基于TM/ETM+影像的不同水体指数对比研究

本文以草海国家级自然保护区为例,基于Landsat ETM+影像从区分度、水体错提率和面积精度3方面对比研究了NDVI植被指数和NDWI、MNDWI、RNDWI、NWI、NEW 5种归一化水体指数提取湿地水体信息的准确度。结果表明,NDVI提取水体效果较差,5种水体指数均能对水体进行有效提取,其中NWI法综合精度最高,其次是MNDWI、NEW,较差的是RNDWI和NDWI,从而为水体的快速提取提供了参考。     

TM/ETM+影像大气校正产品质量评价方法研究

对TM/ETM+的大气校正产品质量进行评价是改进影像质量的必要手段。提出采用已有高质量TM/ETM+表面反射率产品作为参考影像评价TM/ETM+的大气校正产品质量的方法。该方法设计了面向产品质量评价的影像光谱采样方案和多时相遥感影像PIFs(pseudo invariant features,PIFs)样本自动识别方法,能对多时相/季相TM/ETM+大气校正产品质量进行评价。试验表明该方法能准确识别PIFs地物,评价结果真实反映了遥感影像大气校正结果准确度。方法具有快速和低成本等特点,能开展规模化应用。     

基于多时像TM/ETM+影像的兖州市土地利用/覆盖变化

本文利用多时相Landsat TM/ETM+影像分析了兖州市1998年和2002年的土地利用/覆盖变化。综合考虑波段间相关系数和OIF指数,选择最佳波段组合进行图像解译,并在此基础上运用最大似然分类器(MLC)和支持向量机(SVM)的分类方法对遥感影像进行分类。进而利用SVM分类结果进行土地利用遥感动态监测,获取兖州市土地利用/覆盖变化信息,并与社会经济统计资料的统计结果进行比较。最后提取TM/ETM+影像的RDVI,基于线性混合像元分解模型分析了植被覆盖的变化。结果表明,基于多时相TM/ETM+影像分析的土地利用/覆盖变化与实际统计数据较吻合,适合动态监测土地利用变化,且精度较高。     

基于TM/ETM+和MODIS的漓江流域生态环境遥感动态监测

为调查漓江流域近30 a来的生态环境变化，开展了基于TM/ETM+和MODIS遥感长、短周期结合的动态监测研究。通过对3期 Landsat-5/7 TM/ETM+遥感影像的信息提取、模式识别和实际调查，发现造成漓江上游生态环境退化的主要原因与漓江水源林遭人 为破坏、城市化扩展和水质污染等因素有关。通过对MODIS-NDVI和水体反射波谱分析，初步探明了流域区植被总量的季节变化规律 和漓江水体污染的遥感反射波谱特征，确定了水质遥感监测的最佳MODIS波段，得到了研究区的植被覆盖、城市扩展变化及河流水 质变化信息。     

基于影像的Landsat TM/ETM~+数据正规化技术

阐述了基于影像的Landsat TM/ETM+的数据正规化技术及其发展。该技术通过将Landsat影像的亮度值转换成传感器处的辐射值和反射率来对影像进行辐射校正。实例表明,使用正规化技术处理后的影像可以明显削弱日照和大气的影响,去除它们产生的噪声;其所求的传感器处的反射率与地面实测反射率的RMS值非常小。     

ASTER和TM/ETM+遥感数据融合监测土地覆盖变化

在人们纷纷选择IKONOS、QUICKBIRD、SPOT-5等高分辨率影像监测土地利用/覆盖变化之际,以北京海淀区为例,尝试采用Brovey变换和主成分分析(PCA)法融合ASTER、TM/ETM+中等分辨率影像,充分利用ASTER、TM/ETM+数据的多光谱和较高空间分辨率特性,挖掘其在土地覆盖变化监测中的潜力,为大规模监测土地利用/覆盖变化提供科学参考。研究将2003年ASTER多光谱3N、2、1波段与1999年ETM+PAN波段进行Brovey变换;1992年TM543与1999年ETM+PAN波段进行PCA融合,快速发现土地覆盖变化信息。经验证,变化发现精度达92.50%,符合项目精度要求。试验表明:在缺乏高分辨率影像的地区,选择价格相对便宜的AS-TER和TM/ETM+数据,采用Brovey变换和主成分分析(PCA)法进行融合,可有效监测土地覆盖变化,节约动态监测成本,二者具有很大的应用价值,值得推广。     

