An automated approach to the classification of the slope units using digital data

Digital elevation and remote sensing data sets contain different, yet complementary, information related to geomorphological features. Digital elevation models (DEMs) represent the topography, or land form, whereas remote sensing data record the reflectance/emittance, or spectral, characteristics of surfaces. Computer analysis of integrated digital data sets can be exploited for geomorphological classification using automated methods developed in the remote sensing community. In the present study, geomorphological classification in a moderate- to high-relief area dominated by slope processes in southwest Yukon Territory, Canada, is performed with a combined set of geomorphometric and spectral variables in a linear discriminant analysis. An automated method was developed to find the boundaries of geomorphological objects and to extract the objects as groups of aggregated pixels. The geomorphological objects selected are slope units, with the boundaries being breaks of slope on two-dimensional downslope profiles. Each slope unit is described by variables summarizing the shape, topographic, and spectral characteristics of the aggregated group of pixels. Overall discrimination accuracy of 90% is achieved for the aggregated slope units in ten classes.     

Use of an expert system to map forest soils from a geographical information system

Abstract

Mapping forest soils using conventional methods is time consuming and expensive. An expert system is described and applied to the mapping of five forest soil-landscape units formed on a single granitoid parent material. Three thematic maps were considered important in influencing the distribution of soils. The first showed the distribution of nine classes of native eucalypt forests, and the second and third were derived from a digital elevation model and represented slope gradient and a soil wetness index combined with topographical position. These layers were input to a raster based geographical information system (GIS) and then geometrically co-registered to a regular 30 m grid. From a knowledge of soil distributions, the relationships between the soil-landscape units and the three data layers were quantified by an experienced soil scientist and used as rules in a rule based expert system. The thematic layers accessed from the GIS provided data for the expert system to infer the forest soil-landscape unit most likely to occur at any given pixel. The soil-landscape map output by the expert system compared favourably with a conventional soil-landscape map generated using interpretation of aerial photographs.     

Landslide susceptibility mapping using geological data, a DEM from ASTER images and an Artificial Neural Network (ANN)

An efficient and accurate method of generating landslide susceptibility maps is very important to mitigate the loss of properties and lives caused by this type of geological hazard. This study focuses on the development of an accurate and efficient method of data integration, processing and generation of a landslide susceptibility map using an ANN and data from ASTER images. The method contains two major phases. The first phase is the data integration and analysis, and the second is the Artificial Neural Network training and mapping. The data integration and analysis phase involve GIS based statistical analysis relating landslide occurrence to geological and DEM (digital elevation model) derived geomorphological parameters. The parameters include slope, aspect, elevation, geology, density of geological boundaries and distance to the boundaries. This phase determines the geological and geomorphological factors that are significantly correlated with landslide occurrence. The second phase further relates the landslide susceptibility index to the important geological and geomorphological parameters identified in the first phase through ANN training. The trained ANN is then used to generate a landslide susceptibility map. Landslide data from the 2004 Niigata earthquake and a DEM derived from ASTER images were used. The area provided enough landslide data to check the efficiency and accuracy of the developed method. Based on the initial results of the experiment, the developed method is more than 90% accurate in determining the probability of landslide occurrence in a particular area.     

喀斯特山地土壤侵蚀和产水量的最优解释力

喀斯特生态系统服务主导影响因子识别是科学治理石漠化的前提,然而环境因子对生态系统服务空间分布的解释力受尺度变换的影响,其尺度效应的定量研究仍需进一步加强。为定量厘定环境因子解释力的尺度效应,本文从多尺度视角出发,利用地理探测器定量分析不同空间分辨率下环境因子对土壤侵蚀和产水量的解释力,并探求其在不同地貌形态类型区的差异性规律。结果表明,坡度和植被覆盖度是影响土壤侵蚀空间分布的主导因子,两者的交互作用对土壤侵蚀空间分布的解释力更强。受研究区地形起伏普遍性和景观破碎化的影响,坡度和土地利用类型在低分辨率下解释力最优。降水、海拔和土地利用类型是产水量空间分异的主导因子。降水和土地利用类型的交互作用对产水量的解释力达95%以上,海拔在不同地貌形态类型区的空间变异性影响其最优解释力水平。具体表现为：在台地、丘陵类型区海拔空间变异性较小,在高分辨率下其解释力最优;在山地类型区,海拔空间变异性较大,在低分辨率下其解释力更强。本文通过多尺度分析定量甄别生态系统服务变量的最优解释力,以期为喀斯特山地生态系统服务的主导因子精准辩识和分区优化提供途径和依据。     

