• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.60 no.2
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• pp.152-160
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• 2024

We analyzed risk factors of coastal gillnet fishers during fishing process and considered work safety measures to reduce safety accidents during fishing using a UWB (ultra wideband) based positioning system. The static position accuracy of the UWB based positioning system was 45 cm. When entering a port, there is a risk of falling overboard. When casting a net, there was a risk of falling overboard due to being hit by fishing gear or guards, or getting caught in a buoy line or sinker line. When hauling a net, there is a risk of getting caught between fishing gear and net hauler, and the risk of musculoskeletal disorders due to repetitive work over a long period of time. Most safety accidents during work on fishing boats are blamed on human errors of the fisher and skipper, but safety accidents occur due to a mixture of mechanical and equipment factors, work and environmental factors, and management factors in addition to human errors. Therefore, the 4E were presented as countermeasures against the 4M, which are causes of safety accidents, and the proposed measures were used to identify risk factors for operation process, comply with work safety rules, and ensure the wearing of personal protective equipments. We need to reduce safety accidents during work by making it part of our daily routine. These research results can be used in the future for optimal placement of fishing gear and fishing nets in other coastal industries where safety accidents occur frequently.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.60 no.3
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• pp.277-289
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• 2024

Climate change has led to a significant increase in jellyfish populations globally, causing various problems. For power plants that use nearby seawater for cooling, the intrusion of jellyfish into intake systems can block the flow, leading to reduced output or even shutdowns. This issue is compounded by other small marine organisms like shrimp and salps, making it urgent to develop solutions to prevent their intrusion. This study addressed the problem using the BioSonics DT-X 120 kHz scientific fish finder to conduct preliminary tank experiments. We also deployed underwater acoustic and camera buoys around the intake of nuclear power plant, utilizing a bidirectional communication system between sea and land to collect data. Data collection took place from July 31, 2023 to August 1, 2023. While harmful organisms such as jellyfish and salps were not detected, we successfully gathered acoustic data on small fish measuring backscattering strength (SV). Analysis showed that fish schools were more prominent in the evening than during the day. The highest fish distribution was observed at 3:30 AM on July 31 with an SV of -44.8 dB while the lowest was at 12:30 PM on the same day with an SV of -63.4 dB. Additionally, a solar-powered system was used to enable real-time data acquisition from sea buoys with smooth communication between the land server and the offshore buoy located 1.8 km away. This research developed an acoustic-based monitoring system for detecting harmful organisms around the intake and provided foundational data for preventing marine organism intrusion and planning effective measures.

• Journal of the Korean earth science society
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• v.39 no.2
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• pp.139-153
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• 2018

The sea surface wind field has long been obtained from satellite scatterometers or passive microwave radiometers. However, the importance of satellite altimeter-derived wind speed has seldom been addressed because of the outstanding capability of the scatterometers. Satellite altimeter requires the accurate wind speed data, measured simultaneously with sea surface height observations, to enhance the accuracy of sea surface height through the correction of sea state bias. This study validates the wind speeds from the satellite altimeters (GFO, Jason-1, Envisat, Jason-2, Cryosat-2, SARAL) and analyzes characteristics of errors. In total, 1504 matchup points were produced using the wind speed data of Ieodo Ocean Research Station (IORS) and of Korea Meteorological Administration (KMA) buoys at Marado and Oeyeondo stations for 10 years from December 2007 to May 2016. The altimeter wind speed showed a root mean square error (RMSE) of about $1.59m\;s^{-1}$ and a negative bias of $-0.35m\;s^{-1}$ with respect to the in-situ wind speed. Altimeter wind speeds showed characteristic biases that they were higher (lower) than in-situ wind speeds at low (high) wind speed ranges. Some tendency was found that the difference between the maximum and minimum value gradually increased with distance from the buoy stations. For the improvement of the accuracy of altimeter wind speed, an equation for correction was derived based on the characteristics of errors. In addition, the significance of altimeter wind speed on the estimation of sea surface height was addressed by presenting the effect of the corrected wind speeds on the sea state bias values of Jason-1.

