Shape indexes for semi-automated detection of windbreaks in thematic tree cover maps from the central United States     

《International Journal of Applied Earth Observation and Geoinformation》2017

Windbreaks are an important ecological resource across the large expanse of agricultural land in the central United States and are often planted in straight-line or L-shaped configurations to serve specific functions. As high-resolution (i.e., <5 m) land cover datasets become more available for these areas, semi- or fully-automated methods for distinguishing windbreaks from other patches of trees are needed for use with thematic raster datasets. To address this need, we created three shape indexes: a morphology-based index that we have named the Straight and Narrow Feature Index (SNFI), a windbreak sinuosity index, and an area index indicating the occupied fractional area of a bounding box. The indexes were tested in two study areas: (1) a riparian area dominated by sinuous bands of trees but mixed with row crop agriculture and (2) an agricultural area with a mix of straight-line and L-shaped windbreaks. In the riparian area, a Kruskall–Wallis rank sum test indicated class differences for all three indexes, and pairwise comparisons indicate windbreaks and riparian trees are separable using any of the three indexes. SNFI also produced significant differences between windbreaks oriented in different directions (east–west vs. north–south). In the agricultural area, the Kruskall–Wallis rank sum test indicated differences between classes for all three indexes, and pairwise comparisons show that all class pairs have significant differences for at least one index, with the exception of L-shaped windbreaks vs. non-windbreak tree patches. We also used classification trees to objectively assign representative samples of tree patches to classes using both single indexes and multiple indexes. Classes were correctly assigned for more than 90% of the samples in both the riparian and agricultural study areas. In the riparian area, combining indexes did not improve accuracy compared to using SNFI alone, whereas in the agricultural area, combining the three indexes produced the best result. Thematic datasets derived from high-resolution imagery are becoming more available, and extracting useful information can be a challenge, partly due to the large amount of data to assess. Calculating the three shape indexes presented can assist with efficient identification of candidate windbreaks and as such, hold good promise for value-added analysis of tree function in the central United States.  相似文献   

反向沙丘近地层气流变化及其对沙丘形态的影响     

潘凯佳  张正偲  梁爱民 《中国沙漠》2021,41(2):1-8

反向沙丘形态-动力学过程是风沙地貌的重要研究内容。选择腾格里沙漠东南缘推平沙地发育的反向沙丘为研究对象,采用二维超声风速仪对沙丘表面5个位置0.25 m和0.5 m高度的气流进行野外观测。结果表明：（1）气流方向影响近地层气流特征。以沙丘脊线垂线为轴,0.25 m高度处沙丘脊线的垂线两侧风向变化不完全对称。当丘顶气流方向与脊线垂线角度差值为负时,迎风坡底部风速恢复较慢。（2）背风坡气流特征受风向控制。背风坡0.25 m与0.5 m高度气流变化规律相似,在背风坡中部发生偏转,但沙丘顶部气流方向与脊线垂线相差<10°时发生反向偏转。丘顶风向为285°—315°（左偏）时,0.25 m高度的偏转角度大于0.5 m高度的偏转角度。背风坡0.25 m与0.5 m高度处风速表现为脊线垂线两侧风速变化不一致。（3）沙丘表面气流影响沙丘形态。观测期间沙丘脊线发生明显移动,移动值为0.33 m。背风坡发生堆积,最大堆积厚度为0.44 m,迎风坡发生风蚀,最大风蚀深度为0.43 m。该研究结果证实了风在风沙地貌演化中的重要作用,为反向沙丘形态演化数值模拟提供数据支持。  相似文献   

An overview of focuses of research on otolith element characteristics and general testing methods     

GAO Yong-Hua LI Qing-Rong LIN Dong-Ni JIAO Chi FENG Qiang-Ling 《地学前缘》2008,15(6):11

  相似文献   

规则格网DEM局地坡面凸凹性精度分析     

王春  徐燕  江岭  赵明伟 《地球信息科学学报》2020,22(3):361-369

DEM地表形态精度分析理论与方法的建立,对DEM数据的生产和广泛应用具有重要意义。本文从局地坡面形态的凸凹性角度,剖析规则格网DEM格网点位置、格网分辨率对DEM局地坡面凸凹性的影响,以期进一步完善和发展DEM质量分析的理论与方法。论文首先阐述了DEM局地坡面凸凹性的基本概念,研究建立了规则格网DEM的局地坡面凸凹性量化分析方法,并以黄土丘陵5、10、15、25、……、155 m DEM为例,采用比较分析方法研究了局地坡面凸凹性随DEM格网点位置和格网分辨率的变化特征。研究表明:对于本研究中的1:5万DEM,10 m(跃变率≤0.3%)是其最佳的格网分辨率阈值,当DEM实际格网分辨率高于该阈值时,实际DEM与最佳格网分辨率DEM具有近乎相同的局地坡面凸凹性,主要在正地形与负地形的过渡区域会发生不同程度的坡面凸凹性变化;当DEM实际格网分辨率低于该阈值时,实际DEM的局地坡面凸凹性,会随着DEM格网点布设位置和DEM格网分辨率发生较大的不确定性变化。  相似文献   

