Abiotic predictors of fine sediment accumulation in lowland rivers     

Morwenna McKenzie  Judy England  Ian D.L.Foster  Martin A.Wilkes 《国际泥沙研究》2022,37(1):128-137

The delivery of excessive fine sediment (particles<2 mm in diameter) to rivers can cause serious deleterious effects to aquatic ecosystems and is widely acknowledged to be one of the leading contributors to the degradation of rivers globally.Despite advances in using biological methods as a proxy,physical measures remain an important method through which fine sediment can be quantified.The aim of this study was to provide further insights into the environmental variables controlling sediment ...  相似文献   

2021年漾濞M_S 6.4地震云南数字化井水位同震响应特征分析     

段胜朝  张山元  番绍辉  孙自刚 《地震地磁观测与研究》2022,43(4):131-139

通过对漾濞M_S 6.4地震云南数字化井水位分钟值数据同震响应特征进行分析,分析观测仪器采样率对井水位映震能力的影响,并对水位同震响应机理进行初步分析。结果表明,对于漾濞M_S 6.4地震,13口同震响应观测井主要分布在震中距200 km范围内的红河断裂带北侧和小滇西地区;同震响应形态可分为阶升（上升）型、阶降（或缓降）型、阶变（阶升、阶降）—复原型等3种变化类型,阶升型同震响应幅度相对大于其他2种类型;由漾濞M_S 6.4地震烈度长轴和短轴共同划定的椭圆区域来划分此次地震静态应力和动态应力的影响范围,可以从各观测井受力状态初步分析水位同震响应变化形态的力学机理;在静态应力影响范围内,井水位同震响应主要表现为阶升变化;在静态应力影响范围以外,除以阶变（阶升、阶降）—复原变化为主外,还有阶降（缓降）、阶升变化。观测仪器采样率对井水位映震能力的影响较大,水位秒钟值数据的同震响应变化形态更加完整,但目前水位秒钟值数据的收集和使用都还在不便之处,这种情况有待改进。  相似文献   

Variable character and diverse origin of hybrid event beds in a sandy submarine fan system,Pennsylvanian Ross Sandstone Formation,western Ireland     

《Sedimentology》2018,65(3):952-992

Hybrid event beds comprising both clean and mud‐rich sandstone are important components of many deep‐water systems and reflect the passage of turbulent sediment gravity flows with zones of clay‐damped or suppressed turbulence. ‘Behind‐outcrop’ cores from the Pennsylvanian deep‐water Ross Sandstone Formation reveal hybrid event beds with a wide range of expression in terms of relative abundance, character and inferred origin. Muddy hybrid event beds first appear in the underlying Clare Shale Formation where they are interpreted as the distal run‐out of the wakes to flows which deposited most of their sand up‐dip before transforming to fluid mud. These are overlain by unusually thick (up to 4·4 m), coarse sandy hybrid event beds (89% of the lowermost Ross Formation by thickness) that record deposition from outsized flows in which transformations were driven by both substrate entrainment in the body of the flow and clay fractionation in the wake. A switch to dominantly fine‐grained sand was accompanied initially by the arrest of turbulence‐damped, mud‐rich flows with evidence for transitional flow conditions and thick fluid mud caps. The mid and upper Ross Formation contain metre‐scale bed sets of hybrid event beds (21 to 14%, respectively) in (i) upward‐sandying bed set associations immediately beneath amalgamated sheet or channel elements; (ii) stacked thick‐bedded and thin‐bedded hybrid event bed‐dominated bed sets; (iii) associations of hybrid event bed‐dominated bed sets alternating with conventional turbidites; and (iv) rare outsized hybrid event beds. Hybrid event bed dominance in the lower Ross Formation may reflect significant initial disequilibrium, a bias towards large‐volume flows in distal sectors of the basin, extensive mud‐draped slopes and greater drop heights promoting erosion. Higher in the formation, hybrid event beds record local perturbations related to channel switching, lobe relocations and extension of channels across the fan surface. The Ross Sandstone Formation confirms that hybrid event beds can form in a variety of ways, even in the same system, and that different flow transformation mechanisms may operate even during the passage of a single flow.  相似文献   

超声波取样钻机电耦合特性研究          下载免费PDF全文

梁彩红  韦旌坤  史立京  卜长根 《探矿工程》2015,42(11):46-49

压电驱动的超声波取样钻具有质量轻、能耗低、无回转部件的特点,可以满足地外岩石采样的需求。电能通过压电陶瓷转换为致动器高频振动的机械能,使其在特定频率做超声的共振。这种超声取样钻的机电耦合特征,使超声致动器的设计变得复杂。基于ANSYS环境,研究超声致动器在机电耦合场边界条件下的动力学特性,其耦合场的模态频率、激励响应与单一机械结构场条件得到的结果具有较好的一致性。结果表明,超声致动器把电能转换机械能过程的机电耦合场相互作用是很弱的。因此,采用解耦方法,超声致动器的设计过程将大大简化。  相似文献   

