Exploring the stemflow dynamics and driving factors at both inter- and intra-event scales in a typical subtropical deciduous forest     

Haixia Zhang  Congsheng Fu  Aimin Liao  Can Zhang  Jiufu Liu  Niu Wang  Bin He 《水文研究》2021,35(3):e14091

Numerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter-event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra-event scale. An in-depth investigation of the inter- and intra-event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (F_V), stemflow funnelling ratio (F_R), and stemflow ratio (F_%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter- and intra-event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the F_V, F_R and F_% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on F_V and F_% was more obvious under low intensity rainfall types. At the inter-event scale, F_V had a strong positive linear correlation with rainfall amount (G_P) and event duration (D_E) for both tree species, whereas F_R and F_% had a positive logarithmic correlation with G_P and D_E only under high-intensity, short-duration rainfall type. F_R and F_% were mainly affected by wind speed and the maximum 30-min rainfall intensity under low-intensity, long-duration rainfall type. At the intra-event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high-intensity, short-duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high-amount, long-duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5-min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter- and intra-event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.  相似文献   

高分六号遥感卫星新增波段下的树种分类精度分析     

张沁雨  李哲  夏朝宗  陈健  彭道黎 《地球信息科学学报》2019,21(10):1619-1628

高分六号卫星具有覆盖广、多种分辨率、波段多的优势,能为遥感解译提供更丰富的信息。为探究高分六号卫星新增波段在森林树种识别上的应用,本文以覆盖根河市阿龙山林业局的一期高分六号宽幅影像为数据源,基于特征优化空间算法（Feature Space Optimization,FSO）和最大似然分类法,分别利用高分六号的前4个波段和所有波段（8波段）的光谱、纹理等特征进行了森林树种分类,并逐一添加新增波段特征确定了各波段的贡献率排名。结果表明：在加入了优选出的均匀性纹理、均值纹理和角二阶矩纹理3种纹理特征后,前4波段和8波段的分类精度比只基于光谱特征时的精度分别高出13.23%和24.63%;利用8波段信息比只利用前4波段在基于光谱特征上的精度高11.88%,在基于光谱+纹理特征上则高23.24%;基于8波段光谱+纹理特征的树种分类精度最高,达到68.74%,新增4波段的贡献率排名为B6>B5>B8>B7,说明新增红边波段对于本次树种分类试验的贡献率最高,能为北方树种识别提供有效帮助。  相似文献   

Closed-loop randomized kinodynamic path planning for an autonomous underwater vehicle     

《Applied Ocean Research》2019

A randomized kinodynamic path planning algorithm based on the incremental sampling-based method is proposed here as the state-of-the-art in this field applicable in an autonomous underwater vehicle. Designing a feasible path for this vehicle from an initial position and velocity to a target position and velocity in three-dimensional spaces by considering the kinematic constraints such as obstacles avoidance and dynamic constraints such as hard bounds and non-holonomic characteristic of AUV are the main motivation of this research. For this purpose, a closed-loop rapidly-exploring random tree (CL-RRT) algorithm is presented. This CL-RRT consists of three tightly coupled components: a RRT algorithm, three fuzzy proportional-derivative controllers for heading and diving control and a six degree-of-freedom nonlinear AUV model. The branches of CL-RRT are expanded in the configuration space by considering the kinodynamic constraints of AUV. The feasibility of each branch and random offspring vertex in the CL-RRT is checked against the mentioned constraints of AUV. Next, if the planned branch is feasible by the AUV, then the control signals and related vertex are recorded through the path planner to design the final path. This proposed algorithm is implemented on a single board computer (SBC) through the xPC Target and then four test-cases are designed in 3D space. The results of the processor-in-the-loop tests are compared by the conventional RRT and indicate that the proposed CL-RRT not only in a rapid manner plans an initial path, but also the planned path is feasible by the AUV.  相似文献   