• Ocean Systems Engineering
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• v.1 no.4
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• pp.285-296
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• 2011

Spar platforms have several advantages for deploying wind turbines in offshore for depth beyond 120 m. The merit of spar platform is large range of topside payloads, favourable motions compared to other floating structures and minimum hull/deck interface. The main objective of this paper is to present the response analysis of the slack moored spar platform supporting 5MW wind turbine with bottom keel plates in regular and random waves, studied experimentally and numerically. A 1:100 scale model of the spar with sparD, sparCD and sparSD configuration was studied in the wave basin ($30{\times}30{\times}3m$) in Ocean engineering department in IIT Madras. In present study the effect of wind loading, blade dynamics and control, and tower elasticity are not considered. This paper presents the details of the studies carried out on a 16 m diameter and 100 m long spar buoy supporting a 90 m tall 5 MW wind turbine with 3600 kN weight of Nacelle and Rotor and 3500 kN weight of tower. The weight of the ballast and the draft of the spar are adjusted in such a way to keep the centre of gravity below the centre of buoyancy. The mooring lines are divided into four groups, each of which has four lines. The studies were carried out in regular and random waves. The operational significant wave height of 2.5 m and 10 s wave period and survival significant wave height of 6 m and 18 s wave period in 300 m water depth are considered. The wind speed corresponding to the operational wave height is about 22 knots and this wind speed is considered to be operating wind speed for turbines. The heave and surge accelerations at the top of spar platform were measured and are used for calculating the response. The geometric modeling of spar was carried out using Multisurf and this was directly exported to WAMIT for subsequent hydrodynamic and mooring system analysis. The numerical results were compared with experimental results and the comparison was found to be good. Parametric study was carried out to find out the effect of shape, size and spacing of keel plate and from the results obtained from present work ,it is recommended to use circular keel plate instead of square plate.

• 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 the Korean Association of Geographic Information Studies
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• v.10 no.2
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• pp.47-57
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• 2007

Real-time oceanographic information system was developed using platforms of aquaculture farms to examine causes of mass mortality of hatchery fishes, and to reduce the damage of mass mortality which has been occurred frequently off coast by abnormal change of ocean conditions. The system had the advantages of direct data distribution to fishermen at the farm and instant maintenance of equipments due to easy access to the farms and residents at the farms in comparison with offshore mooring buoy system. To avoid discontinued measurement of the system, repairs caused by malfunction of equipments, bimonthly preventive maintenances and daily monitoring of measured data were systematized. Confidence intervals calculated by a statistical method using accumulated data were applied to data management. Such activities could minimize discontinuance of measurement and keep information more trustful. In addition, the system has various ways of data distribution. Through homepage and e-mail in the internet, information was provided to public. Display units which were connected to equipments at the farm gave the measured data directly to fishermen, which guided them to run their farm scientifically. Finally large display unit was installed at a fish market and showed the measured data at the nearest station with tide and weather information. Proper region for aquaculture and wintering region were studied using temperature data obtained by the system in 2006. The system will contribute to reduce economic damage of coastal fishery and to understand coastal marine environment.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.426-434
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• 2022

Bubbles generated by various causes in the ocean are known to persist for long periods of time. Although the volume occupied by bubbles in the ocean is small, the presence of bubbles in ocean due to resonance and attenuation greatly affects the acoustic properties. Accordingly, bistatic reverberation experiment was performed in the ocean where artificial bubbles exist. A number of transducers and receivers were installed on 6 buoys arranged in a hexagonal shape, and blowing agents were dropped in the center of the buoy to generate bubbles. For reverberation modeling that reflects acoustic characteristics changed by bubbles, the spatial distribution of bubbles was estimated using video data and received signals. A measurement-based bubble spectral shape was used, and it was assumed that the bubble density within the spatial distribution of the estimated bubble was the same. As a result, it was confirmed that the bubble reverberation was simulated in a time similar to the measured data regardless of the bubble density, and the bubble reverberation level similar to the measured data was simulated at a void fraction of about 10^-7 ~ 10^-6.8.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.206-211
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• 2011

