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Radiometric calibration utilizing the Moon as a reference source is termed as lunar calibration. It is a useful method for evaluating the performance of optical sensors onboard satellites orbiting the Earth. Lunar calibration provides sufficient radiometric calibration opportunities without requiring any special equipment, and is suitable for nano/microsatellites. This study applies lunar calibration to a multispectral sensor, Ocean Observation Camera (OOC), on board a microsatellite named Rapid International Scientific Experiment Satellite. Simulating the brightness of the Moon based on the RObotic Lunar Observatory and SELENE/Spectrum Profiler models, sensitivity degradation was proven to be negligible in any of the four spectral bands of the OOC with the sensor temperature correction. A bluing trend in the OOC’s sensor sensitivity was revealed, indicating a shorter observation wavelength shows larger irradiance. Comparing the top-of-atmosphere reflectance of Railroad Valley Playa with the Radiometric Calibration Network dataset revealed that the derived calibration parameter from the lunar calibration was valid for correcting the bluing trend in the visible range. Although the lunar and vicarious calibration parameters for the infrared band were unexpectedly inconsistent, lunar calibration could potentially contribute toward estimating the contaminated background radiance in the Earth observation images.
Masataka Imai; Junichi Kurihara; Toru Kouyama; Toshinori Kuwahara; Shinya Fujita; Yuji Sakamoto; Yuji Sato; Sei-Ichi Saitoh; Takafumi Hirata; Hirokazu Yamamoto; Yukihiro Takahashi. Radiometric Calibration for a Multispectral Sensor Onboard RISESAT Microsatellite Based on Lunar Observations. Sensors 2021, 21, 2429 .
AMA StyleMasataka Imai, Junichi Kurihara, Toru Kouyama, Toshinori Kuwahara, Shinya Fujita, Yuji Sakamoto, Yuji Sato, Sei-Ichi Saitoh, Takafumi Hirata, Hirokazu Yamamoto, Yukihiro Takahashi. Radiometric Calibration for a Multispectral Sensor Onboard RISESAT Microsatellite Based on Lunar Observations. Sensors. 2021; 21 (7):2429.
Chicago/Turabian StyleMasataka Imai; Junichi Kurihara; Toru Kouyama; Toshinori Kuwahara; Shinya Fujita; Yuji Sakamoto; Yuji Sato; Sei-Ichi Saitoh; Takafumi Hirata; Hirokazu Yamamoto; Yukihiro Takahashi. 2021. "Radiometric Calibration for a Multispectral Sensor Onboard RISESAT Microsatellite Based on Lunar Observations." Sensors 21, no. 7: 2429.
In the Bering Sea around and off the Yukon River delta, surface sediment plumes are markedly formed by glacier-melt and rainfall sediment runoffs of the Yukon River, Alaska, in June– September. The discharge and sediment load time series of the Yukon River were obtained at the lowest gauging station of US Geological Survey in June 2006–September 2010. Meanwhile, by coastal observations on boat, it was found out that the river plume plunges at a boundary between turbid plume water and clean marine water at the Yukon River sediment load of more than ca. 2500 kg/s. Grain size analysis with changing salinity (‰) for the river sediment indicated that the suspended sediment becomes coarse at 2 to 5‰ by flocculation. Hence, the plume’s plunging probably occurred by the flocculation of the Yukon suspended sediment in the brackish zone upstream of the plunging boundary, where the differential settling from the flocculation is considered to have induced the turbid water intrusion into the bottom layer.
Kazuhisa Chikita; Tomoyuki Wada; Isao Kudo; Sei-Ichi Saitoh; Mitsuhiro Toratani. Effects of River Discharge and Sediment Load on Sediment Plume Behaviors in a Coastal Region: The Yukon River, Alaska and the Bering Sea. Hydrology 2021, 8, 45 .
AMA StyleKazuhisa Chikita, Tomoyuki Wada, Isao Kudo, Sei-Ichi Saitoh, Mitsuhiro Toratani. Effects of River Discharge and Sediment Load on Sediment Plume Behaviors in a Coastal Region: The Yukon River, Alaska and the Bering Sea. Hydrology. 2021; 8 (1):45.
