Papers by Mitsuhiro Toratani
Transactions of the Japan Society for Aeronautical and Space Sciences, aerospace technology Japan, 2018
Japan Aerospace Exploration Agency (JAXA) will launch an Earth observing satellite for climate st... more Japan Aerospace Exploration Agency (JAXA) will launch an Earth observing satellite for climate studies named "Global Change Observation Mission -Climate (GCOM-C)" in 2017 which carries a multi-spectral optical sensor named Second-Generation Global Imager (SGLI). The GCOM-C satellite will observe various geophysical variables such as vegetation, land surface temperature, aerosol, clouds, ocean color, sea surface temperature, snow cover extent, snow grain size and so on. The objectives of the SGLI observations are to elucidate the roles of the geophysical variables in the recent changing Earth's climate system and to establish long-term satellite data record of the variables. Three kinds of target accuracies to be achieved for the SGLI observations are defined for evaluating the success of the GCOM-C satellite mission. First one is the minimum thresholds to be achieved for the first SGLI data release at one year after the launch of GCOM-C. Second and third thresholds are the standard and goal accuracies to be achieved at five years after the launch for evaluating the full and extra success of the mission. The target accuracies for individual SGLI products are available at the GCOM-C web site (). The quality and accuracies of SGLI products are planned to be evaluated and maintained through validation activities organized by the SGLI validation team consisting of JAXA and SGLI principal investigators (PIs). Uncertainties of the SGLI data products will be characterized through the comparison with in-situ observations, similar products derived from other satellites, climatological data, and/or numerical model simulations. This paper summarizes the overall validation plan for the SGLI geophysical variable products.
Geophysical Research Letters, Mar 1, 2004
The eruption of the Miyake‐jima Volcano (34.08°N, 139.53°E) in the Izu Islands, Japan, 180 km SSW... more The eruption of the Miyake‐jima Volcano (34.08°N, 139.53°E) in the Izu Islands, Japan, 180 km SSW of Tokyo, began on 8 July 2000. A substantial amount of NH3 gas was found to be emitted from the Miyake‐jima Volcano together with SO2 gas and that geochemically significant quantities of aerosol particles composed of ammonium sulfate form in the plume. Through the use of satellite images, the additional atmospheric deposition of ammonium sulfate caused an increase of phyto‐plankton in the nutrient‐deficient region south of the Kuroshio. The emission of volcanic gases from the Miyake‐jima has likely been modifying the marine air quality as well as the open ocean ecosystem over parts of the western North Pacific for the past several years.
Doboku gakkai ronbunshu, 2020
Japan Geoscience Union, Mar 14, 2019
Doboku gakkai ronbunshu, 2015
Doboku gakkai ronbunshu, 2012
Doboku gakkai ronbunshu, 2013
Blue tides, upwelling of anoxic waters, have been a serious environmental problem in Tokyo Bay. I... more Blue tides, upwelling of anoxic waters, have been a serious environmental problem in Tokyo Bay. It is essential to figure out the behavior of the blue tide distribution occurrence area. To observe the blue tide distribution, the variation of the optical properties for the blue tide was investigated by measuring the backscattering coefficient, the light absorption coefficient and the remote sensing reflectance. Based on the results of the optical properties, we developed the estimation model for blue tide distribution. It was helpful not only monitoring extent of the distribution but also identification of the upwelling region of blue tides because it is able to express color strength of blue tide. In addition, estimated blue tide distribution was verified by 3-dimensional numerical simulation and the reason of the upwelling was understood.
International Symposium on Remote Sensing, Oct 1, 1995
Mineral dust-rich aerosol, such as of Saharan dust or Asian dust, is important in terms of its ef... more Mineral dust-rich aerosol, such as of Saharan dust or Asian dust, is important in terms of its effect on radiation budget as well as a source of micro-nutrient in the oceanic phytoplankton ecosystem. The authors introduce an empirical scheme for detecting dust aerosol over the ocean using satellite ocean color data such as of Sea Wide Field-of-View Scanner (SeaWiFS) or Ocean Color and Temperature Scanner (OCTS). The dust detection scheme uses estimated aerosol reflectance at 4 bands to detect spectral curvature in the aerosol reflectance. A series of dust index images over the north Pacific is derived from the SeaWiFS data obtained in April, 1998 when major Asian dust events were reported. The satellite-derived dust imagery is compared with the TOMS Aerosol Index imagery as well as the results of a dust transport simulation. The comparison reveals several small-scale differences although their dust distribution patterns show good agreement generally.
