• Journal of Environmental Science International
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• v.3 no.3
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• pp.229-239
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• 1994

By laying emphasis on the intermediate layer, water property distribution in the Northwest Pacific is studied using the hydrographic data obtained by Japan Meteorologica] Agency in the period from 1960 to 1986. The scattering of water type in T-S diagram is relatively small in the Kuroshio Region. Both the envelopes of saline side and of fresh side of the scattered data points shifts gradually from saline side to fresh side as the observation line moves from southwest to northeast. In the Mixed Water Region, the scattering of water type increases rapidly as the observation line moves north; The envelope of fresh cold side moves towards fresh cold side much faster than that of same side. The thermosteric anomaly value at the salinity minimum decreases as the observation line moves from north to south or southwest. This suggests that the water does not advect along the salinity minimum layer, but that the salinity minimun layer is understood as a boundary of two different waters aligned vertically. We defined the typical water masses for the Oyashio Water and the Kuroshio Water. The water mass below the salinity minimum layer may be created by isopycnal mixing of these two water masses with a fixed mixing rate. While, the water mass above the salinity minimum cannot be created simply by isopycnal mixing. The salinity minimum layer may be eroded from upper side due to active mixing processes in the surface layer, while the water of the salinity minimum layer moves gradually southward. This appears to give an explanation why the thermosteric anomaly value at salinity minimum decreases towards south.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.2
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• pp.49-62
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• 2001

Hydrographic surveys were carried out seven times during May 31, 1998 and September 24, 1998 in order to study the physical environments of the coastal area between Narodo Is. and Sorido Is. in the southern sea of Korea (the South Sea) where the occurrence of Cochlodinium polykrikoides red tide is frequently observed in summer. Temperature and salinity of the water column from the surface to the depth of 30 m exhibit large seasonal variations. Mean temperature of the water column increased by 6 and mean salinity of the water column decreased by 2.71 psu during the observation period. Both the freshwater supplied from the adjacent land and the precipitation over the study area cannot account for the observed salinity variations. The influx of the low salinity water from the offshore area is considered to be the main cause for the observed salinity changes. Surface salinity in the study area shows different spatial distribution in the period of outbreaking, mid-stage and disappearance of the red tide. Especially, salinity was abruptly lowered at the stage of disappearance of red tide as compared to salinity of the previous observation period. Vertical structure of water properties also became vertically homogeneous at the disappearance stage, while it was highly stratified in the previous observation. Such changes can only be explained by the inflow of low salinity water from the offshore, which is considered as the most possible cause for the disappearance of the red tide in the study area. This study suggests that exchanges of water, and chemical and biological factors between coastal areas and of shore area in the South Sea need to be studied in association with the general circulation of the South Sea in order for the better understanding of the occurrence and disappearance of the red tide in the coastal area of the South Sea.

• Ocean and Polar Research
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• v.33 no.3
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• pp.309-319
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• 2011

This is a preliminary study of the feasibility of obtaining reliable tidal current harmonic constants, using one month of current observations, to verify the accuracy of a tidal model. An inference method is commonly used to separate out the tidal harmonic constituents when the available data spans less than a synodic period. In contrast to tidal constituents, studies of the separation of tidal-current harmonics are rare, basically due to a dearth of the long-term observation data needed for such experiments. We conducted concurrent and monthly harmonic analyses for tidal current velocities and heights, using 2 years (2006 and 2007) of current and sea-level records obtained from the Tidal Current Signal Station located in the narrow waterway in front of Incheon Lock, Korea. Firstly, the l-year harmonic analyses showed that, with the exception of $M_2$ and $S_2$ semidiurnal constituents, the major constituents were different for the tidal currents and heights. $K_1$, for instance, was found to be the 4th major tidal constituent but not an important tidal current constituent. Secondly, we examined monthly variation in the amplitudes and phase-lags of the $S_2$ and $K_1$ current-velocity and tide constituents over a 23-month period. The resultant patterns of variation in the amplitudes and phase-lags of the $S_2$ tidal currents and tides were similar, exhibiting a sine curve form with a 6-month period. Similarly, variation in the $K_1$ tidal constant and tidal current-velocity phase lags showed a sine curve pattern with a 6-month period. However, that of the $K_1$ tidal current-velocity amplitude showed a somewhat irregular sine curve pattern. Lastly, we investigated and tested the inference methods available for separating the $K_2$ and $S_2$ current-velocity constituents via monthly harmonic analysis. We compared the effects of reduction in monthly variability in tidal harmonic constants of the $S_2$ current-velocity constituent using three different inference methods and that of Schureman (1976). Specifically, to separate out the two constituents ($S_2$ and $K_2$), we used three different inference parameter (i.e. amplitude ratio and phase-lag diggerence) values derived from the 1-year harmonic analyses of current-velocities and tidal heights at (near) the short-term observation station and from tidal potential (TP), together with Schureman's (1976) inference (SI). Results from these four different methods reveal that TP and SI are satisfactorily applicable where results of long-term harmonic analysis are not available. We also discussed how to further reduce the monthly variability in $S_2$ tidal current-velocity constants.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.23 no.1
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• pp.1-19
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• 2018

