Accuracy Assessment of Alos W3d30, Aster Gdem and Srtm30 Dem: A Case Study of Nigeria, West Africa

Digital Elevation Models (DEMs) depict the configuration of the earth surface and are being applied in many areas in earth and environmental sciences. In this study, the accuracy of the Advanced Land Observing Satellite World 3D Digital Surface Model version 2.1 (ALOS W3D30), the Shuttle Radar Topography Mission Digital Elevation Model version 3.0 (SRTM30) and the Advanced Space borne Thermal Emission and Reflection Radiometer Global DEM version 2.0 (ASTER GDEM2) was statistically assessed using high accuracy GPS survey data. Root-Mean-Square errors of ~5.40 m, ~7.47 m and ~20.03 m were obtained for ALOS W3D30, SRTM30 and ASTER GDEM2 respectively. In further analyses, we discovered that ALOS W3D30 and SRTM30 were much more accurate in regions where the height intervals were within 201 m - 400 m and >801 m. ALOS W3D30 proved to be the most accurate DEM that best represents the topography of the earth’s surface and could be used for some earth and environmental applications in Nigeria. We recommend that this study should serve as a guide in the use of any of these DEMs for earth and environmental applications in Nigeria.

An Object-based Approach for Two-level Gully Feature Mapping Using High-resolution DEM and Imagery： A Case Study on Hilly Loess Plateau Region, China

Gully feature mapping is an indispensable prerequisite for the motioning and control of gully erosion which is a widespread natural hazard. The increasing availability of high-resolution Digital Elevation Model(DEM) and remote sensing imagery, combined with developed object-based methods enables automatic gully feature mapping. But still few studies have specifically focused on gully feature mapping on different scales. In this study, an object-based approach to two-level gully feature mapping, including gully-affected areas and bank gullies, was developed and tested on 1-m DEM and Worldview-3 imagery of a catchment in the Chinese Loess Plateau. The methodology includes a sequence of data preparation, image segmentation, metric calculation, and random forest based classification. The results of the two-level mapping were based on a random forest model after investigating the effects of feature selection and class-imbalance problem. Results show that the segmentation strategy adopted in this paper which considers the topographic information and optimal parameter combination can improve the segmentation results. The distribution of the gully-affected area is closely related to topographic information, however, the spectral features are more dominant for bank gully mapping. The highest overall accuracy of the gully-affected area mapping was 93.06% with four topographic features. The highest overall accuracy of bank gully mapping is 78.5% when all features are adopted. The proposed approach is a creditable option for hierarchical mapping of gully feature information, which is suitable for the application in hily Loess Plateau region.

Multi-Resolution Landslide Susceptibility Analysis Using a DEM and Random Forest

Landslide susceptibility (LS) mapping is a requisite for safety against sediment related disasters, and considerable effort has been exerted in this discipline. However, the size heterogeneity and distribution of landslides still impose challenges in selecting an appropriate scale for LS studies. This requires identification of an optimal scale for landslide causative parameters. In this study, we propose a method to identify the optimum scale for each parameter and use multiple optimal parameter-scale combinations for LS mapping. A random forest model was used, together with 16 geomorphological parameters extracted from 10, 30, 60, 90, 120, 150, and 300 m digital elevation models (DEMs) and an inventory of historical landslides. Experiments in two equal-sized (625 km2) areas in Niigata and Ehime, Japan, with different geological and environmental settings and landslide density, demonstrated the efficiency of the proposed method. It outperformed all other single scale LS analysis with a prediction accuracy of 79.7% for Niigata and 78.62% for Ehime. Values of areas under receiver operating characteristics (ROC) curves (AUC) of 0.877 and 0.870 validate the application of the multi-scale model.

