多普勒天气雷达组网拼图有效数据区域分析   总被引：3，自引：0，他引：3       下载免费PDF全文

杨洪平  张沛源  程明虎  李柏  熊毅  高玉春  陈大任 《应用气象学报》2009,20(1):47-55

在正常情况下, 由于天线仰角和地球曲率原因, 雷达波束位置在远距离处要比近距离处高。当雷达电磁波能量被部分阻挡时, 回波强度观测值低估; 被完全挡住时, 探测不到地物后的目标。该文利用高分辨率地形高程数据计算波束阻挡率, 确定组网拼图有效数据区域以及波束部分阻挡时的回波强度订正方法。根据业务观测模式VCP11及VCP12的14个仰角值, 在标准大气假定下, 对湖南、江西、浙江、福建、广东、广西和海南已建多普勒天气雷达组网的数据有效区域进行计算, 绘制出海拔1500 m, 3000 m和6000 m高度上有效区域图。分析结果表明:CAPPI数据有效范围比等射束高度图更能反映出多普勒天气雷达业务观测范围; 若采用VCP12模式观测, 与采用VCP11或VCP21模式观测相比, 不仅增加低层探测密度, 而且可扩大雷达实际探测距离, 其回波数据更适合于组网拼图。  相似文献   

The Beila Ophiolite from the Bangong-Nujiang Suture Zone, Northern Tibetan Plateau     

ZHAI Qingguo  TANG Yue  HU Peiyuan  XIAO Xuchang  WANG Haitao 《《地质学报》英文版》2017,91(Z1):51-51

The Beila ophiolite is located in the middle part of the Bangong-Nujiang suture zone,northern Tibetan plateau.It is a complete ophiolite suite,and plays a key role in understanding the evolution of the Bangong-Nujiang suture zone,as well as the Meso-Tethys Ocean.The Beila ophiolite was composed of peridotite,serpentinite,gabbro,pillow basalt,and minor rodingite.Peridotites comprisemainlymedium–tocoarse–grained serpentinized harzburgites and minor plagioclase-bearing lherzolites and dunites.There are some felsic-ultramafic dykes within the peridotite and they are mainlypegmatoidal pyroxenites,coarse to fine-grained gabbros,and diabases.Gabbros included isotropic and cumulate gabbros,and they commonly contain minor pegmatoidal gabbros veins.Pillow basalts and basaltic andesites overlaid on the margin of the serpentinized peridotites.Rodingite occurs as lenses and/or dykes within the host serpentinized peridotites.Zircon SHRIMP U–Pb dating for two rodingite samples yielded the ages ranging from172 to 164 Ma.Whole-rock geochemical and zircon Hf isotopic data show that the Beila ophiolite shows SSZ-type ophiolite affinity.Finally,we suggest that the Beila ophiolite was generated in an initial subduction process at the middle Jurassic(164–172 Ma).  相似文献   

Analysis of resistance factors for LFRD of soil nail walls against external stability failures     

Peiyuan Lin  Jinyuan Liu 《Acta Geotechnica》2017,12(1):157-169

This paper presents reliability analyses of soil nail walls against two external ultimate limit states, global and sliding stabilities, which are related to the external stability failures of soil nail walls. Reliability analyses are conducted using Monte Carlo simulation technique. Soil nailing is a popular retaining system in highway construction and slope stabilization, and its current design practice is still based on the working stress design. There remains a need to establish a more rational design framework—load and resistance factor design—based on the concept of limit state design and reliability analysis for soil nail walls. The development of load and resistance factor design approach must consider multiple ultimate limit states, associated with external, internal, and facing failures. The analyses of resistance factors against two external failures are conducted in this study considering various influencing factors, including statistical parameters of soil friction angle, ultimate bond strength between soil and nails, soil type, wall geometry (wall height, back slope angle, and face batter angle), and nail configurations (nail inclination angle, drillhole diameter, and nail spacing). In the end, a series of resistance factors are proposed for potential application of load and resistance factor design approach against external failures for soil nail walls according to different design codes.  相似文献   

Statistical analysis of the effective stress method and modifications for prediction of ultimate bond strength of soil nails     

Peiyuan Lin  Richard J. Bathurst  Sina Javankhoshdel  Jinyuan Liu 《Acta Geotechnica》2017,12(1):171-182

