基于MATLAB平台的遥感影像沙丘脊线提取与地貌格局表征参数计算

随着现代科学技术的发展,遥感影像为区域风沙地貌形态的研究提供了可靠的资料。近年来,有地貌学者提出了沙丘地貌格局分析法,通过在遥感影像上绘制沙丘脊线,量测和计算得到沙丘地貌格局表征参数,分析沙丘概率分布和空间变化规律、影响因素及形成时间。本文选取腾格里沙漠典型横向沙丘区域为研究对象,发展基于MATLAB平台的遥感影像沙丘脊线提取方法,利用沙丘迎风坡与落沙坡在遥感影像中成像的灰度差异, 对沙丘的沙脊线进行提取, 继而获得沙丘脊线长度、沙丘间距、走向、缺陷密度等沙丘地貌格局表征参数。结果表明,该方法快捷、可靠,为沙丘脊线的绘制提供了一种新方法。     

腾格里沙漠东南缘沙丘迎风坡风速变化的初步研究

对腾格里沙漠东南缘格状沙丘表面气流的观测结果表明,迎风坡风速的增加程度因坡成形态和原始气流的方向,强度而不同。迎风坡风速放大率介于１．０６～１．９１之间,且在格状沙丘主梁,主要与坡形系数和高度有关;在副梁随原始风入射角,坡形系数而变化,风速放大率对沙丘形态的影响主一要增加丘顶区域的输沙率和活动性,且因区域气流的方向和强度而不同,在横向气流条件下,其迎风坡随区域气流强度和增加而变缓,变长,在双向（斜     

Sand dune movement in the Victoria Valley, Antarctica

We use vertical aerial photographs and LiDAR topographic survey data to estimate dune migration rates in the Victoria Valley dunefield, Antarctica, between 1961 and 2001. Results confirm that the dunes migrated an average of 1.5 m/year. These values are consistent with other estimates of dune migration from cold climate deserts and are significantly lower than estimates from warm deserts. Dune migration rates are retarded by the presence of entrained ice, soil moisture and a reversing wind regime. Dune absorption, merging and limb extension are apparent from the time-series images and account for significant changes in dune form and the field-scale dune pattern. Dune-field pattern analysis shows an overall increase in dune-field organization with an increase in mean dune spacing and a reduction in total crest length and defect density. These data suggest that dunes in other cold desert environments on Earth, Mars or Titan, that may also have inter-bedded frozen laminae, still have the potential to migrate and organize, albeit at lower rates than dunes in warm deserts.     

A wind tunnel simulation of the dynamic processes involved in sand dune formation on the western coast of Hainan Island

The western coast of Hainan Island exhibits a savanna landscape. Many types of sand dunes, including transverse dune ridges, longitudinal dune ridges, elliptical dunes, coppice dunes, and climbing dunes, are widely distributed in the coastal zone. In winter, high-frequency and high-energy NE winds (dominant winds) are prevalent, with a resultant drift direction (RDD) of S35.6°W. In spring, low-frequency and low-energy SW secondary winds prevail, with a RDD of N25.1°E. Wind tunnel simulations revealed that the airflow over the dune surface is the main factor controlling the erosion and deposition patterns of dune surfaces and the morphological development of dunes. In the region's bidirectional wind en-vironment, with two seasonally distinct energy levels, the airflow over the surface of elliptical dunes, barchan dunes, and transverse dune ridges will exhibit a transverse pattern, whereas the airflow over longitudinal dunes ridges exhibits a lateral pattern and that over climbing dunes exhibits a climbing-circumfluent pattern. These patterns represent different dynamic processes. The coastal dunes on the western coast of Hainan Island are influenced by factors such as onshore winds, sand sources, coastal slopes, rivers, and forest shelter belts. The source of the sand that supplements these dunes particularly influences the development pattern: when there is more sand, the pattern shows positive equilibrium deposition between dune ridges and dunes; otherwise, it shows negative equilibrium deposition. The presence or absence of forest shelter belts also influences deposition and dune development patterns and transformation of dune forms. Coastal dunes and inland desert dunes experience similar dynamic processes, but the former have more diversified shapes and more complex forma-tion mechanisms.     

