汉江上游现代大洪水滞流沉积物的粒度分布特征研究

对汉江上游现代大洪水高水位滞流沉积物(SWD)系统地采样测试分析,结果表明:汉江上游现代大洪水SWD沉积物性质是沙质粘土或粘土质沙、沙质粉沙或粉沙质沙。其分布特征大致分为两大类:安康段以上基本是以粉沙质沙或沙质粉沙为主,安康段以下基本是沙质粘土或粘土质沙。粒度成分和粒度参数都反映现代洪水SWD经过充分的分选,但是受多种因素影响,其粒径组成具有明显的空间变化。水库或大坝对大洪水SWD的粒度自然分布频率单峰曲线尖窄的形状没有明显的影响,而更多与其沉积的微地貌环境和水动力条件有关。     

大型测绘工程标准化——以国家西部测图工程为例

大型测绘工程的标准化工作是保障工程效率和质量的重要工作。本文提出大型测绘工程标准化工作的分步研制、试验验证、重视反馈等一组工作方法,并提出在建立大型测绘工程标准体系时宜较多视点思考,忌太小粒度划分原则。以国家西部测图工程标准化为例,证明上述方法和原则的可行性。     

计算机兵棋棋盘中投影变形及坐标转换问题研究

兵棋是对作战过程进行逻辑推演研究和评估的军事科学工具,其三大组成要素包括棋盘、棋子和规则。棋盘的经典样式就是六角格兵棋棋盘,计算机兵棋中也常采用六角格棋盘描述战场地形环境,而棋盘的投影变形和坐标转换分别是制约兵棋推演可信度和推演效率的重要因素。首先分析了棋盘所用投影方式的变形规律,提出了个体值法和平均值法对变形进行修正;然后针对经纬度坐标和六角格编码的转换,提出了直接转换和间接转换两种方法,分析其基本转换原理,并给出了坐标转换公式;最后通过实验对所述方法进行验证,结果证实平均值法对于修正投影变形具有很好的实用性,且间接坐标转换法具有更高的转换效率。     

An application of Coons patch to generate grid-based digital elevation models

We have presented a new method for generating grid-based digital elevation models (DEMs) based on Coons patch. A series of Gaussian synthetic surfaces with various surface complexities were employed to comparatively analyze the simulation accuracies of Coons patch and the classical interpolation methods, such as IDW, Natural neighbor, SPLINE and KRIGING. Results indicate that irrespective of terrain complexity, Coons patch is much more accurate than the classical interpolation methods, and the accuracy of Coons patch is about 327.30, 15.19, 3.66 and 40.07 times as high as the accuracies of IDW, Natural neighbor, SPLINE and KRIGING on average. A real-world test area was used to test the effect of sampling density on the simulation accuracy. The results indicate that Coons patch has a higher accuracy than the classical interpolation methods regardless of sampling density. In a word, Coons patch as an accurate interpolation method can be used for grid-based DEM construction.     

An Examination of ENSO’s Effect on the Monthly and Seasonal Climate of Hong Kong from a Statistical Perspective

This study aims to examine the effect of El Nino and La Nina on the monthly and seasonal climate of Hong Kong against the ENSO-neutral situation from a statistical perspective. Monthly and seasonal temperature and rainfall of Hong Kong and monthly number of tropical cyclones (TCs) coming within 500 km of the city over the 59-yr (1950-2008) period are examined under three ENSO situations, namely El Nino, La Nina, and ENSO-neutral. It is found that, compared with the ENSO-neutral situation, El Nino tends...     

气溶胶光学厚度谱特征判断粒子大小方法初探

当气溶胶谱满足Junge分布时,Angstrom指数 (α) 可以准确地描述粒子大小,但真实大气气溶胶很少完全满足这一条件,仅用α判断粒子大小会有较大出入。基于北京、香河、兴隆、太湖4个Aeronet观测站21世纪以来各站历时都超过1年的气溶胶光学厚度资料,获得5511组lnτ与lnλ的二次拟合参数a₂,a₁,尝试找到一种结合α,a₂,a₁判断粒子大小的方法。结果表明:当气溶胶为粗粒子时 (V_fine/V_total＜0.2),α均小于0.75,仅用α就可以较好地判断粒子大小,但当气溶胶以细粒子为主时 (V_fine/V_total＞0.7),该方法会有较大出入,此时a₂,a₁可以有效地辅助α判断粒子大小,α＞0.75,a₂＜-0.5或a₂＜-0.5,a₁＜-1.0是较好的判据。此外,分析发现国外研究提出的用a₂-a₁判断粒子大小的方法效果并不理想,尤其在1＜a₂-a₁＜2的情况下,粒子的组成有多种可能。     