新疆地形复杂度的空间格局及地理特征

地形复杂度（TCI）是区域地表外在形态结构的数字化表达,既可表征坡面单元的多样性及其组合形式的复杂性,也可映射地球内外营力在地表留下“烙印”的过程,其客观描述和定量表达可为地表形态定义、刻画及分异等地形地貌理论研究提供重要依据。新疆独特的山盆地貌结构为地貌学研究提供了理想的场所。本文基于“倒金字塔滤网系统”逐步筛选微观和宏观坡面因子并确定权重进而构建地形复杂度模型;运用均值变点法确定新疆地形复杂度的最佳窗口,分析不同地貌单元地形复杂度的空间异质性,进一步探究不同营力作用对地表复杂程度的贡献。结果显示：① 地形复杂度模型综合相关性分析、聚类分析、变异系数法与主成分分析等方法对地形因子进行客观筛选与科学组合,使其具有全面客观性及独立有效性。② 地形复杂度以ASTER GDEM数据（30 m）为基础,得到最佳窗口（14×14）下全疆TCI介于0.13~46.36。山地与盆地相同地貌类型TCI面积占比峰值相近,不同地貌类型可比较其斜率、偏度及峰度得以区分。在经纬向上能更好的刻画出独立山峰及深切峡谷等局部地形分异,TCI≈1可作为平原与山地地貌单元之间的分界值。在高程分区下TCI>2时为各山系（山群）震荡高程区起始处,山麓处TCI曲线差异显著。③ 地形复杂度能较好的体现不同外营力在地表留下的痕迹,一定程度上也可表征外营力对不同成因地貌类型的贡献度。本研究对新疆地形地貌的形态特征和形成原因等方面提供理论依据和科学方法,可为地形地貌研究、生态环境影响以及区域发展评价提供实践指导。     

Correlation and dating of Quaternary alluvial-fan surfaces using scarp diffusion

Great interest has recently been focused on dating and interpreting alluvial-fan surfaces. As a complement to the radiometric methods often used for surface-exposure dating, this paper illustrates a rapid method for correlating and dating fan surfaces using the cross-sectional shape of gullies incised into fan surfaces. The method applies a linear hillslope-diffusion model to invert for the diffusivity age, κt (m²), using an elevation profile or gradient (slope) profile. Gullies near the distal end of fan surfaces are assumed to form quickly following fan entrenchment. Scarps adjacent to these gullies provide a measure of age. The method is illustrated on fan surfaces with ages of approximately 10 ka to 1.2 Ma in the arid southwestern United States. Two areas of focus are Death Valley, California, and the Ajo Mountains piedmont, Arizona. Gully-profile morphology is measured in two ways: by photometrically derived gradient (slope) profiles and by ground-surveyed elevation profiles. The κt values determined using ground-surveyed profiles are more consistent than those determined using photo-derived κt values. However, the mean κt values of both methods are comparable. The photometric method provides an efficient way to quantitatively and objectively correlate and relatively-date alluvial-fan surfaces. The κt values for each surface are determined to approximately 30–50% accuracy.     

