• Journal of Wetlands Research
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• v.23 no.2
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• pp.154-162
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• 2021

The naturally opened Han river estuary is a place where the flows of the Han river, Imjin river, Yaesung river meet with West Sea of Korea, so the hydrodynamic mechanism(Impact-Response) structure of Han river estuary is complex. Continuous observation and measurement due to the morphological characteristics at the estuary are required to maintain the estuary environment and river management facilities. However, the Sannam wetland(the study area) is in the military operation area. Therefore, Sannam wetland has the limited access under the control from military office. In 2020, there had a natural disaster due to flooding in August and COVID-19, and it made a survey hard. The noncontact survey technique, the analysis of LANDSAT images at Sannam wetland, was applied to analyze riverbed fluctuation and morphological transformation around Sannam wetland. LANDSAT images obtained from EarthExplorer, USGS and analyzed by QGIS. The analysis was performed based on the area and the distance near Sannam wetland. As a result, an erosion was happened on the downstream of the study area, and the upstream of the study area did not have any serious sediment transport. Considering the resolution of LANDSAT images, this noncontect survey technique is applicable to manage the study area. From the analysis of LANDSAT images, it is assumed that the tidal effect is greater than the inflow from the upstream. The pattern change of tidal response causes the damage of the river facilities near the Hangang river estuary.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.269-269
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• 2022

최근 낙동강 하구 기수생태 복원에 있어서 중요한 요소 중 하나는 하굿둑 외해측의 보다 높은 정도를 가지는 조석예보치 산정과 이를 통해 하굿둑 방류량과 해수 유입량을 추정하여 주변 환경 등을 예측할 수 있다. 기수생태 복원이 본격으로 논의가 진행 전인 2016년까지는 하구에서 수km 떨어진 기존 조위관측소(부산 및 가덕도)를 활용하여 하류수위를 예측하여 왔지만 조위 높이와 위상 차이로 인하여 활용이 용이하지 않다. 따라서, 낙동강 하굿둑 인접 외해역에서 조석 영향을 받는 수위관측치를 이용하여 조석조화분해를 통해 조위 예측을 보다 정밀하게 산정하는 것이 필요하다. 연구방법으로는 낙동강 하굿둑 외해역에서 관측된 2016년, 2017년 각각 1년간 10분간격으로 관측자료의 저장상태 및 이상자료 유무를 확인하고, 조석조화분해 프로그램인 TASK2000(Tidal Analysis Software Kit) Package를 이용하여 2016년, 2017년 낙동강 하굿둑 인접 외해역에서 관측된 조위자료를 각각 조석조화분해한 결과로 관측조위와 예측조위 비교하였고, 관측조위와 예측조위를 뺀 성분인 조석잔차성분을 구했다. 조화분해결과, 낙동강 하굿둑 외해역은 일반적인 연안역의 조석과는 달리 하천수의 유출, 배수갑문의 조작, 연안사주지형에 의한 조석변형 등 매우 복잡하고 불규칙적인 특성인 기상성분(기압, 바람 등)에 의한 교란을 고려한다면 예측정확도가 상당부분 확보되는 것으로 나타났다. 또한 장주기 성분과 비선형 조석성분의 크기를 비교해 볼 때 거의 편차가 없이 나타나 조석조화상수를 이용한 예보 가능성을 확인할 수 있었다. 조위검증은 2016년의 1년치의 조석자료를 이용하여 조화분해된 조화상수 63개를 이용하여 2017년의 조석 예보치를 산정하였으며, 이를 2017년의 낙동강 하굿둑 외해역의 조석관측치와 조석예측치를 1대 1 비교하는 방식으로 검증하였고, 이들의 상관관계를 파악하기 위하여 두 성분에 대하여 Regression Analysis를 수행하여 예측조위와 관측조위 사이에는 Pre=0.9535×Obs+0.396과 같은 관계식이 성립하는 것으로 분석되었다. 또한, 두 성분간의 상관도는 0.9535로 높게 나타났다. 조위예측 프로그램인 TASK2000 Package 중 MARIE를 이용한 조위예측 프로그램의 신뢰도가 매우 높은 것으로 판단되고, 해당년도 조위예측 시에는 가능하면 직전년도의 1년 조석관측자료를 조화분해하고 얻어진 조화상수를 이용하여 조위예측을 실시하면 보다 정확한 자료를 얻을 수 있다.

