The effect of atmospheric and topographic correction on pixel-based image composites: Improved forest cover detection in mountain environments

Quantification of forest cover is essential as a tool to stimulate forest management and conservation. Image compositing techniques that sample the most suited pixel from multi-temporal image acquisitions, provide an important tool for forest cover detection as they provide alternatives for missing data due to cloud cover and data discontinuities. At present, however, it is not clear to which extent forest cover detection based on compositing can be improved if the source imagery is firstly corrected for topographic distortions on a pixel-basis. In this study, the results of a pixel compositing algorithm with and without preprocessing topographic correction are compared for a study area covering 9 Landsat footprints in the Romanian Carpathians based on two different classifiers: Maximum Likelihood (ML) and Support Vector Machine (SVM). Results show that classifier selection has a stronger impact on the classification accuracy than topographic correction. Finally, application of the optimal method (SVM classifier with topographic correction) on the Romanian Carpathian Ecoregion between 1985, 1995 and 2010 shows a steady greening due to more afforestation than deforestation.     

地图要素图形冲突处理方法——以线状要素(道路、水系和境界)为例

按照目前的专业制图规范对地图表达的质量要求,计算机制图原理和技术无法避免制图过程中需要大量人工处理地图要素图形冲突的工作。这种由于数据模型间(数字地理景观模型与数字制图模型间)的差别而产生的技术难题一直是实现快速制图的瓶颈。本文基于"先处理、后符号化"的策略,通过分析引起图形冲突的形式以及地图制图规范对冲突处理的要求,提出了针对图形重叠和图形衔接两类图形冲突处理的基本操作,即将对地图要素(地理要素符号化)的图形处理转变为对地理要素本身的处理,从而减少了后期图形冲突处理的工作量;基于这些基本操作,以地形图制图中产生大量冲突处理的道路、水系和境界要素类型为例,说明如何综合利用这些基本操作,实现对图面冲突自动处理的方法;最后,两幅实际地形图数据试验表明本操作可以提高制图效率。     

Evaluating methods to quantify sediment volumes trapped behind check dams,Salda(n)a badlands (Spain)

The determination of sediment yield in catchments based on the sediment trapped by check dams is becoming a subject of interest.In fact,several methods have been developed in recent years to estimate the sediment retained by check dams.The complexity,precision and accuracy of each method vary greatly.In this study,we evaluate the sediment trapped by check dams comparing the Sections method respect to the Prism,Pyramid,DTMs and Trapezoid methods.We analyzed a sample of 25 check dams(α-1=90%;ε=10%) in the Saldana badlands(Spain).The results showed that the Sections method offered a volume of retained sediment between the others,which gave an absolute variation from 22%to40%.The high variability of the check dam and sediment wedge sizes made necessary to compare methods in groups combining both characteristics.No significant differences in sediment volumes could be found between the methods for very small(height(h):1.8-2.3 m;trapped volume(V):6-102 m~3) or large check dams(h 2.3 m;V:165-387 m~3),while significant differences are found for small(h 1.5 m;V:1-229 m~3) or middle-sized check dams(h:2.2-3.2 m;V:65-235 m3).Nevertheless,volume differences between groups ranged up to + 25%.For these reason,the size of the check dam,the shape of the sediment wedge and the accuracy of the measure methods must considered when selecting an appropriate method to obtain the volume of retained sediment by check dams.A correct estimation of the sediment retention is needed to evaluate the role and efficiency of check dams in restoration projects or to estimate sediment yields.     

地形起伏对基于地震波形的浅源地震深度反演影响——以2017年9月3日朝鲜M6.3事件为例

震源深度是核试验以及塌陷等浅源地震研究中的关键参数,可以为事件成因分析提供关键信息.然而朝鲜核试验区域地形起伏较大,地形效应可能对震源深度反演的结果造成影响.本文基于理论地震图进行测试,研究了地形起伏对震源深度反演的影响.发现震源深度小于2km时,不考虑地形影响,反演得到的震源深度会系统偏浅0.2km左右.然后利用MDJ2速度结构模型,我们反演了2017年9月3日朝鲜M6.3事件的震源参数,结果显示震源深度约为0.8km.进一步基于带地形的格林函数重新反演了该事件的震源深度,发现在1km处波形拟合结果较好.不同速度模型测试结果显示该事件的震源深度反演误差约为1km.案例研究表明,基于层状均匀速度模型,利用区域地震波形资料反演的震源深度可以为浅源事件成因分析提供关键约束.     