Glacier extraction based on ASAR,DEM and texture feature of ASAR using SVM in the Western Qilian Mountains,Northwest China

This paper is focused on the method for extracting glacier area based on ENVISAT ASAR Wide Swath Modes （WSM） data and digital elevation model （DEM） data, using support vector machines （SVM） classification method. The digitized result of the glaci- er coverage area in the western Qilian Mountains was extracted based on Enhanced LandSat Thematic Mapper （ETM＋） imagery, which was used to validate the precision of glacier extraction result. Because of similar backscattering of glacier, shadow and wa- ter, precision of the glacier coverage area extracted from single-polarization WSM data using SVM was only 35.4%. Then, texture features were extracted by the grey level co-occurrence matrix （GLCM）, with extracted glacier coverage area based on WSM data and texture feature information. Compared with the result extracted from WSM data, the precision improved 13.2%. However, the glacier was still seriously confused with shadow and water. Finally, DEM data was introduced to extract the glacier coverage area. Water and glacier can be differentiated because their distribution area has different elevations; shadow can be removed from the classification result based on simulated shadow imagery created by DEM data and SAR imaging parameters; finally, the glacier coverage area was extracted and the precision reached to 90.2%. Thus, it can be demonstrated that the glacier can be accurately semi-automatically extracted from SAR with this method. The method is suitable not only for ENVISAT ASAR WSM imagery, but also for other satellite SAR imagery, especially for SAR imagery covering mountainous areas.

Amery ice shelf DEM and its marine ice distribution

The Amery Ice Shelf is the largest ice shelf in East Antarctica. A new DEM was generated for this ice shelf, using kriging to interpolate the data from ICE- Sat altimetry and the AIS-DEM. The ice thickness distribution map is converted from the new DEM, assuming hydrostatic equilibrium. The Amery Ice Shelf marine ice, up to 230 m thick, is concentrated in the northwest of the ice shelf. The volume of the marine ice is 2.38 × 10^3 km^3 and accounts for about 5.6% of the shelf volume.

3D DEM simulation of hard rock fracture in deep tunnel excavation induced by changes in principal stress magnitude and orientation

To achieve the loading of the stress path of hard rock,the spherical discrete element model(DEM)and the new flexible membrane technology were utilized to realize the transient loading of three principal stresses with arbitrary magnitudes and orientations.Furthermore,based on the deep tunnel of China Jinping Underground Laboratory II(CJPL-II),the deformation and fracture evolution characteristics of deep hard rock induced by excavation stress path were analyzed,and the mechanisms of transient loading-unloading and stress rotation-induced fractures were revealed from a mesoscopic perspective.The results indicated that the stressestrain curve exhibits different trends and degrees of sudden changes when subjected to transient changes in principal stress,accompanied by sudden changes in strain rate.Stress rotation induces spatially directional deformation,resulting in fractures of different degrees and orientations,and increasing the degree of deformation anisotropy.The correlation between the degree of induced fracture and the unloading magnitude of minimum principal stress,as well as its initial level is significant and positive.The process of mechanical response during transient unloading exhibits clear nonlinearity and directivity.After transient unloading,both the minimum principal stress and minimum principal strain rate decrease sharply and then tend to stabilize.This occurs from the edge to the interior and from the direction of the minimum principal stress to the direction of the maximum principal stress on theε1-ε3 plane.Transient unloading will induce a tensile stress wave.The ability to induce fractures due to changes in principal stress magnitude,orientation and rotation paths gradually increases.The analysis indicates a positive correlation between the abrupt change amplitude of strain rate and the maximum unloading magnitude,which is determined by the magnitude and rotation of principal stress.A high tensile strain rate is more likely to induce fractures under low minimum principal stress.

Assessing cutter-rock interaction during TBM tunnelling in granite:Large-scale standing rotary cutting tests and 3D DEM simulations

The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standing rotary cutting tests on granite in conjunction with high-fidelity numerical simulations based on a particle-type discrete element method(DEM)to explore the effects of key cutting parameters on the TBM cutter performance and the distribution of cutter-rock contact stresses.The assessment results of cutter performance obtained from the cutting tests and numerical simulations reveal similar dependencies on the key cutting parameters.More specifically,the normal and rolling forces exhibit a positive correlation with penetration but are slightly influenced by the cutting radius.In contrast,the side force decreases as the cutting radius increases.Additionally,the side force shows a positive relationship with the penetration for smaller cutting radii but tends to become negative as the cutting radius increases.The cutter's relative effectiveness in rock breaking is significantly impacted by the penetration but shows little dependency on the cutting radius.Consequently,an optimal penetration is identified,leading to a low boreability index and specific energy.A combined Hertz-Weibull function is developed to fit the cutter-rock contact stress distribution obtained in DEM simulations,whereby an improved CSM(Colorado School of Mines)model is proposed by replacing the original monotonic cutting force distribution with this combined Hertz-Weibull model.The proposed model outperforms the original CSM model as demonstrated by a comparison of the estimated cutting forces with those from the tests/simulations.The findings from this work that advance our understanding of TBM cutter performance have important implications for improving the efficiency and reliability of TBM tunnelling in granite.