Rainfall uncertainty for extreme events in NWP downscaling model

Limited area numerical weather predication (NWP) models such as MM5 have become a popular method for generating rainfall estimates for hydrological analysis, particularly for catchments where rainfall data are sparse. Although several studies have been undertaken to investigate the appropriateness of MM5 parameterization schemes for hydrological applications, the size of the nested domains and the distance between them have been overlooked as a source of uncertainty in model precipitation estimates for hydrological purposes. This study examines the uncertainty of model rainfall estimates derived from MM5 by varying the domain size and the distance between the domains. The results from this study show that domain size and buffer zone have a significant impact on model rainfall estimates, which should not be overlooked by hydrologists. Copyright © 2010 John Wiley & Sons, Ltd.     

Variations in texture of beach sediments in the vicinity of the Tirumalairajanar river mouth of India

The distribution of grain size parameters along 11 km stretch of the beach sediments between Karikal and Nagore,reveals that the mean grain size exhibits a marked decreasing trend on either side of the mouth of the Tirumalairajanar River which flow from west to east.The sediments are mainly of medium to coarse grained,moderately sorted,near-symmetrical skewed to fine skewed and leptokurtic to mesokurtic in nature.Interrelationship of various parameters shows bimodal nature of sediments having dominance of medium to coarse sand.The major part of the sediment fall in a coarse to fine grained category(sand and silt).Based on the CM(Coarser one percentile value in micron) pattern,the sediment fall in rolling and suspension field.These factors includes the sediments discharged from the river mixes with offshore sediments and with the sediments eroded from a source rock.The effect of wave sorting, and the northward drifting of sediments by littoral current are understandable.Results indicate that the Tirumalairajanar River is the most important source for modern sediments in the study area.The agitation by waves is an important sorting mechanism in the study area,and the net sediment transport in the study area is northward.The findings are based on the grain sizes and also corroborated by shortterm observations of the beach sediment dynamics and transport during the monsoon and summer seasons between Karaikal and Nagore region.     

Plastic marine debris on the Portuguese coastline: a matter of size?

Plastic debris is a worldwide threat to marine environments and Portugal is not immune to it. Though never quantified, items of all sizes can be found in the Portuguese coastline; therefore the objective of this work is the identification of main size classes in stranded plastic debris. Beaches sediment was sampled and in the laboratory plastic items were sorted in 11 classes from <1 to >10 mm, counted and weighted. Plastic size ranged from 50 μm to 20 cm and microplastics (<5 mm) were the majority (72%). Most plastic fits in the smaller size classes, due to expected high residence time in the sea enhancing degradation processes, which increase surface exposure and potentially persistent organic pollutants (POP) adsorption. These results point out the important contribution of microplastics to marine debris pollution, its risks, and the need to set a higher focus on this size class.     

Vertical mixing of gravel over a long flood series

Vertical sediment exchange is a fundamental component of bedload transport in gravel‐bed channels. This paper describes the characteristic depth of exchange achieved over a long flood series. Analysis is based on 11 recoveries of magnetically tagged gravels deployed in Carnation Creek, Canada, completed between 1990 and 2008. Vertical grain exchange mixes gravels throughout the streambed relatively rapidly. Within one to eight floods the mean burial depth approaches two times the surface layer thickness, quantified by the 90th percentile of the size distribution. Finer gravels are mixed more rapidly into the bed than coarser gravels. Both active and passive grain exchanges throughout most of the bed produce the overall vertical distribution of marked grains. Gravel exchanges exhibit fairly consistent patterns once tracers are well mixed by large floods. Results highlight the role of flood sequence in determining exchange depths, support the notion of an upper limit to exchange, and underscore the importance of passive grain exchange. Copyright © 2011 John Wiley & Sons, Ltd.