Remote Sensing Monitoring And Driving Factors Of Temporal And Spatial Changes In Urban Built-up Areas In Nyingchi Area

Built up area is one of the important indicators to measure the speed of a region's development.At the same time,relying on the regional advantages,it gathers the region's economy,population and natural resources.To some extent,the expansion of built-up areas means that the focus of regional economy,population and natural resources has shifted.Therefore,the dynamic monitoring of the expansion of built-up areas is conducive to understand the regional economic development and formulate a reasonable urban development plan.Remote sensing provides important technical means and data support for monitoring large-scale dynamic change of land use.Remote sensing can quickly and effectively extract the built-up area,and has great significance for the study of characteristics and influencing factors of large-scale dynamic change of built-up area.In this study,Nyingchi Region with poor urban development foundation and complex terrain was taken as the research area.The built-up area was preliminarily extracted by CART decision tree classification based on Landsat remote sensing images,and the mask range of built-up area was extracted by determining the threshold value by mutation detection method based on night light data.Finally,the obtained boundary mask of built-up area was used to filter the initial results of Landsat remote sensing image extraction,and the spatio-temporal dynamic changes of built-up area from 1995 to 2020 were obtained by combining visual interpretation and correction principles.Based on the extracted results,the spatial expansion characteristics of nyingchi region in the past 25 years were quantitatively described and analyzed.Finally,the driving factors of nyingchi region's expansion were analyzed based on multi-source information such as terrain,population,economy and transportation.This study explores the optimization of extraction methods and analysis of spatio-temporal dynamic changes of typical regions with weak urban development foundation and complex terrain,which has certain reference significance for other urban built-up areas in Tibet Autonomous Region.The main conclusions are as follows:(1)The nighttime light data can effectively optimize the extraction results of Landsat remote sensing data,and effectively filter out the bare soil and villages around the built-up area.The average accuracy of Landsat remote sensing data is 81.57%,while the average accuracy of noise filtering optimization based on DMSP and NPP/VIIRS data is 92.40%,and the average accuracy is improved by 10.83%.The final extraction results can be used for the quantitative analysis of spatiotemporal dynamics of the built-up area.(2)Based on the extraction of Landsat remote sensing data,the spatial and temporal characteristics of the expansion of the built-up area in Nyingchi region from 1995 to 2020were quantitatively described and analyzed.Generally speaking,each district and county in Nyingchi region expanded along the valley and plain in an east-west direction.In the past 25years,the expansion rate of nyingchi region has increased significantly,and it entered the period of rapid development after 2005 with an expansion rate of 7.278 km~2/year.The overall expansion intensity of nyingchi region is lower than that of northwest China.(3)From the perspective of spatial characteristics,the center of built-up area in Nyingchi has been migrating to the west,and the west direction is the main orientation of the expansion of built-up area in nyingchi.The center of built-up area in Nyingchi has been falling within the administrative area of Bayi District,and the center of built-up area in the border area has been falling between Motuo county and Millin County.(4)From the perspective of morphology,the urban structure of each district and county is relatively scattered.The urban built-up area is long and narrow,and the construction of the built-up area gradually spreads outward.The boundary outline of the built-up area in the study area is simple,the connectivity between the districts and counties is generally high,and the radiation effect of the city center is good.(5)By analyzing the driving factors of the expansion of the built up area in Nyingchi region,it is found that the expansion of the built up area in Nyingchi region is guided by the government's strategy and development planning,and the positive development strategy and capital investment can effectively promote the rapid development of the local city.In addition,the new built-up areas in Nyingchi region are mainly concentrated in the valley plain section of the mountain valley with a relatively low terrain of 1000-3500m above sea level.The continuous expansion of built-up areas is closely related to the local population,economic growth and urban transportation network and shows a significant positive correlation.Among them,the value of the primary industry in this area has the highest correlation with the expansion of built-up areas and is closely related to the development of local characteristic agriculture and animal husbandry industry.