多源遥感影像水体指数的交互对比

在对地观测系统中,Landsat和EO-1数据比较适合于监测城市水体变化。但是这两种传感器数据的水体指数之间的关系不清楚,针对这一问题。该文利用两对同日过空的Landsat-7ETM+与EO-1ALI影像来查明二者水体指数之间的定量关系,通过回归统计分析来求出两种传感器水体指数之间的转换方程。结果表明,Landsat-7ETM+与EO-1ALI影像分别基于DN数据、IACM反射率数据计算的MNDWI水体指数间,均存在较好的线性相关关系,决定系数均在0.75以上;基于EO-1ALI的MNDWI指数影像信息更为丰富,因为其动态范围大于Landsat-7ETM+。     

基于多时相Landsat TM/ETM的阿尼玛卿山冰川变化监测

采用遥感及地理信息系统技术,利用多时相Landsat TM/ETM影像和数字高程模型(SRTMDEM),结合中国冰川目录,获得阿尼玛卿山地区不同年份的冰川范围,进行冰川变化监测。综合分析该冰川的变化情况,计算冰川进退变化速率,并对其中4个变化较大的冰川进行详细的分析统计。结果表明:从1991年至2009年,阿尼玛卿山地区既有退缩冰川也有前进冰川,其中冰川退缩面积为15.30km2,前进面积为4.46km2。总体面积持续退缩,其中退缩最大的冰川长度缩短了900m,其它冰川也存在不同程度的变化。     

地形抹平与半经验模型的Landsat TM/ETM+地形校正方法

地形校正可以减小地形起伏对地物光谱的影响,提高计算机分类在山区的精度。设计了针对全球土地覆盖分类的Landsat TM/ETM+数据地形校正方法 SCOS(Smoothed COS余弦),首先对地形的坡度角进行抹平处理,很大程度上削弱了地表非朗伯性对地形校正的影响,然后利用简单有效的余弦校正去除地形效应。该方法与其他常用地形校正算法的对比分析是通过对全球不同区域、不同地表覆盖的有代表性的6景Landsat TM/ETM+数据的试验,采用统计分析与目视判读的方式,从过度校正和类内均一性两个方面进行的。结果表明,该方法在目视效果和统计结果上优于常规方法,并且更加简单有效,无需复杂的大气参数及传感器参数,满足全球地表覆盖分类对地形校正的需求。     

基于ETM+的植被覆盖信息提取及其动态变化分析——以广州市为例

以2000年和2005年ETM+影像为数据源,在水体掩膜和端元光谱优选对比基础上,利用线性光谱模型提取了广州市植被覆盖信息,并对植被覆盖信息的时空动态变化进行了定量分析,结果表明:应用线性光谱模型之前对所占面积不大的水体进行处理是非常必要的,选取植被、硬化地面、土壤三端元法比包含阴影的四端元法更有利于线性光谱分离,而且能达到很高的精度;此外,通过对植被覆盖信息空间结构和景观格局的研究,显示:2000-2005虽然广州市绿化取得了初步成效,但总体植被覆盖状况呈下滑趋势,植被景观破碎程度增加,各植被景观形状趋于复杂化,城市化的发展加之人类活动的干扰,低植被覆盖区不断扩大,而中、高植被覆盖区正处于不断退化时期。     

Coupling urbanization analyses for studying urban thermal environment and its interplay with biophysical parameters based on TM/ETM+ imagery

Studies of urbanization and urban thermal environment are now attracting wide interests among scientists all over the world. This study investigated the influences of urbanization on urban thermal environment as well as the relationships of thermal characteristics to other biophysical variables in Guangzhou, China utilizing three dates of Landsat TM/ETM+ images acquired in 1990, 2000, and 2005, respectively. Vegetation abundances and percent impervious surfaces were derived by means of linear spectral mixture model, and a method for effectively enhancing impervious surface has been developed to accurately examine the urban enlargement. As a key parameter for studying urban thermal characteristics, the land surface temperature (LST) was also retrieved from thermal infrared band of each TM/ETM+ dataset. Based on these parameters, the urban expansion, urban heat island effect and the relationships of LSTs to other biophysical parameters were then analyzed. Results indicated that the area ratio of impervious surface in Guangzhou increased significantly, which grew from 20.56% in 1990, to 34.72% in 2000, and further to 41.12% in 2005, however, the intensity of urban heat island was not always enlarged in observed years. In addition, Geostatistical analyses showed that the mean-centre of the impervious surface was moving towards the northwest during 1990–2005. And correlation analyses revealed that, at the pixel-scale, the association of LSTs to other two variables (vegetation abundance and percent impervious surface) was not straightforward, while LSTs possessed a strong positive correlation with percent impervious surfaces and negative correlation with vegetation abundances at the regional-scale, respectively. This study provided an integrated research scheme and the findings can be very useful for urban ecosystem modeling.     