Error Analysis on Gradient Information of Sloping Land Derived from the Low-resolution DEM

With digital elevation model （DEM）,sloping data were extracted automatically and soil erosion situation was also investigated. Compared with field survey and the related studies,the results showed that parallel range-gorge landform in Three Gorges reservoir area,the inter-bedded structures formed by Jurassic purple clay （page） rocks and human activities were the key controlling factors for small-scale sloping terrain.

Reconstructing DEM using TLS point cloud data and NURBS surface

Underground coal mining inevitably results in land surface subsidence.Acquiring information on land surface subsidence is important in the detection of surface change.However,conventional data acquisition techniques cannot always retrieve information on whole subsidence area.This study focuses on the reconstruction of a digital elevation model（DEM） with terrestrial laser scanning（TLS） point cloud data.Firstly,the methodology of the DEM with terrestrial 3-dimensional laser scanning is introduced.Then,a DEM modeling approach that involves the application of curved non-uniform rational B-splines（NURBS） surface is put forward.Finally,the performance of the DEM modeling approach with different surface inverse methods is demonstrated.The results indicate that the DEM based on the point cloud data and curved NURBS surface can achieve satisfactory accuracy.In addition,the performance of the hyperbolic paraboloid appears to be better than that of the elliptic paraboloid.The reconstructed DEM is continuous and can easily be integrated into other programs.Such features are of great importance in monitoring dynamic ground surface subsidence.

基于CryoSat-2的东南极PANDA断面考察沿线DEM制作及精度分析

基于卫星测高数据,国际上先后发布了ICESat DEM、Bamber DEM等全南极DEM.相对于传统高度计,大轨道倾角、长重访周期的设计使Cryo Sat-2具有更大的数据覆盖范围以及更加密集的轨道覆盖;同时,SARIn模式的启用也提高了Cryo Sat-2对于南极边缘区域的监测能力.针对利用Cryo Sat-2数据提取DEM问题,对Croy Sat-2的轨迹覆盖特征、数据滤波方法、最优内插参数选取以及DEM精度验证等方面进行了探讨,并利用克里金插值法生成了东南极PANDA断面考察沿线1 km分辨率的DEM.结果表明:通过与ICESat数据对比,发现PANDA断面考察沿线DEM整体高程精度约为(1.57±3.30)m;但是,局部区域高程精度分析表明,DEM精度具有不均一性,随着坡度的增加DEM高程精度逐渐下降,高程稳定性也同时下降.

基于DEM差分法的TanDEM-X数据森林高度估测

以现有Lidar获取的DEM(数字高程模型)数据、CHM(冠层高模型)和样地调查数据为辅助数据,基于干涉测高原理,以DEM差分法为例,分析该方法支持下TanDEM-X数据在普洱研究区森林高度估测中的可行性。结果表明,TanDEM-X数据在森林林分高度估测中具有很大的潜力,在有高精度地表DEM数据支持下,采用该法获得估测结果与Lidar数据获取的CHM(冠层高度模型)数据较接近,两者的RMSE为4.39 m,R2为0.70。此外,相位噪声对估测精度有严重影响,相位噪声剔除前后,估测结果与Lidar获取的CHM数据的R^2分别为0.23和0.70。

Research on Model of Flood Disaster's Monitoring and Its Application Based on DEM

In order to assess the flood damage rapidly and accurately,this paper proposed a practical method of flood disaster monitoring based on meso-scale automatic weather stations rainfall data and 1:5 million high-precision DEM (digital elevation model) data.It can predict roughly areas by the automatic weather station rainfall analysis and processing when the floods happen.Using partitions 'horizontal' approximation methods,the model of DEM flooding disaster's monitoring has been constructed based on 1:5 million high-precision DEM.And the technical methods applied to the analysis of experimental area.The result of flood disaster's monitoring is carried on comparison and the analysis through the verification by CBERS-02B.It finds that the area of floods is very consistent by the model of DEM and CBERS-02B flooding disaster's monitoring.So the method of flood disaster's motoring based on DEM can be real-time,dynamic,and can monitor the flood zone accurately and effectively.It also can provide the decision making department with present and assisting scheme of policy making.