沙坡头地区新月形沙丘粒度特征

由腾格里沙漠东南缘沙坡头附近新月形沙丘表面沉积物的系统采集分析结果,发现从北部沙漠主体向黄河南岸,沙丘沙平均粒径变细但分选变差。同时,粒径及分选性在沙丘断面出现两种变化模式,其一是沙漠主体新月形沙丘由两侧坡部向丘顶区域粒径变细分选变好;其二为黄河两岸阶地和湖盆滩地的新月形沙丘丘顶沙粒粗于其它部位但分选仍然最好。根据粒度参数间的相互关系和其它环境条件的分析,对沙丘沙粒度变化的原因及偏度等也作了初步探讨。     

海南岛西海岸沙丘形成动力过程的风洞模拟试验

The western coast of Hainan Island exhibits a savanna landscape. Many types of sand dunes, including transverse dune ridges, longitudinal dune ridges, elliptical dunes, coppice dunes, and climbing dunes, are widely distributed in the coastal zone. In winter, high-frequency and high-energy NE winds (dominant winds) are prevalent, with a resultant drift direction (RDD) of S35.6°W. In spring, low-frequency and low-energy SW secondary winds prevail, with a RDD of N25.1°E. Wind tunnel simulations revealed that the airflow over the dune surface is the main factor controlling the erosion and deposition patterns of dune surfaces and the morphological development of dunes. In the region’s bidirectional wind en- vironment, with two seasonally distinct energy levels, the airflow over the surface of elliptical dunes, barchan dunes, and transverse dune ridges will exhibit a transverse pattern, whereas the airflow over longitudinal dunes ridges exhibits a lateral pattern and that over climbing dunes exhibits a climbing-circumfluent pattern. These patterns represent different dynamic processes. The coastal dunes on the western coast of Hainan Island are influenced by factors such as onshore winds, sand sources, coastal slopes, rivers, and forest shelter belts. The source of the sand that supplements these dunes particularly influences the development pattern: when there is more sand, the pattern shows positive equilibrium deposition between dune ridges and dunes; otherwise, it shows negative equilibrium deposition. The presence or absence of forest shelter belts also influences deposition and dune development patterns and transformation of dune forms. Coastal dunes and inland desert dunes experience similar dynamic processes, but the former have more diversified shapes and more complex formation mechanisms.     

Controls on coastal dune morphology, shoreline erosion and barrier island response to extreme storms

The response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore. While it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge, the underlying causes of the alongshore variation remain poorly understood. This study examines the alongshore variation in dune morphology along a 11 km stretch of Santa Rosa Island in northwest Florida and relates the variation in morphology to the response of the island during Hurricane Ivan and historic and storm-related rates of shoreline erosion. The morphology of the foredune and backbarrier dunes was characterized before and after Hurricane Ivan using Empirical Orthogonal Function (EOF) analysis and related through Canonical Correlation Analysis (CCA). The height and extent of the foredune, and the presence and relative location of the backbarrier dunes, varied alongshore at discrete length scales (of ~ 750, 1450 and 4550 m) that are statistically significant at the 95% confidence level. Cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner-shelf, the backbarrier cuspate headlands, and the historical and storm-related trends in shoreline change. Sections of the coast with little to no dune development before Hurricane Ivan were observed in the narrowest portions of the island (between headlands), west of the transverse ridges. Overwash penetration tended to be larger in these areas and island breaching was common, leaving the surface close to the watertable and covered by a lag of shell and gravel. In contrast, large foredunes and the backbarrier dunes were observed at the widest sections of the island (the cuspate headlands) and at crest of the transverse ridges. Due to the large dunes and the presence of the backbarrier dunes, these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper-shoreface. It is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace. Since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface, it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively. These findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during Hurricane Ivan.     

