State-of-the-art halide perovskite solar cells have bandgaps larger than 1.45 eV, which restricts their potential for realizing the Shockley-Queisser limit. Previous search for low-bandgap (1.2 to ...1.4 eV) halide perovskites has resulted in several candidates, but all are hybrid organic-inorganic compositions, raising potential concern regarding device stability. Here we show the promise of an inorganic low-bandgap (1.38 eV) CsPb
Sn
I
perovskite stabilized via interface functionalization. Device efficiency up to 13.37% is demonstrated. The device shows high operational stability under one-sun-intensity illumination, with T
and T
lifetimes of 653 h and 1045 h, respectively (T
and T
represent efficiency decays to 80% and 70% of the initial value, respectively), and long-term shelf stability under nitrogen atmosphere. Controlled exposure of the device to ambient atmosphere during a long-term (1000 h) test does not degrade the efficiency. These findings point to a promising direction for achieving low-bandgap perovskite solar cells with high stability.
•Shoreline change rates vary spatiotemporally.•Accretion rate is continuing but decreasing.•A close relationship exists between shoreline change and sediment discharge.•Contrasting temporal patterns ...of shoreline change exist between the eastern and northern segments.•Different shoreline segments respond differently to decreasing sediment supply.
Chongming Dongtan, located in the center of the Yangtze estuary, is a Ramsar Wetland of International Importance and National Nature Reserve. The dramatic decrease in river sediment load has attracted considerable scientific interest to this area, but few studies have paid attention to the shoreline dynamics. This study uses Landsat images spanning from 1987 to 2010 and an orthogonal transect method, which was previously developed by the authors, to model the spatial and temporal characteristics of shoreline change and explore its relationship to reduced river sediment load by use of regression analysis on three different spatial scales. Results show a general decrease in the average rates of shoreline change throughout the entire study period. The maximum average shoreline change rate of +115.5m/year occurred in the 1987–1990 interval and the minimum rate of +20.4m/year occurred from 2006 to 2008. Based on average rates of shoreline change, the coast of Dongtan was divided into three segments: the erosion segment, eastern accretion segment, and northern accretion segment. The temporal pattern of the northern accretion segment is almost completely opposite to that of the eastern accretion segment. The strongest-correlation transects are located on the northern side of the eastern tip of Dongtan and the next strongest transects are located on the south side. Other transects have a very low correlation. Transect 19 near the easternmost tip of Dongtan has a near zero correlation (r2=0.0045) but has the fastest accretion rate, and in general an increase in the shoreline change rate. The average rate of shoreline change and the net accretion area in Dongtan as a whole are significantly associated with sediment discharge at Datong Station (r2=0.69 and 0.75, respectively). This implies that shoreline accretion in Dongtan will probably slow down gradually, if the river sediment load continues to decrease in the future. The shoreline change rates achieved using our approach are consistent with previous studies, but the relationship with the river sediment load is different from results in a previous study on intertidal wetland based on bathymetric maps. The results and methods may be helpful in coastal management and understanding the evolution of the entire delta from the perspective of shoreline change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Remote sensing based water occurrence methods can accurately delineate DCNs.•Time-series Landsat images analysis can efficiently track DCNs morphodynamics.•The quantitative framework integrating ...remote sensing and GIS can facilitate river delta mangement.
Delta channel networks (DCNs) are highly complex and dynamic systems that are governed by natural and anthropogenic perturbations. Challenges remain in quickly quantifying the length, width, migration, and pattern changes of deltaic channels accurately and with a high frequency. Here, we develop a quantitative framework, which introduces a water occurrence algorithm based on Landsat time-series data and spatial morphological delineation methods, in order to measure DCN structures and associated changes. In examining the Pearl River Delta (PRD) and Irrawaddy River Delta (IRD) as case studies, we analyze their conditions and trends between 1986 and 2018 at ten-year intervals. Both study areas have undergone various human interventions, including dam construction, sand mining, and land use change driven by urbanization. Our results show the following: (1) the use of a 0.5 water occurrence extraction based on Landsat time-series data, morphological delineation, and spatial change analysis methods can quantify the morphodynamics of DCNs effectively with a root-mean-square error of 15.1 m; (2) there was no evident channel migration in either PRD or IRD with average channel widths of 387.6 and 300.9 m, respectively. Most channels in the PRD underwent remarkable shrinkage, with average rates of 0.4–6.4 m/year, while there were only slight changes in the IRD, which is consistent with observed trends in sediment load variation. The results of this research have the potential to contribute to sustainable river management in terms of flood prevention, riparian tideland reclamation, and water and sediment regulation. Moreover, the proposed framework can be used to develop a new global delta channel network dataset and can be generalized to remotely sensed water discharge and river depth estimation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
