Interferometric Digital Elevation Model Reconstruction – Experiences from SRTM and Multi Channel Approaches for Future Missions

The Shuttle Radar Topography Mission flown in the year 2000 was the first approach to generate a global DEM from interferometric SAR. The C-band and X-band data acquired in 11 days have been processed with great success at NASA/JPL and at the German Aerospace Center DLR, respectively. Both data sets however show problems that should be taken care of in the design of future InSAR DEM missions: - phase unwrapping turned out to be unreliable in rugged mountain areas with very steep slopes - radar shadow and layover rendered significant areas in rugged mountain unusable - the vertical accuracy was limited by the signal to noise ratio (SNR), by the baseline length and by the baseline knowledge The SNR is expensive to improve and future missions like, e.g. the TanDEM-X mission currently studied at DLR, tend to use larger baselines therefore. This, however, will further complicate phase unwrapping. The key to improve phase unwrapping stability while simultaneously increasing height accuracy is a multi channel InSAR system. Multiple channels can be achieved by different frequencies, delta-k processing, multiple simultaneous baselines or multiple observations with different baselines. This paper summarizes the SRTM difficulties and sketches the strategies that could overcome them in future multi satellite missions. A baseline selection and acquisition strategy together with accompanying processing techniques are proposed in order to generate a global high precision DEM of the Earth in a reasonable time with available technologies