Chicago/Turabian StyleKazuhisa Chikita; Tomoyuki Wada; Isao Kudo; Sei-Ichi Saitoh; Mitsuhiro Toratani. 2021. "Effects of River Discharge and Sediment Load on Sediment Plume Behaviors in a Coastal Region: The Yukon River, Alaska and the Bering Sea." Hydrology 8, no. 1: 45.
The green mussel (Perna viridis) is one of the most commercially-important cultured species along the coast of Thailand. In this study, a suitable aquaculture site-selection model (SASSM) was developed to identify the most suitable areas in the inner part of the Gulf of Thailand (InnerGoT) for green mussel culture. Satellite-derived chlorophyll-a (Chl-a) and hydrodynamic model outputs for sea surface temperature (SST), salinity, maximum water current (MWC), and bathymetry between 2018 and 2019 were used as input to the SASSM. The results show that suitability scores in mussel aquaculture areas were lowest (1–3) during the Southwest (SW) monsoon, rainy season (July–August), and highest (6–7) during the Northeast (NE) monsoon, cold season (November–December). Moderate suitability scores (4–5) were obtained during the monsoon transition from the NE monsoon to the SW monsoon, summer (April–May). The study area was further divided into three zones: the western, central, and eastern regions. The western and eastern parts showed high suitability scores (5–7) while the central zone exhibited low suitability scores (2–4). The model results show a similar pattern to the actual mussel production in the study area. Seasonal events (i.e., flood and dry seasons) were incorporated into the model to examine the seasonal effects on the suitable mussel aquaculture areas. The suitability scores during the SW monsoon in 2018 were more sensitive to changes in SST and salinity relative to 2019. The higher freshwater discharge and lower temperature in 2018 relative to 2019 resulted in the accrual of suitable aquaculture areas. This pattern is consistent with the productions of the green mussel, where higher production was recorded in 2018 (2002.5 t) than in 2019 (410.8 t). However, correlations among atmospheric (air temperature, rainfall, and wind) and oceanographic factors (SST and MWC) were significant in the western and central regions, suggesting that the suitability of green mussel aquaculture in these regions is vulnerable to environmental disturbances. Thus, the SASSM can be a powerful tool in providing useful information on spatial management for marine aquaculture in environmentally-dynamic coastal systems.
Hathaichanok Kumgumpol; Yang Liu; Tanuspong Pokavanich; Irene Alabia; Zixu Yin; Sei-Ichi Saitoh; Yongjun Tian. Environmental Habitat Mapping of Green Mussel: A GIS-Based Approach for Sustainable Aquaculture in the Inner Gulf of Thailand. Sustainability 2020, 12, 10643 .
AMA StyleHathaichanok Kumgumpol, Yang Liu, Tanuspong Pokavanich, Irene Alabia, Zixu Yin, Sei-Ichi Saitoh, Yongjun Tian. Environmental Habitat Mapping of Green Mussel: A GIS-Based Approach for Sustainable Aquaculture in the Inner Gulf of Thailand. Sustainability. 2020; 12 (24):10643.
Chicago/Turabian StyleHathaichanok Kumgumpol; Yang Liu; Tanuspong Pokavanich; Irene Alabia; Zixu Yin; Sei-Ichi Saitoh; Yongjun Tian. 2020. "Environmental Habitat Mapping of Green Mussel: A GIS-Based Approach for Sustainable Aquaculture in the Inner Gulf of Thailand." Sustainability 12, no. 24: 10643.
