Mapping of Sahelian vegetation parameters from ERS scatterometer data with an evolution strategies algorithm

The West African Sahel rainfall regime is known for its spatio-temporal variability at different scales which has a strong impact on vegetation development. This study presents results of the combined use of a simple water balance model, a radiative transfer model and ERS scatterometer data to produce map of vegetation biomass and thus vegetation cover at a spatial resolution of 25 km. The backscattering coefficient measured by spaceborne wind scatterometers over Sahel shows a marked seasonality linked to the drastic changes of both soil and vegetation dielectric properties associated to the alternating dry and wet seasons. For lack of a direct observation, METEOSAT rainfall estimates are used to calculate temporal series of soil moisture with the help of a water balance model. This a priori information is used as input of the radiative transfer model that simulates the interaction between the radar wave and the surface components (soil and vegetation). Then, an inversion algorithm is applied to retrieve vegetation aerial mass from the ERS scatterometer data. Because of the nonlinear feature of the inverse problem to be solved, the inversion is performed using a global stochastic nonlinear inversion method. A good agreement is obtained between the inverse solutions and independent field measurements with mean and standard deviation of −54 and 130 kg of dry matter by hectare (kg DM/ha), respectively. The algorithm is then applied to a 350,000 km² area including the Malian Gourma and Seno region and a Sahelian part of Burkina Faso during two contrasted seasons (1999 and 2000). At the considered resolution, the obtained herbaceous mass maps show a global qualitative consistency (r²=0.71) with NDVI images acquired by the VEGETATION instrument.     

Impacts of Vegetation on the Intraseasonal Oscillation Simulated by the Community Atmosphere Model (CAM3)

The influences of vegetation on intraseasonal oscillation (ISO) were examined using the Community Atmosphere Model version 3 (CAM3). Two 15-year numerical experiments were completed: the first was performed with a realistic vegetation distribution (VEG run),and the second was identical to the VEG run except without land vegetation (NOVEG run). Generally speaking, CAM3 was able to reproduce the spatial distribution of the ISO, but the ISO intensity in the simulation was much weaker than that observed in nature: the ISO has a relatively much stronger signal. A comparison of the VEG run with the NOVEG run revealed that the presence of vegetation usually produces a weak ISO. The vegetation effects on ISO intensity were significant over West Africa and South Asia, especially in the summer half-year.Vegetation also plays an important role in modulating ISO propagation. The eastward propagation of the ISO in the VEG run was clearer than that in the NOVEG run over the West African and Maritime Continent regions. The northward propagation of the ISO in the VEG run was more consistent with observation than that in the NOVEG run.     

Advances in estimation methods of vegetation water content based on optical remote sensing techniques

Quantitative estimation of vegetation water content(VWC) using optical remote sensing techniques is helpful in forest fire as-sessment,agricultural drought monitoring and crop yield estimation.This paper reviews the research advances of VWC retrieval using spectral reflectance,spectral water index and radiative transfer model(RTM) methods.It also evaluates the reli-ability of VWC estimation using spectral water index from the observation data and the RTM.Focusing on two main definitions of VWC—the fuel mois...     

历史时期黄土高原的植被及其变迁

距今３０００－２０００年前，黄土高原六盘山以东，吕梁山以西，长城以南地区显域生境植被为疏林灌丛草原，并存在一定的区域差异唐宋时期，黄土高原的植被表现出显著的变化，主要是草原带的南移和某些耐旱植物分布范围的扩大。自北宋以后，人类活动对植被的破坏越来越强烈。掩盖了植被由于自然原因发生的变化。     

制浆废液制备固沙材料及其在植被恢复上的应用(系列报道之四)固沙材料对植被恢复的促进作用

在宁夏沙漠化地区开展了利用禾草制浆废液合成的新型生物质固沙材料对固沙和植物生长作用的研究。结果显示，在流动沙丘上喷施生物质固沙材料，可在24h内与表层沙粒快速形成固结层，具有良好的防风固沙作用，并可促进沙生植物的生长；木质素固沙材料1％～2％的浓度和2．5L／m^2的剂量既可有效固沙，同时还可减缓水分蒸发，对植物的发芽、生长及生物量积累均起到了良好的作用；一年生和多年生固沙植物的合理选配，可有效地提高生物固沙效果。生物质固沙材料的应用实现了化学固沙和生物固沙的有机结合，为干旱、半干旱地区的生态环境建设提供了一项新的技术措施。     