Historical Dune Pattern Dynamics: White Sands Dune Field,New Mexico

Research efforts studying dune fields as spatial units are limited and the historical dynamics associated with dune field-scale pattern attributes are currently not well documented. Historical repeat aerial photography was used to quantify temporal changes in the crescentic dune pattern at the White Sands Dune Field, New Mexico. A Geographic Information System (GIS) was used to digitize ~ 14,000 dune crests from the combined photoset. Crest length, sinuosity, spacing, orientation, transport vector, and defect density were calculated from these measurements and statistically analyzed. The pattern analysis revealed that crest length, sinuosity, and defect density were highly variable pattern elements over a 60-year period. These dune pattern elements also exhibited temporal relationships, such as the inverse relationship between crest length and sinuosity over time. Defect density calculations revealed that the dune field is trending to a possible state of disorganization. This trend was temporarily interrupted in 1985 by a massive period of organization in which crest length was inversely related to defect density and defect density was proportionally related to sinuosity. The temporal variations in these pattern elements and the episodic organizational event in 1985 were likely climatically induced.     

Post-Nipissing Origin of a Backdune Complex Along the Southeastern Shore of Lake Michigan

Relatively low (<25 m) parabolic dunes and dune ridges occur inland of massive parabolic dunes in many dune complexes along the southeastern shore of Lake Michigan. The major study of these backdunes (Tagues, 1946) concluded, based on field criteria, that they were older than the massive parabolic dunes and originate at the Calumet and Algonquin stages of ancestral Lake Michigan (~14-10 ka). Younger ages are indicated by this study in which Optically Stimulated Luminescense (OSL) ages were obtained from the crest of three backdunes southwest of Holland, Michigan. All ages are within statistical error of each other and indicate dune stabilization at ~4 ka. Similarities in surface soil development throughout the backdunes support the conclusion that they all stabilized at about the same time. Radiocarbon ages from paleosols indicate that the massive parabolic dunes were active at 4 ka and that this activity persisted after the back dunes had stabilized. In the Holland area, dune growth and migration occurred in a broad zone, including both back and massive parabolic dunes, immediately after the rise to and drop from Nipissing II high lake levels but became confined to a narrower zone closer to shore after ~4 ka.     

新月形沙丘维持相对稳定的两种过程

新月形沙丘顶部稳定性是风沙地貌学尚未解决的科学问题。研究新月形沙丘的顶部稳定性,对于绿洲边缘风沙运动规律揭示、防沙工程建设和沙区生态环境保护等具有重要的现实意义。选择民勤沙区新月形沙丘,通过测定沙丘各部位风速、风蚀风积和粒度等,分析了新月形沙丘顶部稳定机理。主风向（NW）作用是新月形沙丘最高点与沙脊线重合、沙丘前移和高度降低的过程;反向风（SE）作用是沙丘最高点与沙脊线分离、沙丘背风坡风蚀与沙丘增高的过程。由于研究区以NW风为主,新月形沙丘沿NW-SE方向前移,SE风只能风蚀减缓沙丘背风坡的坡度。人为干预将会阻止或减少从迎风坡向沙丘顶部输送沙量,使得新月形沙丘背风坡尤其是背风坡上部风蚀过程增强,新月形沙丘逐渐过渡为抛物线形沙丘。     

Numerical modelling of flow structures over idealized transverse aeolian dunes of varying geometry

