成都地面最低气温年极值的渐近分布     

孟庆珍  张杏敏 《成都信息工程学院学报》1997,(2)

利用成都１９３３～１９９２年间的地面最低气温年极值记录，采用韦伯分布和耿贝尔分布，分别对其进行了渐近分布拟合。通过统计推断，找出了成都地面最低气温年极值所遵循的最佳渐近分布——韦伯分布。  相似文献   

A general framework for error analysis in measurement-based GIS Part 3: Error analysis in intersections and overlays   总被引：3，自引：1，他引：2  

Yee?LeungEmail author  Jiang-Hong?Ma  Michael F.?Goodchild 《Journal of Geographical Systems》2004,6(4):381-402

This is the third of a four-part series on the development of a general framework for error analysis in measurement-based geographic information systems (MBGIS). In this paper, we study the characteristics of error structures in intersections and polygon overlays. When locations of the endpoints of two line segments are in error, we analyze errors of the intersection point and obtain its error covariance matrix through the propagation of the error covariance matrices of the endpoints. An approximate law of error propagation for the intersection point is formulated within the MBGIS framework. From simulation experiments, it appears that both the relative positioning of two line segments and the error characteristics of the endpoints can affect the error characteristics of the intersection. Nevertheless, the approximate law of error propagation captures nicely the error characteristics under various situations. Based on the derived results, error analysis in polygon-on-polygon overlay operation is also performed. The relationship between the error covariance matrices of the original polygons and the overlaid polygons is approximately established.This project was supported by the earmarked grant CUHK 4362/00H of the Hong Kong Research grants Council.  相似文献   

在卫星授时中电离层误差实时改正的双极化方法     

YANG KeJun 《时间频率学报》1996,(1)

在卫星定位与授时中，电离层折射误差的影响是十分重要的．目前采用的主要改正方法是双频法，还有电离层模型法．双频法要求卫星发射两个工作频率，而电离层模型法的偏差又较大，这对于使用单频接收机的用户来讲，电离层折射改正就成为一个严重问题，笔者提出的双极化法正好可以解决单频接收机所遇到的问题．双极化法是基于电离层的双折射特性．一个线极化波在电离层中传播时被分裂成两个圆极化波，即左旋圆极化波和右旋圆极化波传播，左旋与右旋圆极化波在电离层中传播的速度不同，则到达接收点的时间也就不同，通过测量两个圆极化波到达接收点的传播时廷差，即可确定电离层折射误差的改正量．  相似文献   

Error sources of precipitation measurements using electronic weight systems   总被引：1，自引：0，他引：1  

B. Sevruk  B. Chvíla   《Atmospheric Research》2005,77(1-4):39

Liquid precipitation amounts below 0.05 mm in combination with intervals of measurement greater than 3 min and temperature above 15 °C can considerably affect the measured precipitation using electronic weighing gauges. This was shown by tests using different weights put in the gauge in different intervals in order to simulate different precipitation amounts and measuring intervals. These results were confirmed by field intercomparison measurements using pit gauges in two locations in Slovakia. In total, 1571 weight tests consisting of combinations of simulated precipitation amounts of 0.025, 0.05, 0.2 mm and measuring intervals of 1, 2, 3, 5 and 10 min were carried out. Based on these tests and special software, a new gauge was developed. Using this gauge, the abovementioned error sources were minimized. The Slovak Hydrometeorological Institute now uses it at 90 gauge sites. This type of gauge was selected to participate in the current World Meteorological Organization, WMO, Intercomparison measurements of recording precipitation gauges.  相似文献   

对海峡两岸地震系统震级测定差异的统计研究     

陈惠芳  许江英 《福建地震》2006,(Z1)

本文利用海峡两岸地震系统对台湾花莲、台东等六个地区近几年的地震资料进行震级差异的统计,得出台湾的地震系统记录的震级一般都比福建台网的大。它与福建台网的震级差最大1.2级,最小为0级。平均结果在0.4级左右。(本文利用的是福建台网中心编目室的资料与台湾中央气象局的资料进行统计对比得出结论)。  相似文献   

Calibration of area based diameter distribution with individual tree based diameter estimates using airborne laser scanning     

《ISPRS Journal of Photogrammetry and Remote Sensing》2014

Diameter distribution is essential for calculating stem volume and timber assortments of forest stands. A new method was proposed in this study to improve the estimation of stem volume and timber assortments, by means of combining the Area-based approach (ABA) and individual tree detection (ITD), the two main approaches to deriving forest attributes from airborne laser scanning (ALS) data. Two methods, replacement, and histogram matching were employed to calibrate ABA-derived diameter distributions with ITD-derived diameter estimates at plot level. The results showed that more accurate estimates were obtained when calibrations were applied. In view of the highest accuracy between ABA and ITD, calibrated diameter distributions decreased its relative RMSE of the estimated entire growing stock, saw log and pulpwood fractions by 2.81%, 3.05% and 7.73% points at best, respectively. Calibration improved pulpwood fraction significantly, which contributed to the negligible bias of the estimated entire growing stock.  相似文献   

