大同及邻区地震网格化相关分析及预测意义     

沙海军  刘冬英 《中国地震研究》2012,26(3):391-398

利用华北地区1970年～2009年的ML3.0级以上地震资料,使用相关分析方法,研究了大同及邻区的中小地震空间分布模式,及其在该区中强地震前的异常情况。研究工作首先是确定空间范围、时间窗和时间滑动步长,然后将地震的空间分布进行网格化再转化为序列;对一个时段和它的稍长时段的地震空间分布进行序列化,计算两个序列的相关系数;并分析相关系数在中强地震前是否明显变化。计算结果表明：当空间取以1989年大同-阳高5.9级地震震中为中心,经向长度和纬向长度均为1.6度的矩形区域,时段长度取3600天,稍长时段取3700天,滑动步长取100天的情况下,1980年～2009年的相关系数时间序列数值整体上稳定,在0.94～1之间波动,但在1989年山西大同-阳高5.9级地震、1991年山西大同5.8级地震与1999年山西浑源5.6级地震前2年均出现过相关系数小于0.94的异常现象,表明地震的空间分布上出现明显变化。并讨论了相关系数异常对于中强地震的前兆意义,可以得到以下3点认识：（1）大同及周边地区的中强地震前,中小地震空间分布模式发生显著变化,可作为2年尺度的震兆异常,为该区中期地震预测提供时间上的参考;（2）考虑到研究区的限定范围为震中周边0.8度以内,地震时空分布的相关分析结果对于地震地点的预测也具有指示意义;（3）相关分析可以为识别此类地震空间分布模式的异常变化提供帮助。  相似文献   

Patterns of spatial variation of nutrient content,epiphyte load and shoot size of Posidonia oceanica seagrass meadows (Mediterranean Sea)     

Inés Castejón‐Silvo  Jorge Terrados 《Marine Ecology》2012,33(2):165-175

Knowledge of patterns of spatial variability of vegetative development, epiphyte load and nutrient availability in seagrass meadows is essential for the adequate design of research and environmental monitoring programmes. Differences in shoot size, epiphyte load and nutrient content of leaves and epiphytes of the Mediterranean endemic seagrass Posidonia oceanica at spatial scales ranging from metres to hundreds of metres are evaluated using a hierarchical nested sampling design. The size and epiphyte load of P. oceanica shoots and the nitrogen and phosphorus content of leaves and epiphytes were different in most of the spatial scales considered. Sampling efforts concentrated at the metre scale incorporated most of the variability in size, epiphyte load and nutrient content of the leaves and epiphytes of P. oceanica shoots. Epiphyte load showed no correlation with nutrient content in the epiphytes or in the leaves. However, epiphyte load and shoot size were negatively correlated, which suggests that light penetration in the canopy may be a main determinant of epiphyte load.  相似文献   

Predictive vegetation mapping approach based on spectral data, DEM and generalized additive models     

Chuangye Song  Chong Huang  Huiming Liu 《中国地理科学(英文版)》2013,23(3):331-343

This study aims to provide a predictive vegetation mapping approach based on the spectral data, DEM and Generalized Additive Models (GAMs). GAMs were used as a prediction tool to describe the relationship between vegetation and environmental variables, as well as spectral variables. Based on the fitted GAMs model, probability map of species occurrence was generated and then vegetation type of each grid was defined according to the probability of species occurrence. Deviance analysis was employed to test the goodness of curve fitting and drop contribution calculation was used to evaluate the contribution of each predictor in the fitted GAMs models. Area under curve (AUC) of Receiver Operating Characteristic (ROC) curve was employed to assess the results maps of probability. The results showed that: 1) AUC values of the fitted GAMs models are very high which proves that integrating spectral data and environmental variables based on the GAMs is a feasible way to map the vegetation. 2) Prediction accuracy varies with plant community, and community with dense cover is better predicted than sparse plant community. 3) Both spectral variables and environmental variables play an important role in mapping the vegetation. However, the contribution of the same predictor in the GAMs models for different plant communities is different. 4) Insufficient resolution of spectral data, environmental data and confounding effects of land use and other variables which are not closely related to the environmental conditions are the major causes of imprecision.  相似文献   