Soil depth estimation through soil-landscape modelling using regression kriging in a Himalayan terrain

Soil formation depends upon several factors such as parent material, soil biota, topography and climate. It is difficult to use conventional soil survey methods for mapping the depth of soil in complex mountainous terrains. In this context, the present study aimed to estimate the soil depth for a large area (330.35 km²) using different geo-environmental factors through a soil-landscape regression kriging (RK) model in the Darjeeling Himalayas. RK with seven predictor variables such as elevation, slope, aspect, general curvature, topographic wetness index, distance from the streams and land use, was used to estimate the soil depth. While topographic parameters were derived from an 8-m resolution digital elevation model, the ortho-rectified Cartosat-1 satellite image was used to prepare the land use map. Soil depth measured at 148 sites within the study area was used to calibrate and validate the RK model. The result showed that the RK model with the seven predictors could explain 67% spatial variability of soil depth with a prediction variance between 0.23 and 0.42 m at the test site. In the regression analysis, land use (0.133) and slope (–0.016) were identified as significant determinants of soil depth. The prediction map showed higher soil depth in south-facing slopes and near valleys in comparison to other areas. Mean, mean absolute and root mean-square errors were used to access the reliability of the prediction, which indicated a goodness-of-fit of the RK model.     

Local Extremes in the Lidar‐Derived Snow Cover of Alpine Glaciers

Snow deposition and redistribution are major drivers of snow cover dynamics in mountainous terrain and contribute to the mass balance of alpine glaciers. The quantitative understanding of inhomogeneous snow distribution in mountains has recently benefited from advances in measuring technologies, such as airborne laser scanning (ALS). This contribution further advances the quantitative understanding of snow distribution by analysing the areas of maximum surface elevation changes in a mountain catchment with large and small glaciers. Using multi‐annual ALS observations, we found extreme surface elevation changes on rather thin borders along the glacier margins. While snow depth distribution patterns in less extreme terrain have presented high inter‐annual persistence, there is little persistence of those extreme glacier accumulations between winters. We therefore interpret the lack of persistence as the result of a predominance of gravity‐driven redistribution, which has an inherently higher random component because it does not occur with all conditions in all winters. In highly crevassed zones, the lidar‐derived surface elevation changes are caused by a complex interaction of ice flux divergence, the propagation of crevasses and snow accumulation. In general, the relative contribution of gravitational mass transport to glacier snow cover volume was found to decrease for glaciers larger than 5 km² in the investigated region. We therefore suggest that extreme accumulations caused by gravitational snow transport play a significant role in the glacier mass balance of small to medium‐size glaciers and that they may be successfully parameterized by simple mass redistribution algorithms, which have been presented in the literature.     

中国亚热带丘陵山区植被沿海拔梯度分布格局(英文)

Knowledge of vegetation distribution patterns is very important.Their relationships with topography and climate were explored through a geographically weighted regression(GWR) framework in a subtropical mountainous and hilly region,Minjiang River Basin of Fujian in China.The HJ-1 satellite image acquired on December 9,2010 was utilized and NDVI index was calculated representing the range of vegetation greenness.Proper analysis units were achieved through segregation based on small sub-basins and altitudinal bands.Results indicated that the GWR model was more powerful than ordinary linear least square(OLS) regression in interpreting vegetation-environmental relationship,indicated by higher adjusted R 2 and lower Akaike information criterion values.On one side,the OLS analysis revealed dominant positive influence from parameters of elevation and slope on vegetation distribution.On the other side,GWR analysis indicated that spatially,the parameters of topography had a very complex relationship with the vegetation distribution,as results of the various combinations of environmental factors,vegetation composition and also anthropogenic impact.The influences of elevation and slope generally decreased,from strongly positive to nearly zero,with increasing altitude and slope.Specially,most rapid changes of coefficients between NDVI and elevation or slope were observed in relatively flat and low-lying areas.This paper confirmed that the non-stationary analysis through the framework of GWR could lead to a better understanding of vegetation distribution in subtropical mountainous and hilly region.It was hoped that the proposed scale selection method combined with GWR framework would provide some guidelines on dealing with both spatial(horizontal) and altitudinal(vertical) non-stationarity in the dataset,and it could easily be applied in characterizing vegetation distribution patterns in other mountainous and hilly river basins and related research.     

