Spectral anisotropy of subtropical deciduous forest using MISR and MODIS data acquired under large seasonal variation in solar zenith angle     

《International Journal of Applied Earth Observation and Geoinformation》2015

Recent studies in Amazonian tropical evergreen forests using the Multi-angle Imaging SpectroRadiometer (MISR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) have highlighted the importance of considering the view-illumination geometry in satellite data analysis. However, contrary to the observed for evergreen forests, bidirectional effects have not been evaluated in Brazilian subtropical deciduous forests. In this study, we used MISR data to characterize the reflectance and vegetation index anisotropies in subtropical deciduous forest from south Brazil under large seasonal solar zenith angle (SZA) variation and decreasing leaf area index (LAI) from the summer to winter. MODIS data were used to observe seasonal changes in the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI). Topographic effects on their determination were inspected by dividing data from the summer to winter and projecting results over a digital elevation model (DEM). By using the PROSAIL, we investigated the relative contribution of LAI and SZA to vegetation indices (VI) of deciduous forest. We also simulated and compared the MISR NDVI and EVI response of subtropical deciduous and tropical evergreen forests as a function of the large seasonal SZA amplitude of 33°. Results showed that the MODIS-MISR NDVI and EVI presented higher values in the summer and lower ones in the winter with decreasing LAI and increasing SZA or greater amounts of canopy shadows viewed by the sensors. In the winter, NDVI reduced local topographic effects due to the red-near infrared (NIR) band normalization. However, the contrary was observed for the three-band EVI that enhanced local variations in shaded and sunlit surfaces due to its strong dependence on the NIR band response. The reflectance anisotropy of the MISR bands increased from the summer to winter and was stronger in the backscattering direction at large view zenith angles (VZA). EVI was much more anisotropic than NDVI and the anisotropy increased from the summer to winter. It also increased from the forward scatter to the backscattering direction with the predominance of sunlit canopy components viewed by MISR, especially at large VZA. Modeling PROSAIL results confirmed the stronger anisotropy of EVI than NDVI for the subtropical deciduous and tropical evergreen forests. PROSAIL showed that LAI and SZA are coupled factors to decrease seasonally the VIs of deciduous forest with the first one having greater importance than the latter. However, PROSAIL seasonal variations in VIs were much smaller than those observed with MODIS data probably because the effects of shadows in heterogeneous canopy structures or/and cast by emergent trees and from local topography were not modeled.  相似文献   

三套NDVI长时间序列植被指数的对比——以玛曲为例     

沙莎  郭铌  李耀辉  韩涛 《干旱气象》2013,(4):657-665

NDVI／MODIS、NDVI／GIMMS和NDVI／NSMC是时间长度不同、空间分辨率相差甚远的3套ND—VI数据集,如何集成应用这些不同时间长度、不同分辨率的数据进行相关研究,数据集间的比较是最基础的工作。本文以甘肃省甘南州玛曲县为例,用直方图、相关分析、趋势分析等方法研究了这3套NDVI产品数据集的相互关系。结果表明：1）NDVI／NSMC与NDVI/MODIS的直方图具有类似的图像分布特征,但是NDVI／MODIS数据分布范围更大;2）3套NDVI在数值上表现为NDVI／MODIS〉NDVI／GIMMS〉NDVI／NSMC;3）3套数据集空间图像特征一致,两两间均具有十分显著的空间相关性,其中1月份相对最弱,5、10月份最强,三者相比NDVIfNSMC与NDVI／MODIS的空间相关性更强;4）1—3月、5—8月及年均的NDVI／GIMMS与NDVI／NSMC值存在显著的时间相关性,但两者逐年变化趋势存在较大差别,两者气候倾向率相差最大的高达5倍之多。NDVIfNSMC数据集在处理过程中可能未进行大气订正及交叉定标,这是造成共同源的NDVIfGIMMS与NDVI／NSMC差异较大的重要原因。  相似文献   

Agricultural impacts on ecosystem functioning in temperate areas of North and South America     

Juan Pablo Guerschman  Jos María Paruelo 《Global and Planetary Change》2005,47(2-4):170