基于ESDA的河南艾滋病空间格局   总被引：1，自引：0，他引：1  

徐旳  柯文前  陈培阳 《地理研究》2013,32(7):1199-1208

以2008 年河南省地级市艾滋病分布数据为基础,利用ESDA空间数据挖掘的方法,对河南省艾滋病空间格局进行全面分析。结果表明：① 综合考虑河南省18 个地级市艾滋病确诊人数数据的空间自相关分析结果和不同传播途径感染单因素空间格局的结果,将河南艾滋病感染区域分为以FPD感染途径为主的豫南、豫东南高度流行区和以高危行为传播途径为主的豫北低度流行区;② 河南省艾滋病感染途径分布中,FPD感染、母婴感染、异性传播感染和注射吸毒传播具有明显的空间正相关,而同性传播途径与输血感染则显示出较大的空间随机分布特征;③ 与FPD 感染存在空间正相关的为注射吸毒传播、异性传播以及母婴传播方式,输血、同性以及其他方式传播途径与FPD感染途径分布不存在空间相关性。  相似文献   

An Enhanced Remote Sensing Procedure for Material Mapping in the Western Desert of Egypt: A Tool for Managing Urban Development     

Ahmed Mohamed Youssef 《Natural Resources Research》2008,17(4):215-226

Recently, both the Egyptian government and private sector have been interested in developing low desert zone areas. The low desert zones are located between the recent Nile flood plain and the limestone plateau, from the east and west sides, and represent an important source of aggregate materials. The development of these areas, however, will reduce the supply of aggregate materials so that new sources must be identified. This study describes several processing methods, applied to a Landsat Enhanced Thematic Mapper Plus image of 2001, to develop a reliable method to map the aggregate materials. By using different enhancement techniques with the help of a supervised classification method, it was found that decorrelation stretch and principal component analysis are the most suitable methods to discriminate between different types of aggregates, as well as to isolate these aggregates from the surrounding materials. Field and laboratory investigations indicated that two types of aggregates were recognized, confirming the remote sensing findings.  相似文献   

Regional groundwater flow modelling of Upper Chaj Doab of Indus Basin, Pakistan using finite element model (Feflow) and geoinformatics   总被引：1，自引：0，他引：1  

A. Ashraf  Z. Ahmad 《Geophysical Journal International》2008,173(1):17-24

A 3-D finite element model (Feflow) has been used for regional groundwater flow modelling of Upper Chaj Doab in Indus Basin, Pakistan. The thematic layers of soils, landuse, hydrology, infrastructure and climate were developed using Geographic Information System (GIS). The numerical groundwater flow model is developed to configure the groundwater equipotential surface, hydraulic head gradient and estimation of the groundwater budget of the aquifer. Integration of GIS with groundwater modelling and satellite remote sensing capabilities has provided an efficient way of analysing and monitoring groundwater status and its associated land conditions. The Arcview GIS software is used as additive tool to develop supportive data for numerical groundwater modelling, integration and presentation of image processing and modelling results.
The groundwater behaviour of the regional model shows a gradual decline in watertable from year 1999 onward. The persistent dry condition and high withdrawal rates play an influential role in lowering down the groundwater levels. Different scenarios were developed to study the impact of extreme climatic conditions (drought/flood) and variable groundwater abstraction on the regional groundwater system. The results of the study provide useful information regarding the behaviour of aquifer in order to organize management schemes on local and regional basis to monitor future groundwater development in the area.  相似文献   

Invasion of Sargassum muticum in intertidal rockpools: Patterns along the Atlantic Iberian Peninsula     

《Marine environmental research》2013

Spatial patterns of non-indigenous species show scale-dependent properties. Sargassum muticum is an invasive macroalga widely distributed along the Atlantic Iberian Peninsula. Despite being quite abundant from Norway to South Portugal, there is little information about its patterns of distribution, particularly at a large spatial scale (i.e. thousands of kilometres). Here, we examined the spatial variation in the invasion success of S. muticum from rockpools at multiple spatial scales using a hierarchical design. In addition, we analysed how the richness of native assemblages was related to its invasion success and how this relationship changed over different scales. Most of the variation in the invasion success was found at the smallest scales of pool and plot. Furthermore, the invasibility of native macroalgal assemblages was related to the native species richness, but causes that determined invasion success could not be separated from the effects provoked by the invader. Results suggest that small-scale (centimetres to metres) processes contribute considerably to the heterogeneity of S. muticum invasion success.  相似文献   

