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RESEARCH ARTICLE
Remote sensing observations of phytoplankton increases triggered by successive typhoons
Lei HUANG, Hui ZHAO, Jiayi PAN, Adam DEVLIN
Front. Earth Sci.. 2017, 11 (4): 601-608.   DOI: 10.1007/s11707-016-0608-x
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Phytoplankton blooms in the Western North Pacific, triggered by two successive typhoons with different intensities and translation speeds under different pre-existing oceanic conditions, were observed and analyzed using remotely sensed chlorophyll-a (Chl-a), sea surface temperature (SST), and sea surface height anomaly (SSHA) data, as well as typhoon parameters and CTD (conductivity, temperature, and depth) profiles. Typhoon Sinlaku, with relatively weaker intensity and slower translation speed, induced a stronger phytoplankton bloom than Jangmi with stronger intensity and faster translation speed (Chl-a>0.18 mg·m3 versus Chl-a<0.15 mg·m3) east of Taiwan Island. Translation speed may be one of the important mechanisms that affect phytoplankton blooms in the study area. Pre-existing cyclonic circulations provided a relatively unstable thermodynamic structure for Sinlaku, and therefore cold water with rich nutrients could be brought up easily. The mixed-layer deepening caused by Typhoon Sinlaku, which occurred first, could have triggered an unfavorable condition for the phytoplankton bloom induced by Typhoon Jangmi which followed afterwards. The sea surface temperature cooling by Jangmi was suppressed due to the presence of the thick upper-ocean mixed-layer, which prevented the deeper cold water from being entrained into the upper-ocean mixed layer, leading to a weaker phytoplankton augment. The present study suggests that both wind (including typhoon translation speed and intensity) and pre-existing conditions (e.g., mixed-layer depths, eddies, and nutrients) play important roles in the strong phytoplankton bloom, and are responsible for the stronger phytoplankton bloom after Sinlaku’s passage than that after Jangmi’s passage. A new typhoon-influencing parameter is introduced that combines the effects of the typhoon forcing (including the typhoon intensity and translation speed) and the oceanic pre-condition. This parameter shows that the forcing effect of Sinlaku was stronger than that of Jangmi.

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Sensitivity analysis for the total nitrogen pollution of the Danjiangkou Reservoir based on a 3-D water quality model
Libin CHEN, Zhifeng YANG, Haifei LIU
Front. Earth Sci.. 2017, 11 (4): 609-619.   DOI: 10.1007/s11707-017-0650-3
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Inter-basin water transfers containing a great deal of nitrogen are great threats to human health, biodiversity, and air and water quality in the recipient area. Danjiangkou Reservoir, the source reservoir for China’s South-to-North Water Diversion Middle Route Project, suffers from total nitrogen pollution and threatens the water transfer to a number of metropolises including the capital, Beijing. To locate the main source of nitrogen pollution into the reservoir, especially near the Taocha canal head, where the intake of water transfer begins, we constructed a 3-D water quality model. We then used an inflow sensitivity analysis method to analyze the significance of inflows from each tributary that may contribute to the total nitrogen pollution and affect water quality. The results indicated that the Han River was the most significant river with a sensitivity index of 0.340, followed by the Dan River with a sensitivity index of 0.089, while the Guanshan River and the Lang River were not significant, with the sensitivity indices of 0.002 and 0.001, respectively. This result implies that the concentration and amount of nitrogen inflow outweighs the geographical position of the tributary for sources of total nitrogen pollution to the Taocha canal head of the Danjiangkou Reservoir.