Qualitative landslide susceptibility assessment by multicriteria analysis: A case study from San Antonio del Sur, Guantánamo, Cuba

Geomorphological information can be combined with decision-support tools to assess landslide hazard and risk. A heuristic model was applied to a rural municipality in eastern Cuba. The study is based on a terrain mapping units (TMU) map, generated at 1:50,000 scale by interpretation of aerial photos, satellite images and field data. Information describing 603 terrain units was collected in a database. Landslide areas were mapped in detail to classify the different failure types and parts. Three major landslide regions are recognized in the study area: coastal hills with rockfalls, shallow debris flows and old rotational rockslides denudational slopes in limestone, with very large deep-seated rockslides related to tectonic activity and the Sierra de Caujerí scarp, with large rockslides. The Caujerí scarp presents the highest hazard, with recent landslides and various signs of active processes. The different landforms and the causative factors for landslides were analyzed and used to develop the heuristic model. The model is based on weights assigned by expert judgment and organized in a number of components such as slope angle, internal relief, slope shape, geological formation, active faults, distance to drainage, distance to springs, geomorphological subunits and existing landslide zones. From these variables a hierarchical heuristic model was applied in which three levels of weights were designed for classes, variables, and criteria. The model combines all weights into a single hazard value for each pixel of the landslide hazard map. The hazard map was then divided by two scales, one with three classes for disaster managers and one with 10 detailed hazard classes for technical staff. The range of weight values and the number of existing landslides is registered for each class. The resulting increasing landslide density with higher hazard classes indicates that the output map is reliable. The landslide hazard map was used in combination with existing information on buildings and infrastructure to prepare a qualitative risk map. The complete lack of historical landslide information and geotechnical data precludes the development of quantitative deterministic or probabilistic models.     

近5年青海省植被覆盖变化的遥感监测

This paper used five years （2001-2006） time series of MODIS NDVI images with a 1-km spatial resolution to produce a land cover map of Qinghai Province in China. A classification approach for different land cover types with special emphasis on vegetation, especially on sparse vegetation, was developed which synthesized Decision Tree Classification, Supervised Classification and Unsupervised Classification. The spatial distribution and dynamic change of vegetation cover in Qinghai from 2001 to 2006 were analyzed based on the land cover classification map and five grade elevation belts derived from Qinghai DEM. The result shows that vegetation cover in Qinghai in recent five years has been some improved and the area of vegetation was increased from 370,047 km^2 in 2001 to 374,576 km^2 in 2006. Meanwhile, vegetation cover ratio was increased by 0.63%. Vegetation cover ratio in high mountain belt is the largest （67.92%） among the five grade elevation belts in Qinghai Province. The second largest vegetation cover ratio is in middle mountain belt （61.80%）. Next, in the order of the decreasing vegetation cover ratio, the remaining grades are extreme high mountain belt （38.98%）, low mountain belt （25.55%） and flat region belt （15.46%）. The area of middle density grassland in high mountain belt is the biggest （94,003 km^2）, and vegetation cover ratio of dense grassland in middle mountain belt is the highest （32.62%）, and the increased area of dense grassland in high mountain belt is the greatest （1280 km^2）. In recent five years the conversion from sparse grass to middle density grass in high mountain belt has been the largest vegetation cover variation and the converted area is 15931 km^2.     

Insights into the “tectonic topography” of the present-day landscape of the central Iberian Peninsula (Spain)

The landscape of today's central Iberian Peninsula has been shaped by ongoing tectonic activity since the Tertiary. This landscape comprises a mountain ridge trending E–W to NW–SE, the Central System, separating two regions of smooth topography: the basins of the rivers Duero and Tajo. In this study, we explore interrelationships between topography and tectonics in the central Iberian Peninsula. Regional landscape features were analysed using a digital elevation model (DEM). Slope gradients and slope orientations derived from the DEM were combined to describe topographic surface roughness. Topography trend-surfaces inferred from harmonic analysis were used to define regional topographic features. Low roughness emphasizes the smooth nature of the basins' topography, where surfaces of homogeneous slope gradient and orientation dominate. High roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests, valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins. One of the applications of roughness mapping was its capacity to isolate incised valley segments. The area distribution of incised rivers shows their prevalence in the east. On a regional scale, the topographic surface can be described as a train of NE–SW undulations or waves of 20 km wavelength. These undulations undergo changes in direction and interruptions limited by N–S-trending breaks. E–W and NE–SW troughs and ridges clearly mark structural uplifts and depressions within the Central System. These structures are transverse to the compressive NW–SE stress field that controlled the deformation of the central Iberian Peninsula from the Neogene to the present. They represent the upper crustal folding that accommodates Alpine shortening. N–S breaks coincide with Late Miocene faults that control the basins' sedimentation. Further, associated palaeoseismic structures suggest the recent tectonic activity of N–S faults in the eastern part of the Tajo Basin. Apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 Ma which induced the river incisions appearing in the roughness map. N–S and NE–SW faults could be seismogenic sources for the current moderate to low seismic activity of the east Tajo Basin and southeast Central System. Although N–S fault activity has already been established, we propose its significant contribution to shaping the landscape.     