To examine skipjack tuna’s habitat utilization in the western North Pacific (WNP) we used an ensemble modelling approach, which applied a fisher- derived presence-only dataset and three satellite remote-sensing predictor variables. The skipjack tuna data were compiled from daily point fishing data into monthly composites and re-gridded into a quarter degree resolution to match the environmental predictor variables, the sea surface temperature (SST), sea surface chlorophyll-a (SSC) and sea surface height anomalies (SSHA), which were also processed at quarter degree spatial resolution. Using the sdm package operated in RStudio software, we constructed habitat models over a 9-month period, from March to November 2004, using 17 algorithms, with a 70:30 split of training and test data, with bootstrapping and 10 runs as parameter settings for our models. Model performance evaluation was conducted using the area under the curve (AUC) of the receiver operating characteristic (ROC), the point biserial correlation coefficient (COR), the true skill statistic (TSS) and Cohen’s kappa (k) metrics. We analyzed the response curves for each predictor variable per algorithm, the variable importance information and the ROC plots. Ensemble predictions of habitats were weighted with the TSS metric. Model performance varied across various algorithms, with the Support Vector Machines (SVM), Boosted Regression Trees (BRT), Random Forests (RF), Multivariate Adaptive Regression Splines (MARS), Generalized Additive Models (GAM), Classification and Regression Trees (CART), Multi-Layer Perceptron (MLP), Recursive Partitioning and Regression Trees (RPART), and Maximum Entropy (MAXENT), showing consistently high performance than other algorithms, while the Flexible Discriminant Analysis (FDA), Mixture Discriminant Analysis (MDA), Bioclim (BIOC), Domain (DOM), Maxlike (MAXL), Mahalanobis Distance (MAHA) and Radial Basis Function (RBF) had lower performance. We found inter-algorithm variations in predictor variable responses. We conclude that the multi-algorithm modelling approach enabled us to assess the variability in algorithm performance, hence a data driven basis for building the ensemble model. Given the inter-algorithm variations observed, the ensemble prediction maps indicated a better habitat utilization map of skipjack tuna than would have been achieved by a single algorithm.
Robinson Mugo; Sei-Ichi Saitoh. Ensemble Modelling of Skipjack Tuna (Katsuwonus pelamis) Habitats in the Western North Pacific Using Satellite Remotely Sensed Data; a Comparative Analysis Using Machine-Learning Models. Remote Sensing 2020, 12, 2591 .
AMA StyleRobinson Mugo, Sei-Ichi Saitoh. Ensemble Modelling of Skipjack Tuna (Katsuwonus pelamis) Habitats in the Western North Pacific Using Satellite Remotely Sensed Data; a Comparative Analysis Using Machine-Learning Models. Remote Sensing. 2020; 12 (16):2591.
Chicago/Turabian StyleRobinson Mugo; Sei-Ichi Saitoh. 2020. "Ensemble Modelling of Skipjack Tuna (Katsuwonus pelamis) Habitats in the Western North Pacific Using Satellite Remotely Sensed Data; a Comparative Analysis Using Machine-Learning Models." Remote Sensing 12, no. 16: 2591.
Short- and long-term climate oscillations impact seascapes, and hence, marine ecosystem structure and dynamics. Here, we explored the spatio-temporal patterns of potential squid habitat in the western and central North Pacific across inter-decadal climate transitions, coincident with periods of persistent warming and cooling. Potential habitat distributions of Ommastrephes bartramii were derived from the outputs of multi-ensemble species distribution models, developed using the most influential environmental factors to squid distribution and occurrence data. Our analyses captured the underlying temporal trends in potential squid habitat in response to environmental changes transpiring at each climatic transition, regulated by phase shifts in Pacific decadal oscillation (PDO) from 1999–2013. The spatial differences in environmental conditions were apparent across transitions and presumably modulate the local changes in suitable squid habitat over time. Specifically, during a cold to warm PDO shift, decreases in the summer potential habitat (mean rate ± standard deviation: −0.04 ± 0.02 habitat suitability index (HSI)/yr) were observed along the southern edge of the subarctic frontal zone (162°E–172°W). Coincidentally, this area also exhibits a warming trend (mean temporal trend: 0.06 ± 0.21 °C/yr), accompanied with the prevalence of cold-core mesoscale eddies, west of the dateline (mean temporal trend in sea surface height: −0.19 ± 1.05 cm/yr). These conditions potentially generate less favorable foraging habitat for squid. However, a warm-to-cold PDO transition underpins a northward shift of suitable habitat and an eastward shift of regions exhibiting the highest rate of potential squid habitat loss (170–160°W; mean temporal trend: −0.05 ± 0.03 HSI/yr). Nonetheless, the emergence of the areas with increasingly suitable habitat regardless of climate transitions suggests the ecological importance of these regions as potential squid habitat hotspots and climatic refugia.