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Flora characteristics of Chenier Wetland in Bohai Bay and biogeographic relations with adjacent wetlands
Yanyun ZHAO, Zhaohua LU, Jingtao LIU, Shugang HU
Front. Earth Sci.. 2017, 11 (4): 620-628.   DOI: 10.1007/s11707-016-0599-7
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A key step towards the restoration of heavily disturbed fragile coastal wetland ecosystems is determining the composition and characteristics of the plant communities involved. This study determined and characterized the community of higher plants in the Chenier wetland of Bohai Bay using a combination of field surveys, quadrat approaches, and multivariate statistical analyses. This community was then compared to other adjacent wetlands (Tianjin, Qinhuangdao, Laizhouwan, Jiaozhouwan, and Yellow River Delta wetland) located near the Huanghai and Bohai Seas using principal coordinate analysis (PCoA). Results showed a total of 56 higher plant species belonging to 52 genera from 20 families in Chenier wetland, the majority of which were dicotyledons. Single-species families were predominant, while larger families, including Gramineae, Compositae, Leguminosae, and Chenopodiaceae contained a higher number of species (each≥6 species). Cosmopolitan species were also dominant with apparent intrazonality. Abundance (number of species) of temperate species was twice that of tropical taxa. Species number of perennial herbs, such as Gramineae and Compositae, was generally higher. Plant diversity in the Chenier wetland, based on the Shannon-Wiener index, was observed to be between the Qinhuangdao and Laizhouwan indices, while no significant difference was found in other wetlands using the Simpson index. Despite these slight differences in diversity, PCoA based on species abundance and composition of the wetland flora suggest that the Bohai Chenier community was highly similar to the coastal wetlands in Tianjin and Laizhouwan, further suggesting that these two wetlands could be important breeding grounds and resources for the restoration of the plant ecosystem in the Chenier wetland.

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Assessing the evolution of oases in arid regions by reconstructing their historic spatio-temporal distribution: a case study of the Heihe River Basin, China
Yaowen XIE, Guisheng WANG, Xueqiang WANG, Peilei FAN
Front. Earth Sci.. 2017, 11 (4): 629-642.   DOI: 10.1007/s11707-016-0607-y
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Oasis evolution, one of the most obvious surface processes in arid regions, affects various aspects of the regional environment, such as hydrological processes, ecological conditions, and microclimates. In this paper, the historical spatio-temporal evolution of the cultivated oases in the Heihe River Basin, the second largest inland watershed in the northwest of China, was assessed using multidisciplinary methods and data from multiple sources, including historical literature, ancient sites, maps and remotely sensed images. The findings show that cultivated oases were first developed on a large scale during the Han Dynasty (121 BC–220) and then gradually decreased in extent from the Six Dynasties period (220–581) to the Sui-Tang period (581–907), reaching a minimum in the Song-Yuan period (960–1368). An abrupt revival occurred during the Ming Dynasty (1368–1644) and continued through the Qing Dynasty (1644–1911), and during the period of the Republic of China (1912–1949), oasis development reached its greatest peak of the entire historical period. The oasis areas during seven major historical periods, i.e., Han, Six Dynasties, Sui-Tang, Song-Yuan, Ming, Qing, and Republic of China, are estimated to have been 1703 km2, 1115 km2, 629 km2, 614 km2, 964 km2, 1205 km2, and 1917 km2, respectively. The spatial distribution generally exhibited a continuous sprawl process, with the center of the oases moving gradually from the downstream region to the middle and even upstream regions. The oases along the main river remained stable during most periods, whereas those close to the terminal reaches were subject to frequent variations and even abandonment. Socio-economic factors were the main forces driving the evolution of cultivated oases in the area; among them, political and societal stability, national defense, agricultural policy, population, and technological progress were the most important.

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Impact of reclaimed water in the watercourse of Huai River on groundwater from Chaobai River basin, Northern China
Yilei YU, Xianfang SONG, Yinghua ZHANG, Fandong ZHENG, Licai LIU
Front. Earth Sci.. 2017, 11 (4): 643-659.   DOI: 10.1007/s11707-016-0600-5
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Reclaimed water is efficient for replenishing the dry rivers in northern China, but regional groundwater may be at risk from pollution. Therefore, samples of reclaimed water, river water, and groundwater were collected at the Huai River in the Chaobai River basin in 2010. The water chemistry and isotopic compositions of the samples were analyzed in the laboratory. The reclaimed water had stable compositions of water chemistry and isotopes, and the Na·Ca-HCO3·Cl water type. The water chemistry of the river water was consistent with that of the reclaimed water. A June peak of total nitrogen was the prominent characteristic in the shallow groundwater, which also had the Na·Ca-HCO3·Cl water type. However, the water chemistry and isotopes in most of the deep groundwater remained stable, and the water type was Ca·Mg-HCO3. The amount of reclaimed water recharging the groundwater was about 2.5 × 107 m3/yr. All of the shallow groundwater was impacted by the reclaimed water, with the mixing proportion of reclaimed water ranging from 42% to 80 % in the dry season and from 20% to 86% in the wet season. Only one deep well, with proportions of 67% (dry season) and 28% (wet season), was impacted. TDS, EC, and major ions (Na, K, Cl, NH4-N, NO2-N, and NO3-N) were increased in the impacted wells.

