A method for the extraction of partition lines from long and narrow patches that account for structural features     

Chengming Li  Zhaoxin Dai  Yong Yin  Pengda Wu 《Transactions in GIS》2019,23(2):349-364

The extraction of partition lines for long and narrow patches (LN patches) is an important yet difficult problem in the generalization of thematic data. When current methods are used to process polygons with irregular shapes or complex branch convergence zones, the extracted line structural features tend to be inaccurate and topologically erroneous. In this article, we propose an improved partition lines extraction algorithm of constrained Delaunay triangulation to counter these issues. The proposed method aims to maintain consistency between the extracted line structure characteristics and the actual object structure, especially for complex branch convergence zones. First, we describe three types of aggregation patterns (Type A, B, and C aggregation zones) that occur in partition line extractions for LN patches of complex branch convergence zones using Delaunay triangulation. Then, a partition line extraction algorithm that accounts for the direction between the edges of triangles and the distance of nodes in aggregation zones is proposed. Finally, we test our method for a dataset relating to Guizhou Province, China. Compared with the current method that uses quantitative indicators and visualization, the results indicate that our method not only has applicability for simple situations but also is superior for preserving structural features of complex branch convergence zones.  相似文献   

Long‐term streamflow trends in Hawai'i and implications for native stream fauna     

Hannah M. Clilverd  Yin‐Phan Tsang  Dana M. Infante  Abigail J. Lynch  Ayron M. Strauch 《水文研究》2019,33(5):699-719

Climate change has fundamentally altered the water cycle in tropical islands, which is a critical driver of freshwater ecosystems. To examine how changes in streamflow regime have impacted habitat quality for native migratory aquatic species, we present a 50‐year (1967–2016) analysis of hydrologic records in 23 unregulated streams across the five largest Hawaiian Islands. For each stream, flow was separated into direct run‐off and baseflow and high‐ and low‐flow statistics (i.e., Q10 and Q90) with ecologically important hydrologic indices (e.g., frequency of flooding and low flow duration) derived. Using Mann–Kendall tests with a running trend analysis, we determined the persistence of streamflow trends through time. We analysed native stream fauna from ~400 sites, sampled from 1992 to 2007, to assess species richness among islands and streams. Declines in streamflow metrics indicated a general drying across the islands. In particular, significant declines in low flow conditions (baseflows), were experienced in 57% of streams, compared with a significant decline in storm flow conditions for 22% of streams. The running trend analysis indicated that many of the significant downward trends were not persistent through time but were only significant if recent decades (1987–2016) were included, with an average decline in baseflow and run‐off of 10.90% and 8.28% per decade, respectively. Streams that supported higher native species diversity were associated with moderate discharge and baseflow index, short duration of low flows, and negligible downward trends in flow. A significant decline in dry season flows (May–October) has led to an increase in the number of no‐flow days in drier areas, indicating that more streams may become intermittent, which has important implications for mauka to makai (mountain to ocean) hydrological connectivity and management of Hawai'i's native migratory freshwater fauna.  相似文献   

Enhancement of backtracking search algorithm for identifying soil parameters     

Yin-Fu Jin  Zhen-Yu Yin 《国际地质力学数值与分析法杂志》2020,44(9):1239-1261

In this paper, an enhanced backtracking search algorithm (so-called MBSA-LS) for parameter identification is proposed with two modifications: (a) modifying the mutation of original backtracking search algorithm (BSA) considering the contribution of current best individual for accelerating convergence speed and (b) novelly incorporating an efficient differential evolution (DE) as local search for improving the quality of population. The proposed MBSA-LS is first validated with better performance than the original BSA and some other typical state-of-the-art optimization algorithms on a benchmark of soil parameter identification in terms of effectiveness, efficiency, and robustness. Then, the efficiency of the MBSA-LS is further illustrated by two representative cases: identifying soil parameters from both laboratory tests and field measurements. All comparisons demonstrate that the proposed MBSA-LS algorithm can give accurate results in a short time. Finally, to conveniently solve the problems of parameter identification, a practical tool ErosOpt for parameter identification is developed by integrating the proposed MBSA-LS and some other efficient algorithms for readers to conduct the parameter identification using optimisation algorithms.  相似文献   

Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers          下载免费PDF全文

Tianming Huang  Zhonghe Pang  Jilai Liu  Lihe Yin  W. Mike Edmunds 《水文研究》2017,31(5):1047-1057

Previous studies have shown that shallow groundwater in arid regions is often not in equilibrium with near‐surface boundary conditions due to human activities and climate change. This is especially the case where the unsaturated zone is thick and recharge rate is limited. Under this nonequilibrium condition, the unsaturated zone solute profile plays an important role in estimating recent diffuse recharge in arid environments. This paper combines evaluation of the thick unsaturated zone with the saturated zone to investigate the groundwater recharge of a grassland in the arid western Ordos Basin, NW China, using the soil chloride profiles and multiple tracers (²H, ¹⁸O, ¹³C, ¹⁴C, and water chemistry) of groundwater. Whereas conventional water balance and Darcy flux measurements usually involve large errors in recharge estimations for arid areas, chloride mass balance has been widely and generally successfully used. The results show that the present diffuse recharge beneath the grassland is 0.11–0.32 mm/year, based on the chloride mass balance of seven soil profiles. The chloride accumulation age is approximately 2,500 years at a depth of 13 m in the unsaturated zone. The average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2,842 to 7,856 mg/L, whereas the shallow groundwater Cl content ranges from 95 to 351 mg/L. The corrected ¹⁴C age of shallow groundwater ranges from 4,327 to 29,708 years. Stable isotopes show that the shallow groundwater is unrelated to modern precipitation. The shallow groundwater was recharged during the cold and wet phases of the Late Pleistocene and Holocene humid phase based on palaeoclimate, and consequently, the groundwater resources are nonrenewable. Due to the limited recharge rate and thick unsaturated zone, the present shallow groundwater has not been in hydraulic equilibrium with near‐surface boundary conditions in the past 2,500 years.  相似文献   