CeO2 is an important rare earth (RE) oxide and has served as a typical oxygen storage material in practical applications. In the present study, the oxygen storage capacity (OSC) of CeO2 was enhanced ...by doping with other rare earth ions (RE, RE = Yb, Y, Sm and La). A series of Undoped and RE–doped CeO2 with different doping levels were synthesized using a solvothermal method following a subsequent calcination process, in which just Ce(NO3)3∙6H2O, RE(NO3)3∙nH2O, ethylene glycol and water were used as raw materials. Surprisingly, the Undoped CeO2 was proved to be a porous material with a multilayered special morphology without any additional templates in this work. The lattice parameters of CeO2 were refined by the least–squares method with highly pure NaCl as the internal standard for peak position calibrations, and the solubility limits of RE ions into CeO2 were determined; the amounts of reducible–reoxidizable Cen+ ions were estimated by fitting the Ce 3d core–levels XPS spectra; the non–stoichiometric oxygen vacancy (VO) defects of CeO2 were analyzed qualitatively and quantitatively by O 1s XPS fitting and Raman scattering; and the OSC was quantified by the amount of H2 consumption per gram of CeO2 based on hydrogen temperature programmed reduction (H2–TPR) measurements. The maximum OSC of CeO2 appeared at 5 mol.% Yb–, 4 mol.% Y–, 4 mol.% Sm– and 7 mol.% La–doping with the values of 0.444, 0.387, 0.352 and 0.380 mmol H2/g by an increase of 93.04, 68.26, 53.04 and 65.22%. Moreover, the dominant factor for promoting the OSC of RE–doped CeO2 was analyzed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Estuaries are vulnerable to climate change and are particularly sensitive to extreme river discharge (RD) and sea-level rise (SLR). To understand the effects of extreme RD and SLR on estuaries, an ...integrated modeling approach is adopted to simulate hydrodynamic changes in the Yangtze River Estuary. Model results showed that SLR will intensify the estuarine hydrodynamics in water level, currents, and salinity. Water level, current speed, and salinity increased linearly with the magnitude of SLR. The hydrological model suggested a lower RD in the future. This will increase the saltwater intrusion, which will be more severe during the lower RD and drought extreme hydrological event (EHE) conditions. Model results also suggested that the saltwater intrusion is more sensitive to RD than SLR. In addition, the interplay between the RD and SLR will exacerbate the impacts of coastal oceans on estuarine hydrodynamics, especially during extremely low RD conditions. Moreover, the decrease of RD and deepening of the channel due to human activities will also amplify the effects of SLR on the Estuary, increasing the risk of coastal disasters.
•An integrated hydrologic-hydrodynamic modeling approach was established.•Sea-level rise leads to a linear change of overall estuarine hydrodynamics but a nonlinear change in each bifurcation.•The Yangtze River will be drier in the future, leading to a longer intrusion length of saline water in the estuary.•Extreme hydrological events and human activities will exacerbate the risk of sea-level rise on the estuary.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The rapid, up-to-date, cost-effective acquisition and tracking of intertidal topography are the fundamental basis for timely, high-priority protection and restoration of the intertidal zone. The low ...cost, ease of use, and flexible UAV-based photogrammetry have revolutionized the monitoring of intertidal zones. However, the capability of the RTK-assisted UAV photogrammetry without ground control points, the impact of flight configuration difference, the presence of surface water in low-lying intertidal areas on the photogrammetric accuracy, and the potential of UAV/satellite Synergy remain unknown. In this paper, we used an RTK-assisted UAV to assess the impact of the above-mentioned considerations quantitatively on photogrammetric results in the context of annual monitoring of the Chongming Dongtan Nature Reserve, China based on an optimal flight combination. The results suggested that (1) RTK-assisted UAVs can obtain high-accuracy topographic data with a vertical RMSE of 3.1 cm, without the need for ground control points. (2) The effect of flight altitude on topographic accuracy was most significant and also nonlinear. (3) The elevation obtained by UAV photogrammetry was overestimated by approximately 2.4 cm in the low-lying water-bearing regions. (4) The integration of UAV and satellite observations can increase the accuracy of satellite-based waterline methods by 51%. These quantitative results not only provide scientific insights and guidelines for the balance between accuracy and efficiency in utilizing UAV-based intertidal monitoring, but also demonstrate the great potential of combined UAV and satellite observations in identifying coastal erosion hotspots. This establishes high-priority protection mechanisms and promotes coastal restoration.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Tidal channels (TCs) are geomorphological features of coastal and tidal landscapes. They provide a pathway for the exchange of material and energy between marshes and adjacent water bodies and ...thereby control the hydrodynamic, morphological, and ecological processes on marsh platforms. Due to difficulties in terms of accessibility, limitations on the duration of exposure during low-water stages, and variations in morphology over time, rapid and accurate mapping of such intertidal morphological features at a high frequency is extremely challenging. Here, we present an efficient method integrated unmanned aerial vehicles (UAVs) structure-from-motion (SfM) photogrammetry, and spatial morphological fitting and delineation for accurately quantifying channel three-dimensional (3D) morphological features in terms width, depth, width-to-depth ratio, and cross-sectional area. We also relate these measured proxies to salt marsh species distributions. A two-step thresholding approach combining elevation and slope is developed in order to determinate TC boundaries from salt marsh and tidal flat area, and a Gaussian fit is used to estimate water-bearing channel depth and cross-sectional area. Salt marsh species are identified from fine-resolution multispectral satellite data and a field training dataset using a Random Forest classifier. Our results indicate that (1) UAV-based SfM photogrammetry can achieve centimeter-level accuracy in mapping the topography of TCs, with a root mean square error (RMSE) of 5.7 cm — mainly from the strong reflection of light from smooth TC water surfaces and the presence of water-bearing layers; (2) the morphological features of TCs, ranging from tidal flats to salt marsh areas, demonstrate a similar tendency, which increases at first and then decreases. The maximum depth and cross-sectional area of TCs is in sparse salt-marsh area, up to 4 m and 150 m2, respectively; and (3) TC morphology has a major impact on the distribution of salt marsh plants and such effects vary across different plant species. These results greatly contribute deep understanding of feedbacks between TCs and salt marsh plant species distribution and have significant implications for developing ecological and morphological salt marsh restoration guidelines.
