Huaiping Xue

Super-resolution land-cover mapping using multiple sub-pixel shifted remotely sensed images

Super-resolution land-cover mapping is a promising technology for prediction of the spatial distribution of each land-cover class at the sub-pixel scale. This distribution is often determined based on the principle of spatial dependence and from land-cover fraction images derived with soft classification technology. However, the resulting super-resolution land-cover maps often have uncertainty as no information about sub-pixel land-cover patterns within the low-resolution pixels is used in the model. Accuracy can be improved by incorporating supplemental datasets to provide more land-cover information at the sub-pixel scale; but the effectiveness of this is limited by the availability and quality of these additional datasets. In this paper, a novel super-resolution land-cover mapping technology is proposed, which uses multiple sub-pixel shifted remotely sensed images taken by observation satellites. These satellites take images over the same area once every several days, but the images are not identical because of slight orbit translations. Low-resolution pixels in these remotely sensed images therefore contain different land-cover fractions that can provide useful information for super-resolution land-cover mapping. We have constructed a Hopfield Neural Network (HNN) model to solve it. Maximum spatial dependence is the goal of the proposed model, and the fraction maps of all images are constraints added to the energy function of HNN. The model was applied to synthetic artificial images as well as to a real degraded QuickBird image. The output maps derived from different numbers of images at different zoom factors were compared visually and quantitatively to the super-resolution map generated from a single image. The resulting land-cover maps with multiple remotely sensed images were more accurate than was the single image map. The use of multiple remotely sensed images is therefore a promising method for decreasing the uncertainty of super-resolution land-cover mapping. Moreover, remotely sensed images with similar spatial resolution from different satellite platforms can be used together, allowing a fusion of information obtained from remotely sensed imagery.

Lake area changes in the middle Yangtze region of China over the 20th century.

The Jianghan Plain and the Dongting lake area, located in the middle reaches of the Yangtze River are famous for their abundant freshwater lakes. The lakes have undergone changes in size and number over thousands of years due to natural causes and human activities. The 20th century particularly, witnessed dramatic changes in the freshwater resources of this region. This paper traces and analyzes lake evolution in the middle reaches of the Yangtze River over the past century. Lakes greater than 0.1 km(2) in size are mapped using Geographic Information System. Data is acquired and integrated from drainage network maps, relief maps, historical maps and remotely sensed images for different time periods. The results indicate that while there has been little change in the number of lakes over the past century, the lake area has experienced a dramatic decrease of 58.06%. The paper also examines the natural processes and human activities that may have contributed to the decrease in lake area. The results show that the decrease in total lake area appears to coincide with periods of rapid land reclamation in the middle reaches of the Yangtze River. Moreover, uncontrolled land reclamation activities can create an increase in sediment deposition in lakes thereby further reducing the lake size. Reduction of the lake area directly affects flood-control and has a negative ecological impact on the environment and on human life and property.

Waterline mapping at the subpixel scale from remote sensing imagery with high-resolution digital elevation models

Subpixel mapping technology is a promising method of increasing the spatial resolution of the classification results derived from remote sensing imagery. However, for waterline mapping problems, the traditional spatial dependence principle of subpixel mapping is not suitable as the water flow is always controlled by the topography. This letter presents a novel algorithm based on a high spatial resolution digital elevation model (DEM) to address the subpixel waterline mapping problem. The waterline was mapped at the subpixel scale with a proposed rule according to the physical features of the water flow and additional information provided by the DEM. The method was evaluated with degraded real remotely sensed imagery at different spatial resolutions. The results show that the proposed method can provide more accurate classifications than the traditional subpixel mapping method. Moreover, the fine spatial resolution DEM can be used as feasible supplementary data for subpixel waterline mapping from coarser spatial resolution imagery.