Detailed geomorphological survey of a small mountain drainage area, Abisko, northern Swedish Lapland

A thorough geomorphological survey of a small (2km²) drainage area has been conducted using digital magnification of aerial photographs in conjunction with field visits. The result presented is a geomorphological map where individual geomorphological features down to metre size can be identified. The study was done in connection with a project focusing on the relationship between geomorphological processes and lacustrine sedimentation. Good knowledge of the geomorphological setting and the related process activity in the catchment is important in studies using lacustrine sediments as environmental archives.
The survey reveals a small–scale geomorphology dominated by a number of different periglacial upfreezing forms together with bedrock–controlled slope processes. Three different geographically separated geomorphological assemblages were recognised with few sediment transportation pathways connecting them. Composition of substrate, soil water content and vegetation cover combined with different slope angles are probably the most important factors controlling the distribution of the geomorphological features.     

Combining field and modelling techniques to assess rockfall dynamics on a protection forest hillslope in the European Alps

Adequate management of a mountain forest that protects downslope areas against impacts of rockfall requires insight into the dynamics of the hillslope environment. Therefore, we applied a combined approach, using field and modelling techniques, to assess the determining factors for rockfall source areas, rockfall tracks and rockfall runout zones on a forested slope in mountainous terrain. The first objective of this study was to understand why rockfall occurs in the study area. The second objective was to translate the knowledge obtained in the field into a model that simulates rockfall dynamics on a forested slope realistically. The third objective was to assess which hillslope characteristics primarily determine the distribution of active rockfall tracks. To achieve these objectives, we made a geomorphological map of the whole study area, and we measured the major discontinuity planes in the bedrock that are exposed in the rockfall source areas. Furthermore, a test site for simulation modelling within the larger study area was defined in which both a forest and a hillslope inventory were carried out. The available data and our developed rockfall simulation model allowed us to assess the slope characteristics that mainly determine the distribution of areas affected by rockfall. We found that in decreasing order of importance, both standing and felled trees, the surface roughness and rockfall resistant shrubs primarily determine the distribution of rockfall-affected areas. Simulation tests without a forest cover produced similar rockfall runout zones as fossil rockfall events identified in the field. We believe that the combined field and modelling approach is a prerequisite for understanding how forests can protect against rockfall.     

Detailed geomorphological survey of a small mountain drainage area, Abisko, northern Swedish Lapland

A thorough geomorphological survey of a small (2km²) drainage area has been conducted using digital magnification of aerial photographs in conjunction with field visits. The result presented is a geomorphological map where individual geomorphological features down to metre size can be identified. The study was done in connection with a project focusing on the relationship between geomorphological processes and lacustrine sedimentation. Good knowledge of the geomorphological setting and the related process activity in the catchment is important in studies using lacustrine sediments as environmental archives.
The survey reveals a small–scale geomorphology dominated by a number of different periglacial upfreezing forms together with bedrock–controlled slope processes. Three different geographically separated geomorphological assemblages were recognised with few sediment transportation pathways connecting them. Composition of substrate, soil water content and vegetation cover combined with different slope angles are probably the most important factors controlling the distribution of the geomorphological features.     

