A spectral space partition guided ensemble method for retrieving chlorophyll-a concentration in inland waters from Sentinel-2A satellite imagery

This research proposes an ensemble method for synergistically combining multiple empirical algorithms to better estimate chlorophyll-a (Chl-a) concentration. In previous studies, different empirical algorithms have been employed separately and a single algorithm was often identified as the most suitable predictor for Chl-a retrieval. Our ensemble method combines different individual algorithms to form an ensemble predictor that exploits advantages of each individual algorithm to maximize the overall estimation accuracy. We evaluated two ensemble predictors: the optimally weighted ensemble predictor and the spectral space partition guided ensemble predictor. The ensemble method has been successfully applied to a Sentinel-2A multispectral image acquired over Harsha Lake, Ohio in 2016. Based on in situ water reference data and satellite imagery, we constructed two ensemble predictors that consist of three individual empirical algorithms/estimators, including 2BDA (two-band algorithm), 3BDA (three-band algorithm), and NDCI (Normalized Difference Chlorophyll Index). For the optimally weighted ensemble predictor, the weights for individual algorithms are computed by solving an overdetermined linear system with the pseudoinverse technique. For the spectral space partition guided ensemble predictor, the rules for partitioning spectral space into spectral regions were established as a decision-tree using the CART method. The optimal Chl-a estimate for a pixel is obtained by selectively using the empirical algorithm in the ensemble that has the highest expected accuracy in the spectral region where the pixel is located. Our assessments suggest that the spectral space partition guided ensemble method performs significantly better than three individual empirical algorithms and also better than the optimally weighted ensemble method.     

Distribution of Botia superciliaris (Günther, 1892) ichthyoplankton in the upper mainstem of the Yangtze River preimpoundment and postimpoundment of the upstream dam cascade

Dam cascades have been a major threat to fishes of the upper Yangtze River. The remaining lotic river segment of the upper mainstem between the Xiangjiaba Dam (XJD) and the Three Gorges Reservoir (TGR) may serve as a critical refuge for endemic fishes. We investigated distribution of ichthyoplankton Botia superciliaris, an endemic species, at three sections preimpoundment and postimpoundment of the XJD, that is, Yibin (close to the XJD), Zhuyang (in the middle of the segment), and Mudong (in the tail of the TGR). Preimpoundment of the XJD, larvae occurred in all three sections, and their abundance tended to be highest at Yibin and lowest at Mudong. Postimpoundment, larval abundance dramatically decreased in all three sections. In particular, no larvae were found at Yibin, and larval abundance tended to be higher at Zhuyang than at Mudong. Eggs were collected from all three sections, and those from Zhuyang accounted for over 90% of the total. Initiation of egg occurrence at Yibin was approximately 1 month later than at Zhuyang and Mudong. Water temperature was lower, and water transparency was higher at Yibin than at Zhuyang and Mudong postimpoundment. We suggest that the decrease in abundance and delayed presence of ichthyoplankton at Yibin postimpoundment of the XJD reflected the impact of upstream dam discharge and that the lower abundance of ichthyoplankton at Mudong compared with Zhuyang both preimpoundment and postimpoundment of the XJD reflected the influence of inundation by the TGR. We recommend that the river sections around Zhuyang become high‐priority conservation areas     

层状各向异性岩体的室内单轴压缩试验分析

为研究层状岩体变形及强度的各向异性特征,将不同倾角的层状岩体制成标准试件进行单轴压缩试验,得到岩石试件弹性模量、峰值强度和残余强度,以及它们随层面倾角β的变化规律;并对试件峰值破坏形态进行了分析,最后通过理论计算验证试验结果的正确性。研究结果表明:随着层面倾角β的增大,层状岩体的弹性模量、峰值强度和残余强度呈先减小后增大的变化趋势。β为90°时,其模量和强度最大,β为45°~60°时较小,且β为90°时对应的模量和强度比β为0°时要大,表现出明显的各向异性特征。当β为0°~15°时,岩石产生沿轴向应力方向的劈裂破坏;β30°以后,岩石开始产生沿层理结构面的滑移破坏;β为90°时产生沿层理结构面的劈裂破坏。     

Influence of Rainfall,Model Parameters and Routing Methods on Stormwater Modelling

Quantification of the uncertainty associated with stormwater models should be analyzed before using modelling results to make decisions on urban stormwater control and management programs. In this study, the InfoWorks Integrated Catchment Modelling (ICM) rainfall-runoff model was used to simulate hydrographs at the outfall of a catchment (drainage area 8.3 ha, with 95% pervious areas) in Shenzhen, China. The model was calibrated and validated for two rainfall events with Nash-Sutcliffe efficiency >0.81. The influence of rainfall, model parameters and routing methods on outflow hydrograph of the catchment was systematically studied. The influence of rainfall was analyzed using generated rainfall distributions with random errors and systematic errors (± 30% offsets). Random errors had less influence than systematic errors on peak flow and runoff volume, especially for two rainfall events with larger depths and longer durations. The Monte Carlo simulations using 500 parameter sets were used to verify the equifinality of the nine model parameters and determine the prediction uncertainty. Most of the monitored flows were within the uncertainty range. The influence of two routing methods from rainfall excess to hydrograph was studied. The InfoWorks ICM model incorporating double quasilinear reservoir routing was found to have a larger effect on the simulated hydrographs for rainfall events having larger depths and longer durations than using the U.S. EPA’s Storm Water Management Model nonlinear reservoir routing method did.