• Ocean and Polar Research
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• v.42 no.3
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• pp.195-210
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• 2020

The observed time series from the Korea Ocean Research Stations (KORS) in the Yellow and East China Seas (YECS) have various sources of noise, including bio-fouling on the underwater sensors, intermittent depletion of power, cable leakage, and interference between the sensors' signals. Besides these technical issues, intricate waves associated with background tidal currents tend to result in substantial oscillations in oceanic time series. Such technical and environmental issues require a regionally optimized automatic quality control (QC) procedure. Before the achievement of this ultimate goal, we examined the approach of the Ocean Observatories Initiative (OOI)'s standard QC to investigate whether this procedure is pertinent to the KORS. The OOI QC consists of three categorized tests of global/local range of data, temporal variation including spike and gradient, and sensor-related issues associated with its stuck and drift. These OOI QC algorithms have been applied to the water temperature time series from the Ieodo station, one of the KORS. Obvious outliers are flagged successfully by the global/local range checks and the spike check. Both stuck and drift checks barely detected sensor-related errors, owing to frequent sensor cleaning and maintenance. The gradient check, however, fails to flag the remained outliers that tend to stick together closely, as well as often tend to mark probably good data as wrong data, especially data characterized by considerable fluctuations near the thermocline. These results suggest that the gradient check might not be relevant to observations involving considerable natural fluctuations as well as technical issues. Our study highlights the necessity of a new algorithm such as a standard deviation-based outlier check using multiple moving windows to replace the gradient check and an additional algorithm of an inter-consistency check with a related variable to build a standard QC procedure for the KORS.

• Journal of Environmental Science International
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• v.19 no.11
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• pp.1397-1405
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• 2010

Mass mortalities of cultivated organisms have occurred frequently in Korean coastal waters causing enormous losses to cultivating industry. The preventive measures require continuous observation of farm environment and real-time provision of data. However, line hanging aquaculture farm are generally located far from monitoring buoys and has limitations on installation of heavy equipments. Substituting battery pack for solar panels and miniaturizing size of buoy, newly developed system can be attached to long line hanging aquaculture farm. This system could deliver measured data to users in real-time and contribute to damage mitigation and prevention from mass mortalities as well as finding their causes. The system was installed off Gijang and Yeongdeck in Korea, measuring and transmitting seawater temperature at the sea surface every 30 minutes. Short term variation of seawater temperature, less than one day, in Gijang from June to July 2009 corresponded tidal period of about 12 hours and long term variation seemed to be caused by cold water southeast coast of Korea, particularly northeast of Gijang. Seawater temperature differences between Gijang station and the other station that is about 500 m away from Gijang station were $1^{\circ}C$ on average. This fact indicates that it is need to be pay attention to use substitute data even if it is close to the station. Daily range of seawater temperature, one of crucial information to aquaculture, can be obtained from this system because temperature were measured every 30 minutes. Averages of daily range of temperature off Gijang and Yeongdeok during each observation periods were about $2.9^{\circ}C$ and $4.7^{\circ}C$ respectively. Dominant period of seawater temperature variation off Yeongdeok was one day with the lowest peak at 5 a.m. and the highest one at 5 p.m. generally, resulting from solar radiation.