Land use has a large impact on ecosystem functioning, though evidences of these impacts at the regional scale are scarce. The objective of this paper was to analyze the impacts of agricultural land use on ecosystem functioning (radiation interception and carbon uptake) in temperate areas of North and South America. From land cover maps generated using high-resolution satellite images we selected sites dominated by row crops (RC), small grain crops (SG), pastures (PA), and rangelands (RA) in the Central Plains of USA and the Pampas of Argentina. These two regions share climatic characteristics and the agricultural conditions (crop types) are also very similar. Both areas were originally dominated by temperate grasslands. In these sites we extracted the temporal series of the normalized difference vegetation index (NDVI) from the NOAA satellites for the period 1989–1998 and calculated the mean seasonal NDVI curve for each site. Additionally, we calculated the mean annual NDVI, the maximum NDVI, the date of the year when the max NDVI was recorded and the interannual variability of these three attributes. We compared the mean values of each NDVI-derived attribute between land cover types and between continents. The NDVI seasonal patterns for each land cover type were roughly similar between the Central Plains and the Pampas during the growing season. The largest differences were observed during the winter and spring, when the NDVI of all land cover types in the Central Plains remained at lower values than in the Pampas. This was probably caused by the high annual thermal amplitude in the Central Plains that results in a much more restricted growing season. As a result of these differences in the shape of the NDVI curve, the mean annual NDVI in the Central Plains was lower than in the Pampas for all land cover types but the maximum NDVI did not differ importantly. In both regions, row crops delayed the date of the NDVI peak, small grain crops advanced it and pastures did not change it importantly, compared with rangelands. The interannual variability of the NDVI attributes was higher for small grains than for row crops in both regions. However, small grains crops were consistently more variable between years in the Central Plains than in the Pampas. The opposite occurred with pastures and rangelands, which were more variable in the Pampas than in the Central Plains. This paper confirms and generalizes previous findings that showed important imprints of land use on ecosystem functioning in temperate ecosystems. Our results support the idea that the changes in land cover that have occurred in the Central Plains and the Pampas leaded to similar changes in the way that ecosystems absorb solar radiation and in the patterns of carbon uptake.  相似文献   

京津冀地区植被时空动态及定量归因   总被引：2，自引：0，他引：2  

阎世杰  王欢  焦珂伟 《地球信息科学学报》2019,21(5):767-780

作为气候变化的敏感指示器,植被的物候、生长、空间分布格局等特征及其动态变化主要取决于气候环境中的水热条件,因此在气候变化背景下,气候-植被关系成为了全球变化研究的前沿和热点问题。本文综合平均温度、降水、水汽压、湿度、日照时数、SPEI等气候因子,坡度、坡向海拔等地形因子及人为活动因子,应用地理探测器方法针对2006-2015年京津冀地区不同季节NDVI、不同地貌类型区、不同植被类型区生长季NDVI的定量归因研究,揭示了过去10年间植被时空分布格局,及植被对气候、非气候因素响应的季节差异与区域差异,以期为生态工程的建设与修复提供参考意义。趋势分析表明：①2006-2015年京津冀地区NDVI呈现增加趋势,但存在显著的空间差异,如山地生长季NDVI的增长速率大于平原、台地、丘陵等地;②基于地理探测器的定量归因结果表明,降水是年尺度上NDVI空间分布的主导因子（解释力39.4%）,土地利用与降水的交互作用对NDVI的影响最为明显（q=58.2%）;③NDVI对气候因子的响应存在季节性及区域性差异,水汽压是春季NDVI空间分布的主导因子,湿度是夏、秋两季的主导因子,土地利用是冬季的主导因子;④影响因子对生长季NDVI的解释力因不同地貌类型区、不同植被类型区而差异显著。  相似文献   

利用不同地表比辐射率对ETM＋数据地表温度反演对比研究     

苏建云 《北京测绘》2012,(6):28-33

地表温度作为研究环境生态影响的一个重要指标之一,以Landsat ETM+的热红外波段作为数据源,辅助大气透过率、大气平均气温等参数,利用单窗算法基于混合像元、NDVI、植被和裸露地三种不同地表比辐射率反演泉州市地表温度,对比分析结果表明采用这三种地表比辐射率反演地表温度的方法均是可行的,对于具体采用哪一种地表比辐射率应需要结合实际的研究区域地表地物的实际监测地表温度进行对比后,方可选择合适的地表比辐射率进行地表温度反演,会更具实际意义。反演结果可为城市热岛效应等研究提供支持数据源。  相似文献   

春末夏初青藏高原植被对全球变暖响应的区域特征   总被引：5，自引：3，他引：2       下载免费PDF全文

徐维新  刘晓东 《高原气象》2009,28(4):723-730

利用1982-2002年Pathfinder NDVI遥感数据, 采用REOF和倾向度趋势分析方法, 研究了5～6月青藏高原地表植被变化区域特征及与全球变暖的关系。21年来高原区域春末夏初植被变化存在明显的空间差异, 且存在一个位于高原南北呈带状分布的植被显著变化区域。该区域内植被对全球气温变暖响应显著, 与前期5月北半球平均气温相关系数达到0.7675, 通过0.001显著性水平检验; 植被NDVI随气温升高呈现出显著一致的增加趋势, 增长速率超过10%/10 a, 是全球变暖响应的显著区和敏感区。进一步的分析表明, 对植被全球变暖响应显著的区域基本上处于高山山脉或半荒漠NDVI值低于0.12覆盖度较低的区域。不同植被类型对变暖响应的对比表明, 草地对全球变暖响应明显高于林地, 其植被NDVI 21年约增加10%。  相似文献   

卫星遥感结合地面观测资料对中国西北干旱区地表热力输送系数的估算   总被引：3，自引：0，他引：3  

王慧  李栋梁 《大气科学》2010,34(5):1026-1034

本文利用黑河野外试验 (HEIFE) 地面观测资料, 采用空气动力学方法计算了干旱区内不同下垫面的地表热力输送系数CH, 结合由美国国家海洋和大气局 (NOAA) 系列卫星遥感观测的反映地表植被特征的归一化差值植被指数 (NDVI) 资料, 经拟合得到了针对我国西北干旱区不同下垫面的CH-NDVI参数化关系式, 并对此关系式进行了合理性检验。结果表明: 对于区域尺度而言, 在缺乏用其他方法获得较准确的区域CH值的情况下, 利用卫星遥感结合地面观测资料对其估算是较为可靠的方法。  相似文献   

