北斗Ⅱ载波相位差分定位法在高填方变形监测中的应用

通过对北斗Ⅱ载波相位差分定位技术在高填方变形监测中的应用研究,包括实时动态差分定位(RTK)和静态相对定位,构建了完整的北斗Ⅱ高填方变形监测软硬件系统。该系统采用基于贯序极限学习机的卫星信号周跳探测与修复方法进行数据预处理,并利用基于卫星历元数的分层置信滤波算法对静态相对定位结果进行修正,提高了定位结果的准确性和可靠性。通过自制的精度测试装置,以百分表和钢尺测量的位移变化量为相对真值,完成了上述变形监测系统的精度试验。试验结果表明:该系统的RTK高程测量精度优于2 cm,静态高程测量精度优于2 mm,静态水平位移测量精度优于1.5 mm,可有效抑制卫星信号周跳和卫星历元数量较少等因素的影响。     

Mapping and assessing crop diversity in the irrigated Fergana Valley,Uzbekistan

Crop diversity (e.g. the number of agricultural crop types and the level of evenness in area distribution) in the agricultural systems of arid Central Asia has recently been increased mainly to achieve food security of the rural population, however, not throughout the irrigation system. Site-specific factors that promote or hamper crop diversification after the dissolvent of the Soviet Union have hardly been assessed yet. While tapping the potential of remote sensing, the objective was to map and explain spatial patterns of current crop diversity by the example of the irrigated agricultural landscapes of the Fergana Valley, Uzbekistan. Multi-temporal Landsat and RapidEye satellite data formed the basis for creating annual and multi-annual crop maps for 2010–2012 while using supervised classifications. Applying the Simpson index of diversity (SID) to circular buffers with radii of 1.5 and 5 km elucidated the spatial distribution of crop diversity at both the local and landscape spatial scales. A variable importance analysis, rooted in the conditional forest algorithm, investigated potential environmental and socio-economic drivers of the spatial patterns of crop diversity. Overall accuracy of the annual crop maps ranged from 0.84 to 0.86 whilst the SID varied between 0.1 and 0.85. The findings confirmed the existence of areas under monocultures as well as of crop diverse patches. Higher crop diversity occurred in the more distal parts of the irrigation system and sparsely settled areas, especially due to orchards. In contrast, in water-secure and densely settled areas, cotton-wheat rotations dominated due to the state interventions in crop cultivation. Distances to irrigation infrastructure, settlements and the road network influenced crop diversity the most. Spatial explicit information on crop diversity per se has the potential to support policymaking and spatial planning towards crop diversification. Driver analysis as exemplified at the study region in Uzbekistan can help reaching the declared policy to increase crop diversity throughout the country and even beyond.     

伊犁河谷2001-2014年地表温度时空分异特征

地表温度是地表能量平衡、区域和全球尺度地表物理过程的一个重要因子。为了辨析中国西北干旱区“天山湿岛”——伊犁河谷的地表温度时空分异,采用趋势分析法和空间数据统计法,探讨了2001-2014年不同土地利用/覆盖类型下地表温度时空变化规律,分析地表温度的时空分异特征及原因。结果表明：（1） MODIS LST产品的精度（平均R²=0.90）能够满足伊犁河谷地表温度时空变化分析的要求;（2）空间上,地表温度呈现出中部高四周低的变化趋势,高温区面积约占总面积的41%,低温区面积约占总面积的23%;时间上,伊犁河谷平均地表温度的年际波动较大,以2013年、2006年、2007年和2008年尤为突出;地表温度的年内变化呈现出单峰型分布,地表温度高值集中在3-8月,最高值出现在7月;（3）不同土地利用/覆盖类型下年均地表温度分布的总体特征为建设用地最高,稀疏草地、旱地等次之,冰川/积雪最低;（4）伊犁河谷地表温度变化趋势呈严重减少、基本不变和轻微增加区域面积分别占5%、37%和26%,以基本不变和轻微增加为主。伊犁河谷地表温度时空变化不仅受大尺度气候变化影响,还受土地类型差异影响,两者共同构成了不同地理区域及景观的温场格局,绿色植被对地表温度时空分布具有重要的调节作用。     

