Seong-Ryul Kim

Distribution of Flood Sediment Deposits using the Seafloor Image by Side Scan Sonar near the Northern Coast of Gungchon-ri, East Sea

To analyze the distribution pattern of flood sediment deposits near the mouth of Chucheoncheon (river), side scan sonar images and seafloor sediment properties were investigated in the offshore area within about 50 m deep in water. Based on the analysis result of the sonar images, the seafloor of the study area is divided into three areas of basement, sandy-mud, and dispersed flood sediment. The colors of sonar images in each area are represented by dark black, light grey, and greyish black, respectively. The sediment composition in the grey black area shows 33.73% of gravel, 62.88% of sand, 3.37% of silt, and 0.02% of clay. On the other hand, the composition of the light grey area is 10.31% of sand, 56.42% of silt, and 33.27% of clay. Especially the sediment of the grey black area contains the considerable amount of burned plant fragments in black color, which could distinctly be differentiated from those in the offshore. The distribution pattern of the flood sediment deposits suggests that the land-originated detrital sediments seem to be transported from the Chucheon river into offshore along the shore rather than transversely. In conclusion, the longshore current of the study area is probably dominant to affect the spatial distribution of bottom features.

Experiment on Effect of Screening Hydrophone for Reduction of Flow-Induced Ambient Noise in Ocean

Experimental results, measured in a shallow sea with tidal current for reducing the flow-induced low-frequency ambient noise, are represented. The hydrophone screened with 3-cm-thick 10 ppi open-cell foam showed the reduction of flow-induced ambient noise up to 24 dB below 50 Hz at the current speed of 56 cm/s. The attenuation of acoustic energy caused by the screen, estimated based on the measurements of ship noise in situ and hydrophone sensitivity in a water tank, is considered to be less than 1 dB at 2–10 kHz band when the thickness of the foam is less than 3 cm.

Infrasonic Noise Measurements in Ocean Using Screened Hydrophones

Effects of screening a hydrophone with open-cell foams are determined to reduce the level of infrasonic background noise, which is the self-noise probably induced by the presence of flow around the hydrophone, in shallow and deep seas. The result obtained in shallow sea with bottom-mounted geometry shows that the level of background noise could be reduced by more than 20 dB below 10 Hz if the hydrophone is screened. Also, the result of ship noise measurement conducted in deep sea with drifting geometry shows that a maximum background noise reduction of 15 dB could be achieved in the infrasonic band without affecting the true acoustic signals.

Trace Uranium Assay Using Infrared Photo Diode Electrodes

A voltammetric assay of uranium using an infrared photo diode electrode (DE) was conducted. A square wave stripping cathodic peak appeared at − 0.2 V (vs. Ag/AgCl/KCl) attributed to the reduction of uranium ion. Under optimum analytical conditions, various conventional working electrodes were compared. The analytical working range was found to be 0.1–1.1 mg/L DE, precision range of R2 = 0.9581, and the high range was obtained at 5-130 mg/L with precision R2 = 0.9981. Here, an ammonium phosphate electrolyte pH strength of 2.3, an accumulation time of 0 sec, and an accumulation potential of 0.5 V were used. Under these conditions, the relative standard deviation of 0.5 mg/L was 1.69%. The detection limit was found to be 0.35 ugL−1 (1.49 × 10−9 M) (S/N = 3). The methods developed in this study are applicable in micro-array multi-sensor systems or other analytical instrumental systems.

An Experiment on Reduction of Infrasonic Underwater Self-Noise

The effects of screening hydrophones with open-cell foams for reduction of the infrasonic self-noise induced by the flow around hydrophones are investigated by at-sea experiment. Test results of the 10 ppi polyurethane open-cell foams with different thickness show that the foams of 1 cm and 3 cm thickness reduce the flow-induced self-noises up to 20 dB and 28 dB at the frequency band of 2-10 Hz, respectively.