Study On The Land Cover Change And Urban Expansion In Xiangtan Main City By Remote Sensing

Xiangtan City is a important city of Changsha-Zhuzhou-Xiangtan agglomeration.It has a relatively rapid development during the construction of the Changsha-Zhuzhou-Xiangtan urban agglomeration and the Chang-Zhu-Tan integration.Therefore,the land cover types and urban spatial forms of Xiangtan City are all had significant changes.It is very important to grasp the urban land resource utilization information in a timely manner and correctly understand the spatial patterns of urban land use.This paper takes the Landsat TM/OLI remote sensing image of Xiangtan City in 1991,1999,2005,2012 and 2017 as the base of the data and extracts the land cover information of the study area;Calculate the data in the transition matrix to get net change,exchange change,and total change of each land cover type,then analysis the tendency of land cover conversion in study area from two perspectives of increase and decrease,through the conversion value between land cover types under random conditions.To analysis the pattern of urban expansion in the study area,combine with the landscape pattern indices of different buffer zones;Use urban spatial analysis methods such as compactness index,subdimension index,dilation intensity,change of gravity center,buffer method,and equal segmentation method to analysis the expansion characteristics of Xiangtan City in different directions and different spatial locations;Finally,analysis the urban expansion model of the study area was through certain research methods.In summary,the main conclusions of this paper are as follows:(1)Cultivated land and forest land are the largest covering areas in the study area.Due to the large number of bases,the mutual transformation between the two is the main part of conversion between each land cover types;There are advantages of the conversion type,construction land increases to occupy unused land,cultivated land increases to occupy forest land,unused land decrease to construction land,cultivated land decrease to unused land;(2)The urban land in the study area is not compact enough,with the highest value being 0.44 in 1991 and then decreasing year by year.Most of the fractal dimension indices are between 0.3 and 0.5,the patches are relatively regular,and the shape of the figures are relatively simple.In differente direction,the directions of expansion during 1991-1999 are relatively even.Most of the expansion of the study area in 1999-2017 was in the eastern half sector,with the main directions of East(E),South East(SEE)and East North(NEE);During 1991-1999 and 1999-2005,urban expansion,mainly concentrated in 3000m-4500 m,4500m is the city's edge zone,expansion focused on 6000m-9000m during 2012-2017.(3)There are three types of urban expansion modes in the main urban areas of Xiangtan:marginal,filled,and enclave.The marginal model is the dominant expansion model for the study area and runs through the entire study period.In 1991?1999,the enclave expansion was higher than the filling expansion mode,and then decreased year by year.The marginal expansion model of 2005-2012 exceeded the sum of the other two types of expansion models.