RIPARIAN VEGETATION AND SANDBAR MORPHOLOGY ALONG THE LOWER LITTLE COLORADO RIVER,ARIZONA     

Ginger Hinchman Birkeland 《自然地理学》2013,34(6):534-553

The distribution of riparian vegetation in relation to channel morphology is poorly understood in canyon rivers, which are characterized by in-channel fluvial sediment deposits rather than flood plains. This study focuses on vegetation and sandbar characteristics in two reaches of the lower Little Colorado River canyon in Arizona–one reach with ephemeral flow from the watershed, and another with perennial baseflow from a spring. Both reaches have been colonized by the exotic Tamarix chinensis, a riparian species known for its geomorphic influence on river channels. On the basis of a sampling of 18 bars, results show that vegetation frequency and density is significantly greater in the perennial study reach. However, sandbar morphology variables do not differ between reaches, despite a significantly narrower and deeper ephemeral channel. Hydraulic calculations of flood depths and Pearson correlations between bar and vegetation variables indicate reach-specific biogeomorphic relationships. In the ephemeral reach, higher bars are less affected by flood inundation, support older vegetation, and may be more stable habitat for vegetation. In the wider perennial reach where bars are lower and more expansive, vegetation patterns relate to bar size, Tamarix being most common on the largest bars. Overall results suggest that (1) vegetation variation relates to baseflow hydrology, (2) bar formation relates to high discharge events, and (3) vegetation patterns respond to, rather than influence, sandbar form in this canyon riparian system.  相似文献   

Comparison of methods for integrating biological and physical data for marine habitat mapping and classification     

E.J. Shumchenia  J.W. King 《Continental Shelf Research》2010

An important first step in marine spatial planning and ecosystem-based management efforts is the creation of benthic habitat maps that allow scientists and managers to understand the distribution of living and non-living resources on the seafloor. However, the location of boundaries between and composition of habitats is highly dependent on the approach taken to integrate abiotic and biotic information. The purpose of this study was to test “top-down” and “bottom-up” approaches for integrating physical and biological data derived from commonly used sub-tidal benthic mapping tools to create a habitat map compatible with the US Coastal and Marine Ecological Classification Standard (CMECS). We found that a top-down framework, where we tested for differences in macrofauna assemblages among side scan sonar facies, defined two broad-scale and general habitats. Using the bottom-up approach, where patterns in abiotic and biotic variables were examined with multivariate statistics (BEST, LINKTREE, ANOSIM, SIMPER), we generated seven biotopes based on the macrofauna abundance, percent sand, water depth, and backscatter standard deviation that corresponded well to, but provided more fine-scale detail than the top-down habitats. We were able to use the statistical relationship between abiotic variables and macrofauna assemblages in the LINKTREE to predict the spatial distribution of assemblages over ∼50% of the study area. We created a local catalogue of biotopes specific to our study area that contributes to the CMECS library. In addition, we were able to fully map CMECS Geoform, Surface Geology, and Biotic Cover Components. This mapping effort represented real progress toward reconciling the “data density mismatch” between physical and biological mapping methods, and it provided further evidence that using a bottom-up methodology preserves species–environment relationships.  相似文献   

婴幼儿X线胸片对胸腺增大的分析诊断   总被引：1，自引：0，他引：1  

代燕增  冯建明  张巧权 《CT理论与应用研究》2010,19(2):69-74

目的:探讨婴幼儿胸腺影增大的X线表现。方法:收集我院近年婴幼儿X线胸片观察到增大的胸腺影300例,主要讨论婴幼儿胸腺的影像表现、诊断与鉴别诊断。结果:对X线胸片上显示的300例增大的胸腺影在性别、年龄、形态、位置等方面进行分析总结。其中右上纵隔旁僧帽状90例,双侧纵隔旁杯形90例,右上纵隔旁船帆状75例,右肺尖圆块状30例,左上纵隔旁椭圆形15例。结论:X线胸片对婴幼儿胸腺影增大的诊断与鉴别具有一定作用,定性诊断最后尚需依靠穿刺活检及结合临床综合分析。  相似文献   

水下地貌调查测量精度提高方法研究          下载免费PDF全文

孙庆祥  穆跃东 《海洋测绘》2012,32(6):36-39

海洋调查中,为确保调查信息与实际位置相匹配,提高调查成果的可信度,必须提高作业船拖曳调查设备的定位精度。论述了基于超短基线（USBL）水声定位与差分全球定位系统（DGPS）组合的新方法,消除了因作业船频繁变向、潮流的流向及流速等造成的调查设备位置的测量误差,成功地解决了调查信息错位,提高了海底地貌调查的定位测量精度,实用性较强。  相似文献   