基于TVDI的西藏地区旱情遥感监测   总被引：2，自引：0，他引：2  

扎西央宗  杨秀海  边巴次仁  胡豪然  卓玛 《气象科技》2010,38(4):495-499

西藏大部分地区属干旱或重干旱区,干旱发生较为频繁,是影响农牧业生产最严重的灾害之一。文章利用拉萨接收站的中分辨率成像光谱仪(MODIS)资料提取的归一化植被指数(NDVI)和地表温度(ST),构建ST-IND-VI特征空间,依据该特征空间设计的温度植被旱情指数作为旱情指标,找出适合该地区的旱情判别模式,以2005～2008年6～7月同时段西藏地区卫星资料、气象旱情监测结果以及土壤相对湿度观测数据为例,进行旱情对比分析。结果表明,利用温度植被旱情指数(TVDI)法对西藏地区进行夏季干旱动态监测是可行的。  相似文献   

西北地区MODIS-NDVI指数饱和问题分析   总被引：6，自引：0，他引：6  

杨嘉  郭铌  黄蕾诺  贾建华 《高原气象》2008,27(4)

为了了解西北地区MODIS-NDVI和MODIS-EVI两种植被指数的特点,本文利用美国NASA LP DAAC(Land Process Distributed Active Archive Center)2004年1~12月的250 m分辨率16天植被指数合成的MOD13 Q1数据集,对西北地区不同类型植被NDVI和EVI的特征进行分析,并对西北地区MODIS-NDVI饱和问题进行了初步研究。结果表明:NDVI和EVI对干旱—半干旱气候区植被覆盖度不高的植被类型描述能力相似,月际变化趋势一致。西北地区各种植被类型NDVI比EVI高,NDVI与EVI的差异总体上呈现从半荒漠、草原、农区到林区,随NDVI值的增加而增大的规律。对植被度覆盖度高的阔叶林和针叶林,在植被生长旺盛期,NDVI总在0.8附近波动,NDVI随植被的生长增加的很小,一直维持在一个高且平的范围内,不再能看出植被生长变化的现象,即饱和现象严重;而EVI表现良好,随着植被的生长而增加,能明显地反映出植被生长的季节变化。西北高寒草甸和陕西关中农业区NDVI也出现有不同程度的饱和,饱和时间因植被的不同从1~2月不等。0.8可作为NDVI饱和的阈值。NDVI饱和问题对卫星监测植被的研究和应用会产生误差,EVI能较好地解决NDVI的饱和问题。  相似文献   

遥感反演和站点观测的地气温度分布特征差异     

王念  卢致宇  徐建红  张红  张霄羽 《遥感学报》2021,25(8):1848-1861

地表温度和近地表大气温度是地球系统、大气系统以及地—气相互作用物理过程的重要参量。在陆地—大气的相互作用过程中,水汽含量、NDVI指数、下垫面变化等因素会对地—气热量传输造成一定的影响。本文首先利用地表温度产品（MYD11A1）以及气温站点数据（GSOD）获得全国尺度下地表温度年最大值、近地面气温年最大值。在此基础上,使用趋势分析法分析2003年—2018年地、气温度年最大值时空分布特征及变化趋势,以及地—气温差气候倾向率变化趋势。最后,结合大气总水汽含量产品（MYD05）、NDVI指数（MYD13A3）、二氧化碳平均浓度增长率分析导致地表温度年最大值与近地面气温年最大值趋势发生变化的原因。研究结果表明：（1）在全国尺度下,2003年—2018年地表温度年最大值呈现北高南低的空间分布特征。近地面气温年最大值的空间分布与地表温度年最大值相反。大气总水汽含量年最大值在热带、亚热带季风气候区内总体较高。水汽含量既影响近地面气温的大小,同时也受到近地面气温的影响,因此,水汽含量年最大值与近地面气温年最大值表现出一定的空间分布一致性特征。（2）在2003年—2018年期间,地表温度年最大值的气候倾向率在空间上表现出北高南低的分布特征。近地面气温年最大值的气候倾向率在空间上也表现为北高南低,与地表温度年最大值的气候倾向率变化基本一致。但地表温度年最大值的变化幅度要大于近地面气温年最大值,并且在个别区域表现不一致。主要分布在天山地区、三江平原以及秦岭南侧地区,地—气年最大值变化趋势相反即地—气差减小。（3）大气总水汽含量年最大值的增加可造成近地面气温年最大值的增加,而植被覆盖度的上升可造成地表温度年最大值下降。但在天山地区大气总水汽含量与地—气差的响应不明显,但天山地区的近地面气温年最大值与CO₂平均浓度增长率的关系较为明显。（4）遥感数据反演的地表温度年最大值和站点观测的近地面气温年最大值空间分布表现出差异,但时间变化趋势基本一致。  相似文献