江淮流域极端降水时空变化特征:站点观测和再分析的对比          下载免费PDF全文

吴晶璐  惠品宏  刘建勇  汤剑平 《大气科学学报》2019,42(2):207-220

利用淮河流域1979—2011年260个站点观测、ERA-Interim和NCEP/DOE再分析资料的日降水量数据,选用8个极端降水指数,从空间分布、发展趋势、时间变化等方面对比分析了我国江淮流域极端降水的变化规律,研究了再分析数据的适用性,结果表明:1)持续湿润指数(CWD)、强降水日数(R10mm,R20mm)以及百分位指数(R95p,R99p)具有一致的北少南多的分布特征,而持续干燥指数(CDD)为北多南少,且强度指数(Rx1day,Rx5day)和百分位指数在浙江沿海均有极大值存在。2)大部分地区的强降水日数呈减少趋势,仅在江淮周边地区有弱上升趋势。3)区域平均的降水强度指数具有上升的趋势变化,逐月变化具有先增长后减少的结构特征,5—6月的增长量最大,峰值出现在7月,在夏末、冬季有较明显的随年代增加的趋势,在秋季则随年代减少。4)再分析资料ERA-Interim和NCEP/DOE对不同指数的再现能力有所不同,ERA-Interim对强降水日数(R10mm)、CDD、百分位指数的空间分布以及CDD的变化趋势再现能力较好,与强度指数和百分位指数年际变化的相关性较高,但对CWD变化趋势分布特点的再现能力较弱;NCEP/DOE更善于再现较强降水日数(R20mm)的空间分布以及强度指数和百分位指数的线性变化趋势。5)两种再分析资料能合理地再现强降水日数(R10mm,R20mm)和CDD年际变化特征和强度指数的季节变化特征。  相似文献   

Feature detection and description for image matching:from hand-crafted design to deep learning     

Lin Chen  Franz Rottensteiner  Christian Heipke 《地球空间信息科学学报》2021,24(1):58-74

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大型桥梁钢沉井下沉过程局部冲刷研究     

高正荣  黄建维  赵晓冬 《海洋工程》2006,24(3):31-35

钢沉井下沉过程中局部冲刷的研究是同类桥墩设计和施工十分关心的重要课题,它对保证钢沉井安全有效施工、桥梁设计中施工期桥墩最大冲深、失稳和安全计算有重要参考价值。通过室内试验研究了钢沉井下沉过程中的局部冲刷机理和冲刷形态,探讨了桥墩下部钢沉井基础施工的相对高程对局部冲刷的变化规律,并将试验研究所获得的局部冲刷规律和影响因素,采用墩型系数方法引入局部冲刷计算中,给出了计算公式。研究成果补充了国家行业规范内容,对同类工程的设计、施工具有借鉴和指导意义。  相似文献   

北京怀柔云蒙山地区花岗岩风化过程的地球化学基因     

王旭阳  姚宁  龚庆杰  晁岳德  彭程  吴媛 《地学前缘》2021,28(1):363-374

地球化学基因是近两年提出的一种新的地球化学示踪技术,本文选择北京怀柔云蒙山地区两个邻近的花岗岩风化剖面(编号为B和C)来分析岩性地球化学基因和金矿化地球化学基因的属性特征.剖面B样品的化学蚀变指数CIA变化为51.3～58.9,WIG的范围为89.4～68.6,属于初始风化程度;剖面C样品的CIA变化为52.4～78....  相似文献   

雅安市雨城区壶穴形态特征     

唐笛  马至敏  廖紫伊  漆力健 《云南地理环境研究》2019,(1):55-60

以雅安市雨城区的严桥河和周公河流域的河床壶穴为研究对象,对128处壶穴形态规模与几何参数进行详细测量。运用定量统计方法分析壶穴的分布规模和形态特征。结果表明:周公河流域壶穴大多分布在岸边大石块上,严桥河流域壶穴主要分布于河床的岩坎上;两地壶穴平均分布密度为0.43个/m2,相对其他区域较小,且壶穴的长短轴和平均口径与深度都有相对明显的规律。在平面形态上,壶穴形态多样,周公河以近圆型壶穴最多,占52.5%,严桥河以椭圆型壶穴最多,占63.6%。在垂直剖面形态上,周公河处壶穴90%属于U型,其余为V型;严桥河处壶穴V型和U型分别占52.3%和44.3%,还有3.4%属倒Ω型;两地壶穴都以浅型为主。  相似文献   

Comparative study of otolith and sulcus morphology for stock discrimination of yellow drum along the Chinese coast     

SONG Junjie  ZHAO Bo  LIU Jinhu  CAO Liang  DOU Shuozeng 《海洋湖沼学报（英文）》2019,(4):1430-1439

Otolith morphology is widely used for fish stock identification. The sulcus, a structure on the medial side of the otolith, is an important feature in morphological analysis. This study was conducted to evaluate the feasibility of using sulcus morphology for stock identification and to compare its performance with commonly used otolith morphology analysis. Otoliths were collected and analyzed from three geographical groups (the Huanghe (Yellow) River estuary, HHE;the Jiaozhou Bay, JZB;and the Changjiang (Yangtze) River estuary, CJE) of yellow drum Nibea albiflora. The results show that the analysis of sulcus morphology based on shape indices (SIs), elliptic Fourier coefficients (EFc), and a combination of the two parameters identified stocks at overall classification rates of 51.0%, 72.5%, and 73.2%, respectively. These classification rates are similar to those obtained using otolith morphology analysis (57.0%, 73.8%, and 76.5% by SIs, EFc, and their combination, respectively). The findings suggest that sulcus morphology is comparable to the commonly used otolith morphology for identifying stocks of sciaenids, such as the yellow drum. For both otolith and sulcus morphology, EFc could identify the stocks more efficiently than SIs, while the combination of SIs and EFc was even better.  相似文献   

