Assessment of GOCI radiometric products using MERIS, MODIS and field measurements   总被引：1，自引：0，他引：1  

Nicolas Lamquin  Constant Mazeran  David Doxaran  Joo-Hyung Ryu  Young-Je Park 《Ocean Science Journal》2012,47(3):287-311

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 (?? _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.  相似文献   

Initial validation of GOCI water products against in situ data collected around Korean peninsula for 2010–2011     

Jeong-Eon Moon  Young-Je Park  Joo-Hyung Ryu  Jong-Kuk Choi  Jae-Hyun Ahn  Jee-Eun Min  Young-Baek Son  Sun-Ju Lee  Hee-Jeong Han  Yu-Hwan Ahn 《Ocean Science Journal》2012,47(3):261-277

This paper provides initial validation results for GOCI-derived water products using match-ups between the satellite and ship-borne in situ data for the period of 2010?C2011, with a focus on remote-sensing reflectance (R _rs ). Match-up data were constructed through systematic quality control of both in situ and GOCI data, and a manual inspection of associated GOCI images to identify pixels contaminated by cloud, land and inter-slot radiometric discrepancy. Efforts were made to process and quality check the in situ R _rs data. This selection process yielded 32 optimal match-ups for the R _rs spectra, chlorophyll a concentration (Chl_a) and colored dissolved organic matter (CDOM), and with 20 match-ups for suspended particulate matter concentration (SPM). Most of the match-ups are located close to shore and thus the validation should be interpreted limiting to near-shore coastal waters. The R _rs match-ups showed the mean relative errors of 18?C33% for the visible bands with the lowest 18?C19% for the 490 nm and 555 nm bands and 33% for the 412 nm band. Correlation for the R _rs match-ups was high in the 490?C865 nm bands (R²=0.72?C0.84) and lower in the 412 nm band (R²=0.43) and 443 nm band (R²=0.66). The match-ups for Chl_a showed a low correlation (<0.41) although the mean absolute percentage error was 35% for the GOCI standard Chl_a. The CDOM match-ups showed an even worse comparison with R²<0.2. These match-up comparison for Chl_a and CDOM would imply the difficulty to estimate Chl_a and CDOM in near-shore waters where the variability in SPM would dominate the variability in R _rs . Clearly, the match-up statistics for SPM was better with R²=0.73 and 0.87 for two evaluated algorithms, although GOCI-derived SPM overestimated low concentration and underestimated high concentration. Based on this initial match-up analysis, we made several recommendations -1) to collect more offshore under-water measurements of the R _rs data, 2) to include quality flags in level-2 products, 3) to introduce an ISRD correction in the GOCI processing chain, 4) to investigate other types of in-water algorithms such as semianalytical ones, and 5) to investigate vicarious calibration for GOCI data and to maintain accurate and consistent calibration of field radiometric instruments.  相似文献   

Development of atmospheric correction algorithm for Geostationary Ocean Color Imager (GOCI)   总被引：2，自引：0，他引：2  

Jae-Hyun Ahn  Young-Je Park  Joo-Hyung Ryu  Boram Lee  Im Sang Oh 《Ocean Science Journal》2012,47(3):247-259

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 situ nL _w (??), 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.  相似文献   

Geometric performance evaluation of the Geostationary Ocean Color Imager     

Chan-Su Yang  Jung-Hwan Song 《Ocean Science Journal》2012,47(3):235-246

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 ??rad for navigation) occur in some slots, although the performance during an estimation period of 7 continuous days was within the desired criteria.  相似文献   

GOCI data processing and ocean applications     

Joo-Hyung Ryu  Joji Ishizaka 《Ocean Science Journal》2012,47(3):221-221

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Continuous Observation of Groundwater and Crustal Deformation for Forecasting Tonankai and Nankai Earthquakes in Japan     

Satoshi Itaba  Naoji Koizumi  Norio Matsumoto  Ryu Ohtani 《Pure and Applied Geophysics》2010,167(8-9):1105-1114

In 2006, we started construction of an observation network of 12 stations in and around Shikoku and the Kii Peninsula to conduct research for forecasting Tonankai and Nankai earthquakes. The purpose of the network is to clarify the mechanism of past preseismic groundwater changes and crustal deformation related to Tonankai and Nankai earthquakes. Construction of the network of 12 stations was completed in January 2009. Work on two stations, Hongu-Mikoshi (HGM) and Ichiura (ICU), was finished earlier and they began observations in 2007. These two stations detected strain changes caused by the slow-slip events on the plate boundary in June 2008, although related changes in groundwater levels were not clearly recognized.  相似文献   

Numerical simulation of impact loads using a particle method     

B.-H. Lee  J.-C. Park  M.-H. Kim  S.-J. Jung  M.-C. Ryu  Y.-S. Kim 《Ocean Engineering》2010,37(2-3):164-173

The violent free-surface motions interacting with structures are investigated using the moving particle semi-implicit (MPS) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flow simulation. In the present numerical method, a more efficient algorithm for Lagrangian moving particles is used for solving various highly nonlinear free-surface problems without using the Eulerian approach or the grid system. Therefore, the convection terms and time derivatives in the Navier–Stokes equation can be calculated more directly without any numerical diffusion, instabilities, or topological failure. In particular, the MPS method is applied to the simulation of liquid-entry and slamming problems, such as wet-drop (liquid–liquid collision) tests in an LNG tank and slamming loads (solid–liquid collision) on rigid plates with various incident angles. The numerical results are in good agreement with available experimental data.  相似文献   

Spatial scales of mesoscale eddies from GOCI Chlorophyll-a concentration images in the East/Japan Sea   总被引：2，自引：0，他引：2  

Kyung-Ae Park  Hye-Jin Woo  Joo-Hyung Ryu 《Ocean Science Journal》2012,47(3):347-358

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.  相似文献   

Deep-learning based projection of change in irrigation water-use under RCP 8.5     

Jang Hyun Sung  Jinsoo Kim  Eun-Sung Chung  Young Ryu 《水文研究》2021,35(8):e14315

Stream water-use is essential for both agricultural and hydrological management and yet not many studies have explored its non-stationarity and nonlinearity with meteorological variables. This study proposed a deep-learning based model to estimate agricultural water withdrawal using hydro-meteorological variables, which projected the changes of agricultural water withdrawal influenced by climate change of future. The relationships between meteorological variables and stream water-use rate (WUR) were quantified using a deep belief network (DBN). The influences of precipitation, potential evapotranspiration, and monthly averaged WUR on the performance of the developed DBN model were tested. As a result, this DBN with potential evapotranspiration (PET) provided better performances than precipitation to estimate the WUR. The PET of multi-model scenarios for Representative Concentration Pathways 8.5 would be increased as time goes by, and thus leads to increase WUR estimated by DBN in three basins, located in South Korea during the future period. On the contrary, water availability expected to decrease compared to the current. Therefore, managing water-uses and improving efficiencies can be prepared for the change in agricultural water-use by climate change in the future.  相似文献   

Late Holocene distal mud deposits off the Nakdong delta,SE Korea: evidence for shore-parallel sediment transport in a current-dominated setting     

Jong-Hwa Chun  Yuri Kim  Jang-Jun Bahk  Young Jun Kim  Dong-Hyo Kang  Yong Hoon Kim  Gil Young Kim  Byong-Jae Ryu 《Geo-Marine Letters》2015,35(6):475-485

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