Feng Xue-zhi

China's lakes at present: Number, area and spatial distribution

Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM, changes in the spatial characteristics of all lakes in China were determined following pre-established interpretation rules. This dataset was supported by 6843 digital raster images (1:100000 and 1:50000), a countrywide digital vector dataset (1:250000), and historical literature. Comparative data were corrected for seasonal variations using precipitation data. There are presently 2693 natural lakes in China with an area greater than 1.0 km2, excluding reservoirs. These lakes are distributed in 28 provinces, autonomous regions and municipalities and have a total area of 81414.6 km2, accounting for ∼0.9% of China’s total land area. In the past 30 years, the number of newly formed and newly discovered lakes with an area greater than 1.0 km2 is 60 and 131, respectively. Conversely, 243 lakes have disappeared in this time period.

Relationship between blue algal bloom and water temperature in Lake Taihu based on MODIS

Blue algal bloom in Lake Taihu was dynamically monitored using MODIS of hyper-spectral remotely sensed data,and combined with water temperature,environmental condition of algal blooming was also discussed.Firstly,blue algal biomass was estimated using simple ratio vegetation index,and progress of blue algal bloom was dynamically monitored using six sets of MODIS data.Then synchronous water temperature was retrieved from MODIS infrared bands 31 and 32 using window split model.The main environmental factor of blue algal bloom-water temperature was analyzed,as well as the relationship between blue algal growing and water temperature.The results showed that water temperature was an important environmental factor of blue algal growing;and appropriate water temperature(ranged from 24℃to 30℃)was necessary condition of blue algal bloom;and high temperature(30℃) significantly inhibited the growth of blue algae.

Visualization GML with SVG

A new common Geo-data format known as the Geography Markup Language (GML) has been specified by OGC (Open Geospatial Consortium, Inc.) through a unique marriage of the W3C’s (World Wide Web Consortium’s) Extensible Markup Language (XML). GML maintains a strong separation between presentation and content. To make a map with GML data, GML geographical content must be styled into a suitable graphical presentation that can be interpreted in a Web browser. A suite of new technologies such as XML, SVG, and DOM create a new perspective for it. The Scalable Vector Graphics (SVG) is a new XML-based graphic format for defining 2D graphics, including vector and raster format, for the web and other applications. This paper shows how the Geo-data to be stored and transferred in GML and visualized in SVG, as well as converting from GML to SVG via Extensible Stylesheet Language Transformations (XSLT) and how to make the SVG graphic dynamic with Hypertext Markup Language (HTML) and Document Object Model (DOM). KeywordsGML; SVG; XSLT; DOM; Internet

A method for retrieving water-leaving radiance from Landsat TM image in Taihu Lake, East China

The visible and infrared bands of Landsat Thematic Mapper (TM) can be used for inland water studies. A method of retrieving water-leaving radiance from TM image over Taihu Lake in Jiangsu Province of China was investigated in this article. To estimate water-leaving radiance, atmospheric correction was performed in three visible bands of 485nm, 560nm and 660nm. Rayleigh scattering was computed precisely, and the aerosol contribution was estimated by adopting the clear-water-pixels approach. The clear waters were identified by using the Landsat TM middle-infrared band (2.1 μm), and the water-leaving radiance of clear water pixels in the green band was estimated by using field data. Aerosol scattering at green band was derived for six points, and interpolated to match the TM image. Assuming the atmospheric correction coefficient was 1.0, the aerosol scattering image at blue and red bands were derived. Based on a simplified atmospheric radiation transfer model, the water-leaving radiance for three visible bands was retrieved. The water-leaving radiance was normalized to make it comparable with that estimated from other remotely sensed data acquired at different times, and under different atmospheric conditions. Additionally, remotely sensed reflectance of water was computed. To evaluate the atmospheric correction method presented in this article, the correlation was analyzed between the corrected remotely sensed data and the measured water parameters based on the retrieval model. The results show that the atmospheric correction method based on the image itself is more effective for the retrieval of water parameters from Landsat TM data than 6S (Second Simulation of the Satellite Signal in the Solar Spectrum) code based on standard atmospheric and aerosol models.

Monitoring cyanobacteria bloom based on MODIS data in Lake Taihu

This paper discusses the method and mechanism of identifying and monitoring the cyanobacteria bloom based on MODIS data in Lake Taihu.Through the comparison of spectral reflectance value of different cyanobacteria concentration,it can be found that several wave bands are sensitive to cyanobacteria.Making use of the color composition,we can get the macroscopic distribution information of the cyanobacteria bloom.Furthermore,using the ratio index model,we can further confine the relative content of the cyanobacteria bloom.Finally through overlaying analysis of the cyanobacteria concentration distribution from multi-temporal MODIS data,dynamic changing information of cyanobacteria bloom can he obtained.

URBAN PLANNING:A TOOL FOR URBAN POVERTY ALLEVIATION IN SUDAN

In the past few dacades, urbanization and urban growth have been increasing rapidly in many of the developing countries. It is expected that over 50% of the world population will live in cities in 2005. The growing trend indicates that as many as one fifth of all households still remain with housing tenure problems, which they try to solve through very expensive rentals, insecurity, socially and environmentally-hazardous squatting or unhealthy overcrowding, sometimes ending up with none at all. And hence, proper planning is necessary in urban development policies to improve human settlement managements in a sustainable way. This article has tried to handle urban poverty in the Sudan to a reasonable level of detail. It dealt with selected areas with regard to promotion of sustainable human settlement. The study managed to identity some recent progress in Sudanese human settlements, that is, however, still accompanied by numerous serious instances of decline in the urban environment, especially that of the greater Khartoum. Such instances of environmental deterioration are profiled and analyzed by the study with respect to all human settlement aspects of management, land-use, infrastructure, energy and transport. The paper’s conclusion emphasized that improving all these aspects is of high priority.

Land-cover density-based approach to urban land use mapping using high-resolution imagery

Nowadays, remote sensing imagery, especially with its high spatial resolution, has become an indispensable tool to provide timely up-gradation of urban land use and land cover information, which is a prerequisite for proper urban planning and management. The possible method described in the present paper to obtain urban land use types is based on the principle that land use can be derived from the land cover existing in a neighborhood. Here, moving window is used to represent the spatial pattern of land cover within a neighborhood and seven window sizes (61m×61m, 68m×68m, 75m×75m, 87m×87m, 99m×99m, 110m×110m and 121m×121m) are applied to determining the most proper window size. Then, the unsupervised method of ISODATA is employed to classify the layered land cover density maps obtained by the moving window. The results of accuracy evaluation show that the window size of 99m×99m is proper to infer urban land use categories and the proposed method has produced a land use map with a total accuracy of 85%.

An investigation of urban water automatic extraction based on texture and imaging knowledge from high resolution SAR images

Extracting water body information with SAR images is distinctive and important. Especially for high-resolution SAR images, its hard to extract water accurately because of Speckle Noises, so a Gabor filtering method related to the image texture is proposed. Firstly, frequency spectrum analysis method was used to identify the wedge and ring characters of image texture, and the period and directional parameters of the texture distribution were computed. Based on these characters, Gabor filter were constructed in order to filter the frequency spectrum of the multi-texture image, and best filter parameters were selected. After the filtering in frequency domain, components of corresponding texture were acquired by transforming the filtered frequency spectrum image to time domain image. The test results of terra SAR image indicate that the water body extraction method is good.