夏季黄河流域降水气候特征及其与大气环流的关系

本文基于1958—2015年夏季黄河流域55个观测站降水量和NCEP/NCAR再分析1高度场等资料,使用MannKendall突变检验、合成分析和Monte Carlo检验等气候统计方法,分析了黄河流域58年夏季降水量的气候变化特征,以及导致其变化的大气环流成因。58年期间,黄河流域夏季降水量总体呈减少趋势,尤其在河套北部有显著性减少趋势,其主要原因是欧亚中高纬度等压面升高、西风带减弱所致;1975年和1996年是黄河流域夏季降水的两个明显年代际气候变化转折点,在1958—1975年期间,黄河流域夏季降水量年际变化大,异常偏多和偏少年出现频次较高,期间欧亚中高纬度及其以南包括黄河流域地区高度场偏低,主要受高空低压系统和较强冷空气影响;在1976—1995年期间,黄河流域大部降水偏多,其主要环流成因为乌拉尔山阻塞高压发展、贝加尔湖到东北亚一带受负高度距平控制高空槽加深,同时,来自南方的暖湿气流输送增强;到1996—2015年最近20年间,乌拉尔山北部环流高度场偏低、里海至贝加尔湖再到东北亚一带高度场一致偏高,黄河流域一带西风带强度和冷空气势力均较弱,流域受高压影响导致大部区域降水偏少。不同时期黄河各流域段降水量与中高纬度阻塞高压以及与西北太平洋副热带高压的相关关系分析进一步说明了上述结论。     

A new algorithm to find raster-based least-cost paths using cut and fill operations

We developed a least-cost path analysis algorithm that satisfies a slope threshold condition in hilly terrain. The new algorithm uses an expanding moving-window to explore a combination of cells that satisfy an elevation threshold condition and then supplements this by executing cut and fill operations when there are obstacle cells between source and destination cells. Cut and fill factors regarding the difference in the actual elevation and revised elevation are considered and a least-cost path is analyzed after calculating the accumulated travel cost to the destination point. After applying the developed algorithm to synthetic and real-world data, the least accumulated travel cost from the source point can then be calculated for all cells on the raster surface by considering various slope thresholds, moving-window sizes and raster data resolutions. This algorithm can be implemented as a useful tool in GIS software as well as engineering design software utilized in the construction and mining industries.     

中国南方二叠纪层序地层时空格架及充填特征

据华南二叠纪不同沉积盆地层序地层区域分布、纵向演化及其充填特征分析研究,初步建立了上扬子克拉通-右江盆地-钦防盆地、中扬子克拉通及全区的层序地层时空格架模型;提出层序充填可分为两个阶段:早二叠世碳酸盐缓坡-台地层序充填阶段,晚二叠世陆源碎屑为主与火山碎屑相混层序充填阶段;认为全区二叠纪四个Ⅰ型层序受控于构造隆升事件,晚二叠世层序TST普遍发育火山碎屑沉积,古陆边缘HST或少量SMT/LST大多由三角洲沉积体系进积叠加而成,上扬子克拉通及右江地区的生物礁以海侵和高位型为特色。     

一种基于格网的快速等值线充填算法

本文提出一种基于格网的等值线跟踪,适用于任意边界分割的快速充填算法,实现充填的 量化效果。根据边界线与非封闭等值线间的关系,建立等值线间的拓扑关系,并以树结构方式存储,以准确快速地实现边界线、非封闭等值线之间的封闭和封闭等值线间的嵌套。该算法已成功应用于海量多波束地形数据的成图,克服了常用多波束后处理成图软件栅格充与等值线之间的失配。     

Sedimentary processes and facies of the waterlaid Anvil Spring Canyon alluvial fan, Death Valley, California