传统聚落景观基因的地理信息特征及其理解     

胡最 《地球信息科学学报》2020,22(5):1083-1094

传统聚落是民族传统文化遗产的重要组成部分,对社会经济和文化建设具有重要的价值。针对现有研究缺乏探讨传统聚落景观基因（简称景观基因）蕴藏的地理信息特征及理解方法,论文从以下方面开展了深入分析：① 地理信息包含了语义描述、几何形态、属性特征、维度、时空框架、尺度、要素相互关系（空间关联）、演化过程（存在状态）等属性;② 景观基因是一种特殊的文化因子,蕴含着丰富的哲理,是认识传统聚落特征的分析方法,也是文化符号的集合;③ 景观基因包含了空间定位、载体特征、历史与文化特征等丰富的地理信息。根据前述分析结果,论文从符号化、数据挖掘、谱系分析与空间格局制图等途径系统地探讨了景观基因地理信息特征的理解方法。论文认为：在地理时空大数据与地理服务日益深化发展的背景下,结合GIS原理探讨景观基因的地理信息特征对于延伸地理信息科学的内涵,深化传统聚落的地学认识,促进人文GIS的发展具有积极的意义,今后应该继续加强相关方法探索。  相似文献   

锁块式水下采油树井口连接器性能分析     

程子云  李文博  张玉  段梦兰 《海洋工程》2019,37(2):40-49

水下采油树井口连接器是连接采油树和井口的关键设备,对深海水下勘探开发及采油树的安装连接具有不可或缺的重要意义。以一种锁块式水下连接器为例,介绍其结构组成和工作原理,通过有限元建立连接器的三维模型,分析连接器在下放安装工况、连接锁紧工况、正常生产工况和钻完井工况下的连接性能,得出井口与采油树本体接触面作用力、VX钢圈接触应力和锁块受力情况随外部载荷的相互关系。结果表明,VX钢圈在整个过程中都能够保持良好密封,井口与采油树本体接触面未发生分离,弯矩对连接器连接性能影响很大,在额定弯矩作用时连接器部分锁块已发生弹塑性失效。  相似文献   

近20年京津唐地区不透水面变化的遥感监测     

向超  朱翔  胡德勇  乔琨  陈姗姗 《地球信息科学学报》2018,20(5):684-693

不透水面是衡量城市化程度的重要指标之一,对京津唐城市群的不透水面进行深入研究,可以量化城市群扩张过程及其影响,对该区域多城市协调发展及规划布局具有重要意义。本文结合高分辨遥感影像、生长季及落叶季的Landsat TM遥感影像和夜间灯光数据等,采用分类和回归树（Classification and rRegression Tree, CART）算法,构建了适于京津唐地区不透水面盖度提取的技术方案,获取了京津唐地区1995-2016年共5期地表不透水面盖度专题信息,并分析了地表不透水面的时空演变规律,结论为：① 适于京津唐地区不透水面盖度提取的CART算法的最佳输入变量组合为：生长季和落叶季的Landsat TM图像以及对应的夜间灯光数据;其次为生长季Landsat TM遥感图像和夜间灯光数据组合方案。利用该组合方案,ISP估算输出结果的交叉验证精度R值可以达到约0.85,可以满足地表不透水面纵向对比分析的需要。② 从地表不透水面总面积数量值来看,1995-2016年京津唐主体城市区域整体上呈增长趋势,其中2011-2016年地表不透水面积增加愈加明显;③ 从地表不透水面盖度值的高低来看,1995-2016年京津唐中、高盖度不透水面的占比都是在不断增长的,低盖度不透水面占比存在少量下降现象,且京、津、唐3城市的主体城区各阶段变化差异较大,反映出了各城市扩张具有各自不同的时空演变特征。  相似文献   

