Urban built-up land change detection with road density and spectral information from multi-temporal Landsat TM data

In this article, Landsat TM images acquired during the same season from both 1984 and 1997 were analysed for urban built-up land change detection in Beijing, China, where great changes have taken place during the recent decades. To reduce the spectral confusion between urban 'built-up' and rural 'non built-up' land cover categories, we propose a new structural method based on road density combined with spectral bands for change detection. The road density represents one type of structural information while the multiple Landsat TM bands represent spectral information. Road density maps for both dates were produced using a gradient direction profile analysis (GDPA) algorithm and then integrated with spectral bands. Results from the spectral-structural postclassification comparison (SSPCC) and spectral-structural image differencing (SSID) methods were evaluated and compared with spectral-only change detection methods. The proposed SSPCC method greatly reduced spectral confusion and increased the accuracy of land cover classification compared with spectral classification, which in turn improved the change detection results. This article also shows that the SSID change detection result complemented spectral band differencing by detecting areas with greater structural changes, some of which were missed, by spectral band differencing.     

A regional investigation of urban land-use change for potential landslide hazard assessment in the Three Gorges Reservoir Area,People's Republic of China: Zigui to Wanzhou

The near-completion of the Three Gorges Dam has led to the creation of a narrow reservoir that, when completed in 2009, will stretch over 660 km upstream and result in the displacement of approximately 1.2 million people. This reservoir will drown more than 100 towns, some of which have already been lost due to the rising waters, and result in a significant change in land use. New urban areas have been constructed at higher elevations to avoid the rising water but it is feared that some of these settlements may now be exposed to a greater risk of landslides due to slope failure. A geographic information system (GIS) consisting of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Landsat Thematic Mapper (TM), and Environmental Satellite-Advanced Synthetic Aperture Radar (ENVISAT-ASAR) data has been created and used to monitor the urban changes from before the Dam's construction to the present day as well as changes in landslide susceptibility. To perform this analysis, a new 30 m high-resolution digital elevation model (DEM) was derived by combining an ASTER and Shuttle Radar Topography Mission (SRTM) DEM. Fieldwork was carried out along the Yangtze River, where the urban boundaries were field-checked using GPS to navigate to the satellite-derived checkpoints. The results show that a majority of the new urban areas are in fact located on shallow slopes, but are often positioned below steep slopes, which could pose a future threat of landslide risk to the inhabitants of the new towns.     

Comparisons of regression tree models for sub-pixel imperviousness estimation in a Gulf Coast city of Mississippi,USA

We studied the impact of shaded impervious surface area (ISA), atmospheric correction, and seasonal sensitivity, which have been generally ignored in previous studies, on ISA estimation at the sub-pixel scale using regression tree modelling. The study area is Pascagoula City on the Mississippi Gulf Coast, USA. Results showed that inclusion of shaded ISA as the response variable improved the model performance by reducing average error (AE) from 10.17 to 9.36%. Modelling with model-based atmospherically corrected imagery as predictors further reduced AE to 9.27%. The regression tree model using summer imagery as predictors (summer model) finally improved AE to 8.56%, compared with 9.28%, 9.50%, and 8.80% when using early spring, late spring, and autumn images as predictors, respectively; therefore the summer model was considered the optimal model. It was further applied to other seasonal images (i.e. early spring, late spring, and autumn images, as predictors) and the AE was 9.93%, 10.09%, and 9.12%, respectively, showing low seasonal sensitivity within this region. The findings in our study improved the modelling accuracy and expanded the scope of its future application in ISA estimation.     

Comparison of atmospheric correction algorithms for TM image in inland waters

In order to extract quantitative water‐leaving information from the Thematic Mapper (TM) image accurately in inland waters, atmospheric correction is a necessary step. Based on former researchers' results, the paper presents two atmospheric correction algorithms based on meteorological data (MD) and on Moderate Resolution Imaging Spectroradiometer (MODIS) Vicarious Calibration (MVC) for TM image in inland waters according to the theory of radiative transfer. Studying Taihu lake, China, in this paper we derived water remote sensing reflectance from a TM image of 26 July 2004 by these two atmospheric correction algorithms and we compare the results with that of dark object subtraction (DOS) and 6S code. The results show that the effect of atmospheric correction based on meteorological data and MODIS Vicarious Calibration is much better than that of DOS and 6S code. Although the MD is more accurate, MVC may be an ideal choice for TM images in inland water because TERRA MODIS images can be acquired easily than collecting meteorological data at the time of satellites passing over.     

