Refining low-quality digital elevation models using synthetic aperture radar interferometry

Two-pass synthetic aperture radar (SAR) interferometry (InSAR) is a technique for processing the phase difference between coincident SAR images to obtain the range difference from the two radars to a common point on the earth's surface. The accuracy of the range difference measurement is in the order of one millimeter, and this range information can be processed to obtain digital elevation models (DEMs) of the surface topography.; The objective of this thesis is to use supplemental information in the form of a coarse DEM to make the InSAR processing more accurate and more automatic. We achieve this objective by developing a new algorithm which incorporates the coarse DEM directly into the processing stream, with the result that phase unwrapping and geometry estimation are performed accurately and reliably. While the accuracy of each input DEM point is not very high, the large number of them provide adequate geometric accuracy, particularly as an automatic algorithm can register them directly to the radar data.; There are two key steps in the new algorithm. First of all, the satellite geometry is estimated from the DEM and interferometric phase. This is done with a non-linear, iterative optimization algorithm without having to unwrap the phase. Second, the input DEM along with the refined satellite geometry are used to create a model of the unwrapped interferogram phase that should be received from the two satellite passes. When this phase is wrapped, and compared with the measured phase, a differential interferogram is obtained which represents the difference between the coarse input DEM and the topography as measured by the satellite. The information in the unwrapped interferogram is used to refine the grid spacing and vertical accuracy of the coarse DEM.; We have used mathematical analysis and simulation to develop the algorithm, to obtain statistical quality measures and to understand what system parameters affect the accuracy of the DEM results. We find that the main factors affecting accuracy are the interferometer's sensitivity of phase to height and the number of available DEM points, including the size and variability of the input DEMs' errors.; We have successfully applied the DEM refinement algorithm to ERS Tandem Mission and RADARSAT-1 data. The generated InSAR DEMs had standard deviations of 12 to 20 meters compared to a control DEM with approximately 3 meters standard deviation. The output InSAR-enhanced DEMs had two to four times improvement in height accuracy compared with the input DEMs. We have demonstrated that one can generate reliable estimates of topography for standard SAR scenes without having access to precision orbit data. (Abstract shortened by UMI.)...