LANDMAP: Creating a dem of the British Isles by SAR interferometry

The LANDMAP project will provide an intergrated set of mosaiced SPOT and Landsat-TM images of the British Isles, orthorectified to be easily accessible in a geographical co-ordinate system. In order to orthorectify the imagery (which comed from an archive held for UK academic use), a digital elevation model (DEM) is first needed. A stated aim of the LANDMAP project is that its products should be free of onward copyright or licensing issues. This means that most usual elevation data sources were unsuitable. A first stage of the project is therefore to create a new DEM of the British Isles using the remote sensing technique of synthetic aperture radar (SAR) interferometry (IfSAR). This is to be accomplished in two passes; firstly creating an initial DEM from a minimal coverage of the British Isles by ERS SAR data for initial quality checking (presented here), followed by full DEM creation from three coverages. Full DEM creation involves the interferometric processing, phase unwrapping and orthorectification of pairs of acquisition strips of SAR data. It is then necessary to average together the individual DEMs from seperate pairs to provide an optimum DEM for each strips. The strips are them fitted together across the British Isles using a block-adjustment scheme. A range of kinematic GPS profiles were acquired across the British Isles in September 1999 for quility assessment of intermediate and final DEMs. We demostrate good agreement in planimetric positions without the use of control points and elevation differences standard deviations of the order of 10m.