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Temporal-spatial variation of DOC concentration, UV absorbance and the flux estimation in the Lower Dagu River, China
Min XI, Fanlong KONG, Yue LI, Fanting KONG
Front. Earth Sci.. 2017, 11 (4): 660-669.   DOI: 10.1007/s11707-017-0633-4
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Dissolved organic carbon (DOC) is an important component for both carbon cycle and energy balance. The concentration, UV absorbance, and export flux of DOC in the natural environment dominate many important transport processes. To better understand the temporal and spatial variation of DOC, 7 sites along the Lower Dagu River were chosen to conduct a comprehensive measurement from March 2013 to February 2014. Specifically, water samples were collected from the Lower Dagu River between the 26th and 29th of every month during the experimental period. The DOC concentration (CDOC) and UV absorbance were analyzed using a total organic carbon analyzer and the ultraviolet-visible absorption spectrum, and the DOC export flux was estimated with a simple empirical model. The results showed that the CDOC of the Lower Dagu River varied from 1.32 to 12.56 mg/L, consistent with global rivers. The CDOC and UV absorbance showed significant spatial variation in the Dagu River during the experiential period because of the upstream natural processes and human activities in the watershed. The spatial variation is mainly due to dam or reservoir constructions, riverside ecological environment changes, and non-point source or wastewater discharge. The seasonal variation of CDOC was mainly related to the source of water DOC, river runoff, and temperature, and the UV absorbance and humification degree of DOC had no obvious differences among months (P<0.05). UV absorbance was applied to test the CDOC in Lower Dagu River using wave lengths of 254 and 280 nm. The results revealed that the annual DOC export flux varied from 1.6 to 3.76×105 g C/km2/yr in a complete hydrological year, significantly lower than the global average. It is worth mentioning that the DOC export flux was mainly concentrated in summer (~90% of all-year flux in July and August), since the runoff in the Dagu River took place frequently in summer. These observations implied environment change could bring the temporal-spatial variation of DOC and the exports, which would further affect the land-ocean interactions in the Lower Dagu River and the global carbon cycle.

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Salinity-oriented environmental flows for keystone species in the Modaomen Estuary, China
Menglu ZHANG, Baoshan CUI, Zhiming ZHANG, Xuelian JIANG
Front. Earth Sci.. 2017, 11 (4): 670-681.   DOI: 10.1007/s11707-016-0609-9
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Rapid development and urbanization in recent years have contributed to a reduction in freshwater discharge and intensified saltwater intrusion in the Pearl River Delta. This comprises a significant threat to potable water supplies and overall estuary ecosystem health. In this study, the environmental flows of the Modaomen Estuary, one of the estuaries of the Pearl River Delta in China, were determined based on the salinity demand of keystone species and the linear relationship between river discharge and estuarine salinity. The estimated minimum and optimal annual environmental flows in the Modaomen Estuary were 116.8 × 109 m3 and 273.8 × 109 m3, respectively, representing 59.3% and 139.0% of the natural runoff. Water quality assessments in recent years indicate that the environmental flows have not been satisfied most of the time, particularly the optimal environmental flow, despite implementation of various water regulations since 2005. Therefore, water regulations and wetland network recoveries based on rational environmental flows should be implemented to alleviate saltwater intrusion and for the creation of an ideal estuarine habitat.

