• 한국위성정보통신학회논문지
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• 제7권1호
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• pp.116-121
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• 2012

저궤도 기상위성 개발을 위한 기술기준을 도출하기 위하여 이론적으로 접근, 적외선 및 마이크로파 탑재체 센서의 특성 분석하였다. 또한, 저궤도 기상위성 탑재체 개발과 관련하여 현존하는 국외 저궤도 기상위성에 탑재된 마이크로파센서들의 채널요구사항 및 위성체 접속 요구사항을 분석하였다. 본 논문에서는 저궤도 기상위성시스템의 접속 요구사항으로 다목적위성 버스와 소형위성 플렛폼인 CAS 500, 그리고 위성관제시스템의 핵심 서브시스템 및 주요 기능 요구사항을 제시 하였다.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.305-311
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• 2016

The spatial size and variation of Arctic sea ice play an important role in Earth's climate system. These are affected by conditions in the polar atmosphere and Arctic sea temperatures. The Arctic sea ice concentration is calculated from brightness temperature data derived from the Defense Meteorological Satellite program (DMSP) F13 Special Sensor Microwave/Imagers (SSMI) and the DMSP F17 Special Sensor Microwave Imager/Sounder (SSMIS) sensors. Many previous studies point to significant reductions in sea ice and their causes. We investigated the variability of Arctic sea ice using the daily sea ice concentration data from passive microwave observations to identify the sea ice melting regions near the Arctic polar ice cap. We discovered the abnormal melting of the Arctic sea ice near the North Pole during the summer and the winter. This phenomenon is hard to explain only surface air temperature or solar heating as suggested by recent studies. We propose a hypothesis explaining this phenomenon. The heat from the deep sea in Arctic Ocean ridges and/or the hydrothermal vents might be contributing to the melting of Arctic sea ice. This hypothesis could be verified by the observation of warm water column structure below the melting or thinning arctic sea ice through the project such as Coriolis dataset for reanalysis (CORA).

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2012년도 학술발표회
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• pp.265-265
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• 2012

한반도 지역의 강설(snowfall)은 전체 연 강수량의 약 10% 이하로 매우 적은 양을 차지하고 있다. 하지만 강설은 대기질(air quality)을 개선하고 산불 발생률을 저감시키며, 특히 봄철 수자원의 제공과 가뭄피해 경감 등 수문학적으로도 중요한 기능을 가진다. 하지만 최근 기후변화로 인해 폭설 현상이 빈번하게 발생하여 사회 경제적 손실을 유발하고 있다. 따라서 강설로 인한 피해를 최소한으로 줄이기 위해서는 정확한 강설탐지 및 강설 추정 방법이 필요하다. 최근 해외의 수많은 연구들을 통하여 수동 마이크로파 센서 자료를 활용한 강설 추정의 가능성이 확인되고 있다. 하지만 수동 마이크로파 센서의 휘도온도를 이용한 추정 방법들은 대기의 연직 구조 파악에 어려움이 있기 때문에 정확한 강설량을 추정하는 데에 한계가 있다. 그러나 2006년 발사된 CloudSat의 Cloud Profiling Radar는 강설의 연직 프로파일에 대한 가치 있는 정보를 제공하기 때문에 수동 마이크로파 센서 자료와의 결합을 통해 보다 정확한 강설 추정 알고리즘을 제시할 수 있을 것으로 판단된다. 따라서 본 연구에서는 CloudSat의 Cloud Profiling Radar (CPR) 자료와 수동 마이크로파 센서인 NOAA의 Microwave Humidity Sounder (MHS) 센서 자료를 결합하여 한반도 강설 추정에 적합한 알고리즘을 개발하고자 한다.

• Journal of Astronomy and Space Sciences
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• 제36권3호
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• pp.121-131
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• 2019

The ionospheric mid-latitude trough (IMT) is the electron density depletion phenomenon in the F region during nighttime. It has been suggested that the IMT is the result of complex plasma processes coupled to the magnetosphere. In order to statistically investigate the characteristics of the IMT, we analyze topside sounding data from Alouette and ISIS satellites in 1960s and 1970s. The IMT position is almost constant for seasons and solar activities whereas the IMT depth ratio and the IMT feature are stronger and clearer in the winter hemisphere under solar minimum condition. We also calculated transition heights at which the densities of oxygen ions and hydrogen/helium ions are equal. Transition heights are generally higher in daytime and lower in nighttime, but the opposite aspects are seen in the IMT region. Utilizing the Incoherent Scatter Radar (ISR) electron temperature measurements, we find that the electron temperature in the IMT region is enhanced at night during winter. The increase of electron temperature may cause fast transport of the ionospheric plasma to the magnetosphere via ambipolar diffusion, resulting in the IMT depletion. This mechanism of the IMT may work in addition to the simply prolonged recombination of ions proposed by the traditional stagnation model.

