The rainfall intensity–duration control of shallow landslides and debris flows: an update     

Fausto Guzzetti  Silvia Peruccacci  Mauro Rossi  Colin P. Stark 《Landslides》2008,5(1):3-17

A global database of 2,626 rainfall events that have resulted in shallow landslides and debris flows was compiled through a thorough literature search. The rainfall and landslide information was used to update the dependency of the minimum level of rainfall duration and intensity likely to result in shallow landslides and debris flows established by Nel Caine in 1980. The rainfall intensity–duration (ID) values were plotted in logarithmic coordinates, and it was established that with increased rainfall duration, the minimum average intensity likely to trigger shallow slope failures decreases linearly, in the range of durations from 10 min to 35 days. The minimum ID for the possible initiation of shallow landslides and debris flows was determined. The threshold curve was obtained from the rainfall data using an objective statistical technique. To cope with differences in the intensity and duration of rainfall likely to result in shallow slope failures in different climatic regions, the rainfall information was normalized to the mean annual precipitation and the rainy-day normal. Climate information was obtained from the global climate dataset compiled by the Climate Research Unit of the East Anglia University. The obtained global ID thresholds are significantly lower than the threshold proposed by Caine (Geogr Ann A 62:23–27, 1980), and lower than other global thresholds proposed in the literature. The new global ID thresholds can be used in a worldwide operational landslide warning system based on global precipitation measurements where local and regional thresholds are not available..  相似文献   

Jason-2卫星阈值重跟踪算法比较     

范雕  李姗姗  孟书宇  曲政豪  刘帆  冯进凯 《测绘科学技术学报》2017,34(2)

选取Jason-2卫星在中国南海北纬15°~18.5°范围1 276个波形数据,依据Threshold算法和SeaIce算法对波形进行重跟踪,得到不同阈值水平下的距离改正结果。结果表明:当星下点轨迹靠近陆地时,距离改正值增大。然后,依据不同方法、不同阈值水平对应的距离改正值对卫星观测的海面高实施修正,得到相应的海面高结果。作为验证,选取法国国家太空研究中心(CNES)发布的海面高作为外部检核条件。将修正后的海面高与CNES公布的海面高进行较差比较,较差值的统计分析表明:SeaIce重跟踪算法在阈值水平为50%时,差值的标准差明显小于其他方法的计算结果。  相似文献   

These lit areas are undeveloped: Delimiting China’s urban extents from thresholded nighttime light imagery     

《International Journal of Applied Earth Observation and Geoinformation》2016

Nighttime light imagery is a powerful tool to study urbanization because it can provide a uniform metric, lit area, to delimit urban extents. However, lit area is much larger than actual urban area, so thresholds of digital number (DN) values are usually needed to reduce the lit area. The threshold varies greatly among different regions, but at present it is still not very clear what factors impact the changes of the threshold. In this study, urban extent by province for China is mapped using official statistical data and four intercalibrated and geometrically corrected nighttime light images between 2004 and 2010. Lit area in the imagery for most provinces is at least 94% greater than the official amount of urban area. Regression analyses show a significant correlation between optimal thresholds and GDP per capita, and larger thresholds more commonly indicate higher economic level. Size and environmental condition may explain a province’s threshold that is disproportionate to GDP. Findings indicate one threshold DN is not appropriate for multiple (adjacent) province urban extent mapping, and optimal thresholds for one year may be notably different than the next. Province-level derived thresholds are not appropriate for other geographic levels. Brightness of nighttime lights is an advantage over imagery that relies on daylight reflection, and decreases in brightness indicate faster growth in the horizontal direction than the vertical. A province’s optimal threshold does not always maintain an increase with population and economic growth. In the economically developed eastern provinces, urban population densities decreased (and this is seen in the brightness data), while urban population increased.  相似文献   

A practical method for outlier detection in autoregressive time series modelling   总被引：1，自引：1，他引：0  

M. C. Hau  H. Tong 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(4):241-260

A practical method is developed for outlier detection in autoregressive modelling. It has the interpretation of a Mahalanobis distance function and requires minimal additional computation once a model is fitted. It can be of use to detect both innovation outliers and additive outliers. Both simulated data and real data re used for illustration, including one data set from water resources.  相似文献   

Wind tunnel modeling and measurements of the flux of wind-blown sand   总被引：1，自引：0，他引：1  

X. Liu  Z. Dong  X. Wang 《Journal of Arid Environments》2006,66(4):657-672

This paper presents a way to empirically fit experimental data for the horizontal flux of various sizes of wind-blown dry sand using data from wind tunnel experiments. We measured vertical wind profiles to derive threshold shear velocity and estimated shear velocity and the flux of sand mass as a function of the height for nine different grain sizes. We propose a fitting model based on the experimental data and a least-squares method and derive an explicit form of sand flux as a function of height and shear velocity for these grain sizes. We also obtained an explicit form of the empirical equation for the measurement of sand transport per unit width and unit time by integrating the empirical equation as a function of height. Finally, we compared the effectiveness of Bagnold's equation, Kawamura's expression and Lettau and Lettau's equation, for predicting sand transport with the results of our empirical equation. The results show that the transport predicted by all of the equations were always lower than the measured results from the empirical equation for all grain sizes and shear velocities. However, the empirical equation matched Bagnold's equation, Kawamura's equation, and Lettau and Lettau's equation if the coefficients in these equations were adjusted instead of using their original coefficients. The empirical equation for sand transport in the present study contradicts previous conclusions generated by Bagnold's equation, which predict that for a given wind drag, the transport of a coarse sand is greater than that of a fine sand.  相似文献   