基于TerraSAR-X/TanDEM-X干涉DEM的森林冠层高度估测

森林树高的大面积估测一直是森林资源调查和林业遥感所面临的技术难题。以云南省勐腊县森林资源为研究对象,将DEM差分法与TerraSAR-X/TanDEM-X全极化干涉数据、地形图相结合,用TerraSAR-X/TanDEM-X数据干涉生成各极化通道带有森林冠层高度的DSM,从地形图上提取地表高度DTM;对2个高度模型进行水平位置匹配,并提出用参考面将DSM与DTM转换为相对高度模型RDSM和RDTM,以消除高程基准差异;最后对RDSM和RDTM进行差分运算,估测出研究区各极化通道下的森林冠层高度分布。采用森林资源二类调查数据,对各极化通道的冠层估测高进行了合理性验证。研究表明:DTM的高程基准面低于DSM,平坦农地适合作为参考面提取相对高度模型。在小班尺度上与森林资源二类调查数据的对比显示:各极化通道的冠层估测高与小班林分高均呈显著的中等正相关,冠层高度估测值大小合理,人工林的估测结果略优于天然林;人工林与天然林的冠层估测结果均在主要坡度分布区间内与小班林分高的相关性高;各极化通道的估测结果整体上没有明显差异。从总体上来看,基于地形图和TerraSAR-X/TanDEM-X数据,利用DEM差分法来大面积估测森林冠层高度是一种有效可行的途径,为辅助森林资源调查工作提供了新思路。

利用多时相Landsat影像生成白洋淀湖底DEM的研究

该文使用多时相Landsat影像,以白洋淀地区为例,阐述基于中等分辨率的可见光—近红外遥感影像生成具有较高精度数字高程模型的非常规方法。对覆盖同一研究区的不同时相影像分别进行淹没区与非淹没区的分类,提取不同水位高度时的水域边界,并以此为相应水位高度的等高线,对获得的等高线进行插值生成数字高程模型(DEM)。这种由一系列遥感影像提取的水域图生成数字高程模型的方法适用于人为干预较少、地形相对简单的湿地或季节性湖泊,可以弥补该类地区数字高程信息不足或精度不够的缺陷。

An Empirical Study on China＇s Energy Supply-and-Demand Model Considering Carbon Emission Peak Constraints in 2030

China＇s energy supply-and-demand model and two related carbon emission scenarios, including a planned peak scenario and an advanced peak scenario, are designed taking into consideration China＇s economic development, technological progress, policies, resources, environmental capacity, and other factors. The analysis of the defined scenarios provides the following conclusions： Primary energy and power demand will continue to grow leading up to 2030, and the growth rate of power demand will be much higher than that of primary energy demand. Moreover, low carbonization will be a basic feature of energy supply-and-demand structural changes, and non-fossil energy will replace oil as the second largest energy source. Finally, energy- related carbon emissions could peak in 2025 through the application of more efficient energy consumption patterns and more low-carbon energy supply modes. The push toward decarbonization of the power industry is essential for reducing the peak value of carbon emissions.