A Computational Fluid Dynamics (CFD) model (PHOENICS™ 3.5) previously validated for wind tunnel measurements is used to simulate the streamwise and vertical velocity flow fields over idealized transverse dunes of varying height (h) and stoss slope basal length (L). The model accurately reproduced patterns of: flow deceleration at the dune toe; stoss flow acceleration; vertical lift in the crest region; lee-side flow separation, re-attachment and reversal; and flow recovery distance. Results indicate that the flow field over transverse dunes is particularly sensitive to changes in dune height, with an increase in height resulting in flow deceleration at the toe, streamwise acceleration and vertical lift at the crest, and an increase in the extent of, and strength of reversed flows within, the lee-side separation cell. In general, the length of the separation zone varied from 3 to 15 h from the crest and increased over taller, steeper dunes. Similarly, the flow recovery distance ranged from 45 to >75 h and was more sensitive to changes in dune height. For the range of dune shapes investigated in this study, the differing effects of height and stoss slope length raise questions regarding the applicability of dune aspect ratio as a parameter for explaining airflow over transverse dunes. Evidence is also provided to support existing research on: streamline curvature and the maintenance of sand transport in the toe region; vertical lift in the crest region and its effect on grainfall delivery; relations between the turbulent shear layer and downward forcing of flow re-attachment; and extended flow recovery distances beyond the separation cell. Field validation is required to test these findings in natural settings. Future applications of the model will characterize turbulence and shear stress fields, examine the effects of more complex isolated dune forms and investigate flow over multiple dunes.     

Internal structure of the aeolian sand dunes of El Fangar spit, Ebro Delta (Tarragona, Spain)

This paper presents an analysis of the dune field dynamics of El Fangar Spit in the Ebro Delta (Spain), associating it with the internal structure of dunes carried out with ground-penetrating radar and supported by data from topographic DGPS. These analyses are of great importance to ascertain the state of the internal structure of dunes as an important element in their stability and, therefore in their evolution. The internal structure shows accretion and progradation sequences of dunes over beach deposits, which depend on dune morphology (height, crest orientation) and location, as well as the processes acting on them.     

腾格里沙漠东南缘格状沙丘表面气流及其地貌学意义

对腾格里沙漠东南缘沙丘形态与区域气流的分析表明,格状沙丘发育在双向低风能环境。沙丘表面气流及沉积过程的观测结果,主梁长期处在横向气流环境,其形态主要受背风坡分离气流控制,并以迎风坡侵蚀、背风坡净堆积形式顺主风向迁移。副梁处在双向-斜向气流环境,背风坡的附体偏向气流控制其形态和动力学过程,而且其强度是原始风入射角余弦的对数函数。在斜向风作用下,副梁迎风坡侵蚀的同时,背风坡中下部也发生沙粒的纵向输移且堆积于主梁背风坡,从而导致副梁沿年合成输沙方向延伸。由此认为,格状沙丘的主梁形成于主风-西北风的作用,而副梁是在主梁基础上并在主风和次风-东北风的交替作用下形成的;其形态动力学类型应属纵向沙丘置于横向沙丘之上一种复杂型沙丘。     

反向沙丘近地层气流变化及其对沙丘形态的影响

反向沙丘形态-动力学过程是风沙地貌的重要研究内容.选择腾格里沙漠东南缘推平沙地发育的反向沙丘为研究对象,采用二维超声风速仪对沙丘表面5个位置0.25 m和0.5 m高度的气流进行野外观测.结果表明:(1)气流方向影响近地层气流特征.以沙丘脊线垂线为轴,0.25 m高度处沙丘脊线的垂线两侧风向变化不完全对称.当丘顶气流方...     

腾格里沙漠东南缘固沙灌丛林土壤理化性质及分形维数

以腾格里沙漠固沙灌丛林为研究对象,选择大、中、小沙丘的迎风坡、丘顶和背风坡为研究样地,调查不同沙丘微地形土壤理化性质和土壤粒径分布的分形特征,阐明沙丘大小和微地形差异对固沙灌丛林土壤理化性质和土壤分形维数分布的影响规律.结果表明:(1)土壤含水率和全碳含量均表现为背风坡中部显著高于丘顶;土壤容重表现为迎风坡中部、丘顶和...     

