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.     

比值—特征主成分混合分析提取金矿蚀变信息：以赣南遂川地区为例

在分析与金矿有关的两类蚀变岩的ＴＭ波谱特征的基础上,以赣南遂川地区为实验区,利用比值－特征主成分混合分析进行了金矿蚀变岩信息提取,为找矿预测和野外工作指明了方向。     

TM图象数字镶嵌的几何精度分析及镶嵌方法的探讨

本文对ＴＭ数字镶嵌图象的内部几何精度进行分析后指出，传统的利用选取控制点建立图象间坐标转换方程，并利用此方程对图象进行处理，实施图象镶嵌的方法，在保证镶嵌图象几何精度方面存在着不足，用此方法得到的ＴＭ镶嵌图象的内部几何误差约８个象元；在对传统的图象数字镶嵌方法进行分析的基础上，笔者总结大量工作的经验并参照前人的作法，在选定的地图投影下利用旋转方法对ＴＭ图象进行处理，进而完成镶嵌工作、这种方法舍去了控制点选取的繁复过程，使镶嵌工作变得简单，同时可保证ＴＭ镶嵌图象的几何畸变很小，经检测，镶嵌后的ＴＭ图象内部几何误差小于２个象元。     

Localized versus wide-ranging effects of the post-Soviet wars in the Caucasus on agricultural abandonment

Wars are frequent and can affect land use substantially, but the effects of wars can vary greatly depending on their characteristics, such as intensity or duration. Furthermore, the spatial scale of the effects can differ. The effects of wars may be localized and thus close to conflict locations if direct mechanisms matter most (e.g., abandonment because active fighting precludes farming), or wide-ranging, e.g., farther away from conflict locations, if indirect mechanisms predominate (e.g., no access to agricultural inputs). Our goal was to quantify how the very different wars in the Caucasus region during post-Soviet times most likely affected agricultural abandonment at different scales. We analyzed data on conflict locations plus Landsat-derived land-cover data from 1987 to 2015, and applied matching statistics, difference-in-differences estimators, and logistic panel regressions. We examined the localized versus wide-ranging effects of the different wars on permanent agricultural abandonment and inferred to direct and indirect mechanisms that may have resulted in agricultural abandonment. While permanent agricultural abandonment was overall surprisingly limited across the Caucasus, up to one third of abandonment was most likely related to the wars. Among the wars, the war in Chechnya was by far the most intense and longest, but its effect on abandonment was similar to the less intense and relatively short war in Abkhazia. 47 % and 45 % of agricultural abandonment was related to each war, respectively. The reason was that the effect of the war in Chechnya was more localized, and abandonment occurred near conflict locations, in contrast to Abkhazia, where the effect was wide-ranging and abandonment occurred farther away from conflict locations. In contrast, the war in South Ossetia showed no significant effect on abandonment, and the war in Nagorno-Karabakh had the surprising pattern that abandonment was higher where no war had occurred. For each of the wars, abandonment was predominately related to the nearest conflict locations, but in Abkhazia additional conflict locations within 10 km further increased the probability of abandonment. We infer that the direct mechanisms of the war such as bombing, and active fighting most likely resulted in a localized effect close to conflict locations in Chechnya and in Nagorno-Karabakh. However, in Nagorno-Karabakh subsidies for new settlers after the war, (i.e., a positive wide-ranging effect), potentially reduced the amount of abandonment there. In contrast, negative wide-ranging effects such as refugee movements and post-war restrictions on their return is related to broad-scale abandonment in Abkhazia. In summary, permanent agricultural abandonment was not necessarily higher in a war with a high overall intensity. Instead, the effect of a given war varied in scale, and was related to the relative importance of direct and localized versus indirect and wide-ranging mechanisms, including postwar events and policies, which is likely the case for other wars, too.     

