基于遥感和GIS的川西绿被时空变化研究

Abstract

A method for analyzing the change in green vegetation cover is proposed and applied to reveal the features of change in green vegetation cover in the western area of Sichuan province of the P.R.of China between 2002 and 2008.The western area of Sichuan includes GanZi,Aba,Liangshan,and Panzhihua.First,a time series of Moderate-resolution Imaging Spectroradiometer(MODIS) images acquired between 2002 and 2008 for western Sichuan were matched,processed to remove cloud,and normalized.Second,the time series of the normal difference vegetation index was calculated as the difference between the near infrared and red bands divided by the sum of the near infrared and red bands of the time series of MODIS images.Third,a model for extracting green vegetation cover from MODIS images was formulated by spectral analysis,and used to extract multi-temporal green-vegetation cover data from the time-series of MODIS images acquired of western Sichuan between 2002 and 2008.Fourth,the multi-temporal green-vegetation cover data were used to determine the temporal and spatial changes in green-vegetation cover between 2002 and 2008 using overlay and statistics analysis in ArcGIS software.Finally,the correlation among green-vegetation cover,temperature and rainfall were analyzed.The temporal and spatial changes in green-vegetation cover were deduced.In 2002,43.3 percent of western Sichuan was covered by green vegetation for more than 195 days,25.4 percent was covered for more than 285 days,and 4.3 percent was rarely covered.Green-vegetation cover extended from southeast to northwest from January to August,and retreated from northwest to southeast from September to December.Vegetation in the southeast grew for longer than that in the northwest during a year.The area of green vegetation in the study area varied largely by 20064 km2,accounting for 6.6 percent of the total study area,in the spring between 2002 and 2008.The area of green vegetation in the study area rarely varied in autumn between 2002 and 2008.The decreasing order of the area of green vegetation between 2002 and 2008 was the area for summer,autumn,spring and winter.The maximum area of green vegetation between 2002 and 2008 was 289037 km2 in the summer of 2006,accounting for 94.9 percent of the study area,and the minimum was 137193 km2 in the winter of 2005,accounting for 45 percent of the study area.The average of the difference in the area of green vegetation between summer and winter from 2002 to 2008 was 142224 km2,accounting for 46.7 percent of the study area.The green-vegetation area was significantly related to temperature and rainfall at the 0.01 confidence level according to season.Correlation coefficients were respectively 0.82 and 0.84.In summer,the vegetation area was significantly related to temperature at the 0.01 confidence level.Increasing temperature and rainfall are beneficial to vegetation growth.With the combination of light,heat,water,fertilizer and soil data,the spatial and temporal features of green-vegetation cover obtained here can be used to determine a methodology for improving the area and number of days of green-vegetation cover.The results presented here are important for improving vegetation growth,agriculture productivity and ecological construction.