河北昌黎黄金海岸横向沙脊表面的粒度分布模式

河北昌黎黄金海岸自然保护区内的横向沙脊规模高大、形态典型,对其表面采集的47个沙丘表面沉积物粒度样品的分析结果,该海岸横向沙脊表面粒度总体上是中砂、分选好、对称和中等峰态,但脊顶、坡部及坡脚的粒度分异明显,自沙脊两侧坡脚向脊顶粒径变细、分选变好,向陆背风坡的细化与分选优于向海迎风坡,脊顶粒径最细,向陆背风坡脚最粗,是一种新型的沙丘表面粒度分布模式。该粒度分布模式是该区域主风向与强风向交替变化及其风速差异、沙脊高大且两侧不对称等组合作用的结果。     

Observations of coastal aeolian dune movements at Feicuidao, on the Changli Gold Coast in Hebei Province

High-precision RTK GPS technology was used to survey the movements of typical coastal dunes, including a coastal crescent dune and a coastal transverse ridge, in the Feicuidao region of the Changli Gold Coast in Hebei Province in 2006–2008. Our data provide information on the direction, type, and velocity of coastal dune movements, and indicate that the coastal dunes in this region are characterized as slow and landward advancing, with to-and-fro fluctuations. The bottom of the studied coastal transverse ridge was stable during the observation period but the position of its crest advanced eastward (seaward) during summer and autumn, and moved landward (westward) in winter and spring. Thus, its crest moved generally landward (westward) but fluctuated to-and-fro eastward and westward. In contrast, the entire coastal crescent dune advanced landward (westward) in a to-and-fro manner, and the velocity of its movement was faster than that of the transverse ridge dune. These results are mainly related to the wind conditions in the research area, the height and volume of the two types of coastal dunes.     

腾格里沙漠东南缘反向沙丘形态演化过程

沙丘形态演化是风沙地貌研究的重要内容。反向沙丘是指在相反方向风作用下形成的沙丘,有两个落沙坡,分别对应两个风向,在主风向作用下形成横向沙丘,但在相反方向风作用下,沙丘顶部向主风方向移动,从而形成反向沙丘。反向沙丘存在于任何有两个相反方向风的地区。以腾格里沙漠东南缘平坦沙地上发育的反向沙丘为研究对象,2010年对沙丘迎风坡和背风坡不同部位坡度进行1年期野外测量,旨在阐明反向沙丘的形态演化过程。结果表明：反向沙丘形态演化包括3个阶段：横向沙丘—过渡态—反向沙丘,但研究区的沙丘形态演化经历5个阶段：横向沙丘—过渡态—反向沙丘—过渡态—横向沙丘。不同演化阶段的沙丘迎风坡和背风坡角度发生明显变化。该研究结果增加人们对反向沙丘形态演化过程的认识,对区域风沙地貌改造利用提供理论依据。     

中国温带海岸沙丘分类系统初步探讨

海岸沙丘分类一直是海岸风沙地貌研究的重要基础问题之一。本文以已有的国内外海岸沙丘分类研究为基础,根据我国温带海岸的自然地理环境和海岸沙丘的类型特点,制定了一个三级10类的我国温带海岸沙丘的分类系统,并简单介绍了我国温带海岸主要海岸沙丘类型的分布与基本形态特征。     

河北昌黎翡翠岛海岸沙丘移动的初步观测

采用RTK GPS技术与测量方法,于2006-2008年对中国海岸沙丘主要分布区域之一的河北昌黎黄金海岸翡翠岛的典型海岸新月形沙丘和横向沙脊的移动进行了高精度观测。观测结果表明,翡翠岛海岸沙丘的移动总体呈现出缓慢、向陆、往复式前进的特征,但不同沙丘类型以及沙丘不同部位的移动间存在差异,其中海岸横向沙脊是底部基本稳定下脊顶在夏秋季向海东移、冬春季向陆西移的往复变化中向陆西移,而新月形沙丘则是沙丘的整体陆向位移且移动速度相对较快,主要与风况、沙丘高度与规模及人类活动有关。