Automatic recognition of loess landforms using Random Forest method

The automatic recognition of landforms is regarded as one of the most important procedures to classify landforms and deepen the understanding on the morphology of the earth. However, landform types are rather complex and gradual changes often occur in these landforms, thus increasing the difficulty in automatically recognizing and classifying landforms. In this study, small-scale watersheds, which are regarded as natural geomorphological elements, were extracted and selected as basic analysis and recognition units based on the data of SRTM DEM. In addition, datasets integrated with terrain derivatives(e.g., average slope gradient, and elevation range) and texture derivatives(e.g., slope gradient contrast and elevation variance) were constructed to quantify the topographical characteristics of watersheds. Finally, Random Forest(RF) method was employed to automatically select features and classify landforms based on their topographical characteristics. The proposed method was applied and validated in seven case areas in the Northern Shaanxi Loess Plateau for its complex andgradual changed landforms. Experimental results show that the highest recognition accuracy based on the selected derivations is 92.06%. During the recognition procedure, the contributions of terrain derivations were higher than that of texture derivations within selected derivative datasets. Loess terrace and loess mid-mountain obtained the highest accuracy among the seven typical loess landforms. However, the recognition precision of loess hill, loess hill–ridge, and loess sloping ridge is relatively low. The experiment also shows that watershed-based strategy could achieve better results than object-based strategy, and the method of RF could effectively extract and recognize the feature of landforms.

Geomorphological inheritance for loess landform evolution in a severe soil erosion region of Loess Plateau of China based on digital elevation models

The influence of pre-quaternary underlying terrain on the formation of loess landforms, i.e., the geomorphological inheritance issue, is a focus in studies of loess landforms. On the basis of multi-source information, we used GIS spatial analysis methods to construct a simulated digital elevation model of a pre-quaternary paleotopographic surface in a severe soil erosion area of the Loess Plateau. To reveal the spatial relationship between underlying paleotopography and modern terrain, an XY scatter diagram, hypsometric curve, gradient and concavity of terrain profiles are used in the experiments. The experiments show that the altitude, gradient and concavity results have significant linear positive correlation between both terrains, which shows a relatively strong landform inheritance relationship, particularly in the intact and complete loess deposit areas. Despite the current surface appearing somewhat changed from the original shape of the underlying terrain under different erosion forces, we reveal that the modern terrain generally smoothes the topographic relief of underlying terrain in the loess deposition process. Our results deepen understanding of the characteristics of geomorphological inheritance in the formation and evolution of loess landforms.

Paleotopographic controls on modern gully evolution in the loess landforms of China

The inhomogeneous and non-flat paleotopography in a depositional landform area profoundly controls the process of modem gully evolution and shapes the structure of a gully network. However, this controlling effect of paleotopography on modem gully evolution is mostly ignored because of the difficulties in paleotopography reconstruction. In this study, loess area in China is selected as case area for its typical depositional landform area and inhomogeneous and non-flat paleotopography during the Quaternary. The paleotopography underlying loess is considered while evaluating its controlling effects on the gully evolutionary process. On the basis of the geophysical prospecting, detailed geological information, and high-resolution digital elevation model, we reconstruct the pre-Quaternary paleotopographic surface in the case area. Comparative analysis is conducted to reveal the modern gully evolution in relation to the paleotopography. Results show that the concave area of the paleotopography acts as the basement of the high-order modern gully evolution in the hilly-gully area, although this concave area can be covered and buried by the loess depositional process during the Quaternary. A significant controlling effect of paleotopography on high-order modern gully evolution can be observed in a depositional landform with a hilly-gully underlying topography, whereas a relatively weak controlling effect exists in a flat underlying topograpnlcal area oecause of the strong horizontal shift effect of gully formation process. Several low-order modern gullies also exist and limit the controlling effect of paleotopography. These results reveal a controlled high-order modern gully evolutionary process and a rather dynamic low-order modem gully evolutionary process in the hilly-gully area. These results also help us understand the variations in different modern gully evolution in relation to paleotopography and the different management schemes for soil conservation and ecological restoration during the gully evolutionary process.

