Korea Ocean Satellite Center

Ansan, South Korea

Korea Ocean Satellite Center

Ansan, South Korea

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Yamaguchi H.,Japan Aerospace Exploration Agency | Ishizaka J.,Nagoya University | Siswanto E.,Japan Agency for Marine - Earth Science and Technology | Baek Son Y.,Korea Ocean Satellite Center | And 2 more authors.
Continental Shelf Research | Year: 2013

Seasonal and spring interannual variations in chlorophyll-. a (Chl) and total suspended matter (TSM) in the Yellow and East China Seas through a 10-year period were examined by using new datasets from Yellow Sea Large Marine Ecosystem Ocean Color Project (YOC) algorithms. YOC SCHL calculations are based on a combination of the SeaWiFS standard algorithm and a local empirical algorithm for areas of low and high normalized water-leaving radiance 555. nm, respectively. YOC SCHL was lower than the standard SCHL in areas with high concentrations of resuspended sediment, especially along the Chinese and Korean coasts and around the Changjiang Bank from fall to spring. YOC SCHL was high in areas of low TSM in the middle of the Yellow Sea, and offshore of the Changjiang Bank in April, indicating the occurrence of spring blooms. In these areas, TSM was dominated by phytoplankton cells and phytoplankton-related organic particles. Offshore from the Changjiang River mouth and around the Changjiang Bank, YOC SCHL and TSM in March were low and high, respectively, with maximum YOC SCHL values occurring around the Changjiang Bank in May. Spring bloom started with decrease in resuspended sediment concentrations in these areas. During summer, YOC SCHL values were high and TSM concentrations were low; TSM was dominated by organic particles related to phytoplankton activity when Changjiang River diluted water moved from the river mouth to east of the bank. YOC SCHL in spring offshore from the Changjiang River mouth increased significantly during the 10 years, and correspond to an increase in red tide events. In the middle of the Yellow Sea, maximum YOC SCHL in spring increased gradually and significantly during the 10 years. Many of the spatial and temporal variations in YOC SCHL were consistent with a range of earlier in situ descriptions. Our results indicate that the satellite ocean data with proper algorithms is a powerful tool to analyze phytoplankton dynamics in moderate-high suspended sediment area. © 2013 Elsevier Ltd.


Doxaran D.,French National Center for Scientific Research | Lamquin N.,ACRI ST | Park Y.-J.,Korea Ocean Satellite Center | Mazeran C.,ACRI ST | And 3 more authors.
Remote Sensing of Environment | Year: 2014

The objectives of this study are to: (i) compare the potential of the Moderate Resolution Imaging Spectroradiometer (MODIS), the Medium Resolution Imaging Spectrometer (MERIS) and the Geostationary Ocean Color Imager (GOCI) in retrieving the particulate backscattering coefficient, robust proxy of the concentration of suspended particulate matter (SPM), in the turbid waters of the East China Sea, then (ii) combine ocean color satellite data to field data recorded by an autonomous bio-optical profiling float to reconstitute and explain the dynamics of SPM within the whole water column in the middle of the East China Sea. MODIS, MERIS and GOCI seawater reflectance products at green, red and near-infrared (NIR) wavelengths are generated using atmospheric correction algorithms designed for turbid coastal waters then compared. Good agreement is obtained in the green and red while significant differences are observed in the NIR. The standard GOCI algorithm and a new one based on a regional empirical relationship established using MODIS satellite data are both proved to perform well over the whole range of water turbidity. Finally the dynamics of SPM is reconstituted along a three-month period to highlight a steady-state and stratified situation before the overpass of a large typhoon which mixed the water column, destroyed the deep-chlorophyll maximum and enhanced resuspension of bottom sediments varying according to tidal cycles. © 2013 Elsevier Inc.


Lamquin N.,ACRI ST | Mazeran C.,ACRI ST | Doxaran D.,University Pierre and Marie Curie | Ryu J.-H.,Korea Ocean Satellite Center | Park Y.-J.,Korea Ocean Satellite Center
Ocean Science Journal | Year: 2012

The first Geostationary Ocean Color Imager (GOCI) launched by South Korea in June 2010 constitutes a major breakthrough in marine optics remote-sensing for its capabilities to observe the diurnal cycles of the ocean. The light signal recorded at eight wavelengths by the sensor allows, after correction for Solar illumination and atmospheric effects, the retrieval of coloured biogeochemical products such as the chlorophyll, suspended sediment and coloured dissolved organic matter concentrations every hour between 9:00 am and 4:00 pm local time around the Korean peninsula. However operational exploitation of the mission needs beforehand a sound validation of first the radiometric calibration, i. e. inspection of the top-of-atmosphere reflectance, and second atmospheric corrections for retrieval of the water-leaving reflectance at sea surface. This study constitutes a contribution to the quality assessment of the GOCI radiometric products generated by the Korea Ocean Satellite Center (KOSC) through comparison with concurrent data from the MODerate-resolution Imaging Spectroradiometer (MODIS, NASA) and MEdium Resolution Imaging Spectrometer (MERIS, ESA) sensors as well as in situ measurements. These comparisons are made with spatially and temporally collocated data. We focus on Rayleigh-corrected reflectance (ρ RC) and normalized remote-sensing marine reflectance (nRrs). Although GOCI compares reasonably well with MERIS and MODIS, what demonstrates the success of Ocean Colour in geostationary orbit, we show that the current GOCI atmospheric correction systematically masks out data over very turbid waters and needs further examination and correction for future release of the GOCI products. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Park K.-A.,Seoul National University | Woo H.-J.,Seoul National University | Ryu J.-H.,Korea Ocean Satellite Center
Ocean Science Journal | Year: 2012

