Influence of topography on wind speed over a coastal dune and blowout system at Jockey's Ridge,NC, USA

This study examines the spatial distribution of wind speed across a coastal dune system located at Jockey's Ridge State Park, North Carolina. The study area consists of a trough blowout through a foredune ridge, and the landforms that have developed behind the foredune. Wind speed and direction were measured simultaneously with single sensors placed at a fixed height in 13 locations across the blowout/dune complex. Fractional wind speed‐up is computed for sampling stations using data from a mast located on the beach as the reference. Results show that wind speeds were generally accelerated across the study site. The highest speeds were recorded on the foredune ridges adjacent to the blowout. Wind was accelerated through the center of the blowout throat and along the downwind lateral wall. Further into the blowout, at the base of the ramp to the depositional lobe, higher wind speeds shifted to the upwind lateral wall and continued to accelerate up the ramp as air exited to the rear. Significant variations in the wind speed‐up pattern were associated with different wind approach angles, with greater speed‐up occurring when the winds were aligned normal to the dune system. The speed‐up decreased as the angle of approach became increasingly oblique to the ridge. The patterns of wind speed‐up across the site point to the influence of topography on airflow. To quantify the relationship, measures of several topographic variables were obtained along sample transects running upwind from each sample station along flow lines representing different wind approach angles. Examination of correlation coefficients between wind speed‐up and topographic variables suggests that for groups of stations with similar topographic characteristics, 30–50% of the variations in speed‐up may be explained by the upwind topographic variability. Copyright © 2014 John Wiley & Sons, Ltd.     

Erosion of a high‐altitude,low‐relief area on the Korean Peninsula: implications for its development processes and evolution

The processes involved in the development of high‐altitude, low‐relief areas (HLAs) are still poorly understood. Although cosmogenic nuclides have provided insights into the evolution of HLAs interpreted as paleo‐surfaces, most studies focus on estimating how slowly they erode and thereby their relative stability. To understand actual development processes of HLAs, we applied several techniques of cosmogenic nuclides in the Daegwanryeong Plateau, a well‐known HLA in the Korean Peninsula. Our denudation data from strath terraces, riverine sediments, soils, and tors provide the following conclusions: (1) bedrock incision rate in the plateau (~127 m Myr^?1) is controlled by the incision rate of the western part of the Korean Peninsula, and is similar to the catchment‐wide denudation rate of the plateau (~93 m Myr^?1); (2) the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate; (3) a discrepancy between the soil production and catchment‐wide denudation rates implies morphological disequilibrium in the plateau; (4) the tors once regarded as fossil landforms of the Tertiary do not reflect Tertiary processes; and (5) when compared with those of global paleo‐surfaces (<20 m Myr^?1), our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape, and thus is not a paleo‐surface. Our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo‐surfaces around the world. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling long‐term (300 ka) upland catchment response to multiple lava damming events

Landscapes respond in complex ways to external drivers such as base level change due to damming events. In this study, landscape evolution modelling was used to understand and analyse long‐term catchment response to lava damming events. PalaeoDEM reconstruction of a small Turkish catchment (45 km²) that endured multiple lava damming events in the past 300 ka, was used to derive long‐term net erosion rates. These erosion rates were used for parameter calibration and led to a best fit parameter set. This optimal parameter set was used to compare net erosion landscape time series of four scenarios: (i) no uplift and no damming events; (ii) no uplift and three damming events; (iii) uplift and no damming events; and (iv) uplift and three damming events. Spatial evolution of net erosion and sediment storage of scenario (iii) and (iv) were compared. Simulation results demonstrate net erosion differences after 250 000 years between scenarios with and without dams. Initially, trunk gullies show less net erosion in the scenario with damming events compared with the scenario without damming events. This effect of dampened erosion migrates upstream to smaller gullies and local slopes. Finally, an intrinsic incision pulse in the dam scenario results in a higher net erosion of trunk gullies while decoupled local slopes are still responding to the pre‐incision landscape conditions. Sediment storage differences also occur on a 100 ka scale. These differences behaved in a complex manner owing to different timings of the migration of erosion and sediment waves along the gullies for each scenario. Although the specific spatial and temporal sequence of erosion and deposition events is sensitive to local parameters, this model study shows the manner in which past short‐lived events like lava dams have long‐lasting effects on catchment evolution. Copyright © 2014 John Wiley & Sons, Ltd.     

