• Korean Journal of Remote Sensing
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• v.29 no.6
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• pp.645-655
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• 2013

As one of segmentation techniques for Synthetic Aperture Radar (SAR) image with oil spill, we applied a bimodal histogram method to discriminate oil pixels from non-oil pixels. The threshold of each moving window was objectively determined using the two peaks in the histogram distribution of backscattering coefficients from ENVISAT ASAR image. To reduce the effect of wind speed on oil spill detection, we selected ASAR image which satisfied a limit of wind speeds for successful detection. Overall, a commonly used adaptive threshold method has been applied with a subjectively-determined single threshold. In contrast, the bimodal histogram method utilized herein produces a variety of thresholds objectively for each moving window by considering the characteristics of statistical distribution of backscattering coefficients. Comparison between the two methods revealed that the bimodal histogram method exhibited no significant difference in terms of performance when compared to the adaptive threshold method, except for around the edges of dark oil spots. Thus, we anticipate that the objective method based on the bimodality of oil slicks may also be applicable to the detection of oil spills from other SAR imagery.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.45 no.3
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• pp.157-164
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• 2009

Due to change of various marine environments according to seawater temperature rising, Japanese common squid(Todarodes pacificus), which was distributed in East Sea, was recently caught in Yellow Sea during a summer season from 2006. The fishery resources density research was carried out in Korea-China Provisional Water Zone using trawl fishing gear and acoustics in National Fisheries Research & Development Institute in Korea. This paper showed the analysis on the acoustical backscattering strength by two frequencies(38kHz, 120kHz) for Japanese common squid by acoustical scattering theoretical model based on size distribution for survey period, and estimate the density distribution for squid s integrated layer which was extracted from any scatterers distributed in water column using two frequency difference method which has been used to distinguish fish shoals or specific target scatterers from sound scattering layer which is composed of various zooplankton. Furthermore, the entire range of their density estimation was suggested using by Monte Carlo simulation under considering each uncertainty such as size distributions or swimming angle and so on in survey area.

• Journal of Korea Water Resources Association
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• v.33 no.4
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• pp.427-435
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• 2000

It is often crucial to obtain a map of flood inundated area with more accurate and rapid manner. This study attempts to evaluate the potential of satellite synthetic aperture radar (SAR) data for mapping of flood inundated area in Imjin river basin. Multitemporal RADARSAT SAR data of three different dates were obtained at the time of flooding on August 4 and before and after the flooding. Once the data sets were geometrically corrected and preprocessed, the temporal characteristics of relative radar backscattering were analyzed. By comparing the radar backscattering of several surface features, it was clear that the flooded rice paddy showed the distinctive temporal pattern of radar response. Flooded rice paddy showed significantly lower radar signal while the normally growing rice paddy show high radar returns, which also could be easily interpreted from the color composite imagery. In addition to delineating the flooded rice fields, the multitemporal radar imagery also allow us to distinguish the afterward condition of once-flooded rice field.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.6
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• pp.749-756
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• 2003

Hydroacoustic and open-closing zooplankton net survey were conducted to understand the characteristics of the sound scattering layer (SSL) and to estimate the density of an euphausiid (Euphausia pacifica) in the SSL, in the northwestern part of the East China Sea. The survey was carried out during July 6-9 2002 at 8 sampling stations for zooplankton. The virtual echogram technique was used to identify E. pacifica from all acoustic scatters. Mean volume backscattering strength difference $(MVBS_{120kHz-38kHz})$ and target strength equation for E. pacifica were derived from the Distorted-wave Born Approximation (DWBA) model. Although vertical migration of the SSL is similar to the general pattern, dispersion at night shows some differences. Estimated mean density using acoustic data ranged from $20.4-221.4\;mg/m^3$ over the whole depth, and $87.1-553.5\;mg/m^3$ in the SSL. The density using the zooplankton net ranged from $0.2-362.4\;mg/m^3$ and was not related to net deploying method. The results from the acoustic and net survey suggest that E. pacifica might be an important zooplankton community in the northwestern part of the East China Sea.

• Korean Journal of Remote Sensing
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• v.21 no.2
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• pp.145-162
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• 2005

To improve the accuracy of land-cover discrimination in SAB data classification, this paper presents a methodology that includes feature extraction and fusion steps with multi-temporal SAR data. Three features including average backscattering coefficient, temporal variability and coherence are extracted from multi-temporal SAR data by considering the temporal behaviors of backscattering characteristics of SAR sensors. Dempster-Shafer theory of evidence(D-S theory) and fuzzy logic are applied to effectively integrate those features. Especially, a feature-driven heuristic approach to mass function assignment in D-S theory is applied and various fuzzy combination operators are tested in fuzzy logic fusion. As experimental results on a multi-temporal Radarsat-1 data set, the features considered in this paper could provide complementary information and thus effectively discriminated water, paddy and urban areas. However, it was difficult to discriminate forest and dry fields. From an information fusion methodological point of view, the D-S theory and fuzzy combination operators except the fuzzy Max and Algebraic Sum operators showed similar land-cover accuracy statistics.