Evaluation of different topographic correction methods for Landsat imagery

The recent free availability of Landsat historical data provides new potentials for land-cover change studies. Multi-temporal studies require a previous radiometric and geometric homogenization of input images, to better identify true changes. Topographic normalization is one of the key steps to create consistent and radiometricly stable multi-temporal time series, since terrain shadows change throughout time. This paper aims to evaluate different methods for topographic correction of Landsat TM-ETM+ data. They were assessed for 15 ETM+ images taken under different illumination conditions, using two criteria: (a) reduction of the standard deviation (SD) for different land-covers and (b) increase in temporal stability of a time series for individual pixels. We observed that results improve when land-cover classes where processed independently when applying the more advanced correction algorithms such as the C-correction and the Minnaert correction. Best results were obtaining for the C-correction and the empiric–statistic correction. Decreases of the SD for bare soil pixels were larger than 100% for the C-correction and the empiric–statistic correction method compared to the other correction methods in the visible spectrum and larger than 50% in the IR region. In almost all tests the empiric–statistic method provided better results than the C-correction. When analyzing the multi-temporal stability, pixels under bad illumination conditions (northern orientation) improved after correction, while a deterioration was observed for pixels under good illumination conditions (southern orientation). Taken this observation into account, a simple but robust method for topographic correction of Landsat imagery is proposed.     

Landsat TM/ETM+与HJ-1A/B CCD数据自动相对辐射处理及精度验证

全球地表覆盖遥感制图与关键技术研究项目要求对两个基准年度(2000年,2010年)的全球覆盖30 m分辨率遥感数据进行辐射处理,转换到地表反射率,数据以Landsat TM/ETM+为主,HJ-1A/B CCD数据为补充。海量数据中有些不适宜进行绝对大气校正,为了保证全球覆盖,对这些数据设计开发了一套自动的相对辐射处理及精度验证流程算法,利用相邻数据重叠区域进行相对辐射校正的方式,将数据由Oigital Number(DN)值直接转换为地表反射率,精度验证以MODIS地表反射率产品MOD09GA作为参考,比较对应波段数据的相对一致性,算法采用了图像分块处理技术及OpenMP加速技术提高效率,实际应用结果表明该算法流程可以满足项目对辐射处理精度、速度及自动化程度的要求。     

Evaluation of directional normalization methods for Landsat TM/ETM+ over primary Amazonian lowland forests

Biodiversity mapping in extensive tropical forest areas poses a major challenge for the interpretation of Landsat images, because floristically clearly distinct forest types may show little difference in reflectance. In such cases, the effects of the bidirectional reflection distribution function (BRDF) can be sufficiently strong to cause erroneous image interpretation and classification. Since the opening of the Landsat archive in 2008, several BRDF normalization methods for Landsat have been developed. The simplest of these consist of an empirical view angle normalization, whereas more complex approaches apply the semi-empirical Ross–Li BRDF model and the MODIS MCD43-series of products to normalize directional Landsat reflectance to standard view and solar angles. Here we quantify the effect of surface anisotropy on Landsat TM/ETM+ images over old-growth Amazonian forests, and evaluate five angular normalization approaches. Even for the narrow swath of the Landsat sensors, we observed directional effects in all spectral bands. Those normalization methods that are based on removing the surface reflectance gradient as observed in each image were adequate to normalize TM/ETM+ imagery to nadir viewing, but were less suitable for multitemporal analysis when the solar vector varied strongly among images. Approaches based on the MODIS BRDF model parameters successfully reduced directional effects in the visible bands, but removed only half of the systematic errors in the infrared bands. The best results were obtained when the semi-empirical BRDF model was calibrated using pairs of Landsat observation. This method produces a single set of BRDF parameters, which can then be used to operationally normalize Landsat TM/ETM+ imagery over Amazonian forests to nadir viewing and a standard solar configuration.