     

基于高分辨率PSP-InSAR技术的深圳市长岭皮水库坝体形变监测应用研究

水库边坡的形变一直是评估其稳定性的重要指标。以2013~2016年内COSMO-Sky Med系统采集的SAR数据为输入,利用PSP-In SAR技术对深圳市内大部分水库边坡开展了形变监测。在重点分析长岭皮水库坝体边坡形变的过程中,结合水位变化数据,建立了目标点随水位和时间变化的形变模型,成功分解出由水库水位变化导致的形变和水库自身沉降而引起的形变,并对水库不同坡面的形变分量进行了对比分析。相比于传统技术,InSAR技术能在水库边坡及周边区域获取密集的监测点,能全面揭示水库及周边的形变信息,未来有能力为水库边坡的形变机理研究和稳定性分析提供基础数据支持。     

水下爆炸冲击荷载下混凝土重力坝的破坏效应

在相同炸药量下水下爆炸对混凝土重力坝的破坏效应强于空中爆炸,因此需重点关注水下爆炸冲击下的混凝土重力坝的毁伤机理。考虑爆炸作用下混凝土的高应变率效应、冲击波与结构的动态相互作用以及结构的非线性动态响应等复杂问题,基于Lagrangian-Eulerian全耦合方法建立水下爆炸混凝土重力坝耦合模型,对近坝水下爆炸冲击波传播特性进行分析,得到了水下爆炸冲击下混凝土重力坝的毁伤破坏过程及毁伤机理。研究表明,水下爆炸冲击荷载作用下混凝土重力坝的毁伤模式主要有爆炸成坑破坏、气穴冲切破坏、震塌拉伸破坏、冲击波冲切破坏、弯曲破坏和整体拉伸破坏。     

隧洞塌方抢通技术研究

结合锦屏水电站工程区域内"8.30"特大地质灾害中的交通隧洞抢通的经验,主要对交通隧洞运行期因泥石流、山体滑坡、地震等自然灾害造成交通隧洞洞口塌方的应急修复施工技术进行了研究,旨在为类似情况提供参考。     

Estimation of Wind-Driven Coastal Waves Near a Mangrove Forest Using Adaptive Neuro-Fuzzy Inference System

At the coastline of the Carey Island, mangroves provide natural protection against the wind-driven coastal waves. The area is located at the west Malaysia within the waters of the Straits of Malacca. Recently, its coastline has been exposed to increasing rates of coastal erosion due to mangrove deforestation. In order to provide mitigating measures, it is necessary to study wave characteristics in this region. For this purpose, we collected 5 years (2009 to 2013) of hourly measurements for wind direction, wave height, wind speed and wave period. Moreover, we used the adaptive neuro-fuzzy inference system (ANFIS) to estimate the wave period and height. The model was trained using the measured data. The validation of the model gave satisfactory R² values of 0.8484 and 0.9496 for wave height and wave period, respectively. The findings from this study suggest that fuzzy logic based technique satisfactorily predicts the differences between multiple inputs and single output in terms of non-linear relationship. The developed model can be used to further study the effect of non-linear wind-driven waves on the depleting coastal mangrove forests in similar tropical and sub-tropical areas. We suggest further research to test the model in different geographical locations, such as in deep-ocean, narrow straits and other coastal sites, which were not covered in this study.     

地下水补给对河流水质扩散影响的数值模拟

为能够实时、量化研究地下水补给对河流水质扩散的影响,论文以某平原河流为研究对象,在地下水线源补给假定的基础上,通过基流分割方法对河流总流量进行了分割,借用MIKE11 AD对流扩散模块,分别建立了不考虑地下水补给作用的传统数值模型和加入分割后流量的新数值模型。通过分析河道沿程各点时间上的水质浓度变化过程,量化研究了两模型的差异及其产生原因。结果表明:在上游各点,两模型浓度曲线增长过程吻合度较高,但最终稳定值存在3%的差异;在下游各点,新模型浓度快速衰减,两模型浓度稀释差异巨大,可达到1000倍。由此得出结论,是否将河流流量进行分割研究对于河流水质扩散结果影响较大,这种影响会随地下水的沿程补给长度增加而快速变大。     

东南亚国际河流水资源合作开发的需求研究

为探究东南亚国际河流水资源开发需求,针对东南亚国际河流水资源开发的规划特征和工程建设现状,采用文本分析法、调研法和文献阅读法,依据国际河流合作项目的公开信息,从经济发展和能源规划视角,对东南亚5国的国际河流水资源合作开发需求进行了分析,得出了东南亚国家国际河流开发的合作需求基本情况以及水资源开发过程中的各项需求的具体分布情况。对我国在参与东南亚各国的国际河流水资源合作中具有实际指导意义。