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Calcification response of Pleurochrysis carterae to iron concentrations in batch incubations: implication for the marine biogeochemical cycle
Xiang ZOU, Shiyong SUN, Sen LIN, Kexuan SHEN, Faqin DONG, Daoyong TAN, Xiaoqin NIE, Mingxue LIU, Jie WEI
Front. Earth Sci.. 2017, 11 (4): 682-688.   DOI: 10.1007/s11707-016-0629-5
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Calcified coccolithophores, a diverse and widely distributed group of marine microalgae, produce biogenic calcite in the form of coccoliths located on the cell surface. Using batch incubations of the coccolithophoridPleurochrysis carterae, we investigated the responses of this calcification process to iron concentrations by changing the iron supply in the initial culture media from a normal concentration to 1 ppm (parts per million), 5 ppm, and 10 ppm. Time-dependent measurements of cell population, production of inorganic carbon (coccoliths), and organic carbon (organic cellular components) showed that elevated iron supply in the growth medium ofP. carterae stimulates carbon sequestration by increasing growth along enhanced photosynthetic activity and calcification. In addition, the acquired time-dependent UV-Vis and FT-IR spectra revealed that iron fertilization-enhanced coccolith calcification is accompanied by a crystalline phase transition from calcite to aragonite or amorphous phase. Our results suggest that iron concentration has a significant influence on the marine carbon cycle of coccolithophores.

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Assessing the effect of desertification controlling projects and policies in northern Shaanxi Province, China by integrating remote sensing and farmer investigation data
Duanyang XU, Alin SONG, Xiao SONG
Front. Earth Sci.. 2017, 11 (4): 689-701.   DOI: 10.1007/s11707-016-0601-4
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To combat desertification, the Chinese government has launched a series of Desertification Controlling Projects and Policies over the past several decades. However, the effect of these projects and policies remains controversial due to a lack of suitable methods and data to assess them. In this paper, the authors selected the farming-pastoral region of the northern Shaanxi Province in China as a sample region and attempted to assess the effect of Desertification Controlling Projects and Policies launched after 2000 by combining remote sensing and farmer investigation data. The results showed that the combination of these two complementary assessments can provide comprehensive information to support decision-making. According to the remote sensing and Net Primary Production data, the research region experienced an obvious desertification reversion between 2000 and 2010, and approximately 70% of this reversion can be explained by Desertification Controlling Projects and Policies. Farmer investigation data also indicated that these projects and policies were the dominating factor contributing to desertification reversion, and approximately 70% of investigated farmers agreed with this conclusion. However, low supervision and subsidy levels were issues that limited the policy effect. Therefore, it is necessary for the government to enhance supervision, raise subsidy levels, and develop environmental protection regulations to encourage more farmers to participate in desertification control.

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ERRATUM
Erratum to: Using isotope methods to study alpine headwater regions in the Northern Caucasus and Tien Shan
E. RETS, J. CHIZHOVA, N. LOSHAKOVA, I. TOKAREV, M. KIREEVA, N. BUDANTSEVA, Yu.K. VASIL’CHUK, N. FROLOVA, V. POPOVNIN, P. TOROPOV, E. TERSKAYA, A. SMIRNOV, E. BELOZEROV, M. KARASHOVA
Front. Earth Sci.. 2017, 11 (4): 702-702.   DOI: 10.1007/s11707-017-0674-8
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RESEARCH ARTICLE
Regression-transgression cycles of paleolakes in the Fen River Graben Basin during the mid to late Quaternary and their tectonic implication
Meijun CHEN, Xiaomeng HU
Front. Earth Sci.. 2017, 11 (4): 703-714.   DOI: 10.1007/s11707-016-0598-8
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An investigation into lake terraces and their sedimentary features in the Fen River Graben Basin shows that several paleolake regression-transgression cycles took place during the mid to late Quaternary. The horizontal distribution of the lowest loess/paleosol unit overlying each lake terrace indicates the occurrence of four rapid lake regressions when paleosols S8, S5, S2, and S1 began to develop. The horizontal distribution of the topmost loess/paleosol unit underlying the lacustrine sediment in each transition zone between two adjacent terraces indicates that following a lake regression, a very slow lake transgression occurred. The durations of three lake transgressions correspond to those of the deposition or development of loess/paleosols L8 to L6, L5 to L3, and L2. It is thereby inferred that regional tectonic movement is likely the primary factor resulting in the cyclical process of paleolake regressions and transgressions. Taking these findings along with published geophysical research results regarding the upper mantle movements underneath the graben basin into account, this paper deduces that a cause and effect relationship may exist between the paleolake regression-transgression cycles and the tectonic activity in the upper mantle. The occurrence of a rapid lake regression implies that the upwelling of the upper mantle underneath the graben basin may be dominant and resulting in a rapid uplifting of the basin floor. The subsequent slow lake transgression implies that the thinning of the crust and cooling of the warm mantle material underneath the graben basin may become dominant causing the basin floor to subside slowly. Four rapid paleolake regressions indicate that four episodic tectonic movements took place in the graben basin during the mid to late Quaternary.