结合MST划分和RHMRF-FCM算法的高分辨率遥感图像分割     

林文杰  李玉  赵泉华 《测绘学报》2019,48(1):64-74

针对基于像素的HMRF-FCM算法抗噪性差以及对地物复杂边界分割精度低的问题,提出一种结合形状信息的静态MST区域划分和RHMRF-FCM算法的高分辨率遥感图像分割方法。该方法定义一种静态MST同质区域划分准则,借助MST能较好表达边界和形状信息、能较好抑制几何噪声的特点,解决地物复杂边界的表达和降低分割结果中几何噪声问题。首先,利用MST静态划分将图像域划分成若干个均质区域,假设每个均质区域内光谱测度服从独立同一的多元高斯分布。然后,在此基础上构建了区域隐马尔可夫随机场模型,以及建立基于信息熵和KL信息正则化项的模糊聚类目标函数。最后,采用偏微分方法对分割模型参数进行求解,从而得到全局最优分割结果。为验证本文方法,对WorldView-3高分遥感图像进行分割试验。定性、定量分析了尺度参数、光谱相似性参数和区域紧致度参数对最优分割结果的影响,并对比分析本文算法和eCognition软件中的多分辨率分割算法、分水岭算法。  相似文献   

Greenness Index from Phenocams Performs Well in Linking Climatic Factors and Monitoring Grass Phenology in a Temperate Prairie Ecosystem     

ZHOU Yuke 《资源与生态学报(英文版)》2019,10(5):481-493

Near-surface remote sensing (e.g., digital cameras) has played an important role in capturing plant phenological metrics at either a focal or landscape scale. Exploring the relationship of the digital image-based greenness index (e.g., Gcc, green chromatic coordinate) with that derived from satellites is critical for land surface process research. Moreover, our understanding of how well Gcc time series associate with environmental variables at field stations in North American prairies remains limited. This paper investigated the response of grass Gcc to daily environmental factors in 2018, such as soil moisture (temperature), air temperature, and solar radiation. Thereafter, using a derivative-based phenology extraction method, we evaluated the correspondence between key phenological events (mainly including start, end and length of growing season, and date with maximum greenness value) derived from Gcc, MODIS and VIIRS NDVI (EVI) for the period 2015-2018. The results showed that daily Gcc was in good agreement with ground-level environmental variables. Additionally, multivariate regression analysis identified that the grass growth in the study area was mainly affected by soil temperature and solar radiation, but not by air temperature. High frequency Gcc time series can respond immediately to precipitation events. In the same year, the phenological metrics retrieved from digital cameras and multiple satellites are similar, with spring phenology having a larger relative difference. There are distinct divergences between changing rates in the greenup and senescence stages. Gcc also shows a close relationship with growing degree days (GDD) derived from air temperature. This study evaluated the performance of a digital camera for monitoring vegetation phenological metrics and related climatic factors. This research will enable multiscale modeling of plant phenology and grassland resource management of temperate prairie ecosystems.  相似文献   

Pricing Weather Derivatives Index based on Temperature: The Case of Bahir Dar,Ethiopia     

Tesfahun BERHANE  Aemiro SHIBABAW  Gurju AWGICHEW 《资源与生态学报(英文版)》2019,10(4):415-423

In this paper we present a stochastic model for daily average temperature to calculate the temperature indices upon which temperature-based derivatives are written. We propose a seasonal mean and volatility model that describes the daily average temperature behavior using the mean-reverting Ornstein-Uhlenbeck process. We also use higher order continuous-time autoregressive process with lag 3 for modeling the time evolution of the temperatures after removing trend and seasonality. Our model is fitted to 11 years of data recorded, in the period 1 January 2005 to 31 December 2015, Bahir Dar, Ethiopia, obtained from Ethiopia National Meteorological Services Agency. The analytical approximation formulas are used to price heating degree days (HDD) and cooling degree days (CDD) futures. The suggested model is analytically tractable for derivation of explicit prices for CDD and HDD futures and option. The price of the CDD future is calculated, using analytical approximation formulas. Numerical examples are presented to indicate the accuracy of the method. The results show that our model performs better to predict CDD indices.  相似文献   

Sandy gravel accumulation in a fluvial environment     

Clive Blacknell 《Geological Journal》1981,16(4):287-297

Particle size, pebble shape, pebble fabric, discharge and flow velocity data are used to introduce a model of sandy gravel formation in Welsh gravel-bed rivers. The development of contact-imbrication of the typically very bladed and very platy cobbles and larger pebbles subsequently acts to significantly affect the depositional modes and patterns of small pebbles and sand particles. An important distinction is drawn between sand deposition, which can occur at or below the bed surface, and pebble and cobble deposition, which is merely a surface phenomenon.  相似文献