Tests on Determining Digital Elevation Models from Ers Tandem Data

The ERS Tandem Mission from August 1995 to May 1996 provided a large resource of data that can be used for a number of applications in the geosciences, based on the principle of interferometry, referred to in this paper as InSAR. InSAR techniques can provide a new and efficient method of deriving DEMs with little manual input. This paper describes research on the determination of digital elevation models (DEMs) by interferometry using the Tandem Mission data, and tests on the quality of the derived elevations for upgrading the digital elevation databases of Australia. Test sites were chosen so that they represent typical areas in Australia, including hilly areas, rivers, cities and towns, in which good details are available for the choice of ground control and check points. Generation of elevations involved the computation of coherence between master and slave images, determination of interferograms, reference of the DEM to the terrain surface either in terms of ground control points (GCPs) derived from reference maps of the area, or using the satellite ephemeris data, generation of the DEMs, and the analysis of their quality. Estimated accuracies of the DEM were determined by comparing the computed DEMs with existing maps and known DEMs of the area. 1. OBJECTIVES OF PROJECT In April 1995 the European Space Agency (ESA) launched its second Earth observation satellite, ERS2, which like the first satellite, ERS1, includes a C-band Synthetic Aperture Radar (SAR) remote sensing imaging system. The 35 day orbits of the two satellites were programmed for the Tandem Mission, so that ERS2 followed approximately 30 minutes behind ERS1 in the same orbital plane, and hence there was a 1day interval between the time when ERS1 and ERS2 looked at the same area on the Earth. The ERS Tandem Mission commenced on the August 16, 1995 and while operating until May1996, it provided a large resource of data that can be used for a number of applications in geosciences, based on the principle of interferometry, referred to in this report as InSAR. Pairs of ERS1/2 satellite data acquired in the Tandem Mission are suitable for DEM generation over almost all of the global land surface, including Antarctica. The main objective of the Tandem Mission, therefore, was to ensure acquisition of a unique and valuable set of SAR data that could be used for InSAR purposes. The aims of this research project were to tes t the suitability of the method of InSAR, using the ERS1/2 Tandem Mission data, for achieving greater efficiencies in upgrading the digital elevation model (DEM) data in Australia. In addition, the objectives were to develop practical methods of using InSAR techniques on the Tandem Mission data in a production environment. The research was undertaken in cooperation with Geoscience Australia (abbreviated to GA), formerly AUSLIG, and funded by the Australian Research Council’s SPIRT Program. Improved DEM data should lead to substantial benefits to the wide variety of users in Australia who require digital elevation data. It should also impact on a much larger group in the community who benefit from the application of this data in achieving better environmental analysis, such as microclimate studies, river drainage delineation, and coastline identification.