• Economic and Environmental Geology
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• v.47 no.5
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• pp.533-540
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• 2014

The Wangdol-cho area, in the Hupo Bank, plays a very important role in main fishing grounds, leisure tourism and marine environmental researches of the East Sea. We analyzed the detailed bathymetry and classified the seabed characteristics of the Wangdol-cho area, based on seafloor backscattering images and sediment grain size. The Hupo Bank is developed in parallel with the eastern coastal line of Korean peninsula, and the shallowest area (Wangdol-cho) of the Hupo Bank is located along the eastern part of Hupo Port. The Wangdol-cho comprises three summits; north summit, middle summit, and south summit. The middle summit area among the three summits has the most shallow water depth with minimum about 6 m. The north summit shows about 8 m minimum depth and the south summit about 9 m. The bathymetry data around three summits represent undulating seabeds with many scattered underwater reefs and shallow water depth. The area between the underwater reefs, the flat seafloor in the northeastern part of the survey site, and the western steep slope area have relatively coarse sediments such as sandy gravel and gravelly sand. The bathymetry in the western side of the Wangdol-cho shows steep slope seabed, extending to the Hupo Basin. Fine sediments including mud and silty sand occur in the Hupo Basin area of the survey site. The submarine detailed topography and the analysis of the seafloor characteristics of the survey area are expected to contribute to management for marine environmental researches and sustainable use of ecosystems in the Wangdol-cho.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.2
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• pp.272-278
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• 2015

The aim of this study is to find out the behavior and acoustic backscattering of the large jellyfish Nemopliema nomurai using hydroacoustics in situ. N. nomurai was distributed at depths ranging from 10~15 m during the day. Regarding the behavior of N. nomurai, there was no significant change in depth, and 3D tortuosity was not high. The vertical direction was ${\pm}10^{\circ}$ from the horizontal, and moving speed was $0.9{\sim}1.5\;m\;s^{-1}$. With regard to hydro-acoustical characteristics, the mean TS of N. nomurai ranged from -69.6~-56.0 dB at 38 kHz and -69.4~-54.5 dB at 120 kHz. TS variation (Max TS-Min TS) at 38 and 120 kHz was 0~10.2 dB and 0.2~16.0 dB, respectively. Mean TS and TS variation (Max TS-Min TS) of N. nomurai were higher at 120 kHz than at 38 kHz. The results showed that the use of hydroacoustics was effective in estimating the distribution depth, behavior, and acoustic characteristics of the target.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.241-248
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• 2002

The combined hydroacoustic and demersal trawl surveys to investigate the distribution characteristics of fish schools in the Yellow Sea and the East China Sea were carried out during the spring of 1997 by the training ship "Nagasaki Maru" of Nagasaki University. Fish samples were collected by bottom trawling from 9 trawl stations randomly selected in the survey area, and the species and length compositions of trawl catches are examined. Hydroacoustic data were collected by using a Furuno FQ-50 scientific echo sounder operating at 50KHz and the data stored in field were later processed in the laboratory. The results obtained can be summarized as follows ：1. In the 9 trawl surveys conducted in the Yellow Sea and the East China Sea, 78 species including 80 species of fishes, 4 species of Cephalopoda and 6 species of Crustacea, were identified. The most abundant species in these stations were swimming crab(Portunus trituberculatus), Japanese horse mackere(Trachurus japonicus), redlip croaker(Larimichthys polyactis) and the catch per one hour in each station ranged 7.7 to 182.5 kg/hour. 2. The mean volume backscattering strength for the entire water column and the bottom layer of the 0-10 m from bottom friction were -74.6 ㏈ and -68.2 ㏈, respectively. That is, the mean volume backscattering strength for the bottom layer was 6.4 ㏈ higher than that for the entire water column 3. In the surveys during the spring of 1997, the geographical distribution characteristics of fish schools suggests a trend of decreasing fish abundance toward the coast area of Korea and the highest demersal concentrations appeared in waters between the Cheju Island and the Tsushima Island 4. The distribution density of fish school in the East China Sea and Yellow Sea during the 1997 acoustic survey were estimated to be 6.65$\times$10$^{-5}$ kg/㎥ in the entire water column and 2.86$\times$l0$^{-4}$ kg/㎥ in the bottom layer, respectively.pectively.

• Journal of electromagnetic engineering and science
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• v.10 no.2
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• pp.61-66
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• 2010

This paper is concerned with an analysis of the back scattering of electromagnetic waves from a target moving along random rough surfaces such as the desert, and sea. First, the discrete ray tracing method(DRTM) is introduced, and then, this method is applied to the back scattering problem in order to investigate the effect of the back scattering from random rough surfaces on the electric field intensities. Finally, numerical examples of various height deviations of the Gaussian type of rough surfaces are shown. It is numerically demonstrated that the back scattering is dominated by the diffractions related to the reflections from the random rough surfaces.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.417-426
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• 2006

A Digital X-ray imaging system using Compton backscattering has been developed to obtain a cross-sectional profile and mass loss of corroded lap-splices of aging aircraft from density variation. A slit-type camera was designed to focus on a small scattering volume inside the material, from which the backscattered photons are collected by a collimated scintillator detector for interpretation of material characteristics. The cross section of the lap-joint is scanned by moving the scattering volume through the thickness direction of the specimen. The mass loss of each layer has been estimated from a Compton backscatter A-scan to obtain the thickness of each layer including the aluminum sheet, the corrosion layer and the sealant. Quantitative information such as location and width of planar corrosion in the lap splices of fuselages is obtained by deconvolution using a nonlinear least-square error minimization method(BFGS method): A simple reconstruction model is also introduced to overcome distortion of the Compton backscatter data due to attenuation effects attributed to beam hardening and quantum noise.