Quantitative mapping of arid alluvial fan surfaces using field spectrometer and hyperspectral remote sensing

Mapping and dating of arid and semi-arid alluvial fans are of great importance in many Quaternary studies. Yet the most common mapping method of these features is based on visual, qualitative interpretation of air-photos. In this study we examine the feasibility of mapping arid alluvial surfaces by using airborne hyperspectral reflective remote sensing methodology. This technique was tested on Late Pleistocene to Holocene alluvial fan surfaces located in the hyperarid southern Arava valley, Israel. Results of spectral field measurements showed that the surface reflectance is controlled by two main surficial processes, which are used as relative age criteria: the degree of desert pavement development (gravel coverage %) controls the absorption feature depths, while the rock coating development influences significantly the overall reflectance of the surface, but its effect on the absorption feature depths is limited. We show that as the percent of the surface covered by gravels increases, the absorption feature depth of the common gravels, in this case carbonate at 2.33 μm, increases as well; whereas the absorption features depth of the fine particle in-between the gravels, decrease (hydroxyl and ferric absorption features at 2.21 μm, and 0.87 μm, respectively), as the fines are removed from the surface. Using these correlations we were able to map the surface gravel coverage (%) on the entire alluvial fan, by calculating the gravel coverage (%) in each pixel of the hyperspectral image. The prediction of gravel coverage (%) is with accuracy of ± 15% (e.g. gravel coverage of 50% can be predicted to be 35% to 65%). Using extensive accuracy assessment data, we show that the spectral based mapping maintained high accuracy degree (R² = 0.57 to 0.83). The quantitative methodology developed in this study for mapping alluvial surfaces can be adapted for other surfaces and piedmonts throughout the arid regions of the world.     

星载雷达高度计沙漠散射特性及定标方法研究

为了提高星载雷达高度计海面风速产品的精度并更好地修正海况偏差的影响,有必要对高度计测量的后向散射系数进行定标。分布目标是星载雷达散射系数定标的有效手段,而沙漠的散射特性特别适于高度计的散射系数定标。检验了Jason-2卫星高度计的沙漠回波波形,在澳大利亚辛普森沙漠和我国的塔克拉玛干沙漠选取了适当的区域,收集了在这些区域长达7a的Jason-2高度计数据。基于这些数据,研究了Jason-2卫星雷达高度计在沙漠上的散射系数特性,并提出了基于沙漠的散射系数定标方法,分析了其原理、可行性和试验方案,探讨了高度计和现场定标散射计足迹匹配等关键技术,并对其定标误差进行了分析,论证了沙漠定标场可实现优于0.5dB的定标精度。该方法有助于进一步提升海洋2号(HY-2A)卫星风速和海况偏差产品的质量和应用前景。     

近20年来腾格里沙漠南缘土地利用/土地覆盖变化及其成因探讨——以甘肃省古浪县冰草湾地区为例

以甘肃省古浪县冰草湾地区1991、2000和2009年3期Landsat TM影像为数据源,采用基于对象的影像分类方法提取研究区各时期的土地利用/土地覆盖信息,在此基础上分析了研究区土地利用结构变化、土地利用类型转换关系和导致土地利用变化的驱动力因素。结果表明:采用基于对象的影像分类方法精度较高,可以达到准确提取土地利用/土地覆盖信息的目的;1991~2009年,冰草湾地区农田和居民用地的面积持续增加,并向沙漠和盐碱地方向扩张,呈现"人进沙退"的格局;2000~2009年各种土地利用类型之间的相互转换速度明显低于1991~2000年,土地利用状况呈现趋于稳定的趋势。造成土地利用/土地覆盖变化的主要驱动力是引黄灌溉和生态移民工程的实施。     

毛乌素沙漠南部植被指数的变化规律研究

为了认识毛乌素沙漠南部植被的变化,基于MODIS的NDVI遥感数据分析了2000-2013年毛乌素沙漠南部植被的变化特征,NDVI年平均值呈上升趋势,年增长率为2.69×10~(-3)/a。各年均值的空间最大值变化幅度不大,基本表现为上升趋势。结合转移矩阵的方法,将NDVI值分为不同级别并建立植被指数转移矩阵,计算分析了NDVI值逐年的级别转移情况。由各年NDVI值较上年的变化及各年植被覆盖级别较上年的变化分析显示,总体NDVI都表现为较上一年变好的趋势,2013年相对2000年的72.37%的像元的植被级别变好。将2013年相对2000年转移矩阵中NDVI值在各等级所占个数进行统计显示,NDVI值由矩阵的下三角向上三角转移,上三角阵中NDVI像元的个数远大于下三角阵,说明NDVI值表现出由低等级向高等级转化的趋势,植被情况逐步转好。整体上,2000-2013年毛乌素沙漠南部整体植被情况在持续转好。     

Forming Climatic Change

The Architectural Association in London is renowned for its unique unit structure in which avant-garde research and design strategies are incubated and hatched. In a new series edited by Michael Weinstock, Academic Head at the AA, the activities of the units are brought under the spotlight. ‘Unit Factor’ kicks off with an account by Steve Hardy and Werner Gaiser of the Environments, Ecology and Sustainability research cluster they lead. Copyright © 2007 John Wiley & Sons, Ltd.     