数值模式的热带气旋强度预报订正及其集成应用   总被引：2，自引：0，他引：2  

余晖  陈国民  万日金 《气象学报》2015,73(4):667-678

提供热带气旋强度预报产品的业务数值天气预报模式有很多,并已表现出一定的预报技巧,为提高对模式热带气旋强度预报产品的定量应用能力,分析2010—2012年7个业务数值模式的西北太平洋热带气旋强度预报,发现预报误差不仅受到模式热带气旋初始强度误差的显著影响,还与热带气旋及其所处环境的初始状况有密切关系,包括热带气旋初始强度、尺度、移速、环境气压、环境风切变、热带气旋发展潜势等。根据这些因子与各模式热带气旋强度预报误差之间的相关性,采用逐步回归方法建立热带气旋强度预报误差的统计预估模型,并通过逐个热带气旋滚动式建模来进行独立样本检验。检验结果表明,基于误差预估的模式订正预报比模式直接输出的热带气旋强度预报有显著改进,在此基础上建立的热带气旋强度多模式集成预报方案相对气候持续性预报方法在12 h有28%的正技巧,在24—72 h则稳定在15%—20%,具有业务参考价值。  相似文献   

A general equation for performance analysis of multi-component propulsor with propeller     

《Applied Ocean Research》2017

An integral panel method (IPM) that treats the different components of multi-component propulsors as a whole is presented for efficient propulsor performance analysis. The IPM requires consider only one blade of the propeller in the performance analysis, which significantly reduces the number of computation grid. The control equations of the IPM are derived in detail for podded propulsors, contra-rotating propellers and hybrid contra-rotating shaft pod propulsors, and based on these derivations, a general control equation for multi-component propulsors with propeller is derived. Comparison between numerical results and experimental data show that the IPM provides good accuracy for the performance analysis of multi-component propulsors with propeller. In addition, the error sources of IPM are discussed, and the reasonableness of these errors is evaluated.  相似文献   

The demographics of energy and mobility poverty: Assessing equity and justice in Ireland,Mexico, and the United Arab Emirates     

《Global Environmental Change》2023

Energy and mobility poverty limits people’s choices and opportunities and negatively impinges upon structural economic and social welfare patterns. It also hampers the ability of planners to implement more equitable and just decarbonization pathways. Research has revealed that climate policies have imposed a financial burden on low-income and other vulnerable groups by increasing food and energy prices, leading as well to global inequality. Similarly, researchers have warned that in developing countries, emission mitigation policies could increase poverty rates and even frustrate progress towards universal access to clean energy. This research explores whether low-income social groups experience a 'double energy vulnerability', a situation that simultaneously positions people at heightened risk of transport and energy poverty. We investigate this 'double vulnerability' through original data collection via three nationally representative surveys of Mexico (N = 1,205), the United Arab Emirates (N = 1,141), Ireland and Northern Ireland (N = 1,860). We draw from this original data to elaborate on the sociodemographic attributes, expenditure and behaviour emerging from energy and transport use, focusing on themes such as equity, behaviour and vulnerability. We propose energy and transport poverty indexes that allow us to summarize the key contributing factors to energy and transport poverty in the countries studied and uncover a strong correlation between these two salient forms of poverty. Our results suggest that energy and transport poverty are common issues regardless of the very different national, and even sub-national, contexts. We conclude that energy and transport poverty requires target policy interventions suitable for all segments of society, thus enabling contextually-tailored, just energy transitions.  相似文献   

Multi-hazard susceptibility mapping based on Convolutional Neural Networks     

《地学前缘(英文版)》2022,13(5):101425

Multi-hazard susceptibility prediction is an important component of disasters risk management plan. An effective multi-hazard risk mitigation strategy includes assessing individual hazards as well as their interactions. However, with the rapid development of artificial intelligence technology, multi-hazard susceptibility prediction techniques based on machine learning has encountered a huge bottleneck. In order to effectively solve this problem, this study proposes a multi-hazard susceptibility mapping framework using the classical deep learning algorithm of Convolutional Neural Networks (CNN). First, we use historical flash flood, debris flow and landslide locations based on Google Earth images, extensive field surveys, topography, hydrology, and environmental data sets to train and validate the proposed CNN method. Next, the proposed CNN method is assessed in comparison to conventional logistic regression and k-nearest neighbor methods using several objective criteria, i.e., coefficient of determination, overall accuracy, mean absolute error and the root mean square error. Experimental results show that the CNN method outperforms the conventional machine learning algorithms in predicting probability of flash floods, debris flows and landslides. Finally, the susceptibility maps of the three hazards based on CNN are combined to create a multi-hazard susceptibility map. It can be observed from the map that 62.43% of the study area are prone to hazards, while 37.57% of the study area are harmless. In hazard-prone areas, 16.14%, 4.94% and 30.66% of the study area are susceptible to flash floods, debris flows and landslides, respectively. In terms of concurrent hazards, 0.28%, 7.11% and 3.13% of the study area are susceptible to the joint occurrence of flash floods and debris flow, debris flow and landslides, and flash floods and landslides, respectively, whereas, 0.18% of the study area is subject to all the three hazards. The results of this study can benefit engineers, disaster managers and local government officials involved in sustainable land management and disaster risk mitigation.  相似文献