山西中部一次积层混合云降水微物理特征研究          下载免费PDF全文

杨俊梅 《沙漠与绿洲气象(新疆气象)》2023,17(6)

基于2011年5月9日山西中部地区一次积层混合云降水的机载探测和地面雨滴谱观测资料,分析了空中云系微物理参量的垂直分布、冰晶形态及演变和地面降水的微物理特征。结果表明：此次积层混合云为冷云结构,垂直分布不均匀,云中过冷水较为丰沛,对流泡的存在造成云内不同区域云水含量不均匀。云滴的凝华增长导致5.3 km处大云粒子和降水粒子数浓度明显增加。小云粒子谱分布以单峰型为主,峰值直径主要位于5～6 μm或9～10 μm,大云粒子谱分布呈多峰型,不同高度处变化较大。此次降水观测到的冰晶形态包括板状、针柱状、柱帽状、辐枝状和不规则形状,4.9 km处受聚合和淞附过程的共同影响,辐枝状和针柱状冰晶增多,在4.1 km处融化层附近淞附状冰晶明显增加。地面降水受到雨滴谱仪布设位置的影响,其微物理结构主要呈现为层状云降水的特征。  相似文献   

现代银杏叶脉参数初步研究     

崔鑫  李想  陈睿  邢天悦  孙跃武 《世界地质》2016,35(3):601-607

对南京现生银杏叶片的长枝阳叶、短枝阳叶和短枝阴叶的形态参数和叶脉参数进行观察和度量。结果显示:长枝阳叶、短枝阳叶和短枝阴叶的叶脉密度分别为14.78±2.44 cm、16.05±2.57cm、15.31±2.34 cm,叶脉指数分别为0.090±0.026、0.098±0.037、0.091±0.027,差别不显著。表明,银杏叶生长位置和光照强度对其叶脉参数影响不大。  相似文献   

胶西北大尹格金矿床成矿机理:载金黄铁矿标型及硫同位素地球化学约束   总被引：4，自引：3，他引：1  

张瑞忠  王中亮  王偲瑞  刘育  秦文凯 《岩石学报》2016,32(8):2451-2464

胶东是我国最重要的金矿集中区,破碎带蚀变岩型金矿床是区内最主要的金矿床类型,该类型金矿床已探明金资源量占全区的90%以上,其巨量金的来源是引人瞩目的关键科学问题。招平断裂带是该区内规模最大的断裂-成矿带,位于招平金矿带中段的大尹格庄金矿床是该金矿带最具代表性的破碎带蚀变岩型金矿床之一,已探明金金属量约283t。大尹格庄金矿床严格受沿胶东群与玲珑花岗岩接触带发育的NNE向招平断裂带控制,矿体赋存在招平断裂下盘黄铁绢英岩化和碎裂岩化玲珑花岗岩中,主要由Ⅰ号和Ⅱ号矿体组成,其具有相似的矿物组成,矿石主要矿物是绢云母、石英、黄铁矿,次要矿物是钾长石、斜长石、黑云母、方解石、黄铜矿、方铅矿、闪锌矿、磁黄铁矿、黝铜矿和自然金、自然银、金银矿、碲银矿等;其中黄铁矿是最主要的载金矿物。根据穿插关系和矿物共生组合,大尹格庄金矿床内成矿作用可划分为4个成矿阶段,分别是黄铁矿-石英-绢云母阶段(I)、石英-黄铁矿阶段(Ⅱ)、石英-多金属硫化物阶段(Ⅲ)和石英-方解石-多金属硫化物阶段(Ⅳ)。各个成矿阶段的黄铁矿的晶体形态标型研究表明,成矿Ⅰ阶段黄铁矿以粗粒自形立方体为主,含有少量五角十二面体;成矿Ⅱ和Ⅲ阶段黄铁矿以细粒五角十二面体为主,且具有更多五角十二面体、八面体和立方体形成的聚形;成矿Ⅳ阶段主要为细粒立方体晶形。不同矿体各个成矿阶段的硫化物的δ~(34)S值集中在4.58‰~7.54‰,具有一定的塔式效应,正向偏离陨石硫,与胶东地区胶东群变质岩、围岩花岗岩类δ~(34)S比较接近,指示大尹格庄金矿床各个成矿阶段的矿石硫源总体一致,与胶东群变质岩和中生代花岗岩间具有继承演化关系。此外,从成矿Ⅰ阶段→Ⅱ阶段→Ⅲ阶段→Ⅳ阶段,大尹格庄金矿床矿石硫化物δ~(34)S呈现出逐渐降低的趋势,反映了成矿过程中物理化学条件的演化趋势:Ⅰ阶段为较高温度(330~350℃)、快速冷却、低过饱和度、低氧逸度和硫逸度的成矿环境;Ⅱ和Ⅲ阶段黄铁矿形成于中-低温(200~300℃)、成矿流体过饱和度高、高氧逸度和硫逸度、缓慢冷却同时物质供应充分的成矿环境;Ⅳ阶段处于较低温度(200℃)、热液流体过饱和度较低、低氧逸度和硫逸度、同时物质供应不足的成矿环境。  相似文献   