• 수산해양기술연구
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• 제55권1호
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• pp.39-49
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• 2019

Acoustics are increasingly regarded as a remote-sensing tool that provides the basis for classifying and mapping ocean resources including seabed classification. It has long been understood that details about the character of the seabed (roughness, sediment type, grain-size distribution, porosity, and material density) are embedded in the acoustical echoes from the seabed. This study developed a sophisticated yet easy-to-use technique to discriminate seabed characteristics using a split beam echosounder. Acoustic survey was conducted in Tongyeong waters, South Korea in June 2018, and the verification of acoustic seabed classification was made by the Van Veen grab sampler. The acoustic scattering signals extracted the seabed hardness and roughness components as well as various seabed features. The seabed features were selected using the principal component analysis, and the seabed classification was performed by the K-means clustering. As a result, three seabed types such as sand, mud, and shell were discriminated. This preliminary study presented feasible application of a sounder to classify the seabed substrates. It can be further developed for characterizing marine habitats on a variety of spatial scales and studying the ecological characteristic of fishes near the habitats.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.187-193
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• 2021

In order to solve the problem of false terrains caused by environmental interferences and tunneling effect in the conventional multi-beam seafloor terrain detection, this paper proposed a seafloor topography detection method based on fast two-dimensional (2D) Censored Mean Level Detector-statistics Constant False Alarm Rate (CMLD-CFAR) method. The proposed method uses s cross-sliding window. The target occlusion phenomenon that occurs in multi-target environments can be eliminated by censoring some of the large cells of the reference cells, while the remaining reference cells are used to calculate the local threshold. The conventional 2D CMLD-CFAR methods need to estimate the background clutter power level for every pixel, thus increasing the computational burden significantly. In order to overcome this limitation, the proposed method uses a fast algorithm to select the Regions of Interest (ROI) based on a global threshold, while the rest pixels are distinguished as clutter directly. The proposed method is verified by experiments with real multi-beam data. The results show that the proposed method can effectively solve the problem of false terrain in a multi-beam terrain survey and achieve a high detection accuracy.

• 한국해양공학회지
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• 제36권1호
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• pp.61-81
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• 2022

The available underwater acoustic spectrum is limited. Therefore, it is imperative to avoid frequency interference from overlapping frequencies of underwater acoustic equipment (UAE) for the co-existence of the UAE. Cognitive technology that senses idle spectrum and actively avoids frequency interference is an efficient method to facilitate the collision-free operation of multiple UAE with overlapping frequencies. Cognitive technology is adopted to identify the frequency usage of UAE to apply cognitive technology. To this end, we investigated two principle underwater acoustic sources: UAE and marine animals. The UAE is classified into five types: underwater acoustic modem, acoustic positioning system, multi-beam echo-sounder, side-scan sonar, and sub-bottom profiler. We analyzed the parameters of the frequency band, directivity, range, and depth, which play a critical role in the design of underwater acoustic cognitive technology. Moreover, the frequency band of several marine species was also examined. The mid-frequency band from 10 - 40 kHz was found to be the busiest. Lastly, this study provides useful insights into the design of underwater acoustic cognitive technologies, where it is essential to avoid interference among the UAE in this mid-frequency band.

• 한국산업융합학회 논문집
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• 제26권1호
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• pp.133-141
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• 2023

Accurate measurement of seafloor topography plays a crucial role in developing marine industries such as maritime safety, resource exploration, environmental protection, and coastal management. The seafloor topography is constructed using side scan sonar (SSS) and single beam echosounder (SBES) or multibeam echosounder (MBES), which transmit and receive ultrasound waves through a device attached to a marine survey vessel. However, the use of a sonar system is affected by noise pollution areas, and the single beam has a limited scope of application. At the same time, the multibeam is mainly applicable for depth observation. For these reasons, it is difficult to determine the boundaries and areas of seafloor topography. Therefore, this study proposes a method to improve the backscatter data of multibeam echosounder, which has a relationship with the seafloor quality, by using digital image processing to classify the shape of the underwater surface.

• 대한토목학회논문집
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• 제26권1D호
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• pp.141-147
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• 2006

강우에 의해서 발생하는 토양유실은 비옥한 표토를 유실시켜 생산성의 저하를 초래하고, 유실된 토양입자는 하천이나 호수, 댐 등에 퇴적되어 저수용량의 감소와 수질관리에 어려움을 야기 시키므로 이에 대한 대처가 필요하다. 본 연구에서는 위성 영상과 GIS 기법을 활용하여 유역내 토양침식에 영향을 미치는 토양조건, 피복조건, 지형조건들을 추출하고 이 요소들을 범용토양유실공식(USLE; Universal Soil Loss Equation)에 적용하여 유입퇴적량 및 유입 가능성이 높은 위치를 파악하였다. 또한 유입되어 하상에 쌓여 있는 퇴적량은 투과성이 강한 음향측심기를 활용하여 퇴적층과 지층의 고도 정보를 획득하여 산정하고 유실량과 퇴적량을 비교하여 퇴적되는 비율을 도출하였다.

• 한국인터넷방송통신학회논문지
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• 제13권3호
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• pp.17-24
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• 2013

본 논문은 781MHz 대역에서 안테나 상관도를 고려한 MIMO 채널 측정을 통해, 측정 데이터를 분석하고 채널 특성을 도출하였다. 상기 주파수 대역은 DTV 시스템에서 이동통신 주파수로 할당이 예정된 대역이다. 781MHz 주파수 대역은 900MHz 이동통신 시스템의 채널특성이 일정부분 유사하지만, 상당히 다른 부분이 있음을 기존 연구를 통해 증명하였다. 또한, 안테나의 상관도를 고려할 경우 신호전달 과정에 대한 보다 정확한 예측을 위해서는 채널 특성 연구가 필요하다. 기존 DTV 방송과 혼신을 피하기 위하여 측정은 제주도 인근 도심지역에서 채널사운더와 $4{\times}4$ 안테나로 채널특성을 측정하였다. 측정된 데이터를 바탕으로 도심지역에서 안테나 상관도를 고려한 채널특성을 도출하였다.