Journal of Oceanography, Jun 1, 2007
The performance of the "version 2" Global Imager (GLI) standard atmospheric correction algorithm,... more The performance of the "version 2" Global Imager (GLI) standard atmospheric correction algorithm, which includes empirical absorptive aerosol correction and sun glint correction, was evaluated using data collected with handheld above-water SIMBADA radiometers during 23 cruises of opportunity (research vessels, merchant ships), mostly in the North Atlantic and European seas. A number of 100 match-up data sets of GLI-derived and SIMBADA-measured normalized water-leaving radiance (nL W ) and aerosol optical thickness (AOT) were sorted out, using objective selection criteria, and analyzed. The Root-Mean-Square (RMS) difference between GLI and SIMBADA nL W was about 0.32 µ µ µ µ µW/cm 2 /nm/sr for the 412 nm band, showing improvement by 30% in RMS difference with respect to the conventional "version 1" GLI atmospheric correction algorithm, and the mean difference (or bias) was reduced significantly. For AOT, the RMS difference was 0.1 between GLI estimates and SIMBADA measurements and the bias was small (a few 0.01), but the Ångström exponent was systematically underestimated, by 0.4 on average, suggesting a potential GLI calibration offset in the near infrared. The nL W differences were not correlated to AOT, although performance was best in very clear conditions (AOT less than 0.05 in the 865 nm band). Despite the relatively large scatter between estimated and measured nL W , the derived chlorophyll-a concentration estimates, applying the same ratio algorithm (GLI OC4V4) to GLI and SIMBADA, were consistent and highly correlated in the range of 0.05-2 µ µ µ µ µg/l. The large variability in chlorophyll-a concentration estimate for clear clean water areas (e.g. with the concentration range lower than about 0.05 µ µ µ µ µg/l) turns out to be due to the nature of the "band ratio" based in-water algorithm. tem. Despite its relatively short lifetime, GLI acquired a unique data set over ocean, land, atmosphere, and cryosphere in a wide spectral range from near ultraviolet through thermal infrared with a spatial resolution of 1 km, 500 m, or 250 m at nadir. Uniqueness is also enhanced by the data collected by other instruments aboard the ADEOS-II satellite, which were operated concurrently with GLI. Of the 36 observation channels of GLI, up to about 10, extending from 380 nm to 865 nm, could be used for ocean color remote sensing with 1 km spatial resolution at nadir. The instrument has a tilt mechanism to avoid
Journal of Oceanography, Sep 1, 1998
This paper first describes the atmospheric correction algorithm for OCTS visible band data used a... more This paper first describes the atmospheric correction algorithm for OCTS visible band data used at NASDA/EOC. Sharing a basic structure with Gordon and Wang's SeaWiFS algorithm, it uses 10 candidate aerosol models including the "Asian dust model" introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670 and 865 nm bands, the algorithm selects a pair of aerosol models that account best for the observed spectral reflectances, and synthesizes the aerosol reflectance used for the atmospheric correction. Two different schemes for determining the value of the parameter for the aerosol model selection are presented and their anticipated estimation error is analyzed in terms of retrieved water reflectance at 443 nm. The results of our numerical simulation show that the standard deviation of the estimation error of the "weighted average" scheme is mostly within the permissible level of ±0.002, reducing the error by 18% on average compared to the "simple average" scheme. The paper further discusses the expected error under the old CZCS-type atmospheric correction, which assumes constant aerosol optical properties throughout the given image. Although our algorithm has a better performance than the CZCS algorithm, further analysis shows that the error induced by the assumption taken in the algorithm that the water-leaving radiance at 670 nm band is negligibly small may be large in high pigment concentration waters, indicating the necessity for future improvements.
Journal of advanced simulation in science and engineering, 2015
To determine the factors contributing to large-scale blue tide occurrences, blue tide distributio... more To determine the factors contributing to large-scale blue tide occurrences, blue tide distributions captured from satellite images were estimated using the estimation model for blue tides. This model was developed based on the observation results of the optical properties of Tokyo Bay and numerical simulation by a three-dimensional hydrodynamics and ecological model. By complementing the information from the results of both satellite image analysis to estimate the blue tide reflectance and the numerical simulation to calculate the dissolved oxygen (DO) concentration, the upwelling areas of sulfide-containing anoxic water were distinguished from those of non-sulfide-containing anoxic water.