Clustering gully profiles for investigating the spatial variation in landform formation on the Chinese Loess Plateau

The gully is the most dynamic and changeable landform unit on the Loess Plateau,and the characteristics of gully landforms are key indicators of gully evolution.Different gully profiles are connected and combined through runoff nodes.Thus,it is necessary to cluster gully profiles into a gully profile combination(GPC)to reveal the spatial variation in gully landforms throughout the Loess Plateau.First,the gradient and gully evolution index(GEI)of two sample areas in Changwu and Suide in Shaanxi Province,China are calculated and analysed based on GPC.Then,the gradient and GEI are calculated by using 90-m-resolution digital elevation model(DEM)data for the severe soil erosion area with the basin as the research unit.On this basis,the spatial variation in the development degree is analysed with Getis-Ord Gi*.The results show that the degree of gully undercutting decreases from southeast to northwest under the influence of rainfall.Due to the soil properties,the loess in the northwest is more prone to collapse,resulting in the decrease of GEI from northwest to southeast.The development degree of gullies is closely related to rivers.The strong erosive capacity of rivers leads to greater differences in gullies within the basin.At the same time,the skewness and kurtosis of the gully index in the basin are correlated;when the distribution of the gully index in the basin is less normal,the distribution of the gully index is more concentrated.These results reveal the spatial variation characteristics of the Loess Plateau based on GPC.

等高线形态知识与图神经网络联合作用下的黄土地貌类型识别

地貌类型识别是多因素联合影响下的复杂决策问题。由于地貌区域环境的广泛性、差异性及地学要素作用的复杂性,简单地引入人工智能方法,通过典型样本监督学习并不能获得该问题的满意结果。因此,本文尝试将等高线形态知识这种测绘自然智能与人工智能结合,在地形形态表达规则和典型地貌类型样本训练联合驱动下,开展混合智能下黄土地貌类型识别研究,提出了整合等高线形态知识与带池化操作图神经网络(graph neural network,GNN)的地貌类型识别方法。本文方法将地貌单元的等高线建模为图结构,并将提取的等高线顶点的形态知识嵌入图节点中,采用带池化操作的GNN模型,挖掘图结构中的高层次特征和上下文信息,以识别地貌类型识别。试验结果证明了本文方法在黄土地貌类型识别上的有效性:在测试数据上获得了86.1%的F 1值,比两个对比方法高出3.0%~8.2%。

Extraction and Analysis of Gully Head of Loess Plateau in China Based on Digital Elevation Model

In China′s Loess Plateau area, gully head is the most active zone of a drainage system in gully areas. The differentiation of loess gully head follows geospatial patterns and reflects the process of the loess landform development and evolution of its drainage system to some extent. In this study, the geomorphic meaning, basic characteristics, morphological structure and the basic types of loess gully heads were systematically analysed. Then, the loess gully head′s conceptual model was established, and an extraction method based on Digital Elevation Model(DEM) for loess gully head features and elements was proposed. Through analysing the achieved statistics of loess gully head features, loess gully heads have apparently similar and different characteristics depending on the different loess landforms where they are found. The loess head characteristics reflect their growth period and evolution tendency to a certain degree, and they indirectly represent evolutionary mechanisms. In addition, the loess gully developmental stages and the evolutionary processes can be deduced by using loess gully head characteristics. This study is of great significance for development and improvement of the theoretical system for describing loess gully landforms.

黄土高原洛河流域地貌发育特征与形成演化

黄土地貌形态特征、发育机理及演化过程等一直是地学研究的热点和前沿。选取黄土高原洛河流域作为研究对象,从坡面尺度、流域尺度、区域尺度分类选取14项地貌因子,较为全面地构建了流域地貌发育形态定量参数体系;提取646个小流域为分析单元,利用主成分分析法,获得了描述流域黄土地貌形态特征的4个主因子;这4个主因子分别反映了4种地貌形态空间格局,即南北渐变型、单中心扩散型、东西过渡型、多中心扩散型。结合流域地貌类型和地貌发育程度特征,认为黄土地貌地形起伏和垂直侵蚀特征反映了研究区的总体地貌空间格局,洛河流域黄土地貌主要是在多种因素影响下,随着水系由下游向上游不断地溯源侵蚀、下切扩展,最终形成了现今形态空间分异格局。

