• Ocean Systems Engineering
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• v.14 no.2
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• pp.101-114
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• 2024

Seafloor sediment mapping is an essential research topic in shallow coastal waters, especially in port development, benthic habitat mapping, and underwater communications. The seafloor sediments can be interpreted by collecting sediment samples directly in the field using a grab sampler or corer. Another method is optical, especially using underwater cameras and videos. Both methods each have weaknesses in terms of area coverage (mechanic) and accurate positioning (optic). The latest technology used to overcome it is the acoustic method (echosounder) with Global Navigation Satellite System (GNSS) Real Time Kinematic (RTK) positioning. Therefore, in this study will propose the classification of seafloor sediments in coastal waters using acoustic method that is Multibeam Echosounder (MBES) multi-frequency with five frequency (200 kHz, 250 kHz, 300 kHz, 350 kHz, and 400 kHz). In this study, the deep neural network (DNN) used the bathymetric multi frequency, bathymetric difference inters frequencies, and bathymetric features from 5 (five) frequencies as input layer and 4 (four) sediment types in 74 (seventy-four) sample sediment as output layer to make a seafloor sediment map. Results of sediment mapping using the DNN method show an overall accuracy of 71.6% (significant) and a kappa coefficient of 0.59 (moderate). The distribution of seafloor sediment in the study area is mainly silt (41.6%), followed by clayey sand (36.6%), sandy silt (14.2%), and silty sand (7.5%).

• Journal of the Korean earth science society
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• v.26 no.8
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• pp.836-843
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• 2005

Two data sets of repeated hydrographic surveys with a single beam echo-sounder were obtained to investigate morphological changes on a sand mining site within EEZ near the Eocheong Islands, West Sea of Korea. Their accuracies of depth measurement, estimated from the crossover analysis, correspond to the Oder 2 of IHO standards. Bathymetric maps show a feature of 300m wide and 10m deep hollow, whose evolution can be seen in difference grids of the two bathymetric maps. However, data of higher accuracy and resolution enable precise quantification of extracted sand volume. Since this morphological change could affect sedimentary environment as well as benthic ecology, environmental impact assessment based on scientific research data is required for management and sustainable development of limited sand resource.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.57 no.1
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• pp.60-68
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• 2024

The size distribution, maturation, and molting stages of the snow crab Chionoecetes opilio in the coastal sea of Gyeongbuk were investigated to understand its monthly and bathymetric occurrence patterns. C. opilio was collected from three depth strata (A1, 100-120 m; A2, 120-180 m; A3, 180-220 m) from May to November 2020. The average sex ratio was 0.8. The mean carapace width was largest in females in October, and in males in November. The occurrence rate of small immature crabs was the highest in A1. The ratio of ovigerous females at 75-80 mm was highest at A2 and A3. There was a significant difference in carapace width in females and depth in both sexes in September and October. The occurrence rate of immature crabs was the highest in A1, whereas that ovigerous and spawned females was higher in A2 and A3 than in A1. Very old-shelled females occurred highly in September and October. The occurrence rate of newly shelled males was higher throughout the study period. This research indicated that the size distribution, maturation conditions, and molting stages of C. opilio varied with water depth strata in the coastal sea of Gyeongbuk, Korea.

• Korean Journal of Remote Sensing
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• v.39 no.5_4
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• pp.1135-1144
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• 2023