The spatial scales of mesoscale eddies are of importance to understand physio-biogeochemical processes in the East/Japan Sea. Chlorophyll-a concentration images from the Geostationary Ocean Color Imager (GOCI) revealed numerous eddies during the phytoplankton bloom in spring. These eddies were manually digitized to obtain geolocation information at the peripheries from GOCI images and then least-square fitted to each ellipse. The elliptic elements were the geolocation position of the eddy center, the rotation angle from due east, the eccentricity, the lengths of the semi-major and semi-minor axes, and the mean radius of the ellipse. The spatial scales of eddies had a mean radii ranging from 10 km to 75 km and tended to be smaller in the northern region. The scales revealed a linear trend of about -7.26 km/°N as a function of the latitude. This tendency depended on the latitudinal variation of the internal Rossby radius of deformation, which originates from the substantial difference in the density structure of the water column. The scales from the sea surface temperature image were larger by 1.30 times compared to those from ocean color image. This implies that physical processes along the periphery of the eddy affect the nutrient dynamics. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Ahn J.-H.,Korea Ocean Satellite Center | Ahn J.-H.,Seoul National University | Park Y.-J.,Korea Ocean Satellite Center | Ryu J.-H.,Korea Ocean Satellite Center | And 3 more authors.
Ocean Science Journal | Year: 2012

This paper describes an atmospheric correction algorithm for Geostationary Ocean Color Imager (GOCI) and its early phase evaluation. This algorithm was implemented in GOCI Data Processing System (GDPS) version 1.1. The algorithm is based on the standard SeaWiFS method, which accounts for multiple scattering effects and partially updated in terms of turbid case-2 water correction, optimized aerosol models, and solar angle correction per slot. For turbid water correction, we used a regional empirical relationship between water reflectance at the red (660 nm) and near infrared bands (745 nm and 865 nm). The relationship was derived from turbid pixels in satellite images after atmospheric correction, and processed using aerosol properties derived for neighboring non-turbid waters. For validation of the GOCI atmospheric correction, we compared our results with in situ measurements of normalized water leaving radiance (nL w) spectra that were obtained during several cruises in 2011 around Korean peninsula. The match up showed an acceptable result with mean ratio of the GOCI to in situnL w(λ), 1.17, 1.24, 1.26, 1.15, 0.86 and 0.99 at 412 nm, 443 nm, 490 nm, 555 nm, 660 nm and 680 nm, respectively. It is speculated that part of the deviation arose from a lack of vicarious calibration and uncertainties in the above water nLw measurements. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Lee Z.P.,University of Massachusetts Boston | Jiang M.,University of Massachusetts Boston | Davis C.,Oregon State University | Pahlevan N.,University of Massachusetts Boston | And 2 more authors.
Ocean Science Journal | Year: 2012

Ocean-color imagers on conventional polar-orbiting satellites have a revisit time of ~2 days for most regions, which is further reduced if the area is frequently cloudy. The Geostationary Ocean Color Imager (GOCI), the first ocean-color imager on a geostationary satellite, provides measurements 8 times a day, thus significantly improving the frequency of measurements for studies of ocean environments. Here, we use results derived from GOCI measurements over Taihu Lake to demonstrate that the extra sampling can be used to improve the accuracy of statistically averaged longer-term (daily) measurements. Additionally, using numerical simulations, we demonstrate that the coupling of diurnal variations of both biomass and photosynthetic available radiation can improve the accuracy of daily primary production estimates. These results echo that higher sampling frequency can improve our estimates of longer-term dynamics of biogeochemical processes and highlights the value of ocean color measurements from geostationary satellites. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Lee K.H.,Kyungil University | Ryu J.H.,Korea Ocean Satellite Center | Ahn J.H.,Korea Ocean Satellite Center | Kim Y.J.,Gwangju Institute of Science and Technology
Ocean Science Journal | Year: 2012

