• Korean Journal of Remote Sensing
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• v.18 no.4
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• pp.209-220
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• 2002

We carried out studies on SAR image intensity and interferometric phase over oyster sea farms. Strong backscattering was observed in amplitude images, and that was considered as a radar signal double bouncing from horizontal bars. These sea farming structures are not visible in satellite optical images except IKONOS image, so that it demonstrates the value of radar remote sensing as an effective tool in support of sea farm detection. The intensity of the image is sensitive to system parameters including wavelength, polarization, and look direction, but does not correlate to tide height. We found that the strongest backscattering can be obtained by L-band HH-polarization with a look direction perpendicular to the horizontal bar. We also succeeded in generating 21 coherent JERS-1 SAR interferometric pairs over the oyster farms. The general trend of the fringe rate of the interferometric phases appeared to be governed by altitude of ambiguity. The general trend was modeled by an inverse function and removed to have a residual phase. The residual phase showed a linear relation with the tide height. The results demonstrate for the first time that SAR can possibly be used to estimate sea level. However, the r.m.s. error of a regression line is 11.7 cm, and that is so far too large to make reliable assessments of sea level in practical applications. Further studies is required to improve the accuracy specifically using multi-polarization SAR data.

• Korean Journal of Remote Sensing
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• v.16 no.3
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• pp.221-233
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• 2000

An intertidal topography is continuously changed due to morphodynamics processes. Detection and measurement of topographic change for a tidal flat is important to make an integrated coastal area management plan as well as to carry out sedimentologic study. The objective of this study is to generate intertidal DEM using leveling data and waterlines extracted from optical and microwave remotely sensed data in a relatively short period. Waterline is defined as the border line between exposed tidal flat and water body. The contour of the terrain height in tidal flat is equivalent to the waterline. One can utilize satellite images to generate intertidal DEM over large areas. Extraction of the waterline in a SAR image is a difficult task to perform partly because of the presence of speckle and partly because of similarity between the signal returned from the sea surface and that from the exposed tidal flat surface or land. Waterlines in SAR intensity and coherence map can effectively be extracted with MSP-RoA edge detector. From multiple images obtained over a range of tide elevation, it is possible to build up a set of heighted waterline within intertidal zone, and then a gridded DEM can be interpolated. We have tested the proposed method over the Gomso Bay, and succeeded in generating intertidal DEM with relatively high accuracy.

• Geophysics and Geophysical Exploration
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• v.27 no.1
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• pp.37-50
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• 2024

The magnetotelluric (MT) survey can be affected by external environmental factors. In particular, when acquiring MT data in islands, it is essential to consider the combined effect of topography and sea to understand the results and make accurate interpretations. To analyze the MT response (apparent resistivity, phase) with consideration of the effect of topography and sea, a small cone-shaped island model surrounded by deep sea was created. Two-dimensional (2-D) and three-dimensional (3-D) forward modeling were performed on the terrain model considering topography and the island model considering both topography and sea. The 2-D MT response did not reflect the topographic and sea effect of the direction orthogonal to the 2-D profile. The 3-D MT response included topographic and sea effects in all directions. The XY and YX components of the apparent resistivity were separated on undulating topography, such as a hill. A conductor at 1 km below sea level could be distinguished from topographic and sea effects in the MT response, and low resistivity anomaly was attenuated at greater depths. This study will facilitate understanding of field data measured on small islands.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.2
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• pp.71-80
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• 2001