Many agricultural reservoirs in South Korea, constructed before 1970, have become aging facilities. The majority of small-scale reservoirs lack measurement systems to ascertain basic specifications and water levels, classifying them as unmeasured reservoirs. Furthermore, continuous sedimentation within the reservoirs and industrial development-induced water quality deterioration lead to reduced water supply capacity and changes in reservoir morphology. This study utilized Light Detection And Ranging (LiDAR) sensors, which provide elevation information and allow for the characterization of surface features, to construct high-resolution Digital Surface Model (DSM) and Digital Elevation Model (DEM) data of reservoir facilities. Additionally, bathymetric measurements based on multibeam echosounders were conducted to propose an updated approach for determining reservoir capacity. Drone-based LiDAR was employed to generate DSM and DEM data with a spatial resolution of 50 cm, enabling the display of elevations of hydraulic structures, such as embankments, spillways, and intake channels. Furthermore, using drone-based hyperspectral imagery, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) were calculated to detect water bodies and verify differences from existing reservoir boundaries. The constructed high-resolution DEM data were integrated with bathymetric measurements to create underwater contour maps, which were used to generate a Triangulated Irregular Network (TIN). The TIN was utilized to calculate the inundation area and volume of the reservoir, yielding results highly consistent with basic specifications. Considering areas that were not surveyed due to underwater vegetation, it is anticipated that this data will be valuable for future updates of reservoir capacity information.

• 한국해양학회지
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• v.18 no.2
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• pp.125-141
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• 1983

Micropaleontological analyses of the bathic foraminifera of 132 subtidal surface samples of Asan Bay located in the middle of the western coast of Korea, fringing the Yellow Sea collected during late May-early June 1982, shows the results as follows; -Forainiferal numbers of total assemblages are influenced by hydrodynamic and ecologic factors as well as by the sedimentation in the study area. -Badly preserved faunas including replaced faunas seemed to be fossils, all having living counterparts in the study area and showing a somewhat similar type of wall structures with those of the total assemblages and showing no characteristic bathymetric occurrence compared to that of the biocoenose s.1. of the species, lead to infer theirprobable derivation from the environment without a remarkable environmental difference from the study area. But this inference demands further study in consideration of the physical conditions of the study area. -Living/total ratios show a strong negative correlation with the total foraminiferal numbers excluding replaced faunas. But this trend is somewhat deviated in the relatively high ratios. -Fisher-alpha diversity indices of the total assemblages excluding replaced faunas are lying between 1.7 and 3.7. Totals assemblages are mainly composed of hyaline forms with limited porcelaneous and agglutinated ones.

• Journal of Korean Port Research
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• v.12 no.1
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• pp.75-86
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• 1998

To design a coastal structure in the nearshore region, engineers must have means to estimate wave climate. Waves, approaching the surf zone from offshore, experience changes caused by combined effects of bathymetric variations, interference of man-made structure, and nonlinear interactions among wave trains. This paper has attempted to find out the effects of two of the more subtle phenomena involving nonlinear shallow water waves, amplitude dispersion and secondary wave generation. Boussinesq-type equations can be used to model the nonlinear transformation of surface waves in shallow water due to effect of shoaling, refraction, diffraction, and reflection. In this paper, generalized Boussinesq equations under the complex bottom condition is derived using the depth averaged velocity with the series expansion of the velocity potential as a product of powers of the depth of flow. A time stepping finite difference method is used to solve the derived equation. Numerical results are compared to hydraulic model results. The result with the non-linear dispersive wave equation can describe an interesting transformation a sinusoidal wave to one with a cnoidal aspect of a rapid degradation into modulated high frequency waves and transient secondary waves in an intermediate region. The amplitude dispersion of the primary wave crest results in a convex wave front after passing through the shoal and the secondary waves generated by the shoal diffracted in a radial manner into surrounding waters.

• Journal of the Korean Association of Geographic Information Studies
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• v.21 no.3
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• pp.119-126
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• 2018

In this study, In this study, the Datum Level-based hydrography surveying system and the ellipsoid-based system were analyzed to acquire more consistent depth data. For the study, the ellipsoid-based surveying for hydrography was conducted twice for the same track line. And the depth was calculated by correcting rise and fall of water level (water level change by tidal energy and other marine environmental energies) respectively by the traditional water level correction method and ellipsoidally referenced water level correction method. there is able to check that Ellipsoid-based hydrographic surveying data is more improved than Datum Level-based hydrographic surveying data in aspect of level difference phenomenon in the same area (surveying line). This result shows that if the Ellipsoid-based hydrographic surveying is performed, the sea level change (tidal energy and other marine environmental energy) of the survey area in real time could be reflected to more consistent generating bathymetric data.