Irene D. Alabia; Sei-Ichi Saitoh; Hiromichi Igarashi; Yoichi Ishikawa; Yutaka Imamura. Spatial Habitat Shifts of Oceanic Cephalopod (Ommastrephes bartramii) in Oscillating Climate. Remote Sensing 2020, 12, 521 .
AMA StyleIrene D. Alabia, Sei-Ichi Saitoh, Hiromichi Igarashi, Yoichi Ishikawa, Yutaka Imamura. Spatial Habitat Shifts of Oceanic Cephalopod (Ommastrephes bartramii) in Oscillating Climate. Remote Sensing. 2020; 12 (3):521.
Chicago/Turabian StyleIrene D. Alabia; Sei-Ichi Saitoh; Hiromichi Igarashi; Yoichi Ishikawa; Yutaka Imamura. 2020. "Spatial Habitat Shifts of Oceanic Cephalopod (Ommastrephes bartramii) in Oscillating Climate." Remote Sensing 12, no. 3: 521.
The assessment of extreme weather events on suitable sites for aquaculture could help in establishing sustainable coastal environmental resource management. Japanese scallop culture is an economically important marine farming activity in the coastal communities of Shandong, China and Funka Bay, Japan. In this study, we improved the suitable aquaculture site-selection model (SASSM) by using Geostationary Ocean Color Imager (GOCI) data instead of Moderate Resolution Imaging Spectroradiometer (MODIS) data, as a complementary source for higher temporal and spatial resolution data that are useful for monitoring fine-scale coastal and oceanic processes. We also applied the newly developed SASSM to the Japanese scallop production site along the Shandong coast. Finally, we analyzed the correlations between environmental factors (chlorophyll a concentration, sea surface temperature (SST), and total suspended sediment), meteorological factors (precipitation, temperature, and wind), and climatic events (winter East Asian monsoon (EAM) and El Niño/La Niña Southern Oscillation), and the impacts of climate events on suitable zones for scallop aquaculture. The new SASSM maps show that GOCI products have the potential for oceanographic investigations in Shandong, China and Funka Bay, Japan. Our results highlighted higher aquaculture site suitability for scallop in Funka Bay than in Shandong coast. During the winter with a strong EAM (2011), the suitable area for Japanese scallop aquaculture increased. Conversely, in the winter during a strong El Niño (2016), we found fewer areas that were highly suitable for scallop aquaculture in Funka Bay. SST was extremely low in Funka Bay during spring and summer 2017, which caused fewer highly suitable areas (scores of 7 and 8) for scallop aquaculture relative to other years. These findings suggest that extreme climatic events significantly impact the availability of suitable sites for marine farming and thus, should be considered in the development and design of coastal aquaculture sites.
Yang Liu; Yongjun Tian; Sei-Ichi Saitoh; Irene D. Alabia; Kan-Ichiro Mochizuki. Impact of Climate Extremes on Suitability Dynamics for Japanese Scallop Aquaculture in Shandong, China and Funka Bay, Japan. Sustainability 2020, 12, 833 .
AMA StyleYang Liu, Yongjun Tian, Sei-Ichi Saitoh, Irene D. Alabia, Kan-Ichiro Mochizuki. Impact of Climate Extremes on Suitability Dynamics for Japanese Scallop Aquaculture in Shandong, China and Funka Bay, Japan. Sustainability. 2020; 12 (3):833.
Chicago/Turabian StyleYang Liu; Yongjun Tian; Sei-Ichi Saitoh; Irene D. Alabia; Kan-Ichiro Mochizuki. 2020. "Impact of Climate Extremes on Suitability Dynamics for Japanese Scallop Aquaculture in Shandong, China and Funka Bay, Japan." Sustainability 12, no. 3: 833.