Assessment of the effect of modern transformation on the traditional settlement ‘Ksar’ of Ouargla in southern Algeria

The architecture of the Ouargla Ksar has long been recognized as an example of adaptation to harsh climate in the deep desert of Algeria. Over the last few decades, it has undergone some changes in its initial urban structure, due to accelerated and uncontrolled modern urbanization, that had negative implications and devaluation of its thermal characteristics. This article tries to understand the bioclimatic concept of adaptation of this Ksar and assess to what extent its morphological transformation has impacted its microclimatic conditions. This assessment is made through a comparative study between two different areas: one untransformed and the other transformed. A referential weather station situated in the suburbs was also exploited for consolidation of comparison. The investigation was undertaken using site measurements and observations.     

双竖直井开采美国沙漠峰深层地热数值模拟

建立了沙漠峰双井式增强型热储的概念模型, 并利用TOUGH2求解了模型。结果表明, 利用双井系统开采沙漠峰热储是可行的, 系统的流体循环量为30 kg/s, 30年内的产热功率和产电功率分别为18.90 MW和3.42 MW左右, 储层水流阻抗最大为0.095 MPa/(kg/s); 在0.7~17.30年间储层温度和压强逐渐降低, 水流阻抗逐渐增大, 系统只产出液态水, 而17.30~30年间储层温度、压强、水流阻抗基本保持不变, 生产井井口附近液态水不断汽化, 系统产出液态水和蒸汽的混合物, 且气体产量逐渐增大。     

北京以北沙漠砂样的选频释光特征研究

采用BG2003释光仪对北京北方科尔沁沙地和浑善达克沙地表层砂的选频释光特征进行了研究,发现在热激发条件下,在85℃-135℃和350℃-400℃温度区间光子计数最多的来源于4.13 eV(300nm)、4.00 eV(310nm)、3.88 eV(320 nm)和2.70 eV(460 nm);在绿光(2.33 eV,532 nm)激发条件下,释光光子的能量分别为4.00eV(310 nm)、3.88 eV(320 nm)和2.70 ev(460 nm).同时,8个采样点上述能量的释光光子计数在一定剂量范围内随辐照剂量增加而增大.特征波长具备了对辐射剂量响应的条件,可分别用于年代测定.     

Overview on the subsurface structure-tectonic controls in the northwest Bahariya,Western Desert,Egypt

A regional structural investigation was done on the northwestern part of Bahariya Oasis, using the potential field maps aided by geo-seismic sections and wells data. The gravity and magnetic maps were reinterpreted in context of geotectonic evolution of the north Western Desert to throw more light on the source of subsurface structures. Several processing methods and filtering techniques were applied to delineate locations, trends and depths of main source structures. Qualitatively, the study indicates that Bahariya horst is the highest in gravity, Sitra platform has the strongest magnetism, whereas Misawage graben is the largest in depth to the basement surface. The results were integrated to construct a tentative tectonic map, which exhibits an older folding in the NW direction intersected by a younger ENE trend, which seems to be crossed by a set of NW-trending faults. The map underlines regional folding in NE-SW trend (Syrian arc), forming four major structural features (Misawage graben, Sitra platform, Bahariya uplift and Dirrut basin), each has distinctive characteristics. The tectonic model suggests two different forces (NNW-compression and ENE-tension) affected the area, forming two main fold trends and five cycles of deformation. The models indicate a rough basement surface with a regional dip regime toward the north, overlain by a sedimentary cover ranges between 1 and 4.5 km in thickness. The basement is generally of acidic composition with some basic intrusions penetrate the boundary faults.     

Synthesis of MgSiO3 ceramics using natural desert sand as SiO2 source

High-quality inorganic minerals are being increasingly consumed in the fabrication of ceramics. In the present work, desert sand was adopted as the source of SiO₂ to synthesize MgSiO₃ and MgSiO₃SiC composite ceramics in an endeavor to economize on mineral resources and improve the desert ecosystem through the industrial application of desert sand. Experimental results show that the use of drift sand enabled the formation of glass phase at lower temperatures, which promoted protoenstatite transformation, prevented sintering cracking, and densified the ceramic bodies. The composites consisted of MgSiO₃ (protoenstatite), SiC, glass phase, and small amounts of forsterite and SiO₂. The addition of SiC particles caused the green bodies to resist densification, but this was improved by increasing the sintering temperature. The composite ceramic containing 30 wt % of SiC and sintered at 1350 °C had the highest bending strength, whereas that containing 50 wt% of SiC and sintered at 1400 °C had the highest hardness and the lowest coefficient of thermal expansion among all the samples.