自动提取土地利用变化信息后处理方法的研究   总被引：1，自引：1，他引：1  

吴海平  黄世存 《国土资源遥感》2005,16(1):41-44

 研究目的是对计算机自动提取的土地利用变化信息进行后处理，以提高信息提取精度； 研究方法是模板判断法，该方法有效 地改善了单像元判断的效果，提高了变化信息的提取精度，可以应用于土地利用动态遥感监测。  相似文献   

基于MATLAB的遥感图像变化检测     

张孟君  李晨钊  舒红  杨志敏 《国土资源遥感》2005,(4):16-19,23

主要讨论了遥感图像变化检测的图像几何配准和阈值选取理论,利用MATLAB强大的数值计算功能实现了遥感图像变化检测.在拓展数学符号计算软件包MATLAB应用领域的同时,探索了一种遥感图像处理软件的快速开发方式.  相似文献   

Thresholds in small rivers? Hypotheses developed from fluvial morphological research in western Germany     

Stefan Harnischmacher   《Geomorphology》2007,92(3-4):119

The objective of this study was the formulation of fluvial morphological regularities for small rivers with a wide range of morphological and geological characteristics in North-Rhine-Westphalia (Germany) based on a statistical research methodology. Such empirical quantitative information on reference conditions is required for the restoration of small rivers in the former highly industrialised Ruhr-Area. Following the approach of some classic empirical works in fluvial morphology of the last century, several natural reference rivers in the entire research area have been observed in order to provide a statistical correlation between independent and dependent morphological variables. Regressions between valley-floor slope, bankfull discharge and stream power on the one hand and several variables describing the longitudinal profile and river planform on the other hand have shown some significant results. The regularities found are a quantitative contribution to the establishment of reference conditions as well as a useful tool for the restoration of small rivers, if the specific properties and values of the underlying random sampling are taken into account. In addition, the relation between stream power and sinuosity shows the likely existence of a threshold: Exceeding a stream power of 100 W/m, the sinuosity decreases after an increase for lower stream power values. Comparable thresholds were found for the relation between stream power and pool depth as well as stream power and step steepness. The thresholds could be explained by a change in the type of energy dissipation, due to different physio-geographical settings in highland rivers within forested v-shaped valleys. Here, large-woody debris seems to increase the channel roughness and possibly replaces the significance of coarse-grained bed material, pool depth and step steepness as contributors to energy dissipation.  相似文献   

沙尘天气过程沙地下垫面沙尘通量的获取与分析研究   总被引：9，自引：0，他引：9  

张宏升  朱好  彭艳  康凌  陈家宜  Soon-Ung Park 《气象学报》2007,65(5):744-752

利用浑善达克沙地地区2004年春季沙尘暴和微气象学加强观测实验资料,计算了浑善达克沙地地区不同沙尘天气条件下湍流交换系数、湍流动量通量和感热通量、沙尘浓度通量;研究了沙尘暴过程中湍流作用、沙尘输送特征及起沙条件。结果显示:浑善达克沙地地区非沙尘天气白天近地层热力湍流作用强于动力湍流,湍流交换以感热交换为主;沙尘天气过程中,近地面层湍流动力作用明显增加,湍流动量和感热交换都对湍流输送有主要贡献,感热通量数值有不同程度的降低。较强沙尘暴天气过程中动力湍流强于热力湍流。随着沙尘天气经历起沙、平衡、沉降的演变过程,沙尘通量数值呈现由正值为主,过渡到向上和向下数值相当、向下数值比例增加。非沙尘天气、扬沙天气和沙尘暴天气过程的沙尘通量值范围分别是±5μg/(m2.s)、±30μg/(m2.s)和-200—300μg/(m2.s)之间。浑善达克沙地地区,非沙尘天气也存在一定量的沙尘输送,但数值较小。浑善达克沙地地区沙尘通量与摩擦速度的三次方成正比,为F=Cu3*。临界起沙风速和临界摩擦速度分别约为6m/s和0.4m/s。  相似文献   

基于TM的城市温度异常区分析     

黄妙芬  陈波  刘素红  程灿  彭睿 《国土资源遥感》2007,18(3):23-27

利用实时探空数据和单窗算法对2004年7月6日北京市TM图像进行地表温度反演，根据反演结果，采用阈值法将北京城区地表温度空间分布分为植被正常温度区、水体正常温度区、水体高温区、裸地正常温度区、建筑物低温区、建筑物正常温度区、建筑物高温区、植被建筑物混合高温区和植被建筑物混合正常温度区等9种模式。在此基础上，对水体高温区、植被建筑物混合高温区、建筑物低温区和建筑物高温区等4种温度异常区进行了实地抽样调查，详细分析了这些温度异常区形成的原因。  相似文献