• Ocean and Polar Research
• /
• v.28 no.3
• /
• pp.225-236
• /
• 2006

Seagrass meadows are considered as critical habitats for a wide variety of marine organisms in coastal and estuarine ecosystems. In many cases, studies on the spatial/temporal distribution of seagrass have depended on direct observations using SCUBA diving. As an alternative method fur studying seagrass distribution, an application of hydroacoustic technique has been assessed for mapping seagrass distribution in Dongdae Bay, on the south coast of Korea, in September 2005. Data were collected using high frequency transducer (420 kHz split-beam), which was installed with towed body system. The system was linked to DGPS to make goo-referenced data. Additionally, in situ seagrass distribution has been observed using underwater cameras and SCUBA diving at four stations in order to compare with acoustic data. Acoustic survey was conducted along 23 transects with 3-4 blot ship speed. Seagrass beds were vertically limited to depths less than 3.5m and seagrass height ranged between 55 and 90cm at the study sites. Dense seagmss beds were mainly found at the entrance of the bay and at a flat area around the center of the bay. Although the study area was a relatively small, the vertical and spatial distributions of the seagrass were highly variable with bathymetry and region. Considering dominant species, Zostera marina L., preliminary estimation of seagrass biomass with acoustic and direct sampling data was approximately $56.55g/m^2$, and total biomass of 104 tones (coefficient variation: 25.77%) was estimated at the study area. Hydroacoustic method provided valuable information to understand distribution pattern and to estimate seagrass biomass.

• Wind and Structures
• /
• v.22 no.4
• /
• pp.477-501
• /
• 2016

Though hilly topography influences both wind speeds and directions aloft, only the influence on wind speeds, i.e. the speed-up effect, has been thoroughly investigated. Due to the importance of a model showing the spatial variations of wind directions above hilly terrains, it is worthwhile to systematically assess the applicability and limitations of the model describing the influence of hilly topographies on wind directions. Based on wind-tunnel test results, a model, which describes the horizontal and vertical variations of the wind directions separately, has been proposed in a companion paper. CFD (Computational Fluid Dynamics) techniques were employed in the present paper to evaluate the applicability of the proposed model. From the investigation, it has been found that the model is acceptable for describing the vertical variation of wind directions by a shallow hill whose primary-to-secondary axis ratio (aspect ratio) is larger than 1. When the overall hill slope exceeds $20^{\circ}$, the proposed model should be used with caution. When the aspect ratio is less than 1, the proposed model is less accurate in predicting the spatial variation of wind directions in the wake zone in a separated flow. In addition, it has been found that local slope of a hill has significant impact on the applicability of the proposed model. Specifically, the proposed model is only applicable when local slope of a hill varies gradually from 0 (at the hill foot) to the maximum value (at the mid-slope point) and then to 0 (at the hill top).

• Journal of Environmental Science International
• /
• v.20 no.9
• /
• pp.1165-1182
• /
• 2011

The evaluation of potential submarine groundwater is an important research topic for exploring an alternative water resource. Two different approaches, water budget analysis and Rn mass balance method, were employed to investigate the annual variation of submarine groundwater discharge in 2010 at a marine watershed located at the south-eastern part of Korean Peninsula. In order to obtain reliable hydrological data during study period, temporal and spatial variations of rainfall and soil moisture had been collected and hydro-meterological data such as temperature, humidity and wind speed were collected The runoff response was simulated using SCS-CN method with spatial distributions of landuse and soil texture from GIS analysis. Six different methods were used to estimate the monthly variation of evapotranspiration and field measurements of soil moisture were used to account for the infiltration. Comparisons of infiltration and surface runoff between simulation and water balance with measurements showed coincidence. The water budget analysis and Rn mass balance method provide mean daily submarine groundwater as 5.35 and 4.07 $m^3/m/day$ in 2010, respectively.

• Atmosphere
• /
• v.30 no.1
• /
• pp.47-57
• /
• 2020

In this study, the climatological spatio-temporal variation of strong wind and gust wind in Korea during the period from 1993 to 2018 was analyzed using daily maximum wind speed and daily maximum instantaneous wind speed data recorded at 61 observations. Strong wind and gust wind were defined as 14 m s^-1 and 20 m s^-1, which are the same as the KMA's criteria of special weather report. The frequency of strong wind and gust wind occurrence was divided into regions with the higher 25 percent (Group A) and the lower 75 percent (Group B). The annual frequency of strong wind and gust wind occurrence tended to be decreased in most parts of the Korean peninsula. In Group A with stations located at coastal region, strong wind and gust wind occurred most frequently in winter with higher frequency at 1200~1600 LST and 2300~2400 LST due to influence of East Asian winter monsoon. In addition, a marked decreasing trend throughout the four seasons was shown at Daegwallyeong, Gunsan and Wando observations. In contrast, it can be found in Group B that the monthly frequency of strong wind and wind gust occurrence was higher in August and September by effect of typhoon and hourly frequency was higher from 1200 LST to 1800 LST.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.20 no.2
• /
• pp.32-46
• /
• 2017