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An application of two-phase 1DV model in studying sedimentary processes on an erosional mudflat at Yangtze River Delta, China
Chunyang XU, Ping DONG
Front. Earth Sci.. 2017, 11 (4): 715-728.   DOI: 10.1007/s11707-016-0604-1
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A two-phase flow model for predicting sedimentation processes under wave and current conditions is presented. The model is based on solving the one-dimensional continuity and momentum equations for both fluid and solid phases through water column (1DV). The standard mixing length model is modified to take into account the buoyancy effect due to the gradient of suspended sediments near the seabed. The model is applied to study sedimentation processes on an erosional mudflat in the Yangtze River Delta, China, and intra-tide variations of flow properties and mud concentration are predicted and compared with field measurements. It was found that it is necessary to include the wave-induced shear stress in determining sediment erosion and the existence of a fluid mud layer can significantly influence both the flow structure and the distribution of sediment concentration in the water column. The turbulence dissipation induced by the fluid mud layer has the effect of increasing the duration of re-suspension during the early stage of the ebb. The overall good agreement between measured data and model results demonstrates the capability of the model.

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Tectonic subsidence of the Zhu 1 Sub-basin in the Pearl River Mouth Basin, northern South China Sea
Xiaoyin TANG, Shuchun YANG, Junzhang ZHU, Zulie LONG, Guangzheng JIANG, Shaopeng HUANG, Shengbiao HU
Front. Earth Sci.. 2017, 11 (4): 729-739.   DOI: 10.1007/s11707-016-0610-3
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The Pearl River Mouth Basin, which is situated on the northern margin of the South China Sea, has attracted great attention not only because of its tectonic setting but also because of its abundant hydrocarbon resources. We have analyzed the Cenozoic tectonic subsidence history of 4 drilled wells and 43 artificial wells from the Zhu 1 Sub-basin of the Pearl River Mouth Basin by back-stripping, using newly interpreted seismic profiles. We also calculated the average tectonic subsidence rates of the four sags in the Zhu 1 Sub-basin. The rifting and post-rifting stages are separated by abrupt changes in the tectonic subsidence curves and average subsidence rates. In the eastern sags of the Zhu 1 Sub-basin, tectonic subsidence started to slow at ca. 30 Ma, compared with ca. 23.8 Ma in the western sags. This probably corresponds to the timing of break-up and suggests that rifting in the Pearl River Mouth Basin ended earlier in the eastern sags than in the western sags. Anomalously accelerated tectonic subsidence occurred at 17.5–16.4 Ma during the post-rifting stage, with average subsidence rates as high as 301.9 m/Myr. This distinguishes the Pearl River Mouth Basin from classical Atlantic passive continental marginal basins, which demonstrate exponentially decaying post-rift tectonic subsidence.

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Major transgression during Late Cretaceous constrained by basin sediments in northern Africa: implication for global rise in sea level
Kaixuan AN, Hanlin CHEN, Xiubin LIN, Fang WANG, Shufeng YANG, Zhixin WEN, Zhaoming WANG, Guangya ZHANG, Xiaoguang TONG
Front. Earth Sci.. 2017, 11 (4): 740-750.   DOI: 10.1007/s11707-017-0661-0
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The global rise in sea level during the Late Cretaceous has been an issue under discussion by the international geological community. Despite the significance, its impact on the deposition of continental basins is not well known. This paper presents the systematic review on stratigraphy and sedimentary facies compiled from 22 continental basins in northern Africa. The results indicate that the region was dominated by sediments of continental facies during Early Cretaceous, which were replaced by deposits of marine facies in Late Cretaceous. The spatio-temporal distribution of sedimentary facies suggests marine facies deposition reached as far south as Taoudeni-Iullemmeden-Chad-Al Kufra-Upper Egypt basins during Turonian to Campanian. These results indicate that northern Africa underwent significant transgression during Late Cretaceous reaching its peak during Turonian to Coniacian. This significant transgression has been attributed to the global high sea-level during this time. Previous studies show that global rise in sea level in Late Cretaceous may have been driven by an increase in the volume of ocean water (attributed to high CO2 concentration and subsequently warm climate) and a decrease in the volume of the ocean basin (attributed to rapid production of oceanic crust and seamounts). Tectonic mechanism of rapid production of oceanic crust and seamounts could play a fundamental role in driving the global rise in sea level and subsequent transgression in northern Africa during Late Cretaceous.