Physical conditions driving the spatial and temporal variability in aquatic metabolism of a subtropical coastal lake     

《Limnologica》2016

We investigated the importance of meteorological and lake physical conditions for temporal, horizontal and vertical differences in the concentration of dissolved oxygen (DO) and water temperature, and the derived daily estimates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP). Our study was conducted in a subtropical and polymictic lake in Southern Brazil, during a spring–summer transition. Metabolic rates were determined from two sites using the open water oxygen technique. At the central deep site, oxygen sondes were deployed at three depths to assess patterns in vertical variability. During 10 days, an additional DO and temperature sonde was placed near the shoreline allowing us to compare metabolic differences in the surface layers between the central pelagic and littoral site. While GPP was similar, R was significantly higher at the shallower littoral site, causing NEP to be lower, although NEP was still positive. The littoral site had less diel changes in DO and higher daily variability in all metabolic rates. Variability in GPP and R at the littoral site was related to temperature, wind speed and rainfall suggesting that short-term variability in metabolic rates in shallow areas are sensitive to resuspension of sediments caused by a less stable water column. A clear vertical gradient was furthermore found for the metabolic rates at the central deep part of the lake, related to the light extinction, with highest GPP around 0.3 m and decreasing with depth, while respiration showed the inverse pattern. Below subsurface, respiration prevailed at 5.0 m depth and was uncoupled to primary production. Under conditions with high light and temperature, and low wind speeds, the mixing depth became shallower, in turn increasing the water column stability at the deep pelagic site, which resulted in higher mean light available and higher GPP in the water column. Our results confirm that deployment of sensors in different sites and depths allows for spatially, as well as temporally more representative estimates of lake metabolism.  相似文献   

基于小波包和空间相关性分析的人工地震波仿真技术     

黄杜若  王刚  盛志刚 《华南地震》2014,(3)

考虑强震作用下地震动参数的空间相关性,是生命线工程、道路、桥梁等呈空间分布的大型结构抗震设计的重点问题。由于强震观测历史和观测设备的限制,符合设计标准的地震波较为匮乏。因而,人工地震波成为结构抗震时程计算分析的一个重要技术。小波包技术将地震波进行时域和频域分解及合成并通过区域化的强震记录,得出小波包参数在时域和频域的统计特征及其空间相关性。进一步采用克里格插值法对无观测记录场址的地震动小波包参数进行最优估计,从而合成人工地震波。能较好地模拟人工地震波的区域空间相关特征,将为重大工程结构的防灾抗震仿真计算和动力优化设计提供实用可靠的地震波输入。  相似文献   

航空电磁数据主成分滤波重构的噪声去除方法   总被引：1，自引：0，他引：1       下载免费PDF全文

王凌群  李冰冰  林君  谢宾  王琦  程宇奇  朱凯光 《地球物理学报》2015,58(8):2803-2811

主成分分析方法利用低阶主成分重构航空电磁数据,解决了航空电磁探测中噪声与数据在频谱重叠情况下的噪声压制问题,但是参与重构的低阶主成分仍包含高频空间噪声,影响数据成像精度.本文提出的主成分滤波重构去噪方法,根据自适应窗宽平滑算法,设计了主成分低通滤波器组,对参与重构的低阶主成分进行测线滤波,再将滤波后的低阶主成分重构为电磁信号,不仅可以去除低阶主成分中的高频空间噪声,而且去除了高阶主成分包含的不相关噪声.仿真数据的去噪结果表明,主成分滤波重构获得较高的信噪比,较常规测线滤波与主成分重构分别提高了10.96dB和2.52dB;电导率深度成像结果证明了主成分滤波重构方法能够提高地下深部异常体的识别能力.最后通过实测数据的成像结果进一步验证了本文研究的主成分滤波重构去噪方法的有效性.  相似文献