2001-2013年川西高原旱情监测及其地形分异

利用2001-2013年EOS-MODIS归一化植被指数产品数据,应用距平植被指数法（AVI）对川西高原进行了干旱监测,并分析年平均干旱发生频率与海拔高度、坡度和坡向地形因子的关系,进一步结合研究区土地利用数据,分析了不同地形因子干旱频率差异的原因。研究表明：（1）受积雪覆盖的影响,川西地区干旱监测只在一定区域内适用,该适宜区为川西海拔4 300 m以下区域。（2）川西高原干旱发生频率同各地形因子都具有较强的相关性,其中,高程影响最为复杂,与不同高度带地表覆被类型的差异性有关;坡向影响非常明确,主要受稳定水汽来源输入的影响;坡度的影响具有较强的局域性,与不同坡度的保水蓄水能力及覆被类型有关。     

Topographic locations and size of earthquake‐ and typhoon‐generated landslides,Tachia River,Taiwan

Analysis of mapped landslide locations using a high‐resolution (5‐m grid) digital elevation model (DEM) in the Tachia River basin, Taiwan, finds distinct differences in the topographic locations and size of landslides during the 1999 Chi‐Chi earthquake and the 2001 Toraji typhoon. Our analysis supports Densmore and Hovius' hypothesis that earthquake‐induced landslides cluster near ridgetops due to topographic amplification of ground shaking, and that typhoon‐induced landslides occur with greater frequency lower on slopes. In addition, the differing topographic locations of seismically‐induced and subsequent typhoon‐induced landslides shows no evidence of residual post‐earthquake influences on landslides during typhoon Toraji previously hypothesized for drainage basins closer to the earthquake epicenter. Our results support the interpretation that in this tectonically active landscape, seismically‐induced landslides help shatter and erode ridgetops but typhoon‐triggered landslides concentrate erosion farther downslope, with the combination acting to more uniformly lower upland terrain than either process does individually. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of digital channel network derivation methods in a glaciated subalpine catchment

The digital elevation model (DEM) has become an essential tool for an increasing array of mountain runoff analyses, particularly the derivation and mapping of stream channel networks. This study examines how well commonly applied DEM‐based channel derivation methods at different spatial resolutions can represent the channel network for a glaciated Rocky Mountain headwater catchment. The specific objectives are to (1) examine how differences in gridded DEM resolution affect spatially distributed values of local slope, specific contributing area, and topographic wetness index derived from both eight and infinite directional flow algorithms, (2) map the actual stream channel network to examine the influence of surface variables on channel initiation, and (3) assess accuracy of DEM‐derived networks compared with the field surveyed network. Results show that for the same contributing area threshold, increasing grid cell size leads to increased channelization of modeled networks. A plot of local slope versus contributing area reveals a negative relationship similar to that of prior studies in un‐glaciated areas but with breaks in slope at contributing areas that are too small to represent thresholds for channelization. Field survey results and evaluation of DEM‐derived channel networks suggest that channel network formation is not clearly related to surface topographic variables at Loch Vale. Digitally derived channel networks do not accurately predict low order channel locations, but approximations of the channel network with drainage density and headward extent of channelization similar to the observed network can be derived with both a 1 m and 10 m DEM using a contributing area threshold of approximately 4x10⁴ m². Copyright © 2014 John Wiley & Sons, Ltd.     

利用改进的Stokes-Helmert边值理论解算高精度似大地水准面

利用改进的Stokes-Helmert边值问题实现了临沂市厘米级似大地水准面精化。首先,基于Stokes理论和Molodensky理论,联合精密确定地表及其外部扰动引力位的严密解算理论,给出Stokes-Helmert边值问题的数学描述,以及直接地形影响和间接地形影响的严密理论表达式;然后,利用多源观测资料,根据"移去-恢复"技术构建临沂高精度的重力似大地水准面模型;最后,利用GPS/水准高程异常对重力似大地水准面模型进行控制拟合,求得最终的大地水准面模型,其外符合精度达到1.6 cm。     

台湾地区地貌形态的分析研究

数字高程模型(DEM)是地貌解译有力的辅助工具,同时也是对地形地貌分析研究进行量化表达的一个重要手段。在前人研究的方法上通过对研究区台湾地区的SRTM-DEM数据的处理,运用GIS空间分析和统计方法进行地形分析,并在此基础上完成对地形起伏度、坡度、坡向、高程等地形因子相关的拓展分析。根据分析结果对该地区的地貌形态特征进行总结。     

基于地面激光扫描技术的矿区地形图更新

设计了一种基于地面激光扫描系统的矿区地形图更新方法,并探讨了其方法重建矿区三维模型的方法。通过试验表明,矿区地形图测绘效率得到了有效提升,重建的三维模型可用来监测矿区开采量。     

西部测图工程影像地形图产品设计与制作技术

西部测图工程中,在生产技术试验的基础上对影像地形图产品模式和制作技术进行了研究,设计了西部测图工程1∶50 000影像地形图产品模式,研制了图像处理、符号设计、要素提取、地图编辑等产品制作方面的原则和技术方法,编制了《西部测图工程1∶50 000影像地形图技术规定》,并制作了产品样本。