To understand paleoceanographic environmental changes in the Esat Sea during the transitional period between Holocene and last glacial maximum, geochemical high resolution study was conducted by using a piston core(95PC-1) samples collected from the southernmost part of the Ulleung Basin. Geochemical results reveal that major distinctive paleoceanographic variations in transitional period are prominent. Major elemental concentrations show distinctive variations between glacial and Holocene suggesting changes in sediment supply. $TiO_2/Al_2O_3$ ratio of the sediment indicates different sediment composition between Holocene and glacial period. The content of total organic carbon ranging from 0.5% to 4% during transitional period. These vslues showed 2-4 times and two times higher than those of last glacial and Holocene, respectively. The C/N ratios deduced from organic matters exceed10 during transitional period suggesting terrigenous organic matter are supplied from continent, especially during last glacial maximum. Carbonate contents are relatively stable during Holocene and last glacial maximum with gradual decrease during glacial period with high fluctuation during transitional period. The variations of chemical index of weathering (CIW) also show a distinctive variation between glacial and Holocene, which is coincident with those of carbonate and organic carbon. The grain size distribution indicates that the difference content of silt fraction during Holocene and glacial period is closely related with climatic effect during glacial period. Therefore geochemical differences in sediment composition between Holocene and last glacial maximum is thought to be related to paleoceanographic, sea-level change and local paleoclimatic changes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.301-307
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• 2009

The Korean peninsula has a number of coastal sites where the rhythmic rising and lowering of water surface due to tides results in strong tidal current. The kinetic energy of these currents can be efficiently exploited by use of tidal current turbines. This paper investigates the characteristics of helical turbine based on in-field test. The experimental frame was constructed at the Uldolmok narrow channel between Jindo and Haenam and installed the helical turbine of diameter 2.2 m and height 2.5 m. 3-blade turbine had the maximum efficiencies of about 30% in the current velocity range between 1.5 and 2.3 m/s and 6-blade turbine han the maximum efficiencies of about 25%. The efficiency was constant with the current velocity. TSRs of 3-blade and 6 blade turbines were observed as 2.4 and 1.9 respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.1
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• pp.1-9
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• 2012

Tidal residual is being an important factor by the influence of the climate change in terms of the coastal safety and defense. It is one of the most important factor for the determination of the reference sea level in order to check the safety and performance of the coastal structures in company with the typhoon intensity variation. The probability density function (pdf) of tidal residuals in the Korean coasts have a non-ignorable skewness and high kurtosis. It is highly restricted to the application of the normal pdf assumption as an approximated pdf of tidal residuals. In this study, the pdf of tidal residuals estimated using the Kernel function is suggested as a more reliable and accurate pdf of tidal residuals than the normal function. This suggested pdf shows a good agreement with the empirical cumulative distribution function and histogram. It also gives the more accurate estimation result on the extreme values in comparison with the results based on the normal pdf assumption.

• Journal of the Korean Geophysical Society
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• v.9 no.2
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• pp.135-145
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• 2006

The surface temperature and hydrological budget for the last glacial maximum (LGM) is simulatedwith an atmospheric general circulation model of NCAR CCM3 at spectral truncation of T170, corespondingto a grid cel size of roughly 75 km. LGM simulations were forced with the reconstructed CLIMAP sea surface temperatures, sea ice distribution, ice sheet topography, reduced CO2, and orbital parameters.oC in winter, 5.6oC in sumer,and 6oC annual-mean. The decrease of surface temperature leads to a weakening of the hydrologicalcycle. Global-mean precipitation decreases by about 14% in winter, 17% in summer, and 13% annually.However, some regions such as the U.S., southern Europe, northern and eastern Africa, and the SouthAmerica appear to be weter in the LGM winter and Canada and the Midle East are weter in sumer. model captures detailed climate features over land.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.333-333
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• 2023