Retrieval and analysis of aerosol optical characteristics in Hubei Province,China, based on CALIPSO

The aerosol optical characteristics in Hubei Province, China, derived from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), are investigated. Through this spaceborne lidar, some limitations of airborne and ground-based systems can be overcome and a global survey of clouds and aerosol can be provided. First, a lidar ratio selection algorithm is introduced. Since the lidar ratio (the aerosol extinction-to-backscatter ratio, S _a) is an important parameter used in aerosol retrieval, it is required for a reliable aerosol model. After retrieving the original signal, aerosol optical parameters are obtained. Based on these steps, the impacts of atmospheric motion on aerosol diffusion in different layers, the distribution of these aerosols, as well as their time-changing characteristic in Hubei Province are discussed. The studies show that in areas of plains aerosols are easily influenced by wind; furthermore, aerosol distribution in the western Hubei Province is usually influenced by biomass burning and in eastern Hubei by industrial emission. Although errors still exist, the aerosol optical characteristics in different regions are strongly related to the ground surface, wind direction and visible distinctions exist in urban and country areas.     

An integrated spatio-temporal classification method for urban fringe change detection analysis

The urban fringe is the transition zone between urban land use and rural land use. It represents the most active part of the urban expansion process. Change detection using multi-temporal imagery is proven to be an efficient way to monitor land-use/land-cover change caused by urban expansion. In this study, we propose a new multi-temporal classification method for change detection in the urban fringe area. The proposed method extracts and integrates spatio-temporal contextual information into multi-temporal image classification. The spatial information is extracted by object-oriented image segmentation. The temporal information is modelled with temporal trajectory analysis with a two-step calibration. A probabilistic schema that employs a global membership function is then used to integrate the spectral, spatial and temporal information. A trajectory accuracy measurement is proposed to assist the comparison on the performances of the integrated spatio-temporal method and classical pixel- and ‘snapshot’-based classification methods. The experiment shows that the proposed method can significantly improve the accuracies of both single scene classification and temporal trajectory analysis.     

Comparison and improvement of methods for identifying waterbodies in remotely sensed imagery

This article first examines three existing methods of delineating open water features, i.e. the normalized difference water index (NDWI), the modified normalized difference water index (MNDWI) and a method combining the near-infrared (NIR) band and the maximum likelihood classification. We then propose two new methods for the fast extraction of water features in remotely sensed imagery. Our first method is a pixel-based procedure that utilizes indices and band values. Based on their characteristic spectral reflectance curves, waterbodies are grouped into three types – clear, green and turbid. We found that the MNDWI is best suited for identifying clear water. Green water has its maximum reflectance in Landsat Thematic Mapper (TM) band 4 (NIR band), whereas turbid water has its maximum reflectance in TM band 5 (mid-infrared band). Our second method integrates our pixel-based classification with object-based image segmentation. Two Landsat scenes in Shaanxi Province, China, were used as the primary data source. Digital elevation models (DEMs) and their derived slope maps were used as ancillary information. To evaluate the performance of the proposed methods, extraction results of the three existing methods and our two new methods were compared and assessed. A manual interpretation was made and used as reference data. Results suggest that our methods, which consider the diversity of waterbodies, achieved better accuracy. Our pixel-based method achieved a producer's accuracy of 92%, user's accuracy of 90% and kappa statistics of 0.91. Our integrated method produced a higher producer's accuracy (95%), but a lower user's accuracy (72%) and kappa statistics (0.72), compared with the pixel-based method. The advantages and limitations of the proposed methods are discussed.     

基于linux的网页抓取器的设计

网页抓取器是爬虫系统的一个重要部分,其性能的好坏直接影响着搜索引擎的性能.网页抓取器可以分为网络层和应用层,而网络层是关键.基于选取样本页面、定义规则和网页抓取的三个步骤,在linux下使用epoll技术实现了多线程的网页抓取,方法快速有效.     

New global synchronization analysis for complex networks with coupling delay based on a useful inequality

This paper is concerned with the problem of global synchronization for a general complex networks. Based on a useful inequality and Kronecker product technique, a new criterion is obtained, which has fewer unknown variables and is a significant improvement in the performance. Synchronization criteria are derived by some new mathematical skills and Schur complement. The result is expressed by linear matrix inequalities, which can be easily computed and checked in practice. Finally, numerical examples will be used to show the effectiveness of the obtained result.     

中外素混凝土局部承载能力计算方法的对比研究

本文以素混凝土局部受压承载力为研究对象,首先介绍了其破坏机理,然后通过对中国、美国、欧洲规范中相关内容进行对比,分析了中外规范的异同和原因,最后以典型算例进一步验证了研究结论,并对我国相关标准的修订提出了建议.