Urban Structure Mapping and Change Analysis in Highly Dynamic Urban Areas based on Spectral and Three-Dimensional Analysis of VHR Remote Sensing Imagery

Kurzfassung

Rapid growing cities face challenges in planning infrastructure, regarding water and electricity supply, as well as waste treatment. Missing information on spatial population distribution and population trends make urban planning inaccurate and error-prone. To support urban planning, we developed an approach which considers these problems by exploiting very high resolution (VHR) remote sensing data for mapping urban structure and monitoring structural development. In this study, we present an approach based on the analysis of tri-stereoscopic Pléiades imagery from 2015 and 2017 covering the urban area of DaNang (Vietnam). These acquisitions offer a spatial resolution up 50 centimeters, which allows building detection and the generation of VHR digital surface models (DSM). In the first component of our approach, it is intended to derive an initial current state of the urban structure of DaNang from the 2015 acquisition. Pléiades imagery offers three bands covering the visible spectrum and one near infrared band, which allow to precisely detect build-up areas. Streets have been masked out by building block information prior to the classification process. Especially the near infrared band has proven to be very valuable the detect and exclude water bodies and small vegetated areas. The application of object-based image analysis (OBIA) techniques enables classification of building types by means of area, shape and neighboring relations of built-up patches. Based on the statistical analysis of information on building type, built-up area ratio and vegetation cover ratio i.a., urban structure types could be assigned to building blocks. Our results show very good consistency in comparison with in-situ data. The second component of our approach includes the integration of three-dimensional information. We photogrammetrically processed two tri-stereoscopic acquisitions of Pléiades from 2015 and 2017 to derive surface heights of the area. Due to discrepancies in the acquisition geometry, both scenes had to be adjusted vertically based on a linear regression which was based on 950 in-situ reference points and approximately 80.000 control points representing actual ground heights which were distributed with a stratified random sampling outside built-up areas and surfaces covered by vegetation. Both surface models were subtracted to retrieve vertical changes between 2015 and 2017. Based on the near infrared band, a vegetation mask was generated to exclude bushes and trees from interpretation of changes. First findings indicate clear patterns of construction work, especially along the shoreline in the west, in the Hòa Hải district in the South and on the development areas in Hòa Xuân district. Demolishions of buildings are concentrated in the central part of the city and around the airport. Negative differences have to be interpreted with caution because many of the removed buildings are expected to be replaced by more modern ones within short intervals.