The transport of Asian dust particles (KOSA) through the atmosphere to the Northwest Pacific is t... more The transport of Asian dust particles (KOSA) through the atmosphere to the Northwest Pacific is the most intensive one of this kind on the globe and is important in terms of the geochemical ocean cycle. The dust particles are also known to affect atmospheric correction process of satellite ocean color data, resulting in erroneous estimation of phytoplankton pigment concentration which,
Geophysical Research Letters, Jan 12, 2011
Simultaneous observations were made in the marine atmospheric boundary layer and surface ocean du... more Simultaneous observations were made in the marine atmospheric boundary layer and surface ocean during spring 2007 to investigate potential impacts of Asian dust on a semi-pelagic region of the northwestern North Pacific. The results suggest that mineral dust aerosols were scavenged by sea fog, and their deposition to the ocean increased the particle concentration in surface seawater. The atmospheric input of mineral dust to the ocean surface from this event was calculated to be 40 to 680 mg m -2 event -1 . A general relationship for the solubility of iron from dust particles led to an estimate of 20 to 330 mg m -2 for the amount of bio-available iron delivered during the dust event. This input of bio-available iron is comparable to total dissolved iron added during an iron fertilization experiment in the northwestern North Pacific in which an enhancement of primary production was observed.
Geophysical Research Letters, Sep 28, 2011
The biological processes play essential roles after the typhoon passageSlow-moving typhoons would... more The biological processes play essential roles after the typhoon passageSlow-moving typhoons would have strongly impact subtropical ecosystems
The SGLI instrument, which is to be launched by JAXA in March 2017 aboard GCOM-C satellite, condu... more The SGLI instrument, which is to be launched by JAXA in March 2017 aboard GCOM-C satellite, conducts ocean color observation in 250 m spatial resolution (SST in 500 m resolution) over coastal region, in addition to the global ocean observation in 1 km resolution. We first describe here the SGLI Level 2 (L2) ocean standard products, which consist of 6 ocean color parameters and 1 SST parameter, and then briefly describe the product generation data flow together with the algorithms implemented in the production system. The required time and memory size of the Level-2 data generation was evaluated over a simulated SGLI data scene, which indicates that the modules meet the standard L2 data generation system requirements, although further optimization in the processing code will be pursued.
Doboku gakkai ronbunshu, 2014
In order to determine the behavior of red tide distribution by satellite remote sensing, we found... more In order to determine the behavior of red tide distribution by satellite remote sensing, we found out that the optical properties of Tokyo Bay significantly changes in terms of measured AOP (apparent optical properties) and IOP (inherent optical properties) in field observation. Based on the spectrum variation of measured reflectance, we developed the estimation model of high concentration of Chlorophyll-a (Chl-a). By applying the developed model to satellite images, the spatial variation of high concentration of Chl-a in the bay was discussed in this paper. As a result, Chl-a was gradually increasing from the coast of the bay. It was found that the increment of Chl-a is mainly dependent on the spatial variation of temperature when wind was weak and solar radiation was high.
International Symposium on Remote Sensing, Oct 1, 1999
Journal of Oceanography
Second-generation global imager (SGLI) aboard the Global Change Observation Mission -Climate (GCO... more Second-generation global imager (SGLI) aboard the Global Change Observation Mission -Climate (GCOM-C, Shikisai) satellite was launched by Japan Aerospace eXploration Agency (JAXA) on December 23, 2017, to observe the carbon cycle and radiation budget for climate models predicting global warming. Since January 1, 2018, the SGLI has acquired high-quality ocean color and surface temperature data, which have now accumulated over more than 4 years. SGLI measures solar and terrestrial radiance in 13 visible and near-infrared channels with 2 polarizations, 4 shortwave and 2 thermal infrared channels. Observations are made at 250 m resolution in most channels twice every four days. Because of the high spatial and temporal resolutions, the data are expected to be useful in coastal investigations, although they cover the global ocean including polar seas. The ocean standard products, i.e., chlorophyll-a concentration (Chl-a), total suspended matter, and colored dissolved organic matter (CDOM), as well as photosynthetically active radiation, remote sensing reflectance, and sea surface temperature, are freely available from the JAXA Global Portal System (G-portal, al. jaxa. jp) and the JAXA Satellite Monitoring for Environmental Studies (JASMES, . eorc. jaxa. jp/ JASMES/ index_j. html). We anticipate that more oceanographers will be interested in using SGLI data for their studies in numerical modeling, carbon cycle, biogeochemical cycle, marine ecology, and management of marine resources and coastal environments. * Joji Ishizaka
Journal of remote sensing, 2002
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Papers by Mitsuhiro Toratani