从科索沃战争看数字地图在现代高技术战争中的作用

分析了科索沃战争中美军测绘保障状况, 特别是数字地图在指挥自动化、武器控制和数字化战场建设中所起的重要作用, 提出从５ 个方面加强军事测绘高技术研究, 为打赢未来高技术局部战争提供强有力的测绘保障。     

Amplification effects from earthquakes and ambient noise in the Dead Sea rift (Israel)

Seven sites were instrumented in the Parsa area located in the seismically active Dead Sea rift system. Moderate and weak motions generated by earthquakes and ambient noise were used to identify amplifications due to geological and topographic effects.Three observation methods were applied to estimate site effects: (1) conventional soil–bedrock station-pair spectral ratios for earthquake motions and microtremors; (2) horizontal-to-vertical component spectral ratios for shear-waves observed simultaneously at a site (receiver function estimates) and (3) horizontal-to-vertical spectral ratios of microtremor measurements (Nakamura estimate). The site response spectra of soil sites exhibited significant peaks between 1 and 3 Hz with amplification factors typically within the range of 2.5–4.0. A bedrock site on the high plateau near the escarpment top showed a peak between 2 and 3 Hz, mainly due to an EW oscillation of the NS topographic feature. Our observations indicated that seismograms recorded in the tunnel were either enriched or depleted at certain frequencies owing to interference of incident and surface-reflected waves.     

Topocaustics

Deep (2000 m) observations near the Sigsbee escarpment in the Gulf of Mexico show short-period (approximately 5–12 days) energetic currents due to topographic Rossby waves (TRW’s). We suggest that the phenomenon is due to the focusing and accumulation of TRW energy by the slopes coupled with a bend in isobaths, in a topographic caustic (topocaustic). The idea draws on a simple mathematical equivalence between the propagation of internal waves and of TRW’s. Topocaustics occur near regions of maximum N_T = N|h| (N = Brunt–Väisälä frequency; h = water depth). Because of the one-sided propagation property of TRW’s, energy also tends to accumulate at the “western” end of closed contours of N_T. The process is demonstrated here using a nonlinear primitive-equation numerical model with idealized bathymetry and forcing. A Gulf of Mexico simulation initialized with a data-assimilated analysis covering the period of the Sigsbee observation is then conducted. The mooring is near a localized maximum N_T, and Intrinsic Mode Functions confirm the existence of energetic bursts of short-period deep-current events. The strong currents are locally forced from above, either by an extended Loop Current or a warm ring.     

四川地质工作程度数据库的应用及其效果

介绍了四川地质工作程度数据库的建立、应用及其效果。应用情况表明该数据库功能多、使用方便、快捷。     

龙门山沿线暴雨过程的诊断分析及数值试验

利用常规气象观测资料和西南区域模式WRF_RUC产品,对2012年8月17 18日四川盆地西部龙门山脉沿线出现的一次暴雨过程进行了诊断分析和数值试验。结果表明,对流层中低层明显高能、高湿,大气层结极不稳定,为中尺度对流系统的生成和发展提供了有利的热力不稳定条件;对流发展与低层偏东气流密切相关,暴雨开始前,四川盆地内低层偏东气流增强,使盆地西部沿山地区辐合和地形抬升作用增强,是造成垂直上升运动强烈发展的主要动力机制;降低高原地形高度,暴雨区明显西移;降低盆地内初始场温湿条件,降水强度明显减弱;不考虑地面热通量影响,降水强度也将有一定减弱。     

The influence of topography on the cloud-to-ground lightning density in South Brazil

A comparative analysis between cloud-to-ground (CG) lightning density and terrain parameters (altitude and terrain slope) in South Brazil is presented. This region is characterized by a contrasting topography, where a mountain chain separates lower (depression) and higher (plateau) landscapes. The altitude and terrain slope data were obtained from the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM). Two years of CG lightning data (from June 2005 to May 2007) obtained by the Brazilian Lightning Detection Network (BrasilDAT) were used in the study. To avoid intracloud contamination, positive CG flashes with peak currents less than 20 kA were removed from the data set. A relative detection efficiency model was used to correct the lightning data. The results indicate that, for localized areas (following the mountain shape) within this region of Brazil, the CG lightning density is correlated with the terrain slope and not the altitude. This suggests that terrain slope has more influence than altitude on the thunderstorm occurrence and lightning activity. In addition, a temporal analysis shows that over high altitude regions the diurnal variation (amplitude) of lightning activity is stronger and the peak occurs 1 h earlier than over low altitude regions.