微生物基因检测技术在鄂尔多斯盆地神府南气田勘探中的应用

针对鄂尔多斯盆地构造复杂,储层分布差异大,气藏富集规律不明等问题,本文采用微生物基因检测技术的荧光定量PCR法测量研究区样品中油气指示基因的丰度,同时利用高通量基因测序法检测样品中的烃类微生物种群类型,分析认为,本区主要有东北部、西部、南部三个烃类异常带,展布特征与沉积认识吻合,且西部、南部有亲缘关系,东北部与二者无亲缘关系,可能与致密气、煤层气不同层系烃的逸散有关。实钻表明,本技术对于鄂尔多斯盆地致密气和煤层气混源区的含油气性评价方面具有较好的适用性,为油气有利区带筛选提供参考依据。

The paleogeographic implications of loess mounds: Laizhou Bay plain

The loess mounds are a newly discovered type of landforms on the Laizhou Bay plain south of the Bohai Sea. Research shows that they were formed in the late period of the late Pleistocene when the Bohai Sea was exposed in the period of late W黰u glacial age and changed into plain. As the exposed area is not protected by vegetation, the sediments at the sea bottom are blown and transported southward by strong north winds, and deposit on the coastal plains. As thick loess is accumulated, the loess mound landforms are formed in the direction of down wind.

Quantifying spatial scale of positive and negative terrains pattern at watershed-scale:Case in soil and water conservation region on Loess Plateau

The positive and negative terrains(P-N terrains) widely distributed across China's Loess Plateau constitute the dual structure characteristic of loess landforms. Analysis of loess P-N terrains at the watershed scale can serve to elucidate the structural characteristics and spatial patterns of P-N terrains, which benefits a better understanding of watershed evolution and suitable scales for loess landform research. The Two-Term Local Quadrat Variance Analysis(TTLQV) is calculated as the average of the square of the difference between the block totals of all possible adjacent pairs of block size, which can be used to detect both the scale and the intensity of landscape patches(e.g., plant/animal communities and gully networks). In this study, we determined the latitudinal and longitudinal spatial scale of P-N terrain patterns within 104 uniformly distributed watersheds in our target soil and water conservation region. The results showed that TTLQV is very effective for examining the scale of P-N terrain patterns. There were apparently three types of P-N terrain pattern in latitudinal direction(i.e., Loess Tableland type, Loess Hill type, and Transitional Form between Sand and Loess type), whereas there were both lower and higher values for P-N terrain pattern scales in all loess landforms in the longitudinal direction. The P-N terrain pattern alsoclearly presented anisotropy, suggesting that gully networks in the main direction were well-developed while others were relatively undeveloped. In addition, the relationships between the first scales and controlling factors(i.e., gully density, nibble degree, watershed area, mean watershed slope, NDVI, precipitation, loess thickness, and loess landforms) revealed that the first scales are primarily controlled by watershed area and loess landforms. This may indicate that the current spatial pattern of P-N terrains is characterized by internal force. In selecting suitable study areas in China' Loess Plateau, it is crucial to understand four control variables: the spatial scale of the P-N terrain pattern, the watershed area, the main direction of the watershed, and the loess landforms.

Hierarchy structure characteristics analysis for the China Loess watersheds based on gully node calibration

A land surface region can be decomposed into a series of watershed units with a hierarchical organizational structure. For loess landform, the watershed is a basic spatial–structural unit that can express natural landforms, surface morphology characteristics, spatial organization and developmental evolution. In this research we adopted the concept of node calibration in the watershed structure unit, selected six complete watersheds on China Loess Plateau as the research areas to study the quantitative characteristics of the hierarchical structure in terms of watershed geomorphology based on digital elevation model(DEM) data, and then built a watershed hierarchical structure model that relies on gully structure feature points. We calculated the quantitative indices, such as elevation, flow accumulation and hypsometric integral and found there are remarkably closer linear correlation between flow accumulation and elevation with increasing gully order, and the same variation tendency of hypsometric integral also presented. The results showed that the characteristics of spatial structure become more stable, and the intensity of spatial aggregation gradually enhances with increasing gully order. In summary, from the view of gully node calibration, the China Loess watershed structure shows more significantly complex, and the developmental situation variation of the loess landforms also exhibited a fairly stable status with gully order increasing. So, the loess watershed structure and its changes constructed the complex system of the loess landform, and it has the great significance for studying the spatial pattern and evolution law of the watershed geomorphology.