滇东北山区坡耕地水土流失与可持续利用图的基本内容与编制方法

坡耕地水土流失与可持续利用图是综合表示滇东北山区各个坡耕地单元的水土流失状况及其可持续利用的专题地图。该图表示的基本内容是坡耕地类型、土壤类型、坡度级别、侵蚀强度、可持续利用程度、合理利用方向与措施。以土壤流失方程为基础,应用地理信息系统编制了该图。该图的编制为治理本区坡耕地水土流失、合理利用坡耕地资源提供了科学依据。     

Gravitational Seismodislocations in Mountainous regions of Southeastern Kazakhstan

Data on rock falls and landslides caused by strong earthquakes in the Zhetysu Alatau, Ile Alatau, Kungei Alatau and Teriskei Alatau mountain ranges on the territory of Southeastern Kazakhstan are presented. The study revealed more than 60 large seismogenic rock falls and landslides, the volume of 25 of them varies from 10 to 100 mil. m³, and the volume of the four largest exceeds 100 mil. m³. The volume of the largest rock fall in the valley of the Ulken Almaty river in the Ile Alatau mountain range is estimated at 380 mil. m³. The highest density of seismogenic landslides was recorded in the low-mountain zone of the northern slope of the Ile Alatau range where the magnitude 9 earthquake of 1887 caused a massive formation of landslides with the volume totaling more than 400 mil. m³ and a density of 1/5 km². The proportion of landslide-affected areas is estimated at 5% of the area of their occurrence. In the mid- and high-mountain zones of Zhetysu, Ile and Kungei Alatau, the density of seismogenic rock falls varies from 1/100 to 1/50 km², and the proportion of rock fall-affected areas varies from 1 to 1.5%. It is found that seismogenic rock falls have dammed 26 lakes, and the volume of nine such lakes exceeds 10 mil. m³. The largest rock fall-affected lakes is Upper Zhasylkol in the valley of the Aganakty river in Zhetysu Alatau with the volume of 44 mil. m³. Data from earthquake catalog were used to compile the map for the recurrence frequency of earthquakes of magnitude higher than 6, capable of causing seismogenic rock falls and landslides. It is found that during the last 130 years, in Ile and Kungei Alatau such earthquakes recurred four times. It is established that earthquakes with maximum magnitude 9 are possible in the mountainous regions of Southeastern Kazakhstan.     

Nature rehabilitation by floodplain excavation: The hydraulic effect of 16 years of sedimentation and vegetation succession along the Waal River, NL

The “Ewijkse Plaat” is a floodplain along the Waal River, NL. In 1988, the floodplain was excavated as part of a program for enlargement of the discharge capacity and was assigned as a nature rehabilitation area. This paper describes the combined geomorphological and vegetation evolution of the floodplain until 16 years after the initial excavation using elevation data and data on vegetation structure derived from detailed aerial stereographic imagery. The impact of these processes on flow velocity and water surface elevation was evaluated by using a hydraulic model. Within 16 years, the excavated amount of sediment was redeposited in the area. The dominant geomorphological process after excavation was vertical accretion of the floodplain which resulted in the formation of natural levees. The amount of sedimentation was correlated to the across-floodplain flow (R² = 0.89). In the research period, 41% of the sedimentation took place during two single major flood events. The creation of pioneer stages by excavation promoted softwood forest establishment, which influenced the sedimentation pattern significantly. The landscape evolved toward structure-rich vegetation. Nine years after excavation the initial hydraulic gain was lost by the combined effect of sedimentation and vegetation succession. Implications for river and nature management are discussed.     

DEM resolution dependencies of terrain attributes across a landscape

This paper documents resolution dependencies in terrain analysis and describes how they vary across landform location. Six terrain attributes were evaluated as a function of DEM resolution—slope, plan curvature, profile curvature, north–south slope orientation, east–west slope orientation, and topographic wetness index. The research highlights the effect of varying spatial resolution through a spatial sampling/resampling scheme while maintaining sets of indexed sample points at various resolutions. Tested sample points therefore coincide exactly between two directly compared resolutions in terms of their location and elevation value. An unsupervised landform classification procedure based on statistical clustering algorithms was employed to define landform classes in a reproducible manner. Correlation and regression analyses identified sensitive and consistent responses for each attribute as resolution was changed, although the tested terrain attributes responded in characteristically different ways. These responses displayed distinguishable patterns among various landform classes, a conclusion that was further verified by a series of two‐sample, two‐tailed t‐tests.