Research On Rapid Extraction Of Urban Built-up Area Information Based On Spectral Index

This thesis aims to study the rapid extraction method of built-up areas and explore the temporal and spatial characteristics of built-up area expansion.Chongqing City,the typical mountain city,was selected as the research area of this thesis,and the Landsat series of images were used as the data source.Firstly,four kinds of typical land-covers are selected for sampling to obtain their spectral curves.The spectral land-covers characteristics of various land-covers are analyzed and their separation is discussed.Secondly,based on the spectral characteristics of various types of land-covers,a new build-up index is proposed and a comprehensive extraction model of built-up area is established by Improved Double-window Flexible Pace Search(IDFPS)algorithm,which is veified by visual interpretation data.Finally,nine images in 21 years are processed using the proposed model.Based on the data of building area,this paper exlplores the spatial and temporal characteristics of the evolution of building area in Chongqing.The specific research contents and main conclusions are as follows:1.In order to study the separability between the built-up area and other land-covers,combined with the visual interpretation of the year 2016 remote sensing image of Chongqing and the Google Earth image,the imagery of the study area is divided into four types.The spectral characteristics of different land-covers are different in each band.From this land-cover,the spectral difference between the built-up area and other land-cover types is analyzed.From the overall perspective,the variation of spectral curve of the built-up area is very different from that of the vegetation and the water body.The trend changes in the fourth and fifth bands are significantly different from those of other land-covers,which can be used to weaken the information of such land-covers purposes.However,the spectral curve between the bare land and the built-up area is very similar.It is impossible to separate the two types of ground objects by simple inter-band operation,and it is necessary to introduce an index to solve this problem.2.In order to improve the accuracy of rapid extraction of building areas and overcome the difficulties of band land and built-up area due to the phenomenon of that different surface features have the same spectral characteristics,this thesis proposed a model of built-up area extraction based on multiple indices.The experimental results show that:(1)The spectral laws of the built-up areas,bare land and water bodies,vegetation on the fourth,fifth and sixth bands can be used to widen the gap between them,thus,the interference of water bodies and vegetation information on the extraction of built-up areas is eliminated;The index value of the built-up areas is made higher than that of the bare land,so that the bare land information can be excluded by setting the threshold.(2)In the research area of Chongqing,the overall accuracy of the Bareness-Restrained Built-up Index(BRBI)presented in this thesis is 4.7%~23.2%higher than other indices,and the kappa coefficient is 0.031~0.29 higher other indices.In the research area of Xi’an,the overall accuracy of BRBI is 3.7%~30.2%higher than other indices,and the kappa coefficient is 0.042~0.33 higher than other indices.3.The evolution of the built-up areas of Chongqing has obvious spatial and temporal characteristics.In terms of time,from 1995 to 2016,the area of the built-up increased from 44.26 km~2to 288.36 km~2,which has expanded by nearly 7 times.From the perspective of space,the expansion of the construction area in Chongqing experienced two stages:the external radioactive expansion and the internal constrictive expansion,and showed a tendency of internal concentration;The results of equal-fan-analysis show that the expansion of building area has obvious directivity.In the eight regions divided by the equal fan,the expansion speed in the whole research period is mainly concentrated in the direction of due north and northwest,followed by the direction of due west,southwest and south.The expansion speed in the east,northeast and southeast directions has been at a relatively low level during the period studied in this thesis;In the quantitative analysis of driving force,there is a strong positive correlation between the driving force factors and the building area,and the regression quation between the building area and the principal components determined by the principal component analysis is established.