Variations of PM10 concentrations in Wuhan, China

Concentrations of PM10 (particulate matter as a key urban air pollutant) were obtained from nine monitor stations within the city of Wuhan for analysis after an intensive observational data collection period that commenced in January 2006 and concluded in December 2008. According to our data, PM10 pollution intensified and reached a high alert level of air pollution during the month of November each year. It remained at a high alert level until the following April where it again decreased to a low alert level during the summer months. During the winter and spring months, the occurrence rate (in percent)of PM10 was five to eight times higher (high alert level) than measurements detected during the summer months. The effects of intrinsic factors (pollution sources) and remote preconditions (dust storm propagation and formation of secondary aerosol) on severe PM10 concentrations in Wuhan are first analyzed. After which, suggestions to reduce PM10 pollutants are provided.

Assessment of ASTER GDEM performance by comparing with SRTM and ICESat/GLAS data in Central China

Recently, a new Global Digital Elevation Model (GDEM) from optical stereo data acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was released with the resolution of 1 arc sec. In this study, the performance of the new ASTER GDEM is assessed by comparing with SRTM (the Shuttle Radar Topography Mission) and point data from ICESat/GLAS (Ice, Cloud, and land Elevation Satellite/ Geoscience Laser Altimeter System). A 5°×5° area (30°-35°N, 110°-115°E) with varied terrain was chosen as the study area. Standard DEM-to-DEM comparison, DEM-to-control-point comparison and visual analysis were used to evaluate the ASTER GDEM quality. The results show that the ASTER GDEM has much fewer voids than SRTM V2 (the version 2 SRTM). The ASTER GDEM has lower elevations (approximately −5m) compared with SRTM, whereas the ASTER GDEM has higher elevations (approximately 15m) compared with ICESat/GLAS points. To the vertical accuracy, the results of the ASTER GDEM compared with SRTM V4 (the version 4 SRTM), SRTM V2 and ICESat/GLAS points are 39.55m, 25.99m, 33.99m at 95% confidence respectively, exceeding 20m estimated prior to the ASTER GDEM production. The poor accuracy may be related to the high terrain relief and high ratio of lower stack number of the ASTER GDEM in the study area. The ASTER GDEM shows better performance in the flat areas than that in the mountainous areas, and the accuracy improves with the increasing stack number. The ASTER GDEM has many artifacts including inland water noises and straight lines related to the irregular stack number boundaries, which are caused by the methodology to produce the ASTER GDEM.

Characteristics of nutrients in natural wetland in winter: a case study

The transformation, composition, and distribution characteristics of nutrients in natural wetlands are significantly affected by human activities, such as large-scale water conservancy projects and agricultural activities. It is necessary to reveal the composing and distribution characteristics of nutrients for elucidating its complex removal and retention mechanisms in natural wetlands. In this study, the composition and the spatial distribution characteristics of nitrogen in a natural wetland in central China were illustrated and analyzed. The self-organizing map (SOM) model was used in this study to assess the water quality dataset of the wetland. The relationships between nitrogen and other water quality parameters were revealed by the visualization function of the SOM model with the pre-processed data; the modeling result was in agreement with the linear correlation analysis. The results indicated that the SOM model was suitable for the assessment of field-scale date of natural wetlands, and finally a potential approach for predicting the nutrients concentrations in natural wetlands was also found.

Research on flood monitoring system for middle reaches of Yangtze China using RS and GIS

based on RS, and GIS. In the paper, Flood Monitoring System for middle reaches of Yangtze is studied. The goal, structure and working principles of the system are introduced firstly. Then, the system functions and key implementation technology are stated. The system is unique and complicate mainly because its function is wide, which covers flood monitoring, simulation, assessing and so on. The application of the system will provide decision support for middle reach areas of the Yangtze in finding flood, designating relief schemes and rebuilding after flood.

Evaluating and analyzing the sustainable development using PCA

The Principal Component Analysis (PCA) method can be used for managing numerous correlative indexes. In this paper we attempt to apply this method to evaluating and analyzing the sustainable development, a case study in Honghu City China. Firstly, according to the theory of system, we regard Honghu City as one compound system including population, economy, society, and resource environment subsystems, and set up evaluation index system of Honghu city. Then evaluate and analyze the state of sustainable development using PCA. The results show: Honghu city develops towards the benign direction generally, and some reasons for the development state are analyzed. Above evaluation and analysis process indicate: PCA is a good method to evaluate and analyze sustainable development. Keywords-evaluating, analyzing, sustainable development, PCA, Honghu City China