长江河口主槽地貌形态观测与分析   总被引：4，自引：3，他引：1       下载免费PDF全文

吴帅虎  程和琴  胥毅军  李九发  郑树伟  徐韦  陆雪骏 《海洋工程》2016,34(6):65-73

人类活动可以改变流域至河口的泥沙输运与沉积。尽管一些近期的研究已经调查了长江河口的形态演变,然而,流域和河口工程如何影响河口河床的形态演变仍然是不清楚的。该文利用2010年至2015年多波束测深系统和浅地层剖面仪等先进现场测量仪器的长江口主槽走航测量资料,并结合主槽表层沉积物资料,分析了近年来人为强干扰下的长江河口主槽底床微地貌形态,以理解近期人类活动对河口的影响。结果显示:近年来长江河口主槽底床上除了存在平床、沙波、冲沟和冲刷痕等常见微地貌形态外,还存在着疏浚痕和凹坑等人为微地貌形态。在流域和河口大型工程的共同影响下,近年来南北港中上段、横沙通道和南槽上段均受到不同程度的冲刷,其主槽底床上呈现出不同程度冲沟和冲刷痕等侵蚀性微地貌。而由于疏浚工程的影响,南港下段、圆圆沙航槽和北槽航道底床上出现了大范围的疏浚痕和凹坑。近年来包括南槽上段、北槽主槽中段和下段的局部区域和北港拦门沙河段局部区域在内的长江河口最大浑浊带的河床沉积物有粗化趋势。南北港中上段和横沙通道的大部分区域均发育了大量沙波微地貌;总体上,长江河口沙波的波高在0.12~3.12 m,波长在2.83~127.89 m,波高/波长在0.003~0.136,长江河口中上段的沙波尺度(波高的均值为0.91 m,波长的均值为20.08 m)大于密西西比河下游(波高的均值为0.87 m,波长的均值为17.62 m),且两区域沙波的几何形态差异性较小。  相似文献   

Development and Extension of An Aggregated Scale Model: Part 1 – Background to ASMITA     

Ian TOWNEND  Zheng Bing WANG  Marcel STIVE  Zeng ZHOU 《海洋工程》2016,(4):483-504

Whilst much attention has been given to models that describe wave, tide and sediment transport processes in sufficient detail to determine the local changes in bed level over a relatively detailed representation of the bathymetry, far less attention has been given to models that consider the problem at a much larger scale (e.g. that of geomorphological elements such as a tidal flat and tidal channel). Such aggregated or lumped models tend not to represent the processes in detail but rather capture the behaviour at the scale of interest. One such model developed using the concept of an equilibrium concentration is the Aggregated Scale Morphological Interaction between Tidal basin and Adjacent coast (ASMITA). In this paper we provide some new insights into the concepts of equilibrium, and horizontal and vertical exchange that are key components of this modelling approach. In a companion paper, we summarise a range of developments that have been undertaken to extend the original model concept, to illustrate the flexibility and power of the conceptual framework. However, adding detail progressively moves the model in the direction of the more detailed process-based models and we give some consideration to the boundary between the two.  相似文献   

Regional Variability in Occurrence and Distribution of Polymetallic Nodules in the Central Indian Basin     

Anil B. Valsangkar 《Marine Georesources & Geotechnology》2016,34(6):542-549

Regional scale morphological studies on different-sized polymetallic nodules from the Central Indian Basin show that only 2–5 cm sized nodules have highest occurrence per station (92–94% along latitudes; 88–94% along longitudes). A nodule size shows an inverse relationship with the nodule distribution, grade, and abundance. Interestingly, only 3–4 and 4–5 cm sized nodules have highest grade, abundance, and distribution percentages along longitudes in P₁, first generation mine site and relinquished area, which further implies that the nodule mining along the longitude would be beneficial. Different-sized nodule groups suggest their formation under variable environmental conditions that existed in the Central Indian Basin. The coexistence of different-sized nodules suggests different environmental conditions existed in the Central Indian Basin.  相似文献