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Interannual variations in length of day and atmospheric angular momentum, and their seasonal associations with El Niño/Southern Oscillation-like sea surface temperature patterns
Yuefeng LI, Ziniu XIAO, Wenjing SHI, Qi ZHONG, Qiguang WANG, Huanlian LI
Front. Earth Sci.. 2017, 11 (4): 751-764.   DOI: 10.1007/s11707-016-0602-3
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This study examines the seasonal connections between the interannual variations in LOD (length of day)/AAMglobe (the relative atmospheric angular momentum for the whole globe) and the ENSO-like SST (El Niño/Southern Oscillation-like sea surface temperature) pattern and corresponding zonal and vertical circulations. Consistent with previous studies, the ENSO-like SST impact the following season LOD/AAMglobe, with the strongest correlations in DJF (December, January, and February), when it is likely to be the peak El Niño/La Niña period. Lag correlations between the interannual variations in LOD/AAMglobe and surface temperature, and the interannual variations in LOD and both zonal circulation and vertical airflow around the equator, consistently indicate that the LOD/AAMglobe reflect the potential impacts of variations in the Earth’s rotation rate on the following season’s sea surface temperatures (SST) over the tropical central and eastern Pacific (where the ENSO-like SST pattern is located). Moreover, the centers of strongest variation in the AAMcolumn (the relative atmospheric angular momentum for an air column and the unit mass over a square meter) are located over the mid-latitudinal North Pacific in DJF and MAM (March, April, and May), and over the mid-latitudinal South Pacific in JJA (June, July, and August) and SON (September, October, and November). This suggests that the AAMcolumn over the mid-latitudinal Pacific around 30°N (30°S) dominate the modulation of Earth’s rotation rate, and then impact the variations in LOD during DJF and MAM (JJA and SON).

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Optimized extreme learning machine for urban land cover classification using hyperspectral imagery
Hongjun SU, Shufang TIAN, Yue CAI, Yehua SHENG, Chen CHEN, Maryam NAJAFIAN
Front. Earth Sci.. 2017, 11 (4): 765-773.   DOI: 10.1007/s11707-016-0603-2
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This work presents a new urban land cover classification framework using the firefly algorithm (FA) optimized extreme learning machine (ELM). FA is adopted to optimize the regularization coefficientC and Gaussian kernel s for kernel ELM. Additionally, effectiveness of spectral features derived from an FA-based band selection algorithm is studied for the proposed classification task. Three sets of hyperspectral databases were recorded using different sensors, namely HYDICE, HyMap, and AVIRIS. Our study shows that the proposed method outperforms traditional classification algorithms such as SVM and reduces computational cost significantly.

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A mutual information-Dempster-Shafer based decision ensemble system for land cover classification of hyperspectral data
Parham PAHLAVANI, Behnaz BIGDELI
Front. Earth Sci.. 2017, 11 (4): 774-783.   DOI: 10.1007/s11707-016-0611-2
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Hyperspectral images contain extremely rich spectral information that offer great potential to discriminate between various land cover classes. However, these images are usually composed of tens or hundreds of spectrally close bands, which result in high redundancy and great amount of computation time in hyperspectral classification. Furthermore, in the presence of mixed coverage pixels, crisp classifiers produced errors, omission and commission. This paper presents a mutual information-Dempster-Shafer system through an ensemble classification approach for classification of hyperspectral data. First, mutual information is applied to split data into a few independent partitions to overcome high dimensionality. Then, a fuzzy maximum likelihood classifies each band subset. Finally, Dempster-Shafer is applied to fuse the results of the fuzzy classifiers. In order to assess the proposed method, a crisp ensemble system based on a support vector machine as the crisp classifier and weighted majority voting as the crisp fusion method are applied on hyperspectral data. Furthermore, a dimension reduction system is utilized to assess the effectiveness of mutual information band splitting of the proposed method. The proposed methodology provides interesting conclusions on the effectiveness and potentiality of mutual information-Dempster-Shafer based classification of hyperspectral data.

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