Analytical method of radiation by a wave energy device with dual rectangular floating bodies     

WANG Wensheng  YOU Yage  ZHANG Yunqiu  WU Bijun  YE Yin 《海洋学报(英文版)》2010,29(3):106-115

The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method.  相似文献   

膏盐岩脆塑性变形特征及封闭能力定量评价   总被引：1，自引：0，他引：1  

吴桐  付晓飞  王海学  丁宇佳 《地质论评》2016,62(1):127-137

膏盐岩盖层作为全球许多含油气盆地最重要的盖层之一,本身物性封闭能力毋庸置疑,野外观察和三轴试验证实随埋深的增加膏盐岩存在脆塑性转化的过程。为了明确其在不同脆塑性域的变形特征和封闭能力定量评价方法,本文以野外露头观测、三轴压缩试验和镜下观察为基础,从变形机制、破裂模式、力学行为和声发射等方面系统总结了不同脆塑性阶段膏盐岩的变形特征。应用莫尔—库伦准则、拜尔利摩擦定律和应力降规律厘定了膏盐岩脆塑性转化的围压和深度。研究结果表明:1针对脆性膏盐岩盖层,首先应用保持力定量评价水力破裂风险性,保持力越小,盖层发生水力破裂的风险就越大。同时利用断接厚度定量表征脆性盖层内断层垂向封闭性;2应用SSF定量评价脆—塑性膏盐岩盖层中涂抹型断裂的垂向封闭性,野外断层解剖确定出膏岩涂抹连续的临界SSF值为3.5~4;3塑性膏盐岩盖层具有流动特征,伴随断层逆冲滑动,膏盐岩沿断面流动,此阶段断层垂向是封闭的,但在差异压实作用下,盐岩流动形成缺失区——"盐窗"可以为油气沿断层向上运移提供通道。因此,膏盐岩盖层封闭性分析要综合考虑盖层脆塑性、不同脆塑性盖层内断裂变形机制及断裂带内部结构,从而完善盖层垂向封闭性评价体系。  相似文献   

Improved hurricane forecasting from a variational bogus and ozone data assimilation (BODA) scheme: case study     

Yin Liu  Wei Zhang 《Meteorology and Atmospheric Physics》2016,128(6):715-732

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卫星臭氧资料的发展与应用     

刘寅  邹晓蕾 《气象学报》2016,74(1):1-17

随着卫星探测技术的进步、天气学和气候学理论的不断完善,以及高性能计算机广泛应用,卫星臭氧资料的种类得到极大丰富并被应用到多个研究领域中,取得了一系列重要成果。文中介绍了主要星载臭氧探测仪的发展概况,回顾了卫星臭氧资料在气象领域的应用研究成果,主要包括卫星臭氧资料在气旋或低压过程中、全球或区域臭氧的气候分布及变化特征、高原臭氧分布及变化特点、数值应用等方面的应用研究,并展望了卫星臭氧资料研究的未来发展趋势。   相似文献   

国家级格点化定量降水预报系统   总被引：10，自引：7，他引：3  

曹勇  刘凑华  宗志平  谌芸  代刊  陈涛  杨寅 《气象》2016,42(12):1476-1482

利用主客观融合降水反演、降水统计降尺度、降水时间拆分等技术构建了国家级格点化定量降水预报系统。该系统结构合理,模块功能明确,于2014年6月在国家气象中心投入业务使用,生成0~168 h时效,10 km分辨率,逐3 h的格点化定量降水预报产品。通过对2015年第13号热带气旋苏迪罗的格点化降水预报个例检验,结果显示,相比欧洲中期数值预报中心的确定性模式预报和预报员主观预报,该产品能更好地体现台风降水的时空精细化分布特点,对福建东北部和浙江东南部的特大暴雨中心位置表现更准确细致。通过对2015年4—9月的格点化产品整体效果检验,结果显示,相比欧洲中期数值预报中心的确定性模式预报和由反距离客观分析后的预报员主观预报,该产品既能保持和预报员主观预报相同的准确率,同时也能较明显地提高降水预报的时空精细化程度。  相似文献   

武威市初、终霜日气候特征   总被引：2，自引：0，他引：2  

丁文魁  杨晓玲  殷玉春  马玉山 《气象科技》2016,44(4):647-652

为了因地制宜,合理调整种植结构和布局,有效利用农业气候资源。利用1961—2014年武威市4个气象站点初、终霜日(最低地温≤0℃)观测资料,采用现代气候诊断分析方法,系统分析了该市年初、终霜日的时空变化特征。结果表明:受海拔高度、地形地势以及植被覆盖情况的影响,在空间分布上,武威市初霜日为山区早于荒漠区早于绿洲平原区,终霜日为山区晚于荒漠区晚于绿洲平原区,各地初、终霜日存在一定的异常性,正常初、终霜日均在60%左右,对农业生产造成危害的偏早和特早初霜日、偏晚和特晚终霜日的概率均在20%左右。在时间变化上,武威市初霜日呈显著推迟趋势,终霜日呈显著提早趋势,霜期呈显著缩短趋势,终霜日提早的幅度比初霜日推迟的幅度更大。初霜日和终霜日的时间序列均分别存在着8~10年和9~11年的准周期变化。初霜日在1998年发生了气候突变,终霜日在1996年发生了气候突变。  相似文献