Yan Changzhen

Developing method of vegetation fraction estimation by remote sensing for soil loss equation: a case in the Upper Basin of Miyun Reservoir

Vegetation fraction is an input parameter to scale, the vegetation cover on the ground for soil loss equation. In order to calculate the yearly volume of losing soil in the Upper Basin of Miyun Reservoir in the north of Beijing, China, it is necessary to develop a model to estimate vegetation fraction using remote sensing technology. Based on the analysis on the existing methods of measuring vegetation fraction, an improved Dimidiate Pixel Model was developed to estimate vegetation fraction from normalized difference vegetation index (NDVI) derived from Landsat TM images, and a new method was also brought forward to quantify NDVI thresholds of soil and vegetation. The. vegetation fraction data have been estimated using improved model in the study area, and was validated with the field survey data. The result shows that the improved model could satisfy with the need for quantifying vegetation cover parameter front TM imagery for soil loss equation

Combining Spot4-vegetation and meteorological data derived land cover map in China

The global version of the 1km spatial resolution land cover map have been finished at the end of 2003, which is initiated by the European Commissions Joint Research Center, named Global Land Cover 2000 Project (GLC-2000). As a part of GLC2000, the China window has been developed with the 10-day composite SPOT VGT NDVI data over a period of 01 January 2000 to 31 December 2000, DEM and the Meteorological data (Multi-annual average temperature, multi-annual average precipitation data) collected from 313 weather stations distributed over the China from 1971 to 2000. In order to remove cloud contamination and interpolate the missing data masked by cloud, the Harmonic Analysis of Time Series (HANTS) was applied to NDVI data. With the assistance of Erdas ISODATA algorithm, the classification has been carried out, and 22 types of land cover has labeled in the whole China by interpreting according to the Land Cover Classification System (LCCS) developed by the UN Food and Agriculture Organization (FAO) in the framework of the AFRICOVER project. Preliminary comparisons with the statistic data from Chinese Statistics Bureau and TM data show very promising results, and the accuracv assessment of the GLC-2000 is underway.

Land use and land cover change and its driving forces in the source region of the Yangtze River during 1990–2005

Land use and cover change (LUCC) is an important field in studying the global change or global warming. The source region of the Yangtze River locates in the northeast of Qinghai-Tibetan Plateau. The ecosystem there is extremely vulnerable and sensitive to global climate change and human activities, which have brought in significant change of eco-environment in this region in recent years. Therefore it is essential to investigate the land use and land cover change, and to explore its driving forces in the source of the Yangtze River. In this study, we used Landsat images obtained in 1990 and 2005 to establish databases of land use and cover. Then we derived LUCC information by overlaying these layers using GIS software. To examine the processes responsible for LUCC, we discussed its driving forces including climatic change, human activities, animal and insect damage. During the past 15 years, the forest, grassland experienced the most significant decrease. The forest and grassland decreased by 2509 hm2, 41847.1 hm2, respectively. However, unused land and water area showed the opposite trend, increased by 33903.8 hm2, 10480.1 hm2 respectively. The farmland and build-up land changed no obvious in past 15 years. These results suggested that the degradation of the eco-environment is obvious, showing a decrease in the forest, grassland, and an increase in the area of unused land. The major factors responsible for LUCC include increasing temperature, decreasing precipitation in summer and autumn, variation in the frozen soil environment, human activity (seasonal overgrazing) and rodent damage.

Detecting vegetation change during the period 1998-2002 in NW China using SPOT-VGT NDVI time series data

The primary objective of this study was to assess the trends of vegetation changes in west of China since 1998 to 2002 with the 1 km/sup 2/-resolution SPOT-Vegetation 10-day maximum-value synthesized normalized difference vegetation index (NDVI) data. The framework for the analysis is the use of the coefficient of variation (COV) of the decadal NDVI as a measure of vegetative biomass change. A higher NDVI COV for a given pixel represents a greater change in vegetation biomass in the ground area represented by that pixel. And then a linear regression was used to determine the trend of COV value for each pixel over the 5-year period. The slope of the linear regression can be gained and acted as the criterion for the change direction. Pixels with a negative slope are considered to represent ground areas with decreasing amounts of vegetation, vice versa. Results showed vegetation ecosystems in west of China are undergoing accelerated change due to natural and anthropogenic disturbances since 1998 had the increase trends in the five years.

Monitoring land desertification in the source region of the Yangtze River Qinghai Province by remote sensing technology

The land desertification is one of the major environmental problems in the Source Region of the Yangtze River, Qinghai Province. With the Three Gorges Dam construction, more and more attention is paid to restoring the degraded eco-environment of the region. In this study, the sandy land was classified into three types, and the desertified land was also inventoried correspondingly into three levels. Through interpreting TM images in 1986 and 2000, the databases of sandy land at two times had been established, respectively. And then the desertified land data was derived through overlaying the databases of sandy land. The result shows that there is 1,459,365 ha of sandy land in the region in 2000, accounting for 9.89% of all study area. There is 11,877 ha of newly sandy land resulted from land desertification, and sandy land has increased by 7.35% during about 14 years in the end of the 20th century.The land desertification is one of the major environmental problems in the Source Region of the Yangtze River, Qinghai Province. With the Three Gorges Dam construction, more and more attention is paid to restoring the degraded eco-environment of the region. In this study, the sandy land was classified into three types, and the desertified land was also inventoried correspondingly into three levels. Through interpreting TM images in 1986 and 2000, the databases of sandy land at two times had been established, respectively. And then the desertified land data was derived through overlaying the databases of sandy land. The result shows that there is 1,459,365 ha of sandy land in the region in 2000, accounting for 9.89% of all study area. There is 11,877 ha of newly sandy land resulted from land desertification, and sandy land has increased by 7.35% during about 14 years in the end of the 20th century.

Evaluating the effects of eco-environment conservation projects in China by remote sensing technology

National key projects of eco-environment conservation have been carried out to combat the environmental degradation in the fragile ecological zone in China since 1998. To evaluate the projects effect on eco-environment restoration, five cases, locating in different eco-environmental zones and representing the different types of practiced measures, were selected to map land cover for each sample area, respectively, using Landsat TM images in 1997 and 2002. The mapping coverage of each sample site was confined within the overlaying extent of two images with the same path and row. And then the land cover changes were detected using overlaying technology in GIS. The results show that the land cover changes of each case site except for the site E located in the northeastern China characterized by farmland decreasing and natural or seminatural vegetation increasing, and that a serious of practiced measures adopted by the conservation projects have an effect on the rehabilitation of ecological environment.