高分二号卫星数据在特高压项目环水保监测中的应用研究

高分二号卫星具有高空间分辨率、高定位精度和快速姿态机动能力等特点。文章以锡盟～胜利1100kV特高压交流输变电工程为研究区,利用NDVI理论,研究基于高分二号卫星数据提取特高压项目环保水保监测内容的扰动区中的应用。结果表明:扰动区提取率为65.2%,在很大程上减少了人工现场调查工作;提取精度优于88%,提取效果优良。利用此方法,能够有效解决特高压项目环保水保监测信息获取不及时、管控不到位的现状。     

基于多时相遥感数据的矿区地表植被与土壤变化监测

基于多时相的Landsat遥感数据,以陕西省榆林市大柳塔矿区为例,通过图像处理得到地面归一化植被指数(NDVI)和土壤指数两个研究要素,结合矿区采掘工作面,提取了采区和非采区样本点的时序数据,使用单一变量法对比分析其时序变化情况,并对研究区域的植被和土壤未来变化趋势作了预测。结果表明:矿井工作面采掘活动破坏了地面植被和土壤的稳定性,降低了其对环境影响的抵抗和恢复能力,矿区植被覆盖度逐年增加,但是土壤受侵蚀情况严重;在未来几年内,大柳塔矿区的植被覆盖度会持续增加,土壤较容易受到侵蚀,特别注意地面采矿活动区域和受扰动影响区域的土壤保护,改善土壤退化现状。     

苔藓结皮光谱的变异性研究

通过测定干、湿苔藓结皮光谱和不同季节的苔藓结皮光谱,研究了其水分变异性和季节变异性.研究得出,湿苔藓结皮光谱曲线与维管植物的光谱曲线相似,即苔藓在生命活动期的光谱曲线具有高等植物光谱曲线特征,干苔藓结皮光谱曲线特征与裸地土壤的光谱曲线相似;苔藓结皮光谱在苔藓营养发育期(7月)与生殖发育期(10月)存在较大差异,即苔藓结皮光谱也如维管植物一样存在季节变异.研究分析认为,苔藓结皮光谱与其所处环境的土壤水分有关,且苔藓结皮光谱象其他高等植物一样具有季节性变异,所以仅通过分析某一状态下的生物结皮的光谱与其他地物光谱的异同,构建的遥感解译方法很难具有普适性.由于湿苔藓结皮光谱与维管植物相似,苔藓结皮可能造成其盖度分布较大区域的植物指数的不稳定性和该区域植被生产力的过高估计.     

A data mining approach for understanding topographic control on climate-induced inter-annual vegetation variability over the United States

The complex feedback relationship between climate variability and vegetation dynamics is a subject of intense investigation for its implications in furthering our understanding of the global biogeochemical cycle. We address an important question in this context: “How does topography influence the vegetation's response to natural climate fluctuations?” We explore this issue through the analysis of inter-annual vegetation variability over a very large area (continental United States) using long-term (13-year period of 1989-2001), monthly averaged, biweekly maximum value composite normalized difference vegetation index (NDVI) data. These data are obtained from satellite remote sensing at 1-km resolution. Through the novel implementation of data mining techniques, we show that the Northern Pacific climate oscillation and the ENSO phenomena influence the year-to-year vegetation variability over an extensive geographical domain. Further, the vegetation response to these fluctuations depends on a variety of topographic attributes such as elevation, slope, aspect, and proximity to moisture convergence zones, although the first two are the predominant controls. Therefore, the dynamic response of terrestrial vegetation to climate fluctuations, which shows tremendous spatial heterogeneity, is closely linked to the variability induced by the topography. These findings suggest that the representation of vegetation dynamics in existing climate models, which do not incorporate such dependencies, may be inadequate. Therefore, climate models that are regularly employed to guide policy decisions need to better incorporate these dependencies for the assessment of terrestrial carbon sequestration under evolving climate scenarios.     

Decomposition of vegetation cover into woody and herbaceous components using AVHRR NDVI time series

A method is developed to separate Normalised Difference Vegetation Index (NDVI) time series data into contributions from woody (perennial) and herbaceous (annual) vegetation, and thereby to infer their separate leaf area indices and cover fractions. The method is formally consistent with fundamental linearity requirements for such a decomposition, and is capable of rejecting contaminated NDVI data. In this study, estimates of annual averaged woody cover and monthly averaged herbaceous cover over Australia are determined using Pathfinder AVHRR Land series (PAL) Global Area Coverage (GAC) Advanced Very High Resolution Radiometer (AVHRR) NDVI data from 1981 to 1994, together with ground-based measurements of leaf area index (LAI) and foliage projective cover (FPC).     