与CT机配套的便携式控温压力舱的研制与应用     

郑剑锋  马巍  赵淑萍  蒲毅彬 《冰川冻土》2014,36(4):928-933

针对冻土CT扫描试验中存在的温度扰动、荷载变化等技术问题,研制了与CT机配套的便携式三端控温压力舱. 通过该仪器能真正实现在CT扫描实验中无损动态观测,并能保证温度场的均匀恒定. 在持续加载过程中进行CT扫描,从而使得土样各个阶段的变化能被真实、连续反映,做到细观结构变化与宏观变量有机联系起来,极大地提升了科研技术水平.  相似文献   

整体最小二乘和最小二乘拟合空间直线的比较     

胡川  陈义  朱卫东  钱承军 《大地测量与地球动力学》2015,35(4):689-692

给出整体最小二乘法拟合空间直线的一种迭代算法。将空间直线垂直投影到坐标平面,分别采用整体最小二乘法和最小二乘法拟合直线。对坐标点等精度观测、非等精度观测和坐标分量非等精度观测3种场景进行模拟计算,比较两种方法估计的参数和验后单位权方差,并对三维激光扫描仪实测数据拟合结果进行分析。  相似文献   

利用线阵像机实现弹丸运动参数测量     

赵竹新  回丙伟  张星  文贡坚 《测绘科学》2012,37(3):26-28

现代靶场中主要采用狭缝摄影技术测量弹丸出膛后的速度、攻角和转速等运动参数,近些年来,采用数字线阵像机代替传统的胶片式相机是目前狭缝摄影的研究方向。对此,本文设计了一种单台线阵像机配合双像器实现等效双像机正交交会测量弹丸的系统,并根据弹丸目标的外形特点,构建了利用圆柱数学模型的弹丸运动参数最优化模型,通过优化算法进行模型求解获得弹丸方位、速度参数,进而求取攻角;设计了一种新的标记线方法,可简单精确地计算弹丸转速。通过仿真实验,验证了本文提出的参数估计方法的精确性。  相似文献   

TLS在滑坡几何特征快速提取中的应用     

赵骞  张锦 《测绘科学》2012,37(5):129-131

滑坡灾害是危险性和破坏力均非常严重的地面灾害之一,滑坡发生后如何快速、高效和高精度地获取滑坡体的几何特征数据是滑坡应急处置重要的测绘保障工作内容。本文应用地面三维激光扫描仪(TLS)进行了快速获取滑坡区域数据和几何特征提取的科学试验,通过ILRIS_36D地面三维激光扫描仪和PolyWorks软件获取和处理数据,提取了滑坡几何特征,数据可供相关部门对滑坡灾害进行快速科学处置。该方法速度快、精度高、信息全,与常规测量方式相比具有多方面的优势。  相似文献   

基于位置签到数据的城市空间分析与可视化     

陈冉  王海起  孟斌  桂丽  刘玉 《地理信息世界》2017,24(3)

微博签到是一种典型的基于位置的社交服务,反映出社交用户与城市公共空间的互动,海量的社交位置签到数据为城市研究提供了全新的视角。本文基于香港、深圳两个城市2014年1月至2015年1月时间段内的新浪微博签到数据,从签到数据空间特性、旅游热点分布和居民活动空间3个方面对城市空间进行了综合分析:空间相关性分析结果表明签到事件在城市空间的分布具有明显的聚集性,并根据空间扫描统计结果依次标识出签到事件高值聚集区;针对旅游类签到数据分析发现两城市旅游关注度的时间变化趋势一致且峰值与我国假期时间分布相吻合,旅游热点主要分布于城市中心地带;以签到事件的规模、强度和集聚程度作为居民活动的表征分析城市活动空间特征,结果表明居民活动的核心圈层受到传统行政区划影响但分布已初步呈现"多心开敞"的空间形态。  相似文献   

肺内小结节三维重建的表现及临床意义   总被引：2，自引：1，他引：1  

黄福气  陈钦  陈义辉 《CT理论与应用研究》2003,12(1):43-46

目的：探讨肺部结节三维重建的应用价值。材料与方法：常规扫描采用螺旋扫描“10mm/10mm/10mm”（即层厚/每螺旋-圈床进距离/重建间隔,Fov300-360mm,标准算法。53例肺内小结节和100例健康体检（包括平扫无阳性发现者）作三维重建（质量透视法-Volume Rendering),取-720HU为重建域下限。结果：阳性者53例中,单个结节47例（左肺21例,右肺26例）,结节直径（0.5cm-3.0cm),比常规扫描更能检出结节边缘凹凸不平及肿瘤供血血管。2个结节2例均为良性（一例手术病理证实为结核,1例抗炎治疗后吸收痊愈）。双肺多发性结节4例（3例为转移瘤,一例为结核）。常规扫描无阳性发现者100例做三维重建,其中92例作健康体检者检出一个结节（0.5cm);8例有癌性病史患者（食道癌6例,肺癌2例）,检出两例有结节。结论：胸部螺旋CT三维重建能提高病变检出率及肿块周边的特征改变,从而有助于肺部结节的诊断可靠性,值得临床推广应用。  相似文献