Low water temperature during the summer associated with the occurrence of cold water zone off Haeundae was studied using the data from CTD observations and a monitoring buoy deployed in Suyeong Bay. Shortterm variability of current was dominant and was not related to the wind. The NE-SW components of wind parallel to the coast contained more than 96% of total variance and could account for major fluctuations of water temperature. Upwelling-response of water temperature was very sensitive so that the temperature began to decrease immediately after the onset of the southwesterly wind. In particular, there were three cases in which SW winds for only two days caused considerable temperature drops. In 2009, four upwelling events shorter than 5 days took place while seven events with periods of 2~18 days were recorded in 2010. During a very intense upwelling for seven days in mid-August 2010, temperature decreased by more than $10^{\circ}C$ in spite of the variable winds. Temperature variability at Gampo, Ulsan, Gijang and Haeundae had similar patterns. CTD observation and satellite imagery showed that the upwelling zone could be extended to the Haeundae-Busan area. According to the wavelet analysis, coherent periods were 2~8 days during the frequent upwelling/downwelling events.

• Korean Journal of Remote Sensing
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• v.24 no.4
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• pp.273-287
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• 2008

Characteristics of skin-bulk sea surface temperature (SST) differences in the Northeast Asia seas were analyzed by utilizing 845 collocated matchup data between NOAA/AVHRR data and oceanic in-situ temperature measurements for selected months from 1994 to 2003. In order to understand diurnal variation of SST within a few meters of the upper ocean, the matchup database were classified into four categories according to day-night and drifter-shipboard measurements. Temperature measurements from daytime drifters showed a good agreement with satellite MCSST (Multi-Channel Sea Surface Temperature) with an RMS error of about $0.56^{\circ}C$. Poor accuracy of SST with an rrns error of $1.12^{\circ}C$ was found in the case of daytime shipboard CTD (Conductivity, Temperature, Depth) measurements. SST differences between MCSST and in-situ measurements are caused by various errors coming from atmospheric moist effect, coastal effect, and others. Most of the remarkable errors were resulted from the diurnal variation of vertical temperature structure within a few meters as well as in-situ oceanic temperatures at different depth, about 20 cm for a satellite-tracked drifting buoy and a few meters for shipboard CTD or moored buoy. This study suggests that satellite-derived SST shows significant errors of about ${\pm}3^{\circ}C$ in some cases and therefore it should be carefully used for one's purpose on the base of in-depth understanding of skin-bulk SST difference and vertical temperature structure in regional sea.

• Journal of the Korean earth science society
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• v.42 no.5
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• pp.536-555
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• 2021

Sea-surface wind is an important variable in ocean-atmosphere interactions, leading to the changes in ocean surface currents and circulation, mixed layers, and heat flux. With the development of satellite technology, sea-surface winds data retrieved from scatterometer observation data have been used for various purposes. In a complex marine environment such as the Korean Peninsula coast, scatterometer-observed sea-surface wind is an important factor for analyzing ocean and atmospheric phenomena. Therefore, the validation results of wind accuracy can be used for diverse applications. In this study, the sea-surface winds derived from ASCAT (Advanced SCATterometer) mounted on MetOp-A/B (METeorological Operational Satellite-A/B) were validated compared to in-situ wind measurements at 16 marine buoy stations around the Korean Peninsula from January to December 2020. The buoy winds measured at a height of 4-5 m from the sea surface were converted to 10-m neutral winds using the LKB (Liu-Katsaros-Businger) model. The matchup procedure produced 5,544 and 10,051 collocation points for MetOp-A and MetOp-B, respectively. The root mean square errors (RMSE) were 1.36 and 1.28 m s^-1, and bias errors amounted to 0.44 and 0.65 m s^-1 for MetOp-A and MetOp-B, respectively. The wind directions of both scatterometers exhibited negative biases of -8.03° and -6.97° and RMSE values of 32.46° and 36.06° for MetOp-A and MetOp-B, respectively. These errors were likely associated with the stratification and dynamics of the marine-atmospheric boundary layer. In the seas around the Korean Peninsula, the sea-surface winds of the ASCAT tended to be more overestimated than the in-situ wind speeds, particularly at weak wind speeds. In addition, the closer the distance from the coast, the more the amplification of error. The present results could contribute to the development of a prediction model as improved input data and the understanding of air-sea interaction and impact of typhoons in the coastal regions around the Korean Peninsula.