• Korean Journal of Geomatics
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• v.2 no.1
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• pp.57-64
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• 2002

Measuring the depth of water is very important in ensuring the protection and safety of seaside. There are many difficulties in making the contour bathymetric map, and contour line due to the limitation of continuous measurement of water depth and collimation with the conventional measuring and positioning methods. But the real-time kinematic GPS (RTK GPS) positioning using a carrier phase enables us to decide a precise position without breaking a signal even under the condition of a moving environment. It is also possible to obtain an accurate depth of water in real time with a fathometer through the measuring of time delay between sending and receiving epochs. This research aims at investigation of accuracy potential of RTK GPS in combination with Echo Sounder(E/S) for the coastal mapping. Apart from this purpose, the accuracy of ambiguity resolution with the OTF(On the Fly) method was tested with respect to the initialization time. The result shows that the accuracy is better than 1cm with 5-minute initialization in the distance of 10km baseline. The seaside topography was measured by the RTK GPS only, on the other hand the seafloor topography was surveyed in combination of RTK GPS and E/S. Comparing to the volume of seaside measured by RTK GPS and digital topographical map, the difference of only 2 % was achieved. This indicates that the coastal mapping with RTK GPS is successfully conducted. In addition it is also demonstrated that the 3-dimensional perspective model resulted from the undersea topography measured by RTK GPS and E/S is very close to that from the digital map. Through this study, it was verified that RTK GPS is to be very useful method in the analysis of coastal morphology owing to its capability of getting the precise DTM for the using of harbor reclamation, dredging, and the estimation of soil movement in a river.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5D
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• pp.739-747
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• 2011

The paper presents implementation & evaluation of survey method with tilted transducer of Multi Beam Echo Sounder (MBES) to increase horizontal & vertical coverage over obstructed port environments with limited physical properties of MBES. Proposed method ($25^{\circ}$ titled transducer) have some discrepancy of bathymetric profiles between normal and tilting method, but we proved average difference is less than IHO Special Order requirements with survey data at port of Dong Ho Port, Masan, Korea. For horizontal mapping coverage of total survey area ($114,961m^2$), normal method covered 53%, $60,895m^2$ of total area but tilting method covered 75%, $5.933m^2$. It is 22% efficient than normal method with similar environments. For vertical mapping coverage of total vertical structure face ($7,421m^2$), normal method covered 14%, $1,046m^2$, proposed methods covered 60%, $4,450m^2$. And we adapt longitudal steel bar to validate MBES results, and provide calibration method with titled transducer of MBES.

• Journal of Korean Society for Geospatial Information Science
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• v.17 no.3
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• pp.23-31
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• 2009

The border of the shorelines in a nation is an important factor in determining the border of a national territory, but Korea's shorelines are rapidly changing due to the recent rise in sea level from global warming and growth-centered economic policy over the decades of years. This research was done centering on the areas having well-preserved shorelines as they naturally are and other areas having damaged shorelines in their vicinities due to artificial structures at the two beaches located at the neighboring areas and having mutually homogeneous ocean conditions with each other. First, this research derived the shorelines using the aerial photographies taken from 1947 until 2007 and revised the tidal levels sounding data obtained from a hydrographical survey automation system consisting of Echosounder[Echotrac 3100] and Differential Global Positioning System[Beacon]by using topographical data and ships on land obtained by applying post-processing Kinematic GPS measuring method. In addition, this research evaluated the changes and dimensional variations for the last 60 years by dividing these determined shorelines into 5 sections. As a result, the Haewundae Beach showed a total of 29% decrease rate in dimension as of the year 2007 in comparison with the year 1947 due to a rapid dimensional decline centering on its west areas, while the dimension of the Gwanganri Beach showed an increase in its dimension amounting to a total of 69% due to the decrease in flow velocity by artificial structures built on both ends of the beach-forming accumulation; thus, it was found that there existed a big difference in deposition & accumulation tendency depending on neighboring environment in spite of the homogeneous ocean conditions.