The Anvil Spring Canyon fan of the Panamint Range piedmont in central Death Valley was built entirely by water-flow processes, as revealed by an analysis of widespread 2- to 12-m-high stratigraphic cuts spanning the 9·7 km radial length of this 2·5–5·0° sloping fan. Two facies deposited from fan sheetfloods dominate the fan from apex to toe. The main one (60–95% of cuts) consists of sandy, granular, fine to medium pebble gravel that regularly and sharply alternates with cobbly coarse to very coarse pebble gravel in planar couplets 5–25 cm thick oriented parallel to the fan surface. The other facies (0–25% of cuts) comprises 10- to 60-cm-thick, wedge-planar and wedge-trough beds of pebbly sand and sandy pebble gravel in backsets sloping 3–28°. Both facies are interpreted as resulting from rare, sediment-charged flash floods from the catchment, and were deposited by supercritical standing waves of expanding sheetfloods on the fan. Standing waves were repeatedly initiated, enlarged, migrated, and then terminated either by gradually rejoining the flood or by more violent breakage and washout. The frequent autocyclic growth and destruction of standing waves during an individual sheetflood resulted in the deposition of multiple coarse and fine couplet and backset sequences 50–250 cm thick across the active depositional lobe of the fan. Erosional intensity during washout of the standing wave determined whether early-phase backset-bed deposits or washout-phase sheetflood couplet deposits were selectively preserved in a given cycle. Two minor facies are also found in the Anvil fan. Pebble–cobble gravel lags (0–20% of cuts) are present above erosional scours into the sheetflood couplet and backset deposits. They consist of coarse gravel concentrated through fine-fraction winnowing of the host sheetflood facies by sediment-deficient water flows. This reworking occurred during recessional flood stage or from non-catastrophic discharge during the long intervals between major flash floods. This facies is common at the surface, giving rise to a ‘braided-stream’ appearance. However, it is stratigraphically limited, present as thin, continuous to discontinuous beds or lenses that bound 50- to 250-cm-thick sheetflood sequences. The other minor facies of the Anvil fan consists of clast-supported and imbricated, thickly stratified, pebbly, cobbly, boulder gravel present in narrow, radially aligned ribbons nested within sheetflood deposits. This facies is interpreted as representing deposition in the incised channel of the fan, a subenvironment characterized by greater flow competence resulting from maintained depth from channel-wall confinement, and by more frequent water flows and winnowing events caused by its direct connection with the catchment feeder channel.     

Cause of dominance by sheetflood vs. debris-flow processes on two adjoining alluvial fans, Death Valley, California

Two large, adjoining alluvial fans of the Panamint Range piedmont, Death Valley, California, are composed of different facies assemblages deposited by contrasting sedimentary processes. The Anvil Spring fan was built solely by water-flow processes (incised-channel floods and sheetfloods), whereas the neighbouring Warm Spring fan has been constructed principally by debris flows. The boundary between these fans delineates a sharp provincial piedmont contact between sheetflood-dominated fans to the south and debris-flow-dominated fans to the north. Factors such as climate, catchment area, fan area, catchment relief, aspect, vegetation types and density, and neotectonic setting are essentially identical for these two fans. The key difference between them is that their catchments are underlain by dissimilar bedrock types, which weather to yield distinctive sediment suites. Weathering of the granite and andesite of the Anvil fan catchment produces significant volumes of medium to very coarse sand, granules, pebbles, cobbles and boulders, but minimal silt and clay. In contrast, the shale, quartzite and dolomite that dominate bedrock in the Warm Spring catchment weather to yield a wide suite of sedimentary particles spanning from clay to boulders. The abundance of mud, and the unsorted character of the yielded sediment, cause precipitation-induced slope failures in the Warm Spring catchment to transform readily into debris flows. This propensity is due to the low permeability of the colluvial sediment, which causes added water to become trapped quickly and pore pressure to rise rapidly, promoting transformations to debris flows. In contrast, the limited volume of sediment finer than medium sand yielded from the Anvil fan catchment causes the colluvium to have high permeability. This factor prevents the transformation of wet colluvium to a debris flow during hydrologically triggered slope failures, instead maintaining sediment transport as entrained bed load or suspended load in a water flow.     

Did Lake Manly overflow at Ash Hill?

Near Ash Hill in the Mojave Desert, California, there is an impressive channel that is cut in bedrock. The channel is in a pass through which Lake Manly, the pluvial lake that occupied Death Valley, could have overflowed. Indeed, the channel has been attributed to such overflow. The pass, however, is 500 m above the highest shorelines of Lake Manly in Death Valley, and evidence from cores from dry lakes on either side of the pass does not support the overflow hypothesis. Despite its size, new field observations suggest that the channel was actually eroded by local runoff. Water from several tributaries collects into a single channel at this point, and the resulting discharge is apparently sufficient to cause retreat of a knickpoint from the downstream edge of the basalt flow into which the channel is cut. © 1998 John Wiley & Sons, Ltd.