• Journal of fish pathology
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• v.18 no.1
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• pp.49-58
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• 2005

Hemacolor stain, histopathological observation and FTM incubation assay were applied to detect Perkinsus sp. infection in Manila clams (Ruditapes philippinarumi taken from culture beds at Tean and Gochang from March 2002 to August 2003. The prevalency was 100% in the clams from Gochang and 20-70% from Tean. Of the three methods, histopathological observation was the most effective to detect the infection. And the parasites was most abundant in gills. When PCR assay was applied to detect Perkinsus sp. for four species of Mollusc such as manila clam, surf clam (Mactra veneriformis), oyster (Crassostrea gigas) and Thomas' rapa whelk (Rapana venosa) taken from Tean and Gochang from April to July 2004, the parasites were detected from all the species at the infection rates of 95%, 62%, 46.9% and 10% in that order. The infection rate was much higher in the species burrowing in the bottom sediments than those attaching on the tidal rock. The results suggest that Perkinsus sp. may affect almost all the molluscs inhabiting western coastal areas of Korea.

• Journal of Marine Life Science
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• v.5 no.2
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• pp.99-106
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• 2020

To investigate effect of variation in physiochemical conditions due to river discharge on phytoplankton, field surveys were conducted in the Seomjin and Yeongsan River estuaries from April to November 2016. The concentrations of DIN and DSi in Seomjin River estuary were gradually low as distance from upstream. On the other hands, the concentrations of DIN and DSi in Yeongsan River estuary were critically high at upstream, due to which is characterized as semi-enclosed eutrophic area. A total of 12 phytoplankton pigments were analyzed, and the distribution of each taxa was investigated using indicator for each phytoplankton taxa. Fucoxanthin, an indicator pigment of diatoms, showed an average of 0.61±1.00 ㎍ l^-1 and 0.76±1.22 ㎍ l^-1 in the Seomjin and Yeongsan River estuaries, respectively. Concentration of fucoxanthin was more than twice that of other pigments except chlorophyll a., indicating that diatoms were dominant taxa. Peridinin, an indicator pigment of dinoflagellate, showed some similar tendency to the microscopic observation, but mismatch results were also present, indicating a technical limitation of pigment analysis. Chlorophyll b, alloxanthin, and zeaxanthin, which are indicator pigments of green algae, cryptomonads, and cyanobacteria, were detected in both estuaries even though those taxa were not detected in microscopic observation. This indicates that the two estuaries were affected by freshwater species. Here, we can suggest that phytoplankton composition in estuary was directly influenced by the inflow from upstream. In particular, the phytoplankton population dynamics in Yeongsan River estuary was greatly associated with a large-scale artificial dyke, especially in summer rainy season. On the other hands, the seasonal and horizontal distribution of phytoplankton in Seomjin River estuary has changed along the salinity gradients and inflow-related changes.

• Journal of Korea Water Resources Association
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• v.55 no.8
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• pp.565-575
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• 2022

Recently, in the field of water resource engineering, interest in predicting time series water levels and flow rates using deep learning technology that has rapidly developed along with the Fourth Industrial Revolution is increasing. In addition, although water-level and flow-rate prediction have been performed using the Long Short-Term Memory (LSTM) model and Gated Recurrent Unit (GRU) model that can predict time-series data, the accuracy of flow-rate prediction in rivers with rapid temporal fluctuations was predicted to be very low compared to that of water-level prediction. In this study, the Paldang Bridge Station of the Han River, which has a large flow-rate fluctuation and little influence from tidal waves in the estuary, was selected. In addition, time-series data with large flow fluctuations were selected to collect water-level and flow-rate data for 2 years and 7 months, which are relatively short in data length, to be used as training and prediction data for the LSTM and GRU models. When learning time-series water levels with very high time fluctuation in two models, the predicted water-level results in both models secured appropriate accuracy compared to observation water levels, but when training rapidly temporal fluctuation flow rates directly in two models, the predicted flow rates deteriorated significantly. Therefore, in this study, in order to accurately predict the rapidly changing flow rate, the water-level data predicted by the two models could be used as input data for the rating curve to significantly improve the prediction accuracy of the flow rates. Finally, the results of this study are expected to be sufficiently used as the data of flood warning system in urban rivers where the observation length of hydrological data is not relatively long and the flow-rate changes rapidly.

