Hyun Yang

Application of the Geostationary Ocean Color Imager (GOCI) to estimates of ocean surface currents

The Geostationary Ocean Color Imager (GOCI) can be utilized efficiently to observe subtle changes in oceanic environments under cloud-free conditions because it receives ocean color images around the Korean Peninsula hourly, for 8 h a day. Here we investigated the applicability of the GOCI for estimating hourly variations in ocean surface currents, which provide significant information on seawater circulation for fisheries, shipping controls, and more. Ocean surface currents were deduced from eight images of GOCI-derived total suspended matter (TSM) from highly turbid coastal waters and images of chlorophyll concentration (CHL) for relatively clear waters. The results showed that GOCI TSM-derived ocean surface currents can effectively estimate and represent fast tidal currents, as well as flood and ebb tides on the west coast of Korea, in comparison with in situ measurements. GOCI-derived CHL scenes successfully illustrated currents moving along boundaries where warm and cold seawaters mix, in addition to mesoscale currents such as the East Korea Warm Current (EKWC) in the East Sea of Korea. Satellite-based sea surface temperature and sea surface height images supported the reliability of GOCI-derived ocean surface currents in the East Sea.

Quantitative estimation of suspended sediment movements in coastal region using GOCI

ABSTRACT Choi, J. K., Hyun Yang, H. J. Han, Ryu, J. H. and Park, Y.J., 2013. Quantitative estimation of the suspended sediment movements in the coastal region using GOCI The Geostationary Ocean Color Imager (GOCI), the worlds first geostationary ocean color observation satellite, is useful for monitoring the temporal dynamics of coastal water turbidity because it can obtain satellite images every hour during the daytime. Temporal variation in turbidity is the key to understanding sediment dynamics in coastal regions. For example, a certain patch of suspended sediment in surface water can be traced every hour by generating a GOCI- derived map of suspended sediment concentration (SSC). By calculating the variations in the position of the patch every hour quantitatively, we can obtain information on the current movement in the region quantitatively. Here, we investigate the applicability of GOCI data to monitoring of the temporal movement of suspended sediment in coastal areas and to the development of algorithms for calculating the current speed and direction. Our study was performed in areas near Gyeonggi Bay on the mid-west coast of the Korean Peninsula. Field work was performed to obtain in situ measurements of SSC and optical properties of the water surface. These data could then be combined to derive an SSC algorithm based on the relationship between the SSC and remote sensing reflectance (Rrs) values. We calculated the suspended sediment movement from hourly SSC images. Current velocity and direction were also measured in the field to validate and identify the calculated movement. GOCI images acquired on the same day as the samples were used to generate a map of turbidity and to estimate the differences in SSC displayed in each image. We found that GOCI could be effectively used to monitor the temporal dynamics of the turbidity of coastal waters, i.e., sediment movements driven by currents along the west coast of the Korean Peninsula. Sediment movements can be applied to develop GOCI-based algorithms that calculate current velocities and generate maps of current vectors in this coastal area.

Risk factors and outcomes of hepatitis B virus reactivation in hepatitis B surface antigen negative patients with hematological malignancies

Current guidelines recommend all patients scheduled to receive chemotherapy should be screened for hepatitis B surface antigen (HBsAg) and antibodies to hepatitis B virus core antigen (anti‐HBc) status. However, still, more research is needed to identify the risk factors for hepatitis B virus (HBV) reactivation. We retrospectively investigated the incidence, risk factors and outcome of HBV reactivation in HBsAg negative patients with hematological malignancies.

Monitoring changes in suspended sediment concentration on the southwestern coast of Korea

ABSTRACT Min, J. E., Choi, J. K., Yang, H., Lee, S., Ryu, J. H. 2014. Monitoring changes in suspended sediment concentration on the southwestern coast of Korea. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 133–138, ISSN 0749-0208. Concentrations and distribution patterns of suspended sediment (SS) are key indicators of marine environmental change, particularly in coastal areas, which gives good information on the deposition and migration of sediments from land. In this study we analyzed 632 scenes (79 days × 8 scenes) of Geostationary Ocean Color Imager (GOCI) data in order to investigate SS variations relating to tides, tidal currents, bottom morphology, river discharge, and so on. We also compared them to the numerical model of tidal currents for the Yellow Sea. The study area, the coastline of Mokpo, is characterized by shallow water depths (<50 m), a relatively large tidal range (8 m) and by strong tidal currents (1 to 2 m/s). The coastal area of Mokpo shows extremely high SS concentrations (SSC) caused by a resuspension of bottom sediments. GOCI, the worlds first geostationary ocean color observation satellite, can obtain data hourly during daylight. Therefore, GOCI is well equipped for the detailed analysis of time-series variations in SSC with regard to tides and tidal currents along Mokpo. The concentrations and distribution patterns of SS in the study area were mainly affected by tidal currents. During flood tide, SSC showed higher values than during ebb tide, and the SS distribution pattern flowed in a northerly direction. On the other hand, during ebb tide, the SS distribution pattern flowed towards the south. Bottom morphology also displayed a similar pattern to the SS distribution.

Application of Geostationary Ocean Color Imager Data to the extraction of ocean fronts

ABSTRACT We attempted for the first time to extract fronts from ocean colour data acquired at a geostationary orbit derived from the Geostationary Ocean Color Imager (GOCI), the world’s first geostationary ocean colour satellite sensor. We extracted fronts from hourly observed GOCI images and then attempted to investigate subtle changes in ocean condition. Suspended sediment (SS)-derived fronts were used to analyse tidal movements in a coastal region having semi-diurnal tides and highly turbid water. We were able to trace fast movements of tidal flows and discovered that the SS-derived ocean fronts are quite relevant to the submarine topography along shallow coasts. In relatively clear waters using chlorophyll concentration (chl)-derived fronts, we were able to discover dynamic variations on sea areas where two independent water masses mixed. We also found that GOCI-derived fronts can provide more detailed information than can SST-derived fronts. We expect that such results can be utilized to search for productive fisheries.