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101.
Review of River Bank Erosion Research 总被引:1,自引:0,他引:1
Riverbank erosion is a critical style of lateral channel change. It threatens the arable land, ecological environment, as well as the people’s lives and properties along the river. Through review on the research process of riverbank erosion globally, four aspects were classified and described: ①Riverbank erosion processes and mechanisms. The occurence and development of riverbank erosion is quite complicated, composed by multiple processes, which are hard to separate with each other. Therefore, the scholars have proposed a lot of theories to describe the processes. Among the theories, “Riverbank Stability Theory” has been widely recognized and developed. ②Factors of riverbank erosion. The key factors that affect riverbank erosion include hydrology conditions of the river, soil properties, geomorphology, vegetation of the river bank and meteorology. However, it should be noted that the importance of different factors in the collapse process is not equivalent and effects of the same factor on different rivers are various. ③Riverbank erosion estimation. With the tremendous improvement of quantification recently, time interval of erosion measurement is shortening continuously, while spatial scale is larger and larger. At the same time, resolution is becoming increasingly high. Erosion pin was commonly used in early studies because of its easy use and low cost, whereas remote sensing and digital photogrammetry have more advantages in modern measurement. ④Modeling of riverbank erosion. At present, the models are mainly based on the fundamental theories of hydraulics and soil mechanics, to study river bank stability. According to the review of the four aspects above, problems of recent researches and prospects of possible development in the future were discussed. The researchers should pay much attention to temporal spatial distribution of riverbank erosion first before further research. The study would be greatly helpful to the researchers for the specific river reach when choosing the proper theories as well as technologies for measurement and quantification, study the riverbank erosion through both macroscopic and microscopic views, and predict the erosion for management purpose. 相似文献
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The measurements of the photosynthetic photon flux density (Qp) and other solar components have been in Beijing for 2-year period. The Qp, broadband solar radiation (Rs) and the PAR fraction (Qp / Rs) showed similar seasonal features that peaked in value during the Summer and reached their lowest value during the Winter. The PAR fraction ranged from 1.68 E M J− 1 (Winter) to 1.98 E M J− 1 (Summer) with an annual mean value of 1.83 E M J− 1. The analysis of the hourly values also revealed a diurnal pattern, with higher values of Qp and Rs being observed around noon. The PAR fraction increased from 1.78 to 1.89 μE J− 1 (hourly values), as the sky conditions changed from clear to cloudy. The monthly mean hourly PAR fraction also revealed a diurnal variation, however, with lower values being observed around noon during most months. In November, the diurnal variations showed an opposite feature in comparison with other months. This is mainly attributed to the diurnal variations in the water vapor concentration.Two models were developed to estimate Qp from Rs. The models consisted of atmospheric parameters that were found to cause substantial changes to the PAR fraction, such as sky clearness, brightness and path length. The estimated Qp obtained via different equations was much closer to the observed values, with relative errors below 20% in Beijing. The Qp and Rs data collected at three stations with featuring different climate types from within Beijing were used for verifying the transferability of the models. The correlation coefficients between the measured and estimated Qp values decreased at these stations, and the relative error increased. This indicates that the estimation models need to be modified accordingly for the local climatic conditions. 相似文献
105.
地质统计学在固体矿产资源/储量分类中的应用 总被引:14,自引:6,他引:14
讨论了地质统计学(空间信息统计学)在固体矿产资源/储量分类中的若干问题,主要包括:1)矿产资源/储量估计方法的选择;2)两个重要概念-估计方差及离差方差;3)支持效应及其在矿产资源/储量评估中的重要作用;4)特异值(特高品位)的识别及处理方法;5)关于吨位-品位曲线;6)确定最优勘探网度及取样间距(及位置)的地质统计学方法;7)地质统计学在确定最优矿床工业指标中的应用;8)储量计算及固体矿产资源/储量分类的地质统计学实施方案。 相似文献
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Data assimilation with inequality constraints 总被引:1,自引:0,他引:1
If values of variables in a numerical model are limited to specified ranges, these restrictions should be enforced when data are assimilated. The simplest option is to assimilate without regard for constraints and then to correct any violations without worrying about additional corrections implied by correlated errors. This paper addresses the incorporation of inequality constraints into the standard variational framework of optimal interpolation with emphasis on our limited knowledge of the underlying probability distributions. Simple examples involving only two or three variables are used to illustrate graphically how active constraints can be treated as error-free data when background errors obey a truncated multi-normal distribution. Using Lagrange multipliers, the formalism is expanded to encompass the active constraints. Two algorithms are presented, both relying on a solution ignoring the inequality constraints to discover violations to be enforced. While explicitly enforcing a subset can, via correlations, correct the others, pragmatism based on our poor knowledge of the underlying probability distributions suggests the expedient of enforcing them all explicitly to avoid the computationally expensive task of determining the minimum active set. If additional violations are encountered with these solutions, the process can be repeated. Simple examples are used to illustrate the algorithms and to examine the nature of the corrections implied by correlated errors. 相似文献
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109.
The ZRE is a very complicated estuary with multi-river inlets. The total sum of river discharge in the upstream(away from the tidal influence region) of the Zhujiang River can be easily measured. However, when the total river discharges into the estuary from eight inlets, it is a very difficult task to obtain a continuous river discharge flux data from each branch of the Zhujiang River. However, the different ratios of river discharges between the river branches can significantly affect the estuarine circulation feature and baroclinic process. Moreover, the accuracy of numerical forecast for the estuarine circulation is very much dependent on the accuracy of the time history of the river discharge flux for each branch. Therefore, it is important to estimate river discharge from each branch in order to improve the accuracy of the model forecast for the circulation of the ZRE. The development of a new estimation method of the river discharges is focused on based on the system identification theory, numerical modeling and the time history data from the CODAR observed sea surface current. The new approach has been appfied to estimating the time history (hourly) of river discharge from each branch in the upstream of the ZRE. 相似文献
110.
Luliang Tang Xia Zhang Fei Sun Xue Yang Qingquan Li 《International journal of geographical information science》2016,30(9):1717-1737
ABSTRACTKernel Density Estimation (KDE) is an important approach to analyse spatial distribution of point features and linear features over 2-D planar space. Some network-based KDE methods have been developed in recent years, which focus on estimating density distribution of point events over 1-D network space. However, the existing KDE methods are not appropriate for analysing the distribution characteristics of certain kind of features or events, such as traffic jams, queue at intersections and taxi carrying passenger events. These events occur and distribute in 1-D road network space, and present a continuous linear distribution along network. This paper presents a novel Network Kernel Density Estimation method for Linear features (NKDE-L) to analyse the space–time distribution characteristics of linear features over 1-D network space. We first analyse the density distribution of each linear feature along networks, then estimate the density distribution for the whole network space in terms of the network distance and network topology. In the case study, we apply the NKDE-L to analyse the space–time dynamics of taxis’ pick-up events, with real road network and taxi trace data in Wuhan. Taxis’ pick-up events are defined and extracted as linear events (LE) in this paper. We first conduct a space–time statistics of pick-up LE in different temporal granularities. Then we analyse the space–time density distribution of the pick-up events in the road network using the NKDE-L, and uncover some dynamic patterns of people’s activities and traffic condition. In addition, we compare the NKDE-L with quadrat method and planar KDE. The comparison results prove the advantages of the NKDE-L in analysing spatial distribution patterns of linear features in network space. 相似文献