기후변화로 인해 전지구적인 이상기후현상이 빈번하게 발생하고 있으며 지구온도와 해수면상승과 더불어 강우패턴의 변화가 세계적인 문제로 대두되고 있다. 특히 아세안 국가의 경우 태풍 및 집중호우에 대한 침수피해의 빈발로 2,000만명 이상이 피해를 입은 것으로 나타났다. 이러한 윈인으로는 자연재해에 의한 인명 및 재산피해관련 대응기술의 개발 및 대응조직의 전문성이 미흡하다는 것이 가장 큰 원인으로 제시되고 있다. 이에 많은 국가 및 기관에서 재난 대응 기술을 ODA사업을 통해 지원하고 있다. 우리나라에서도 지속적인 ODA사업으로 재난 대응 기술, 그 중에서도 홍수대응 기술을 적극적으로 보급하고 있다. 본 연구에서는 ASEAN국가 현지 맞춤형 인공지능 하천수위예측 모형을 개발하여 ASEAN국가의 홍수대응 능력을 향상시키고자 하였다. 연구대상으로는 관측데이터의 수집이 용이하고 양질의 관측자료를 장기간 확보할 수 있는 필리핀의 Montalban 관측소를 대상으로 하였다. Montalban 수위관측소는 마닐라를 관통하는 마리키나 강의 상류에 위치하고 있다. 주변에는 상류쪽에 Mt. Oro 강우관측소가 있으며 해당 관측소의 강우자료와 Montalban 관측소의 수위자료를 입력자료로 활용하여 최대 3시간까지 수위를 예측하였다. 예측수위에 대한 적합도 지표로 NSE(Nash-Sutcliffe model efficiency coefficient)를 사용하였으며 2시간 예측까지는 0.8이상의 유의미한 결과를 나타내 홍수예보에 활용할 수 있을 것으로 판단되나, 3시간 예측결과는 홍수예보에 활용하기 어려운 것으로 판단하였다. 이는 Mt. Oro관측소에 내린 강우가 Montalban 관측소에 도달하기까지 소요되는 시간이 3시간 이내이기 때문으로 판단된다. 관측소의 수위자료와 상류에 위치한 강우관측소의 장기간 고품질의 관측자료가 존재한다면 높은 정확도의 예측결과를 도출 할 수 있을 것으로 판단된다.

• Journal of the Korean earth science society
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• v.45 no.3
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• pp.239-259
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• 2024

In this study, a qualitative meta-analysis was conducted on research papers on earth science education to derive knowledge of students' understanding of specific science topics-greenhouse effect, global warming, and climate change-within the context of collective Pedagogical Content Knowledge (PCK). Twenty-two research papers addressing students' alternative conceptions (misconceptions) about these topics were selected and analyzed for their respective definitions, causes (mechanisms), and impacts. Semantic network analysis and a mental model framework were applied to synthesize the findings. The meta-analysis revealed several key insights: (1) Regarding the greenhouse effect, students often used the terms "greenhouse effect" and "global warming" interchangeably, lacked knowledge about the types of greenhouse gases, and misunderstood their roles. They commonly associated the greenhouse effect with environmental pollution or changes in the ozone layer, failing to recognize its relation to the heat balance between the surface and atmosphere. (2) Concerning global warming, students confused it with sea level rise and linked it to pollution, ozone layer changes, and glacier melting. They understood global warming as a disruption of the heat balance between the surface and atmosphere but had misconceptions about its environmental impacts. (3) In terms of climate change, students used the term interchangeably with global warming, weather change, and climate anomalies. They associated climate change with atmospheric pollution and ozone layer depletion but misunderstood its environmental impacts. As result, three mental models-categorical, mechanistic, and hierarchical misconceptions-were identified as collective PCK. The implications for enhancing earth science teachers' PCK were discussed based on these findings.

• 한국지형공간정보학회:학술대회논문집
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• 2004.10a
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• pp.167-173
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• 2004

The erosion(or sediment) reaches very serious level due to the aftermath by the imprudent reclamation on the coast. Continuous studies for long on coastline erosion may be warranted and possible countermeasures proposed because the change of the coastline has been progressed slowly for a long period of time in a wide area. Many experts anticipate that the global sea level's average increase by 19-35 cm due to global warming may certainly have an effect on the coastal erosion throughout the world. Thus, a more rigorous study on the causes of changing coastlines is particularly proposed to find ways to counteract any possible threats against coastal environments. In this study, Ortho aerial photo and hydrographic survey datum were utilized to quantitatively analyze coastal erosion and sediment patterns. This paper also seeks to prove that a parcel under the sea occurred due to relatively significant changes to the coastline. We created Ortho aerial photo using aerial photos taken each decade ('81, '93, '00), overlaid them onto a cadastral registration map, and calculated each amount of erosion and sediment while accounting for the tide level and without considering it. As the result of this study, we could propose that the methods of Ortho aerial photo and the marine observation datum were the effective ways of change detection in erosion, sediment, and artificial reclamation of the coastline for a long time.