MOOC浪潮下基于“CH-SPOC”视角的测绘类C#课程体系构建     

王明爽  赵晓明 《测绘工程》2015,(9):77-80

MOOS作为一种新型在线网络教育模式,具有大规模、不限定人群和在线开放的特点;而SPOC则秉承了其先进的思想和做法,并在此基础上加以完善,是具有针对性、实效性的小规模在线开放教育模式。SPOC模式更加符合高校在校学生学习的特点,对学生学习督促和考核方式更具有客观性和有效性。文中首先对MOOC、SPOC的基本理念和内涵进行了阐述;结合测绘类学生的专业特点,分析SPOC对当前C#课程教学影响和冲击。在此基础上,从"CH-SPOC"全新视角对测绘类专业C#课程体系进行构建,把"网络虚拟课堂"和"传统课堂"有机融合,注入学生间的"团结协作"要素,实现翻转课堂。这一混合式教学模式可以增加学生课堂参与度和团结协作能力的培养,有助于提高教学质量,提升测绘类专业学生综合设计和创新力。  相似文献   

频域局部上采样的小基高比影像匹配方法     

申二华  范大昭  戴海涛  孙晓昱 《测绘科学》2015,40(2):123-127

针对小基高比摄影测量中交会精度缺失的问题,该文利用相位相关技术计算初始匹配视差,并对相位相关互功率谱进行局部上采样,探讨了一种适用于小基高比立体影像的高精度影像匹配算法。实验结果表明,在一定条件下该算法有着较高的匹配精度,能够用于小基高比立体影像重建可靠的高程信息。  相似文献   

水下地形测量成果质量检验若干问题探讨     

史富贵 《测绘科学》2015,40(7):109-112

由于在GB/T 24356—2009《测绘成果质量检查与验收》中,针对水下地形测量的检验内容过多兼顾相关规范对流速、流向、底质等探测的要求,使得一般的水下地形测量成果检验时参照执行不方便,该文结合实际工作,对水下地形测量成果质量检验方法进行了研究:对水下地形测量成果质量元素及权的划分、样本的确定、特殊水下地形精度检测、粗差率的扣分标准等几个方面作了总结分析,为水下地形测量成果质检提供了操作性较强的方案。  相似文献   

Land cover dynamics monitoring with Landsat data in Kunming,China: a cost-effective sampling and modelling scheme using Google Earth imagery and random forests     

Ning Lu  Alexander J. Hernandez  R. Douglas Ramsey 《国际地球制图》2015,30(2):186-201

Changes in forest composition impact ecological services, and are considered important factors driving global climate change. A hybrid sampling method along with a modelling approach to map current and past land cover in Kunming, China is reported. MODIS land cover (2001–2011) data-sets were used to detect pixels with no apparent change. Around 3000 ‘no change points’ were systematically selected and sampled using Google Earth’s high-resolution imagery. Thirty-five per cent of these points were verified and used for training and validation. We used Random forests to classify multi-temporal Landsat imagery. Results show that forest cover has had a net decrease of 14385?ha (1.3% of forest area), which was primary converted to shrublands (11%), urban and barren land (2.7%) and agriculture (2.5%). Our validation indicates an overall accuracy (Kappa) of 82%. Our methodology can be used to consistently map the dynamics of land cover change in similar areas with minimum costs.  相似文献   

混合集合预报法在华南暴雨短期预报中的试验   总被引：3，自引：1，他引：2       下载免费PDF全文

唐圣钧  王东海  杜钧  周镜石 《应用气象学报》2015,26(6):669-679

-WRF多模式集合3组试验,对比分析混合集合预报法与传统方法的降水预报效果。结果表明:ARPS模式集合改善了广东省南部局地强降水预报,该方法在中雨、大雨、暴雨量级改进效果显著。WRF模式集合对广东省北部强降水预报优于ARPS模式集合,但空报、漏报率较大,该方法有一定局限性。ARPS-WRF多模式集合在降水落区和量级预报上均优于传统方法。混合集合预报法利用低分辨率 (36 km) 集合预报和高分辨率 (12 km) 控制预报实现了高分辨率 (12 km) 集合预报,改善了降水预报效果,该方法可为业务高分辨率集合预报提供参考。  相似文献   

台风预报误差的流依赖特征及混合资料同化中最优耦合系数          下载免费PDF全文

马旭林  李琳琳  周勃旸  朱金焕  和杰  计燕霞 《大气科学学报》2015,38(6):766-775

基于集合卡尔曼变换与三维变分(ETKF-3DVAR)混合资料同化系统和欧洲中期天气预报中心(ECWMF)的全球集合预报,以"梅花"台风为例,分析了台风系统预报误差的流依赖特征,讨论了耦合系数在混合同化和预报中的敏感性及其对预报质量的影响。结果显示,台风系统的预报误差协方差具有显著的中小尺度结构特征,集合估计的预报误差协方差结构能够再现其流依赖属性。相对于3DVAR方案,混合资料同化方案的最优耦合系数对台风系统的分析和预报质量具有更好的改善;但不同的耦合系数对台风路径预报有明显的影响,不合适的耦合系数甚至可能导致更坏的结果,只有耦合了相对合适的预报误差协方差的流依赖信息,混合资料同化方案才可能对分析和预报质量有正效果。这表明在混合资料同化系统中,构造一种具有自适应能力的耦合权重函数,实现相对最优权重的自动选择,对充分发挥混合资料同化方案的潜在优势具有重要意义。  相似文献