Texture classification of Mediterranean land cover

Maximum likelihood (ML) and artificial neural network (ANN) classifiers were applied to three Landsat Thematic Mapper (TM) image sub-scenes (termed urban, agricultural and semi-natural) of Cukurova, Turkey. Inputs to the classifications comprised (i) spectral data and (ii) spectral data in combination with texture measures derived on a per-pixel basis. The texture measures used were: the standard deviation and variance and statistics derived from the co-occurrence matrix and the variogram. The addition of texture measures increased classification accuracy for the urban sub-scene but decreased classification accuracy for agricultural and semi-natural sub-scenes. Classification accuracy was dependent on the nature of the spatial variation in the image sub-scene and, in particular, the relation between the frequency of spatial variation and the spatial resolution of the imagery. For Mediterranean land, texture classification applied to Landsat TM imagery may be appropriate for the classification of urban areas only.     

基于RS与GIS的北京市热岛研究

基于普适性单通道算法,利用2005年5月6日的TM数据反演北京市区的实际地表温度。在此基础上,分析了北京市区的热环境特征、热岛分布的位置。运用GIS空间分析工具,分析了地表温度与地形特征和地表覆盖类型之间的关系。结果表明,北京市热岛分布具有环状和带状分布特征,高程较低处和坡度较小处更容易形成热岛中心,不同地表覆盖类型的热特征具有显著的差异。     

基于Landsat TM影像不同地表温度反演算法的比较

地表温度是反映地表环境的一个重要参数,精确获取地表温度的方法对研究城市热岛效应、进行生态环境监测评价是必不可少的。利用遥感手段进行地表温度的反演是一种较新颖的方法,相对成熟的反演算法主要有单通道算法、辐射传输方程法及单窗算法。本文以山东省威海市Landsat TM数据为例,分别利用辐射传输方程法和单窗算法进行地表温度反演,通过遥感目视解译的方法提取研究区各类典型地物对应的地表温度,进行统计分析,结果表明,两者反演得到的地表温度具有一致的变化趋势,其中单窗算法中不同典型地物的地表温度整体标准差较小,如建设用地为0.530,起伏波动小,算法精度略优于辐射传输方程法。     

Landsat时序变化检测综述

时序变化检测已成为当前Landsat数据主流的变化检测方法。本文从检测算法对比、时序数据构建和精度评价等方面对Landsat时序变化检测进行回顾和评述,进而提出Landsat时序变化检测当前所存在的问题,及其所面临的挑战。Landsat时序变化检测算法可大致归纳为轨迹拟合法、光谱-时间轨迹法、基于模型的方法3大类,这些算法大多基于森林扰动提出;变化检测常用指标有波段型、植被指数型、线性变换型、组合型4大类,每类指标的优势不同,可综合多类指标以更全面地检测不同扰动类型。尽管Landsat时序变化检测已取得长足发展,但仍然面临诸多挑战,其中最大挑战是缺少一致性的参考数据集进行变化检测精度评价。     

基于知识的遥感影像居民地信息提取——以山东省蓬莱市为例

如何自动获得居民地信息是遥感专题信息提取研究的热点问题,该文以山东省蓬莱市为研究区,基于对2004年TM影像光谱特征的分析,建立了基于知识的居民地信息自动提取模型,并对提取结果进行了精度评价。结果表明,利用该模型可以很好地将蓬莱地区的城镇居民地自动提取出来,其提取精度与传统的监督分类方法相比有了很大提高。     

基于USB协议的望远镜多波带控制系统设计

怀柔观测基地的多通道太阳望远镜是通过数十个电机调节晶体偏转角度实现多波带同时观测的自动控制。原有的计算机是通过一个串行接口控制若干个调波带的电机,响应时间长,速度慢且技术比较落后。本文利用当今流行的USB2.0芯片CYPRESS EZ-USB改造原有的串口通信控制系统,大大提高了响应的速度,同时,为解决一个USB应用程序控制多个电机转动的问题,提出了一种"编号"的方法。这样每个USB设备不论其插入顺序,PC主机都能通过识别其固定编号而加以区分,PC主机可以通过4个USB接口(16个电机)控制多通道太阳望远镜滤光嚣的调制角度,实现自动控制。这为大规模改造其他计算机接口提供了研制基础。