黄土高原沟沿线研究进展与展望

沟沿线是黄土地貌正负地形类型划分和形态刻画的重要分界线,蕴含丰富的地貌形态信息,也是衡量沟谷侵蚀及地貌发育演化的重要基础。在前人对黄土地貌与数字地形分析的研究基础上,对沟沿线的概念模型、特征自动提取及其应用等相关研究进行回顾总结与评述,系统归纳当前沟沿线的研究成果与科学理论进展,对当前沟沿线研究现状进行深入思考并对其发展趋势做出展望。沟沿线的研究逐步成熟,目前常用的提取方法有4种:影像手绘法、基于地貌形态学法、基于图像分割法和基于点云数据法,但适用范围不广且提取精度有所差异;基于沟沿线的应用研究较为单一,大范围应用较少。沟沿线是黄土地貌的一条特殊线,将黄土地貌划分为典型二元结构,是深入了解黄土地貌、构建水土流失模型的关键。未来沟沿线的研究将重点从高精度沟沿线自动提取、沟沿线提取算法全局高效及局部保真、沟沿线与黄土高原沟壑之间的耦合关系等方面展开。

基于BP神经网络的黄土侵蚀沟自动提取方法

黄土侵蚀沟信息是研究沟壑地貌土壤侵蚀的重要依据,而目前遥感影像提取方法中存在沟沿陡边的遮挡问题,由此,本文研究了一种基于反向传播神经网络的自动提取方法。首先,利用数字高程模型,基于黄土侵蚀沟的特征分析,选取横向坡度、坡度变率、坡向变率、地形起伏度、地表切割深度、高程变异系数和地表粗糙度作为地形特征因子,通过沟谷网络的计算,制作黄土侵蚀地貌的训练样本数据集;然后,基于反向传播神经网络模型的训练实验,选择Trainbr作为神经网络模型的学习算法;最后,应用侵蚀沟地貌的神经网络模型对测试数据集进行提取实验,并与随机森林和支持向量机方法进行比较。结果表明,本文方法的准确率好于其他方法,漏分情况相对较少,可以满足黄土冲沟信息的高效与准确提取需求。

陕北甘泉丹霞峡谷群地质遗迹景观特征与保护利用

甘泉丹霞峡谷群位于陕北丹霞地质遗迹景观带的中部,地处鄂尔多斯盆地伊陕斜坡,为典型的狭缝式丹霞景观。通过野外调查、实测和研究发现:甘泉丹霞峡谷群地质遗迹景观的造景地层为下白垩统洛河组风成相紫红色碎屑沉积岩,岩石呈厚-巨厚层状;垂向节理较为密集,NE-NEE向、近SN向和NW向节理控制了峡谷群的发育。景观类型以负地形的波浪谷(波浪状凹槽与凸起间或分布)为主,辅以丹霞崖壁、一线天、壶穴、象形石等;景观类别与众不同,为具有国际对比研究价值的黄土覆盖型,主要沿洛河支流展布;景观美学上呈现“窄狭、多弯、纵高、陡峻”+“巨厚、均一、韵律、多彩”特征;景观价值上具有科学研究、科考探险、旅游休闲、科普教育等复合多元的多种功能。由于甘泉丹霞峡谷群地处生态环境脆弱区和经济欠发达区,未来应加大地质遗迹科研力度,划定地质遗迹保护区,明确地质遗迹保护措施,推进地质遗迹科普教育,开展地质文化村建设,以达到持续保护利用的目的。

陕北黄土高原地貌景观资源化探讨

黄土高原地貌类型多样,景观优美,具有极大的观赏价值。以往对这种地质遗迹资源的旅游价值认识不足。现提出黄土高原地貌景观是一种旅游资源,对其进行开发是当地脱贫致富的新途径。为此,论述了黄土地貌景观的旅游资源属性、美学价值以及向旅游资源转化的可行性和景观开发利用思路,并提出了建立黄土地貌世界地质公园的建议。