In order to compare significant wave height (SWH) data from multi-satellites (GFO, Jason-1, Envisat, Jason-2, Cryosat-2, SARAL) and SWH measurements from Ieodo Ocean Research Station (IORS), we constructed a 12 year matchup database between satellite and IORS measurements from December 2004 to May 2016. The satellite SWH showed a root mean square error (RMSE) of about 0.34 m and a positive bias of 0.17 m with respect to the IORS wave height. The satellite data and IORS wave height data did not show any specific seasonal variations or interannual variability, which confirmed the consistency of satellite data. The effect of the wind field on the difference of the SWH data between satellite and IORS was investigated. As a result, a similar result was observed in which a positive biases of about 0.17 m occurred on all satellites. In order to understand the effects of topography and the influence of the construction structures of IORS on the SWH differences, we investigated the directional dependency of differences of wave height, however, no statistically significant characteristics of the differences were revealed. As a result of analyzing the characteristics of the error as a function of the distance between the satellite and the IORS, the biases are almost constant about 0.14 m regardless of the distance. By contrast, the amplitude of the SWH differences, the maximum value minus the minimum value at a given distance range, was found to increase linearly as the distance was increased. On the other hand, as a result of the accuracy evaluation of the satellite SWH from the Donghae marine meteorological buoy of Korea Meteorological Administration, the satellite SWH presented a relatively small RMSE of about 0.27 m and no specific characteristics of bias such as the validation results at IORS. In this paper, we propose a conversion formula to correct the significant wave data of IORS with the satellite SWH data. In addition, this study emphasizes that the reliability of data should be prioritized to be extensively utilized and presents specific methods and strategies in order to upgrade the IORS as an international world-wide marine observation site.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.4
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• pp.195-204
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• 2009

In order to estimate sea surface current fields in the East Sea, we examined characteristics of mean dynamic topography (MDT) fields (or mean surface current field, MSC) generated from three different methods. This preliminary investigation evaluates the accuracy of surface currents estimated from satellite-derived sea level anomaly (SLA) data and three MDT fields in the East Sea. AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic data) provides a MDT field derived from satellite observation and numerical models with $0.25^{\circ}$ horizontal resolution. Steric height field relative to 500 dbar from temperature and salinity profiles in the East Sea supplies another MDT field. Trajectory data of surface drifters (ARGOS) in the East Sea for 14 years provide another MSC field. Absolute dynamic topography (ADT) field is calculated by adding SLA to each MDT. Application of geostrophic equation to three different ADT fields yields three surface geostrophic current fields. Comparisons were made between the estimated surface currents from the three different methods and in-situ current measurements from a ship-mounted ADCP (Acoustic Doppler Current Profiler) in the southwestern East Sea in 2005. For offshore areas more than 50 km away from the land, the correlation coefficients (R) between the estimated versus the measured currents range from 0.58 to 0.73, with 17.1 to $21.7\;cm\;s^{-1}$ root mean square deviation (RMSD). For coastal ocean within 50 km from the land, however, R ranges from 0.06 to 0.46 and RMSD ranges from 15.5 to $28.0\;cm\;s^{-1}$. Results from this study reveal that a new approach in producing MDT and SLA is required to improve the accuracy of surface current estimations for the shallow costal zones of the East Sea.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2329-2341
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• 2013

In this study, we develop an algorithm to predict swell-like significant waves in the east coast of Korea using the directional wave gauge which is installed near Sokcho. Using the numerical wave model SWAN, we estimate wave data in open sea from the wave data observed through the directional wave gauge. Then, using the wave ray method with the open-sea wave data as offshore boundary conditions, we predict the swell-like significant waves at several points in the east coast of Korea. We verify the prediction methods with the SWAN and wave ray methods by comparing numerically predicted data against either target or measured data at the observation site. We can improve the prediction of the swell-like significant waves in the east sea of Korea using both the real-time wave measurement system and the present prediction algorithm.