黄河三角洲NDVI与Albedo时空分布规律

采用MODIS科学组L3级产品,详细分析了黄河三角洲地区NDVI和Albedo的时空分布规律,结果表明:①该产品具备相当高的精度,基本反映了研究区的植被覆盖和地表反照率的变化规律,并与土地利用变化情况吻合较好;②MODIS地表反照率对黄河三角洲地区具有一定的适用性;③黄河三角洲地区人类活动特别是农业耕作的季节性更替对NDVI的年内变化影响显著;④黄河三角洲地区的Albedo也具有明显的季节性变化,但其变化规律要比NDVI复杂得多。     

Natural hydrogen emanations in Namibia: Field acquisition and vegetation indexes from multispectral satellite image analysis

Natural hydrogen exploration is now active in various places of the world. Onshore, correlation between natural H₂ generation and the presence of iron rich rocks especially from Archean and Neoproterozoic cratons have been observed. Emanations and accumulations of H₂ have already been confirmed in such geological settings in Australia, South Africa and Brazil. The geological similitude and the presence of numerous sub circular depressions that are a good proxy for hydrogen emanations suggest that hydrogen resources may also exist in Namibia. We present here the results of a data acquisition campaign which allowed us to confirm the presence of natural hydrogen in this country in the vicinity of Neoproterozoic Banded Iron Formation. The H₂ content in the soil, as in Brazil, is variable within the depressions in time and space and is particularly time sensitive across the day. Comparison of the H₂ signal versus time within these two regions shows a similar behavior of the soils with an increase of the H₂ flow at the middle of the day. In addition, these new data allow us to better constrain the morphological characteristics of such H₂-emiting depressions. By using satellite images and digital elevation model we propose a new proxy to differentiate potentially H₂-emiting features from other type of depressions such as Salt Pan. The Landsat multispectral images and their processing through NDVI and SAVI indexes, that highlight a ring of healthy vegetation around the sub circular area with scarce vegetation already observed appear able to discriminate between H₂ emitting structures and other soft depressions.     

Depicting the Asymmetries of Vegetation Phenology over Northeast China Using Remote Sensing NDVI Dataset

Vegetation phenology is an important ecological indicator for global climate change.Plant greenup phenology in the spring time has been well studied,whereas autumn phenology and its asymmetry with spring phenology still remain unclear.Here,the GIMMS NDVI3g dataset for Northeast China was applied to extract the key phenological parameters during plant growth process,then three phenological asymmetry indices were defined according to the difference between greenup rate and senescence rate(AsyR),growth length in spring and autumn(AsyL),mean vegetation greenness index in spring and autumn(AsyV).First,plant growing curve was fitted with double logistic function and the phenological parameters was calculated.Second,the spatiotemporal pattern of asymmetry indices was explored.The results indicate that the three phenological asymmetry indices show a significant interannual variability and a time cycle of around ten years.The direction of amplitude for AsyV and AsyL was opposite with that of AsyR.Three indices could depict the phenological asymmetries from various perspectives and have a degree of uncertainty.The landscape pattern for AsyV and Asy R is similar.AsyV and AsyR show a capability of distinguishing cropland and natural vegetation cover.AsyL reflects a complex spatial distribution.Phenological asymmetries reveal that coniferous forest and broad-leaved forest present a dominant control of senescence vegetation activities.These natural vegetation commonly show a growth feature of rapid growth in spring and slow decrease in autumn.Cropland exhibits a slowly growing rate in spring and a rapid decrease in autumn.Phenological asymmetry is not significant in grassland area.Phenological asymmetry could enhance our knowledge on ecosystem carbon sink.In a practical way,phenological asymmetry could serve as a useful tools in vegetation type classification,agricultural investigation and plant ecosystem management.     

面向对象的天然绿洲与人工绿洲区分

以地处河西走廊东端、石羊河下游的民勤县湖区绿洲为例,以Landsat 8 OLI影像为数据源,从天然绿洲和人工绿洲的基本概念出发,在影像数据预处理、多尺度分割的基础上,综合考虑光谱、纹理、形状、上下文等信息,引入NDVI、最大化差异、紧致度、形状指数和空间邻接关系等多个特征,构建规则集进行天然绿洲和人工绿洲的区分,并将区分结果与基于最大似然法监督分类的绿洲区分结果进行比较分析。结果表明：使用面向对象的影像分析方法区分天然绿洲和人工绿洲的总体精度达到了91.75%,Kappa系数为0.65;较之面向像元的最大似然法监督分类结果,总体精度提高了10.40%,Kappa系数提高了0.13,其中人工绿洲条件Kappa系数提高了0.19,天然绿洲条件Kappa系数提高了0.30。面向对象的影像分析方法能够在一定程度上克服单一光谱特征分类方法的局限性,避免“异物同谱”和“同物异谱”现象带来的混淆,提高天然绿洲和人工绿洲区分的精度。