Species distributions are changing with various rates and directions in response to recent global warming. The velocity of sea surface temperature (SST) has been used to predict species migration and persistence as an expectation of how species track their thermal niches; however, several studies have found that evidence for species shifts has deviated from the velocity of SST. This study investigated whether estimation of the velocity of shifts in phytoplankton size structure using remote sensing data could contribute to better prediction of species shifts. A chlorophyll-a (Chla) size distribution (CSD) model was developed by quantifying the relationships between the size structure of the phytoplankton community and the spectral features of the phytoplankton absorption coefficient (aph(λ)), based on the principal component analysis approach. Model validation demonstrated that the exponent of CSD (hereafter, CSD slope), which can describe the synoptic size structure of a phytoplankton community, was derived successfully with a relative root mean square error of 18.5%. The median velocity of CSD slope across the ocean was 485.2 km·decade−1, broadly similar to Chla (531.5 km·decade−1). These values were twice the velocity of SST, and the directions of shifts in CSD slope and Chla were quite different from that of SST. Because Chla is generally covariant with the size structure of a phytoplankton community, we believe that spatiotemporal changes in Chla can explain the variations of phytoplankton size structure. Obvious differences in both rate and direction of shifts were found between the phytoplankton size structure and SST, implying that shifts of phytoplankton size structure could be a powerful tool for assessing the distributional shifts of marine species. Our results will contribute to generate global and regional maps of expected species shifts in response to environmental forcing.
Hisatomo Waga; Toru Hirawake; Amane Fujiwara; Takashi Kikuchi; Shigeto Nishino; Koji Suzuki; Shintaro Takao; Sei-Ichi Saitoh. Differences in Rate and Direction of Shifts between Phytoplankton Size Structure and Sea Surface Temperature. Remote Sensing 2017, 9, 222 .
AMA StyleHisatomo Waga, Toru Hirawake, Amane Fujiwara, Takashi Kikuchi, Shigeto Nishino, Koji Suzuki, Shintaro Takao, Sei-Ichi Saitoh. Differences in Rate and Direction of Shifts between Phytoplankton Size Structure and Sea Surface Temperature. Remote Sensing. 2017; 9 (3):222.
Chicago/Turabian StyleHisatomo Waga; Toru Hirawake; Amane Fujiwara; Takashi Kikuchi; Shigeto Nishino; Koji Suzuki; Shintaro Takao; Sei-Ichi Saitoh. 2017. "Differences in Rate and Direction of Shifts between Phytoplankton Size Structure and Sea Surface Temperature." Remote Sensing 9, no. 3: 222.
The understanding of the spatio-temporal distributions of the species habitat in the marine environment is central to effectual resource management and conservation. Here, we examined the potential habitat distributions of Japanese common squid (Todarodes pacificus) in the Sea of Japan during a four-year period. The seasonal patterns of preferential habitat were inferred from species distribution models, built using squid occurrences detected from night-time visible images and remotely-sensed environmental factors. The predicted squid habitat (i.e., areas with high habitat suitability) revealed strong seasonal variability, characterized by a reduction of potential habitat, confined off of the southern part of the basin during the winter–spring period (December–May). Apparent expansion of preferential habitat occurred during summer–autumn months (June–November), concurrent with the formation of highly suitable habitat patches in certain regions of the Sea of Japan. These habitat distribution patterns were in response to changes in oceanographic conditions and synchronous with seasonal migration of squid. Moreover, the most important variables regulating the spatio-temporal patterns of suitable habitat were sea surface temperature, depth, sea surface height anomaly, and eddy kinetic energy. These variables could affect the habitat distributions through their impacts on growth and survival of squid, local nutrient transport, and the availability of favorable spawning and feeding grounds.
Irene D. Alabia; Mariko Dehara; Sei-Ichi Saitoh; Toru Hirawake. Seasonal Habitat Patterns of Japanese Common Squid (Todarodes Pacificus) Inferred from Satellite-Based Species Distribution Models. Remote Sensing 2016, 8, 921 .
AMA StyleIrene D. Alabia, Mariko Dehara, Sei-Ichi Saitoh, Toru Hirawake. Seasonal Habitat Patterns of Japanese Common Squid (Todarodes Pacificus) Inferred from Satellite-Based Species Distribution Models. Remote Sensing. 2016; 8 (11):921.
Chicago/Turabian StyleIrene D. Alabia; Mariko Dehara; Sei-Ichi Saitoh; Toru Hirawake. 2016. "Seasonal Habitat Patterns of Japanese Common Squid (Todarodes Pacificus) Inferred from Satellite-Based Species Distribution Models." Remote Sensing 8, no. 11: 921.