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Spatio-temporal patterns of Secchi depth in the waters around the Korean Peninsula using MODIS data
Kim, S.H.,Yang, C.S.,Ouchi, K. Academic Press in association with the Estuarine a 2015 Estuarine, coastal and shelf science Vol.164 No.-
Secchi depth (Z<SUB>SD</SUB>) is an important variable for the measurements of long-term changes in the water transparency of oceanic and coastal ecosystems. This study aims at analyzing the spatial and temporal variations of MODIS-derived Z<SUB>SD</SUB> time-series during 2000-2012 in the adjacent waters around the Korean Peninsula, highlighting the environmental variables affecting variations of Z<SUB>SD</SUB> with various water depths. A semi-analytical model is used to estimate the diffuse attenuation and beam attenuation coefficients from satellite data, and the reciprocal of the sum of the two parameters was compared with the in-situ Z<SUB>SD</SUB> to retrieve a satellite-based Z<SUB>SD</SUB>. In general, the open sea waters in the East Sea/Sea of Japan have higher Z<SUB>SD</SUB> than the coastal waters in the Yellow Sea. From the analyses, distinct seasonality was found in the monthly average images of MODIS-derived Z<SUB>SD</SUB> data and spatio-temporal patterns of the Empirical Orthogonal Function (EOF), and the seasonal variation of Z<SUB>SD</SUB> was associated with the variability in the ocean-atmosphere dynamics including the wind and current as well as chlorophyll-a. In the coastal and shallow waters in the Yellow Sea, prevailing north westerly winds produce turbid waters in winter, while in deep waters in the East Sea/Sea of Japan, water transparency is reduced by the spring bloom of chlorophyll-a. There are two clear Z<SUB>SD</SUB> peaks within a year in the East China Sea associated with the Kuroshio Current. A similar trend was observed in the South Sea, but less clear due to complex mixing processes of currents and effects of wind. Correlation of in-situ Z<SUB>SD</SUB> with water depth was also found suggesting the need for consideration in analyzing satellite Z<SUB>SD</SUB> data.
Yang, C. S.,Park, S. M.,Oh, Y.,Ouchi, K. CHINESE OCEAN PRESS 2013 Acta oceanologica Sinica Vol.32 No.1
<P>An analysis of the radar backscattering from the ocean surface covered by oil spill is presented using a microwave scattering model and Monte-Carlo simulation. In the analysis, a one-dimensional rough sea surface is numerically generated with an ocean waveheight spectrum for a given wind velocity. A two-layered medium is then generated by adding a thin oil layer on the simulated rough sea surface. The electric fields backscattered from the sea surface with two-layered medium are computed with the method of moments (MoM), and the backscattering coefficients are statistically obtained with N independent samples for each oil-spilled surface using the Monte-Carlo technique for various conditions of surface roughness, oil-layer thickness, frequency, polarization and incidence angle. The numerical simulation results are compared with theoretical models for clean sea surfaces and SAR images of an oil-spilled sea surface caused by the Hebei (Hebei province, China) Spirit oil tanker in 2007. Further, conditions for better oil spill extraction are sought by the numerical simulation on the effects of wind speed and oil-layer thickness at different incidence angles on the backscattering coefficients.</P>
Kim, T. H.,Yang, C. S.,Ouchi, K. Korean Ocean Research Development Institute and Ko 2016 OCEAN SCIENCE JOURNAL Vol.51 No.2
<P>In this paper, results are presented on the comparison of X-band radar backscattering coefficient (RBC) from an oilcovered sea surface that features the Elfouhaily and Durden-Vesecky waveheight spectra. The Durden-Vesecky spectrum applies to a fully-developed sea, while the Elfouhaily spectrum accounts for the fetch of arbitrary length. Using these two waveheight spectra, a one-dimensional random rough surface is simulated by the Monte Carlo method, and the method of moments (MoM) is applied to yield the RBC. Comparison of the results with TerraSAR-X synthetic aperture radar (SAR) data acquired over the coastal waters polluted by the Hebei Spirit oil tanker shows that the Elfouhaily spectrum yields better agreement than the Durden-Vesecky spectrum for the fully-developed sea, and that the fetch- dependent Elfouhaily spectrum improves the agreement with SAR data in comparison with the fetch- independent spectrum for the fully developed sea. A possible application to estimate the amount of spilled oil is also suggested.</P>