New formulae for capacity energy-based assessment of liquefaction triggering     

Yasaman Jafariavval 《Marine Georesources & Geotechnology》2020,38(2):214-222

Abstract

Liquefaction of loose saturated soil deposits is a hazardous type of ground failure occurring under earthquake excitations. Therefore, an accurate estimation of liquefaction potential is extremely important in geotechnical engineering. In the current study, a new model is proposed which estimates the level of strain energy needed for liquefaction initiation. A compiled database containing cyclic tests gathered from previously published works was used to develop new models to predict liquefaction potential. M5′ algorithm was used to find the best correlation between parameters. It was shown that not only the derived formulas are acceptably accurate but also they feature a very simple structure in comparison with available formulas in the literature. The proposed equations are accurate, physically sound and uncomplicated. Furthermore, safety factors were given for different levels of risk, which can be useful for engineering practice. In addition, the influence of different predictors on the liquefaction potential was evaluated and also the significance of input variables was assessed via sensitivity analysis. Finally, a new model was introduced for preliminary estimation of liquefaction potential.  相似文献   

城镇-农业-生态空间划定的多情景模拟     

柯新利  肖邦勇  郑伟伟  马艳春  李红艳 《地球信息科学学报》2020,22(3):580-591

城镇-农业-生态空间划定(简称"三区"划定)是国土空间规划的核心内容,对于科学合理地规划、利用有限的国土资源具有重要的意义。已有研究主要根据区域内土地利用与社会经济发展现状构建指标体系进行"三区"划定,较少将未来土地利用变化纳入"三区"划定过程中,使得划定结果在指导实践过程中缺乏前瞻性。针对这一问题,本文提出一种基于土地利用情景模拟,结合指标体系评价与决策树特征挖掘的"三区"划定方法,并以武汉市2015年土地利用现状为基础,在土地利用变化情景模拟的基础上进行"三区"划定。通过对比,验证了本文提出方法的合理性。研究发现:①不同情景下的"三区"空间在规模、空间分布上具有明显差异,将未来土地利用变化纳入"三区"划定过程中确有必要;②不同土地利用情景下"三区"空间的差异主要出现在三类空间的交界区域,这些区域是国土空间规划应该关注的重点区域。  相似文献   

面向对象方法的时间序列MODIS数据湿地信息提取——以洞庭湖流域为例   总被引：2，自引：0，他引：2  

张猛  曾永年  朱永森 《遥感学报》2017,21(3):479-492

以洞庭湖流域为研究区,对大范围湿地信息遥感提取方法进行了研究。先基于时间序列MODIS EVI及物候特征参数,通过J-M(Jeffries-Matusita distance)距离分析,构建了MODIS(250 m)最佳时序组合分类数据;其次,通过Johnson指数确定了最佳分割尺度,采用面向对象的遥感分类方法(Random tree分类器)提取了洞庭湖流域的湿地信息,并验证该方法的适用性。研究结果表明,基于时序数据与面向对象的Random tree分类的总体精度和Kappa系数分别为78.84%和0.71,较之基于像元的相同算法的总体分类精度和Kappa系数分别提高了5.79%和0.04。同时,基于面向对象方法的湿地整体的用户精度与生产者精度较基于像元方法分别提高了4.56%和6.21%,可有效提高大区域湿地信息提取的精度。  相似文献   

结合双树复小波变换的四阶偏微分影像去噪方法     

戚凯丽  汪汇兵  欧阳斯达  范奎奎  杨朦朦 《测绘科学技术学报》2017,(5):529-534

针对低阶偏微分方程去噪模型通常会使图像的灰度趋于分段常量而产生阶梯效应的问题,结合小波多尺度分解在图像处理中的应用,提出一种结合双树复小波变换(DT-CWT)的四阶偏微分方程(PDE)影像去噪模型。首先采用DT-CWT对噪声影像进行多尺度分解,保留分解后的低频分量不变,其他层复高频分量采用四阶PDE去噪模型去噪,然后重构相应层的高、低频分量,得到最终去噪后影像。对不同噪声强度下的ZY-3卫星影像去噪实验的结果表明,采用本文方法去除遥感影像噪声相比现有方法得到的去噪结果信噪比平均提高了1~2 d B,提高了去噪影像的结构相似度,在有效去除影像高斯噪声的同时能够较好地保留图像细节信息。  相似文献