SPATIAL VARIATIONS OF SHEET FLOW AND SEDIMENT TRANSPORT ON AN AGRICULTURAL FIELD

This paper presents the spatial and temporal variations of sheet flow and sediment transport on an agricultural field under natural rainfall. The study site is located in western France (Rennes, Brittany) where rainfall amount and intensity are moderate. It is a field of garden-peas presenting a convex–concave gentle slope where only sheet flow is observed. A network of simple, low-cost collectors is used to measure sheet flow and sediment transport along the slope and to estimate the spatial variability for a given position on the slope. The water and sediment discharge was measured for each rainfall event from February to June. The analysis of space and time variations according to the characteristics of the rainfall events, changes in vegetation and soil crusting shows that the sheet flow is low and the runoff coefficient decreases as the slope length increases. Infiltration is particularly active in concave parts of the hillslope whatever the characteristics of the rainfall events. Sediment transport decreases in time as the soil crusts and vegetation develops.     

东南极Princess Elizabeth冰盖近地层大气参数的年变化特征

利用2002年东南极Princess Elizabeth冰盖自动气象梯度观测点获得的近地层气象资料,分析了冰盖上的感热通量、潜热通量、大气稳定度、整体输送系数及有关气象要素特征,并与中山站同期的的气象要素进行了对比分析.结果表明,由于两站的海拔高度及地理位置的差异,LGB69站的年平均气温为-25.6℃,比中山站低16.4℃,进入内陆每10km,海拔高度上升约110m,温度下降约1℃.南极内陆冰盖的湍流热通量具有明显的年变化,感热通量年平均值为-17.9W/m2,潜热通量为-0.9W/m2,年平均冷源强度(Q_h+Q_e)为-18.8W/m2,表明地表从大气吸收热量.LGB69站近地层大气以近中性层结为主,中性层结下的整体输送系数为2.6×10-3,当风速大于8m/s后,整体输送系数趋于常数.LGB69站是南极地区典型下降风区,年平均风速比中山站大2.0m/s,其下降风出现的风向频和风速均大于中山站.     

Tidal bedforms in eastern part of the Bohai Sea

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基于CryoSat-2测高数据的全南极冰盖DEM的建立与精度评估

数字高程模型(DEM)是南极冰盖变化研究的基础,由于现场实测数据的稀缺,卫星测高数据是南极地区构建DEM的'主要数据来源.CryoSat-2是新一代用于极地冰盖、海冰监测的测高卫星,本文利用2012-12-2015-01两个完整周期的CryoSat-2测高数据建立一个新的南极冰盖DEM.坡度是影响卫星测高精度的重要因素之一,利用改进的重定位方法对CryoSat-2数据进行坡度改正.插值方法是影响DEM精度的重要因素,通过对几种常用插值方法的比较,最后选用克里金插值方法对测高数据进行插值,建立了1km分辨率的南极DEM.在88°S以南的CryoSat-2数据空白区,利用南极数字数据库(ADD)的等高线数据对DEM进行填补,建立了全南极冰盖DEM.利用ICESat卫星测高数据、IceBridge航空测高数据以及GPS地面实测数据对新建立的CryoSat-2 DEM进行精度验证,并与Bamber 1 km DEM、ICESat DEM、RAMPv2 DEM以及JLB97 DEM等四种国际上常用的南极DEM进行比较.结果表明:新建立的CryoSat-2 DEM的整体精度约为0.730±8.398 m;在冰弯顶部区域,DEM精度优于1 m;在冰架上,DEM精度约为4 m;在内陆冰盖大部分地区,DEM精度优于10 m;在地形复杂的山区和沿海边缘地区,DEM误差超过150 m.     

基于MESSEGER观测对水星磁尾电流片磁场分布的统计研究

本文利用信使号飞船2011-2015年期间在轨磁场数据对水星磁尾电流片的磁场结构分布特征进行了统计分析.为探究磁场结构分布随水星径向距离的变化,电流片划分为近磁尾（-1.5R_M > X > -2.0R_M）和远磁尾（-2.0R_M > X > -2.5R_M）两个区域.所得结果表明：（1）无论是近磁尾还是远磁尾,电流片中的磁场都以+B_z分量为主,磁场方向几乎与磁赤道面垂直.（2）相比近磁尾,远磁尾电流片中磁场强度、B_z分量较弱,B_y分量较强,而且-B_z信号出现概率相对较大,这表明电流片中磁活动相对容易在远磁尾中发生.（3）磁场强度以及B_z分量在晨昏方向上的分布存在晨昏不对称性——在方位角120°~190°范围内相对较弱.弱B_z数据点（B_z<5 nT）也在昏侧（Y>0）发生较为频繁.（4）与B_z分布相反,磁场强B_y分量（|B_y|>5 nT）倾向于在晨侧（Y<0）发生.统计分析还表明,磁场B_y分量与行星际磁场B_y分量并无明显的相关性.对比地球磁尾电流片,我们对水星磁尾电流片B_z分量、强B_y分量的晨昏不对称起源机制作了探讨分析.     

The last ice sheet in Snowdonia

In Snowdonia there is a marked contrast between weathered summits, often with well‐developed blockfields or tors, and lower ice‐moulded terrain. The boundary is interpreted as a trimline marking the upper surface of the last ice sheet. This interpretation is supported by the presence of gibbsite, an end‐product of prolonged weathering, at the base of soils above but not below the trimline. The reconstructed ice surface reaches about 850 m above present sea‐level along an ice divide running NE–SW through the massif. There is no evidence to support the popular view that ice centred further south extended over Snowdonia, and breaching to form the major glacial troughs can be explained by the action of local ice. The field evidence presented here demonstrates that most models of the southern British and Irish Sea ice sheets are significantly flawed, the earliest being far too thick and the most recent far too thin. Copyright © 2000 John Wiley & Sons, Ltd.     

线简化定线图管线分段方法研究

管道分段设计是长输管道工程制图的起点,传统的分段设计方法,主要采用手工的布置方式,虽能充分发挥设计人员的主动性,但由于线路一般长达上百公里,致使设计速度慢,效率不高,影响了后期的制图工作进度。本文针对管道分段的问题,借鉴线简化的思路和方法,在分析管道线路分段设计需要和特点的基础上,提出一套管道线路自动分段设计的方案,辅助分段设计工作,并利用ArcEngine实现了一个实例,与传统的分段方法进行比较,证明方案的可行性和有效性。     

矿产资源储量平衡表填写方法探讨

在矿山储量年度报告中，发现矿产资源储量平衡表有填写错误现象，对当年动用的资源量采用“原级别动用，累查量填数”的方法填写，平衡表的基本功能得不到体现，横向和纵向不平衡，资源量和储量的升级变化、证实储量的增减得不到反映，累查可信储量和证实储量出现错误。为此，提出对当年动用资源量采用“先升级，再动用”的原则，进行矿产资源储量平衡表填写方法的探讨。