典型黄土地貌类型区的地形复杂度分形研究

黄土高原地貌形态与地形复杂度自南向北有序变化,构成了举世瞩目的独特的地理景观。选择陕西省南北剖面六个典型黄土地貌样区为基本实验区,以其1∶1万栅格DEM为数据源,探讨典型黄土地貌类型区的地形复杂度分形与空间分异特征。首先提出的元分维模型方法,以计算得到的DEM元分维值作为特征指标,研究样区的地形复杂度问题。这种通过滑动窗口的扩展分维分析方法,既可以用于分析该区域不同尺度下的地形复杂度变化情况,也可以探讨区域的局部单元复杂程度及其空间分布,从而不再局限于对全区域的单一分维评价。以此为基础,进一步应用元分维谱方法,研究地貌网格单元的元分维分级分布情况。实验结果表明:以绥德和延川为代表的黄土峁状丘陵沟壑区最为复杂,以宜君和甘泉为代表的梁状丘陵沟壑区居中,而以淳化为代表的黄土塬区和以神木为代表的风沙黄土过渡区最为平缓。实验进一步证明了扩展分形方法在黄土地貌研究中的可行性。

子午岭林区北部近50年植被的变化发展

子午岭林区的北部 ,地貌上具有黄土丘陵沟壑的特点。该区植被的演替序列为 :从弃耕地先锋群落开始 ,经草本、灌木群落时期到早期森林群落山杨 (Populus davidiana)林或白桦 (Betula platyphylla)林、侧柏 (Platycladus orientalis)林等 ,进而到后期森林群落辽东栎(Quercus liaotungensis)林或油松 (Pinus tabulaeformis)林。近 5 0年来 ,油松林和侧柏林已经或正完成向辽东栎林方向的发展。山杨林、白桦林和侧柏林为该区演替系列中的过渡时期 ,气候性的演替顶极为辽东栎林 ,油松林为亚顶极。同时该区还表现出整体向前发展的趋势 ,这明显体现在原来林区大部分为山杨林 ,而现在辽东栎林已取代山杨林成为主要林分。只有阳坡下部基岩露出的陡壁上的侧柏林仍无向前发展的征象 ,为该区的一种局部土壤性演替顶极。阴坡、半阴坡从草本群落到顶极的演替全过程需要约 1 5 0 a,阳坡、半阳坡从草本群落演替到顶极但不包含油松林阶段 (目前尚缺少这一阶段 )需要 1 5 0 a左右 ,梁顶部位的演替速度与阴坡、半阴坡大致相近。从植被的类型、分布和演替来看 。

黄土高原小流域不同地形下土壤有机碳分布特征

研究了黄土高原小流域尺度塬面、坡地、沟道和梯田4种地形条件下土壤有机碳总量和活性组分的分布、储量及碳库管理指数的差异。结果表明,小流域土壤有机碳和不同活性有机碳的变异系数介于32%—70%之间,表现出中到高度的变异特征。4种地形下各组分有机碳含量和储量以塬面土壤最高,沟道土壤最低,并随土层深度的增加而降低,降低程度随有机碳活性增强而增加。以塬面土壤为对照所获得的碳库管理指数可灵敏指示有机碳对地形条件的响应特征,中活性有机碳库管理指数的指示效果最好。研究结果可部分解释黄土高原土壤有机碳地带性分布特征。

新疆黄土地貌的遥感判读问题

新疆的黄土地貌及其遥感判读具有不同于我国黄土高原地区的一些特点。根据参与"中国1:1 000 000数字地貌制图(新疆片)"项目工作的实践和体会,从黄土地貌区的位置、色调与色彩、大小、形状、阴影、水系和纹理、植被和土壤、相关体、相关资料和野外经验等方面总结了7项关于新疆黄土地貌的遥感判读依据,并归纳了新疆黄土地貌与风沙、干燥、流水、冰缘、雅丹等地貌类型之间以及与部分特殊情况之间的一些鉴别特征。结果可为新疆未来的地貌制图及相关的科研与教学工作提供参考。

黄土丘陵地貌形成模式与地貌演变

通过对陕西北部典型黄土丘陵区地貌调查,提出了黄土丘陵地貌形成模式,并对地貌演变进行了探讨。黄土高原原生黄土丘陵分布广泛,主要在下伏古丘陵基础上由黄土加积而成;次生黄土丘陵是黄土塬、黄土台塬等经沟谷侵蚀、改造而成。黄土丘陵区河流阶地和沟谷层状地貌反映了河流、沟谷的形成与演变。黄河一级支流形成于早更新世末;早中更新世末、晚中更新世初黄河一级支流和较大的二级支流形成了较完整的水系;中更新世末如韭园沟等较大的沟谷形成;晚更新世末河网、沟谷格局与现在已基本一致;尚未切入基岩的冲沟多形成于全新世;长度百米至数十米的切沟多是历史时期或近几十年来形成的。