TanDEM-X数据干涉地形信息精度分析

以德国宇航中心TanDEM-X数据为信息源,采用干涉技术提取植被覆盖区的地形,将相关系数、山脊线与山谷—水系线作为评价指标,对比5种地形数据(数字化DEM、SRTM–DEM、ASTER GDEM、TanDEM-X Monostatic-DEM,TanDEM-X Bistatic-DEM)在地表起伏表达方面的差异。研究结果显示,数字化DEM精度高,但是获取方式费时费力;SRTM-DEM能表现宏观地形,但分辨率低;ASTER GDEM分辨率有所提升,但是对地形的表达精度偏低;TanDEM-X干涉地形数据分辨率高,但是在林区受到森林冠层高度影响,实为数字表面模型,无法提供准确可靠的林下地形信息。

GEDI与Tandem-X DEM估测密林林下地形性能评价

针对密林情况下,GEDI数据与现有的Tandem-X DEM数字地面模型估测林下地形精度没有进行整体评价问题,拟以密林情况作为主要分析场景,通过提取GEDI L2A数据产品对应光斑的经纬度、林下地形信息与数据质量筛选参数,开展数据质量筛选,用以估测基于GEDI数据的林下地形数据,与Tandem-X DEM数据估测密林情况下研究区林下地形开展比较,并进一步探究冠层高度、森林覆盖度与植被类型对估测精度的影响。GEDI与Tandem-X DEM的R~2分别为0.99和0.98,GEDI估测林下地形结果的RMSE、Average与STD分别6.49、-1.92、4.42 m, Tandem-X DEM估测林下地形结果的RMSE、Average与STD分别为18.15、14.63、7.35 m。GEDI数据在混交林和稀疏草原情况下RMSE与Average分别变化8.05 m和6.04 m, Tandem-X DEM数据在常绿针叶林与农田/天然植被情况下,RMSE与Average变化幅度为21.63、26.43 m。实验结果表明,GEDI与Tandem-X DEM数据与机载验证数据存在强相关性,且GEDI相对Tandem-X DEM数据表现出更优的评价标准;地表植被类型相对冠层高度和植被覆盖度会对两数据估测林下地形精度产生更大的影响。

融合生成对抗网络与SRTM的ASTER GDEM数据重建

航拍死角、匹配偏差、点位不足、云雾遮盖等易使数字高程模型(DEM)存在数据异常。鉴于光学立体摄影测量获得的ASTER GDEM受天气因素影响大,雷达测量得到的SRTM DEM受地形起伏因素影响大,为提高ASTER GDEM数据的质量,该文构建一种多源多尺度残差连接门控卷积生成对抗网络(Multi-Source and Multi-Scale Residual-Connected Gated Convolutional Generative Adversarial Network, MSSRGC-GAN),利用SRTM DEM数据辅助重建ASTER GDEM中异常数据,并以实验区范围内多组不同地貌的ASTER GDEM样本数据重建为例,对模型进行定量评价。结果显示:重建数据RRMSE小于0.06,R~2大于0.9,PSNR大于60,SSIM在0.999 5以上,优于反距离插值法和SRTM镶嵌法等传统方法以及无门控卷积模型和无空洞卷积模型等深度学习方法。

基于倾斜三维模型与机载LiDAR点云的DEM快速更新

随着倾斜摄影技术的发展和实景三维建设的不断推进,地形级实景三维地理场景对DEM现势性要求日益提高。为了解决传统方法更新DEM成本高、工作量大的问题,本文提出了利用倾斜三维模型成果转换点云,融合两期DSM和DOM进行变化检测,替换已有机载LiDAR点云,快速更新DEM的方法,并通过项目验证了该方法的可行性,极大地节约了生产成本,为DEM更新提供了思路。

利用星载激光雷达数据校正森林区DEM误差

在植被区,通过光学遥感或InSAR技术生产的DEM产品不能反映真实林下地形高度。森林区DEM误差主要是植被高引起的系统偏差,植被覆盖度和地形是森林区DEM的主要误差来源。新一代星载激光雷达可以提供大量高精度林下地形控制点产品,为森林区DEM误差的纠正提供了新的契机。鉴于此,文章提出基于机器学习框架下顾及植被覆盖及地形因素的林区DEM误差校正方法。首先,获取高精度星载激光雷达地形控制点与DEM的地形残差;其次,利用光学遥感数据、SAR遥感数据及DEM产品数据计算与植被覆盖和地形有关的特征参数;最后,联合这些特征参数与获取的地形残差点分别建立不同类型DEM产品误差校正模型。选取位于美国田纳西州和北卡罗来纳州交界处的山地林区作为本研究的实验区。研究结果表明,相对原始DEM,校正高程误差后的DEM精度提升超过40%,有效校正了林区DEM误差。