• Korean Journal of Remote Sensing
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• v.33 no.6_1
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• pp.971-980
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• 2017

In this research, it was presented that the strategic approach for the long-term shoreline changes using historic digital aerial images can be effective for the analysis on the bangameori beach, west coast of South Korea. For this purpose, we collected several historic digital aerial images over 9 years in the research filed and conducted GPS-VRS surveying for GCP (Ground Control Point) acquisition. Also we collected existing two dimensional shoreline digital map which was published by KHOA (Korea Hydrographic and Oceanographic Agency) in the year 2013. With these multi data sets, we provided quantitative analysis on coastal erosion using the long-term shoreline changes in the beach. Also, As the results it was found that 2m sea level was retreated in the research period with maximum 0.31m length.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.611-620
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• 1997

The history of Tidal Bench Mark(TBM) at four major tide observation stations on the the Korea West Coast is reviewed. The data concerned with the local mean sea level(LMSL), the datum level(DL), and TBM is collected and checked. The values of LMSL surveyed by Rural Development Corporation(RDC), Office of Hydrographic Affair(OHA), and Office of Port Affair(OPA) are compared so that their unbiased MSLs at four stations are determined. Kriging model is introduced to estimate the design levels for tide; DL, MSL, and high water spring tide(HWOST). The estimated design level is well fitted with the sample data. The value of the identified drifts increase with the latitude. The estimated semi-variograms ${\gamma}(h)$ show self similarity. The values of the ${\gamma}(h)$ for DL and HWOST are 0.005 times as much as the values of ${\gamma}(h)$ of MSL.

• Journal of Korean Society for Geospatial Information Science
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• v.24 no.1
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• pp.3-8
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• 2016

Due to the recent technical development and the enhancement of image resolution, Unmanned Airborne Vehicles(UAVs) have been used for various fields. A low altitude UAV system takes advantage of taking riverbed imagery at small rivers as well as land surface imagery on the ground. The bathymetric data are generated from the low altitude UAV system. The accuracy of the data is analyzed along water depths, comparing GPS observations and a DSM generated from UAV images. It is found that the depth accuracy of the geospatial data below 50 cm depth of water satisfies the regulation(${\pm}10cm$ spatial accuracy) of bathymetric surveying. Therefore this research shows that the geospatial data generated from UAV images at shallow regions of rivers can be used for bathymetric surveying.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.553-556
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• 2004

Spatial and temporal aspects of toxic dinoflagellate Cochlodinium.p blooms and consequences of physical features in complex coastal ecosystems, off the southern Korean coast, have been investigated using data obtained from SeaWiFS and AVHRR as well as in-situ observations. Hydrographic parameters measured using CTD sensors were used to elucidate physical factors affecting the spatial distribution and abundance of Cochlodinium.p blooms. The results show spatial and temporal variations of chlorophyll-a (Chl-a) and sea surface temperature (SST) and reveal significant information about Cochlodinium.p blooms and process underlying their evolution. Satellitederived Chl-a estimates appear to be potential in explicating the evolution, movement and distribution of Cochlodinium.p blooms in the enclosed bays of the South Sea. The existence of thromohaline waters offshore provide favorable conditions for the rapid growth and subsequent southward initiation of Cochlodinium.p blooms that are influenced to flow on the offshore branch (OB) during September. It was observed that there was a significant variation in the sun-induced chlorophyll-a fluorescence signal in the remote sensing fluorescence spectra and its high-intensity was recognized during the period of exponential growth and physical transport. Satellite-derived Chl-a concentration during September 1999 ranged between $3­60mg/m^3$ inside the Jin-hae and adjacent Bays and $1-6mg/m^3$ in offshore waters, with varying Cochlodinium.p abundances 1500 to 26000 cells $ml^{-1}.$ The closely spaced CTD surveys and satellite-derived SST give a complete overview on the initiation of Cochlodinium.p blooms in hydrodynamically active regions of the offshore southern East Sea by the influence of Tsushima Warm Current (TWC).