에 점진적, 선형적으로 변화하는 유효굴절율을 갖기 때문에, 광대역 파장영역뿐만 아니라 다양한 각도에서 입사하는 빛에 대해서도 효과적으로 Fresnel 표면 반사를 낮출 수 있다. 본 연구에서는 실리콘 기판 표면 위에 효율적인 무반사 특성을 갖는 계층적 SWGs 나노구조를 제작하기 위해, 레이저간섭리소그라피 및 열적응집금속 입자를 이용한 식각 마스크 패터닝 방법과 유도결합플라즈마 식각 공정을 이용하였다. 제작된 무반사 실리콘 SWGs 나노구조의 표면 및 식각 프로파일은 전자주사현미경으로 관찰하였고, 표면 접촉각 측정 장비를 이용하여 샘플 표면의 젖음성을 확인하였다. 제작된 샘플의 광학적 특성을 조사하기 위해 UV-vis-NIR 스펙트로미터와 엘립소미터 측정 시스템들을 이용하였다.

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