'Urban villages' is the Chinese version of informal settlement. It is a unique phenomenon that comprises mainly low-rise and congested, often illegal buildings surrounded by new constructions and high-rise buildings. Due to a lack of an unambiguous definition allowing for a spatial delineation of such areas, this article investigates a joint use of high-resolution optical and SAR satellite data through building extraction and 3D reconstruction of urban villages in Shenzhen, China. First, potential urban village footprints are extracted through a combined image fusion analysis of multispectral GaoFen-1 (GF-1) and high resolution TerraSAR-X radar (SAR) imagery. Then, building height estimation is performed on the basis of interferometry principles using interferometric X-band SAR (InSAR) from the Tandem-X mission. It can be demonstrated that urban villages and surrounding urban areas are clearly distinguishable through particular combinations of optical data, SAR data and height information. In particular, a rigid analysis identified three types of information as most suitable: 1) Normalized Difference Vegetation Index (NDVI), 2) contextual parameters such as edge and line density from GF-1 multi-spectral imagery, and 3) textural parameters such as Grey-Level Co-occurrence Matrix (GLCM) variables from TerraSAR-X imagery. The additional height information from InSAR clearly improves the detecting of taller buildings surrounding the urban villages. In conclusion, the fusion of SAR and optical imagery can effectively reveal the footprint characteristics of urban villages. It is an effective means to reduce the effects of layover, shadow and dominant scattering at building location. The 3D building reconstruction model based on urban village footprint maps can reduce the continuous alteration of layover and shadow areas from high-rise buildings in the dense urban area.
Informal settlements are a world-wide phenomenon. Urban villages belong to the Chinese
version of the informal settlement phenomenon. However, there is no definitive definition
of urban villages or a general systematical theory on such locations. Monitoring and
modeling informal settlements is crucial for understanding informal settlements genesis
and development in general. Many previous studies that applied the VHR optical data
have been conducted to detect and analyze informal settlement,
The overall objective of this research is to illustrate the physical characteristics of urban villages and show the natural environmental difference of urban villages with surrounding urban areas. Multi-source data (TerraSAR-X, TanDEM-X and GF-1 optical images) will be integrated to address the following issues attributed to urban village definition: 1 2 3
What physical characteristics of urban villages can be measured using optical and SAR images? Do urban villages in the Pearl River Delta have homogeneous or heterogeneous physical characteristics? Do urban villages have definitive physical differences compared to the surrounding urban structures?
The Pearl River Delta is one of the most densely urbanized regions in the world and one of the main hubs of China’s economic growth with a combined population of 57.15 million at the end of 2013. Urban villages are the by-products of the rapid urbanization in the Pearl River Delta region, where the city develops around what once were isolated farming and fishing villages. They are surrounded by rising skyscrapers, transportation infrastructures and other modern urban constructions. The appearance of urban villages is not only out of urban planning, infrastructure construction and other forms of administrative regulations, but has also led to a number of social problems. Therefore, how to monitor the urban villages and analyze their environmental characteristics is crucial for the sustainable urban development research.
We propose the following applications for the analysis of GF-1 images, TerraSAR-X and TanDEM-X images for urban villages in the Pearl River Delta. The methodology can be subdivided into the following sections (shown in Table 1), to comprehensively study the impact of spectral information, contextual information, textural information and radiometric textural information for urban area mapping in different types of study regions.
This study explores the potential of TerraSAR-X, TanDEM-X data in monitoring urban villages. For high resolution space-borne TanDEM-X, this is a unique opportunity to study the complexity of signal interpretation in the geometrically complex urban village landscape. In addition, the composition of high resolution optical images-GF-1 and TerraSAR data will increase the detection accuracy of the physical characteristics (including the structure, shapes and locations of informal settlements, and the optical (GF-1)-SAR fusion framework will benefit for further urbanization analysis.
Chen, Xiao-Ling, Hong-Mei Zhao, Ping-Xiang Li, and Zhi-Yong Yin. 2006. “Remote Sensing Image-Based Analysis of the Relationship between Urban Heat Island and Land Use/cover Changes.” Remote Sensing of Environment, Thermal Remote Sensing of Urban Areas, 104 (2): 133–46.
Gernhardt, S., N. Adam, M. Eineder, and R. Bamler. 2010. “Potential of Very High Resolution SAR for Persistent Scatterer Interferometry in Urban Areas.” Annals of GIS 16 (2): 103–11.
Graesser, J., A. Cheriyadat, R.R. Vatsavai, V. Chandola, J. Long, and E. Bright. 2012. “Image Based Characterization of Formal and Informal Neighborhoods in an Urban Landscape.” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 5 (4): 1164–76.
Hofmann, P., J. Strobl, T. Blaschke, and H. Kux. 2008. “Detecting Informal Settlements from QuickBird Data in Rio de Janeiro Using an Object Based Approach.” Object-Based Image Analysis, 531–53.