Recent rapid urban expansion and crowding of various industrial facilities has affected the features of a significant part of downtown area, resulting in areas having buildings with a wide range of height and the foothills. To compute a velocity pressure exposure coefficient, namely the design wind speed factor, this study defines ground surface roughness by utilizing concentration analysis for the height of each building. After obtaining spatial data by extracting a building layer from digital maps, the study area was partitioned for the concentration analysis and to allow investigation of the frequency distribution of building heights. Concentration analysis by building height was determined with the Variation-to-Means Ratio (VMR) and Poisson distribution analysis using a buildings distribution chart, with statistical significance determined using Chi-square verification. Applying geographic information systems (GIS) with the architectural information made it possible to estimate a velocity pressure exposure coefficient factor more quantitatively and objectively, by including geographic features, as compared to current methods. Thus, this method is expected to eliminate inaccuracies that arise when building designers calculate the velocity pressure exposure coefficient in subjective way, and to help increase the wind resistance of buildings in a more logical and cost-effective way.

• Journal of Biosystems Engineering
• /
• v.29 no.3
• /
• pp.267-274
• /
• 2004

Using geo-statistical method, yield data of different fields were analyzed to examine their field variability according to examining year, analysis method. Semivariogram and Kriged maps of geo-statistical analysis were used to examine their spatial dependence within a filed. The results obtained were as follows. 1) Descriptive statistical results of the yield showed that the yield and the difference of yield ranged from 100 to 946kg/10a and from 272 to 653kg/10a, respectively within a field. The coefficient of variation also ranged from 5.9 to 22.4 %. 2) More than 90% of yield data were placed between 350 to 850kg/10a. e results indicated that the gram mass flow sensor should have the measuring range from 0.34 to 0.82kg/s considering the yields when 4 rows head-feeding combine with 0.8 m/s of working speed was utilized. 3) A high spatial dependence was found within paddy field. The Q values ranged from 0.20 to 0.97, and the range of spatial dependence was from 6.9 to 53.3m. From this result, the rational sampling interval for yield investigation was estimated 6.9m. 4) Yields within a field between observation years showed considerable variability even if the field was evenly cultivated and managed. To apply precision agriculture in a paddy field, the field test should be continued to build a solid data-base including meteorological data, blight damage and insect damage.

• Ocean Science Journal
• /
• v.42 no.2
• /
• pp.103-116
• /
• 2007

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak $(3-6\;cms^{-1})$ and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and wind-induced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and $12cms^{-1}$ respectively.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2009.05a
• /
• pp.641-646
• /
• 2009

This study examines the effects of water shortage on agricultural wages in Northwest Bangladesh. For this study, meteorological data including information on the monthly temperature, precipitation, wind speed, hour of sunshine and humidity of six weather stations have been utilized during the monitoring period from 1985 to 2005. With the objective to analyze water surplus and water deficiency, a simple soil-water balance model and the modified Penman formula were applied to the Northwest Bangladesh. The seasonality of Mann-Kendell trend statistics has been used to identify the spatial variation of water surplus and deficiency throughout the region. For micro level verification of the result, a detailed field survey has been conducted within the study area. The results showed that the values of the potential evapotranspiration estimated by the modified Penmen equation were negative for certain periods. In this instance, the water deficiency of the district of Rajshahi was observed significantly in the period of pre-monsoon and post-monsoon. The field study also verified that because of such deficiency in water, the agricultural scenario of the area was widely influenced which lead to less agricultural production and less economic benefits.

• Journal of Korean Society for Geospatial Information Science
• /
• v.18 no.3
• /
• pp.91-96
• /
• 2010

Depending on the transportation, information and communication technology development, urban such as the superficial spreading and the changing structure of internal space of the organism has various shape and speed of the changes. In particular, the main cause of these changes is the development of the traffic and this transport system is having a close connection with land use. This study presents the results about characteristics and changes of noise on each land use zoning. Therefore the result shows that the measured data could be used to evaluate noise distributions on urban land use and then make up the basis process for producing noise maps of land use zoning.

• Journal of Environmental Science International
• /
• v.18 no.11
• /
• pp.1299-1307
• /
• 2009

In order to measure in-situ suspended particle size, volume concentration of suspended particulate matter and current speed, mooring observation was performed at the Gwangyang Bay by using of an optical instrument, 'LISST-100' and an acoustic instrument, 'ADV'(St. S1). And the sediment flux was obtained based on the concentration of suspended particulate matter and current speeds measured at three lines of Gwangyang Bay during ebb and flood tide of August 2006. To investigate the spatial variation of suspended particulate matter, profiling observations were measured difference echo intensity and beam attenuation coefficient by using of ADCP and Transmissometer (Line A, B, C). The suspended sediment flux rate at the mouth of Gwangyang Bay was observed to be higher during asymmetrical than symmetrical of current speeds. The flux of suspended particulate matter concentration and current speeds were transported to southeastern direction of surface layer and northwestern direction of bottom layer at the western area at line A of Gwangyang Bay. Small suspended particles have been found to increase attenuation and transmission more efficiently than similar large particles using acoustic intensity (ADV/ADCP) or optical transmit coefficient (LISST-100/Transmissometer). The application and problems as using optical or acoustic instruments will be detected for use in time varying calibrations to account for non-negligible changes in complex environments in situ particle dynamics are poorly understood.