Aerosol optical thickness (AOT) was retrieved from the Geostationary Ocean Color Imager (GOCI) on board the Communication, Ocean, and Meteorological Satellite (COMS) for the first time. AOT values were retrieved over the ocean at a spatial scale of 0.5 × 0.5 km2 by using the look-up table (LUT)-based separation technique. The radiative transfer model (RTM) was used for different models of atmosphere-ocean environmental conditions, taking into account the realistic variability of scattering and absorption. Ocean surface properties affected by whitecaps and pigment content were also taken into account. The results show that the radiance observed by the GOCI amounts to only 5% of the radiation that penetrated the ocean and, consequently, 95% of the radiation is scattered in the atmosphere or reflected at the ocean surface in the visible wavelengths longer than 0.6 ìm. Within these wavelengths, radiance variations at the top of atmosphere (TOA) due to pigment variations are within 10%, while the radiance variation due to wind speed is considerably higher. For verification of GOCI-retrieved AOTs, comparison between GOCI and ground-based sunphotometer measurement at Gosan, Korea (126.10°E, 33.23°N)) showed good correlation (r = 0.99). The GOCI observations obtained by using the proposed technique showed promising results for the daily monitoring of atmospheric aerosol loading as well as being useful for environmental supervisory authorities. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Yang C.-S.,Korea Ocean Satellite Center | Song J.-H.,Korea Aerospace University
Ocean Science Journal | Year: 2012

The Geostationary Ocean Color Imager (GOCI) instrument acquires eight channels of multispectral images, which consist of 16 slots positioned in four lines and columns. GOCI Level 1B data, therefore, consist of a mosaic of 16 images, geometrically corrected with the Image Navigation and Registration Software Module (INRSM) system based on automatic point landmark matching for each slot and band. A study of the geometric performance characteristics of the Level 1B data was conducted over a period from August 2010 to September 2011 using residual data from Bands 7 and 8. To evaluate the geometric performance in detail, this paper examines the following four types of image navigation and registration errors: navigation performance, within-frame registration, frame-to-frame registration, and band-toband registration. In addition to the performance statistics based on mosaic images, we used a slot-based analysis method for the rainy season (here, June 2011) to understand the local distribution of the geometric performance. From the image-based results, the navigation and frame-to-frame accuracies were better than 1 pixel and the band-to-band registration accuracy was better than 0.4 pixels, while the within-frame registration accuracy was less than 1 pixel. However, for the band-to-band performance, the percentage of observations that fell within the specifications was slightly less than 99.7% for all 240 frames from June 2011. The within-frame performance was much lower than the other performance categories and the residual error for the east-west direction was higher than that for the north-south direction. The results from the slotbased performance evaluation suggest that abnormal errors (e. g. above 53 μrad for navigation) occur in some slots, although the performance during an estimation period of 7 continuous days was within the desired criteria. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Son Y.B.,Korea Ocean Satellite Center | Min J.-E.,Korea Ocean Satellite Center | Ryu J.-H.,Korea Ocean Satellite Center
Ocean Science Journal | Year: 2012

The historically massive bloom of the green macroalgae Ulva prolifera reported in June-August 2008 around the Qingdao, Yellow Sea, East China Sea and Japan coasts has recurred in a similar season and region. On June 13, 2011, around Qingdao, China, the world's first Geostationary Ocean Color Imager (GOCI) detected an enormous bloom of floating green algae, which originated from the nearshore Subei Bank, China. The large floating green algae patches were observed along and across the Yellow Sea and in the East China Sea during 2011 summer by various oceanic cruises. To detect the massive macroalgae blooms from space, we analyzed their spectral characteristics from in situ optical measurements and satellite-derived green algae spectra. An "Index of floating Green Algae for GOCI" (IGAG) was developed from the multiple spectral band ratios using three wavelengths (555, 660, 745 nm), which the spectral response of green algae reflected at 555, 745, and 865 nm and absorbed at 660 and 680 nm. The results were compared with those obtained by the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and Korea Ocean Satellite Center (KOSC) approaches. An advantage of the IGAG method was that muted or subtle signals of floating green algae were enhanced and separated from surrounding complex water signals. Although maps of floating green algae derived by the other approaches delineated dense green algae, they were less sensitive to subtle (less dense) features and in cases of nearby cloudy or complex water conditions. The floating green algae maps from IGAG provided a more robust estimate of wide floating green algae blooms than those derived using NDVI, EVI, or KOSC approaches. The IGAG approach should be useful for tracing and monitoring changes in green algae blooms on regional and global scales. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.


Ryu J.-H.,Korea Ocean Satellite Center | Han H.-J.,Korea Ocean Satellite Center | Cho S.,Korea Ocean Satellite Center | Park Y.-J.,Korea Ocean Satellite Center | Ahn Y.-H.,Korea Ocean Satellite Center
Ocean Science Journal | Year: 2012

GOCI, the world's first geostationary ocean color satellite, provides images with a spatial resolution of 500 m at hourly intervals up to 8 times a day, allowing observations of short-term changes in the Northeast Asian region. The GOCI Data Processing System (GDPS), a specialized data processing software for GOCI, was developed for real-time generation of various products. This paper describes GOCI characteristics and GDPS workflow/products, so as to enable the efficient utilization of GOCI. To provide quality images and data, atmospheric correction and data analysis algorithms must be improved through continuous Cal/Val. GOCI-II will be developed by 2018 to facilitate in-depth studies on geostationary ocean color satellites. © 2012 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.

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