•UAV incorporating RTK positioning achieves centimeter-level topographic accuracy in inaccessible intertidal zone.•The uncertainty of UAV-based intertidal topographic mapping was evaluated.•Fine-scale morphological features of tidal salt-marsh channels were investigated for the first time.•Feedback between tidal channels and salt marsh vegetation has significant implications for salt marsh restoration.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, five ocean-colour sensors, the Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite (Terra MODIS), Moderate Resolution Imaging Spectroradiometer aboard the Aqua ...satellite (Aqua MODIS), Medium Range Imaging Spectrometer aboard the Environmental Satellite (Envisat MERIS), Medium Resolution Spectral Imager aboard the FY-3 satellite (FY-3 MERSI), and Geostationary Ocean Colour Imager (GOCI), were selected to examine the compatibility of an algorithm proposed for suspended particulate matter (SPM) retrieval and concordance of satellite products retrieved from different ocean-colour sensors. The results could effectively increase revisit frequency and complement a temporal gap of time series satellites that may exist between on-orbit and off-orbit. Using in situ measurements from 17 cruise campaigns between 2004 and 2012, the SPM retrieval algorithm was recalibrated so as to be universal and adapted for multi-sensor retrievals. An inter-comparison of multi-sensor-derived products showed that GOCI-derived SPM and Envisat MERIS-derived SPM had the best fitting on a 1:1 scatterplot, with a statistic regression slope of 0.9617 and an intercept of 0.0041 (in units of g l
-1
), respectively. SPM products derived from three sensors with nearly synchronous transit, Envisat MERIS, Terra MODIS, and FY-3 MERSI, exhibited excellent accordance with mean differences of 0.056, 0.057, and 0.013 g l
-1
in three field fixed stations, respectively, in the Yangtze estuary. Terra MODIS-derived SPM with GOCI-derived SPM, except in the high SPM waters of Hangzhou Bay, and Aqua MODIS-derived SPM with GOCI-derived SPM, except in the moderate SPM waters of the South Branch and south of the Subei Coast, showed a good correspondence. Meanwhile, synchronous multi-sensor-derived SPM with concurrent in situ SPM time series observed in fixed field stations mostly displayed a good correspondence. Results suggest that the algorithm is feasible and compatible for SPM retrieval by multiple sensors.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Satellite observation is an excellent tool for exploring the variability of the suspended sediment concentration (SSC) of turbid estuarine and coastal waters. We used a recently developed ...semi-empirical radiative transfer model combined with a multi-wavelength switching algorithm for the SSC retrieval from MEdium Resolution Imaging Spectrometer (MERIS) satellite data. This method can successfully retrieve SSC from satellite data in turbid estuarine and coastal waters with a wide range of sediment concentrations (20–2500mgl−1) and is robust for quantifying realistic patterns of the surface sediment dynamics. The seasonal and annual variability of the MERIS-derived SSC from 2003 to 2010 were analysed in this work. Five regions-of-interest (ROIs) in the Yangtze estuary and coast are included in the analysis: the upper estuary, the lower estuary, the outer estuary, the Hangzhou Bay and the Qidong shore. The results reveal that the SSC of the upper estuary has significant seasonal and annual variations in response to seasonal cycling and annual fluctuation of the river discharge. A long-term continuing decrease of river discharge may cause an overall decline of the SSC in the entire estuary and adjacent areas. The existence of horizontal exchanges of the sediments between the Yangtze estuary and the Jiangsu coast implies that the decreased fluvial sediment loads of the estuary may partially be compensated by supplementing contributions from other origins.
•We quantify realistic patterns of suspended sediment concentration (SSC) dynamics.•Remotely sensed SSC distribution presents significant seasonal variations.•The river discharge changes have an impact on the SSC in the whole estuary.•Satellite observations capture the phenomenon of sediment horizontal exchanges.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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