• Journal of Navigation and Port Research
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• v.46 no.6
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• pp.483-490
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• 2022

Floating LiDAR is a system that provides a new paradigm for wind condition observation, which is essential when creating an offshore wind farm. As it can save time and money, minimize environmental impact, and even reduce backlash from local communities, it is emerging as the industry standard. However, the design and verification of a stable platform is very important, as disturbance factors caused by fluctuations of the buoy affect the reliability of observation data. In Korea, due to the nation's late entry into the technology, a number of foreign equipment manufacturers are dominating the domestic market. The west coast of Korea is a shallow sea environment with a very large tidal difference, so strong currents repeatedly appear depending on the region, and waves of strong energy that differ by season are formed. This paper conducted a study examining buoys suitable for LiDAR operation in the waters of Korea, which have such complex environmental characteristics. In this paper, we will introduce examples of optimized design and verification of ship-type buoys, which were applied first, and derive important concepts that will serve as the basis for the development of various platforms in the future.

• Journal of Industrial Technology
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• v.36
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• pp.71-76
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• 2016

In this study, we determined the precise coordinates of TBMs (Tidal Bench Marks), which used as the national reference points in coastal area of Korea, using a GPS data analysis SW for the academic and scientific applications, GAMIT/GLOBK. For accurate 3-D positioning of TBM locations, we performed the GPS point surveying according to the national surveying policy and also acquired the GPS data for 48 TBMs located in the western and southern coastal part of Korea. Considering the results of baseline analysis to each observation session obtained from GAMIT module, the baseline analysis was realized to be done precisely because the values of Normalized RMS (NRMS) were mostly less than ${\pm}0.20mm$. Before the network adjustment using GLOBK module, we evaluated the suitability of observations for each session by applying the chi-squared test (${\chi}^2$ test) to the degree of freedom in observed session. An overall distributions of ${\chi}^2$ test were less than 1.0 for all sessions, and the statistical of ${\chi}^2$ test showed the average, 0.267 with minimum and maximum value, 0.063 and 0.653, respectively. Finally, we analyzed the network adjustment for 48 TBMs to reduce the residuals of baseline analysis on each point by connecting with 42 permanent GPS stations in Korea. In the network adjustment procedure, we set up the weighted values of each permanent station to be allocated between 0.9 and 1.14, and also removed the observed points having residual exceeds 4-times of standard deviation ($4{\sigma}$).

• Water for future
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• v.15 no.3
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• pp.23-36
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• 1982

The stochastic variations and structures of time series data on water quality were examined by employing the techniques of autocorrelation function, variance spectrum, Fourier series, autoregressive model and ARIMA model. These time series included hourly and daily observation on DO, turbidity, conductivity pH and water temperature. The measurement was made by automatic recording instrument at Noryangjin and Dook-do located in the downstream part of Han River during 1975 and 1976. Hourly water quality time series varied with the dominant 24-hour periodicity, and the 12-hour periodicity was also observed. An important factor affecting 24-hour periodic variation of DO is believed to be photosynthesis by algae. These phenomena might be attributable to periodic discharges of municipal sewage. Noryangjin site showed the more distinct 12-hour periodicity than Dook-do site did, and tidal effect might be responsible for the difference. The water quality, as measured by DO and turbidity, was better in the afternoon compared with the quality in the morning. This change can be explained by the periodic variation of DO, temperature and the amount of municipal wewage discharge. It was also observed that the water temperature at Noryangjin was higher than the temperature at Dook-do. This difference might have been caused by the pollutants that were added to the section between two sites. The correlation coefficients between some of the variables were fairly high. For example, the coefficient was -0.88 between DO and water temperature, 0.75 between turbidity and river flow, and 0.957 between water temperature and air temperature. The lag time of heat transfer from the air to the water was estimated as 24 days. The first order auto-regressive model was appropriate for explaning standardized hourly DO time series. The ARIMA model of (1, 0, 0) type provided relatively satisfactory results for daily DO time series after the removal of significant harmonic value.