Uncertainty in the predicted ultimate pullout strength of soil nails can be significant due to the complexity of nail–soil interactions, inherent variability in soil properties and the effects of nail installation. The paper first presents a statistical evaluation of the accuracy of ultimate bond strength of soil nails using the effective stress method (ESM) equation that has been adopted in Hong Kong. A total of 113 ultimate nail capacity data points from field pullout tests were collected from the literature and used to estimate the accuracy of the current ESM. Based on the available data, the current ESM default pullout model is found to be excessively conservative (on average) by at least a factor of three. The spread in prediction accuracy measured by the coefficient of variation (COV) of bias is in the range of 36–43 % after removing anomalous test data. Here, bias is the ratio of measured to predicted pullout load capacity. In addition, the accuracy of the current ESM equation for prediction of nail bond strength is shown to be dependent on the magnitude of predicted ultimate bond strength and magnitude of nominal vertical effective stress which is undesirable. The paper examines four candidate-modified bond strength equations with empirical coefficients that have been back-fitted to measured bond strengths to improve the overall accuracy of the equation and to reduce or remove the undesirable dependencies noted above. One equation with an empirically corrected stress-dependent term is judged to be the best candidate model based on the mean of bias values, spread (COV) of bias values, lack of dependencies and simplicity. Finally, the relative contributions of random variability in soil shear strength to measurement bias in bond strength (prediction accuracy) for each soil type are computed for the best bond strength model. Analysis of the contribution of soil shear strength to prediction accuracy showed that the combination of variability due to factors other than soil shear strength was greater than the variability in soil shear strength alone, where the latter is defined by the soil secant friction coefficient.  相似文献   

Study on Retrieving Three-Dimensional Wind Using Simulated Dual-Doppler Radar Data in the Cartesian Space          下载免费PDF全文

ZHOU Haiguang  ZHANG Peiyuan 《Acta Meteorologica Sinica》2005,19(3):345-354

1. Introduction Armijo (1969) proposed the three-dimensional wind retrieved equations using multiple-Doppler weather radar network in Cartesian space. There are many sources of error for recovering 3D wind using these equations. These factors include advection and turbulence in the weather system, the error of the empirical relationship between the radar reflectivity factor and the terminal fall velocity of the precipita- tion particle, integrating the air mass continuity equa- tion (problem …  相似文献   

多普勒雷达资料四维变分同化   总被引：8，自引：2，他引：8       下载免费PDF全文

杨艳蓉李柏  张沛源 《应用气象学报》2004,15(1):95-110

文章从理论上分析了多普勒雷达资料的四维同化。阐述多普勒雷达资料四维同化的主要过程及其基本思路。着重论述多普勒雷达资料四维变分分析系统(4D-VDRAS)的原理和方法，以及价值函数，共轭方程、伴随方程和多普勒雷达数据处理、Barnes插值技术和4D-VDRAS的应用。  相似文献   

2000年来我国旱涝气候演化的阶段性和突变   总被引：23，自引：3，他引：23       下载免费PDF全文

张丕远  葛全胜  张时煌  刘啸雷 《第四纪研究》1997,17(1):12-20

过去气候的突变以地质方法得到很多证据，但在历史时期则发现不多。本文利用文献档案资料建成2000年来的旱涝气候序列，发现280年和1230年前后有过两次突变。本工作着重给出突变前后的旱涝气候分布类型的差别，即从空间分布上探讨被突变界开的气候阶段所具有的特色，280～1230年间，我国气候大趋势是不稳定的，而且涝的界线一再受到NE-SW走向的等高线阻挡。气候突变事件的证据说明，气候系统的运动具有两种模式：渐变和突变。  相似文献   

近20年来中国第四纪冰川研究的进展   总被引：2，自引：0，他引：2       下载免费PDF全文

孙殿卿  何培元 《地球科学》1994,19(6):838-844

本文从宏观和微观两个方面介绍了第四纪冰川作用的新发现，指出第四纪早冰期即可能是第四纪的开始，其下限年龄为３．４－２．５ＭａＢ．Ｐ．，并将我国某些地点的冰期进行了对比，提出了第四纪冰期今后的研究方向。  相似文献   

中国自然灾害的空间分布特征   总被引：11，自引：1，他引：11  

王铮  张丕远 《地理学报》1995,50(3):248-255

中国自然灾害的分布以秦岭－淮河线、胡焕庸线以及青藏高原外缘为界，可划分为四个大区，即北域、南域、西域和过滤带亚域。以灾害的单位面积失论，黄淮海地区是我国重点灾区，另一个重点区位于川、滇、黔、桂交界地段，它以人员的伤亡而突出。如果以灾害发生的总经济损定义灾害规模，则活动的规模中心位于以洞庭－武汉和郑州为两端点的地区。  相似文献   

A holistic approach to aligning geospatial data with multidimensional similarity measuring     

Li Yu  Peiyuan Qiu  Xiliang Liu  Bo Wan 《International Journal of Digital Earth》2018,11(8):845-862

Semantically aligning the heterogeneous geospatial datasets (GDs) produced by different organizations demands efficient similarity matching methods. However, the strategies employed to align the schema (concept and property) and instances are usually not reusable, and the effects of unbalanced information tend to be neglected in GD alignment. To solve this problem, a holistic approach is presented in this paper to integrally align the geospatial entities (concepts, properties and instances) simultaneously. Spatial, lexical, structural and extensional similarity metrics are designed and automatically aggregated by means of approval voting. The presented approach is validated with real geographical semantic webs, Geonames and OpenStreetMap. Compared with the well-known extensional-based aligning system, the presented approach not only considers more information involved in GD alignment, but also avoids the artificial parameter setting in metric aggregation. It reduces the dependency on specific information, and makes the alignment more robust under the unbalanced distribution of various information.  相似文献