A Methodology for Updating Large Scale Ortho-Photomaps by Means of VHR Satellite imagery

Some authorities (DGPL) of the Walloon Region (Belgium) are involved in the realization of a complete regional coverage (16,844 km²) of natural colour ortho-photomap to be used at large scales (up to 1:4000). These are made of very high-resolution digital ortho-rectified aerial photos presented as raster files. Those rasters are grouped by corresponding administrative boundaries and distributed to the local authorities in order to be used for various land and urban planning purposes. One goal of the DGPL is to provide the local administrations with up to date image data, within the limits of some obvious financial constraints. Because significant changes in the landscape appear at different rates over the time and space, it was suggested to devise a methodology to find out these changes would require a rapid update of the imagery. In regard to this situation, a pilot project has been set up in the year 2000 aiming at detecting the location, the extent and the nature of landscape changes in contrasted areas - urban, suburban, rural - from adequately processed very high resolution (VHR) satellite images - typically Ikonos multi-spectral (4m) and panchromatic (1m) images. Hence, this project had to cope with various issues related to multi-source analysis, geometric and radiometric aspects of the processing VHR data, diachronic analysis, in order to provide the administration with the basic knowledge and the appropriate tools to carry out the proposed task. This communication presents the proposed operational methodology for change detection including all processing steps from the digital image processing (image fusion technique, ortho-rectification analysis, change detection schemes). Along the way it also introduces an assessment of the possible complementarities and convergence of VHR satellite imagery and aerial photography.