生态型植生护坡土工布的性能评价及损伤分析

文章以黏胶短纤维和天然植物纤维为主要原料,采用短纤维干法成网-针刺加固工艺制备生态型植生护坡土工布,并对所制备的不同规格生态土工布的抗拉伸撕破、抗磨损冲击、抗老化和降解性能进行了测试和研究。结果表明,生态土工布的平方米质量和植物纤维含量对样品的性能有明显的影响,当生态土工布平方米质量在400～800 g/m²、植物纤维含量在45%～65%时,其各项性能指标均能够满足相关标准的要求和实际使用需求。所制备的生态土工布在自然环境中具有较好的降解性能,掩埋于土壤中120 d后,其质量损失率为60%～70%,强力损失率为70%～90%,在土石边坡防护及生态修复方面表现出了较好的应用前景。     

Allelopathic potential ofAmbrosia cumanensis H.B.K. (Compositae) in a tropical zone of Mexico

Several experiments were carried out to confirm the allelopathic potential ofAmbrosia cumanensis H.B.K. (Compositae) in a tropical zone of Mexico. The aqueous extracts of leaves and roots inhibited growth of several species used in bioassays. The wash-water of the leaves inhibited some species and stimulated others. The aqueous solutions of soil, in reference to those collected in July, were significant in their general inhibitory action. Decomposition of leaves and roots, in pots where several species were growing, was highly inhibitory to some of the seedlings; microorganisms have a major role in this process.     

斑块状植被遥感检测研究进展

斑块状植被是世界上干旱—半干旱区常见的景观类型,对于它们的形成、结构和演替研究能够提高人们对干旱—半干旱地区生态系统动态及其重要的生态水文过程的理解,具有重要的理论研究意义和应用价值.传统的基于地面调查和长期定位观测的方法观测范围有限,已无法满足目前区域斑块状植被分布及其空间格局特征研究的需要.利用遥感技术快速重复获取...     

黄土高原现状梯田和林草植被的减沙作用分析

2000年以来,黄河来沙明显减少。本文以黄土高原主要产沙区为对象,利用卫星遥感与实地调查相结合方法,获取2012年研究区各支流的梯田面积和质量信息,分析2010—2013年林草植被覆盖率及其较天然时期的变化;提出林草与梯田叠加作用地区的减沙量计算方法。基于流域尺度上构建的黄土丘陵沟壑区林草植被覆盖率与产沙系数、梯田比与减沙幅度之间的响应关系,计算在多年平均降雨条件下黄河龙门、北洛河状头、汾河河津、渭河咸阳和泾河张家山等5站以上现状林草植被和梯田的减沙能力,其值为10.65亿t,占该区天然年均来沙量的60%。     

城市异质植被的覆盖度估算模型比较研究

植被覆盖度是城市生态环境评价的一个重要指标。针对亚热带城市异质植被覆盖特征,选择像元尺度的植被指数(NDVI)转换模型、亚像元尺度的植被—土壤两端元模型(V-S Model)和植被—高—低反射率三端元模型(V-H-L Model)在TM影像上估算植被覆盖度,并结合野外实地调查对比验证3种模型的估算精度及其适用性。结果表明模型尺度和背景亮度对植被覆盖度估算有着不同程度的影响。NDVI转换模型整体高估覆盖度为27%,V-S模型和V-H-L模型整体低估覆盖度分别为23%和5%;验证结果证明:NDVI转换模型对高密度(60%)植被的估算结果最好,低估4%;V-H-L模型对中密度(40%~60%)和低密度(40%)植被的估算结果最优,仅低估2%,并受背景亮度的影响最小。因此,NDVI转换模型适用于高密度植被覆盖度的估算,亚像元尺度下的V-S模型和V-H-L模型适用于低、中密度植被覆盖度的估算,并以V-H-L模型估算较为准确。