Analyzing Land Use Changes and Its Driving Forces in Xi''''An Region During the Past 25 Years
近25年来西安地区土地利用变化及驱动力研究

The land use change in Xi'an during the last 25 years was investigated through land use classification of three sets of Landsat MSS/TM images acquired in September of 1978,August of 1988 and May of 2003 respectively.The BP(back propagation) neural network model has the advantage of non-linear characteristic,it can solve the problems existing in the traditional classifiers which classify images just based on the comparability of the spectral characteristic and has been gradually used in the classification of remote sensing image.In this study,the BP neural network classifier was used to classify the three sets of images.Combing with the statistic data and spatial analysis technique of GIS,the land use change and its driving forces in Xi'an in the past 25 years were analyzed.Due to the deficiency of the initial BP neural network model,great improvement was made to optimize it.In order to make the BP model converge faster,the program was made with the software of Matlab 6.5 to make the learning rate an autoregulative one,and besides,the offset and the momentum were added to the input layer and the hidden layer to store the result of the former process and to make the model easily converge to the overall minimum in stead of the partial minimum.In order to eliminate the misclassification caused by the shadow of the terrain and the angle of incidence,the DEM and the slope that was derived from the DEM were used as two accessorial nerve cells in the input layer of the BP neural network.By doing so,the BP neural network can have a shorter runtime and a higher accuracy than the maximum likelihood classification.The results showed that the area of the build-up increased sharply through occupying arable land and forestland.It was nearly twice the area of what it was in1978.The area of arable land decreased sharply with a rate of 1 percent annually.The area of the orchard increased greatly,and it was 3.4 times the area of what it was in 1978.Besides,the problem of lack water resources was getting more and more serious.Land use change is a complex process,which is affected by many comprehensive factors including both socioeconomic and natural and environment.Generally the governmental policy and the rules play a decisive role to the land use change.The expansion of the railway and the highway was the direct driving force for the rapid growth of the build-up land.The increase of the population and the rapid expansion of the build-up land resulted in large amount of plantation vanished.The increase of the orchard resulted from the development of the primary industry.