Mapping urban change in the UK using satellite radar interferometry W.M.F. Grey a, * , A.J. Luckman a , D. Holland b a Department of Geography, University of Wales Swansea, Singleton Park, Swansea, Wales SA2 8PP, UK b Ordnance Survey, Romsey Road, Southampton SO16 4GU, UK Received 26 December 2002; received in revised form 16 May 2003; accepted 1 June 2003 Abstract A multitemporal sequence of ERS interferometric coherence data acquired between 1993 and 1999 are utilised for automatically mapping urban change within South Wales, UK. Validation of the change map derived from the coherence data is performed using independent, multidate, digital survey data of the city of Cardiff, UK. All major building developments that have occurred within the study area are located. There is evidence to suggest that this approach is generalisable for a wide range of coherence data and to other regions with similar landscapes. D 2003 Elsevier Inc. All rights reserved. Keywords: Urban; Interferometry; Coherence; Decorrelation; Radar; Change; Detection 1. Introduction Urban growth is an important global environmental issue that affects both developed and less-developed countries (World Resources, 1996). In Third World cities, rural – urban migration is the major driving force behind urbanisation, while in industrialised countries, even though the populations of many cities remain more or less unchanged, urban areas continue to expand through pro- cesses of suburbanisation and commercial decentralisation (Champion, 1999). Urban growth is of major ecological concern since growth leads to the conversion of natural land (usually agriculture) to built-up land on the edge of cities. Urban areas are dynamic environments in terms of their land-use, so regular and up-to-date information on urban change, especially growth, is required. In particular, this information is needed for strategic planning purposes, environmental impact assessment, and for the appropriate allocation of services and infrastructure within towns and cities (Bahr, 2001; Donnay, 1999; Weber, 2001). Effective planning policy and appropriate resource management can only be accomplished through informed decisions, but even basic information on urban extent and change is often outdated, inaccurate, or simply does not exist (Barnsley, Moller-Jensen, & Barr, 2001). This is especially so within developing countries (Baudot, 2001). Current approaches to urban monitoring generally in- volve ground surveys and interpretation of aerial photo- graphs but more efficient methods that are capable of automatically mapping change are desirable. To this end, satellite remote sensing can be used to provide an objective and consistent view of urban areas (Jensen & Toll, 1982; Martin & Howarth, 1989). Synthetic aperture radar (SAR) data are particularly well suited for change analysis because these data can be acquired on every satellite pass and are therefore regular, whereas optical image acquisitions are often impeded by cloud cover. Urban areas are generally characterised by high SAR backscatter due to the predominance of single- and double- bounce backscattering (Dong, Forster, & Ticehurst, 1997). However, the geometric relationship between the azimuth angle of the sensor and the orientation of the buildings strongly affects backscatter within towns and cities (Bryan, 1979; Hardaway, Gustafson, & Lichy, 1982). This may cause difficulties during the classification process since the same urban land covers can produce different backscat- ter intensities depending upon the azimuth angle of the radar antenna in relation to the built structures on the ground (Bryan, 1982). Multitemporal backscatter data have also been used for urban change analysis but speckle inevitably 0034-4257/03/$ - see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0034-4257(03)00142-1 * Corresponding author. Tel.: +44-1792-295-524; fax: +44-1792-295- 955. E-mail address: w.m.f.grey@swansea.ac.uk (W.M.F. Grey). www.elsevier.com/locate/rse Remote Sensing of Environment 87 (2003) 16 – 22