Effects of the Interval of Tiepoints on the Reliability of Sar Image Co-registration

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) has been demonstrated to be a potential tool for generating digital elevation models (DEM). The co-registration of SAR complex images is one of the most important processing procedures involved in InSAR . The quality of the co-registration significantly influences the final quality of any SAR interferometric generation, and thus the quality of DEM reliable results can never be achieved if the initial co-registration is not sufficiently reliable.. In SAR image co-registration, the distribution of tiepoint affects the quality or reliability of the results. Due to lack of well defined points, tiepoints are normally selected as the intersections of a grid cells. In this case, the grid interval of the tiepoint grid becomes the critical factor. Theoretically, the smaller the grid interval, (the more tiepoints), more reliable the registration. However, it is not always the case. In this study, some experimental investigations into the effect of grid interval on the co-registration results are conducted. 4 pieces of SAR complex images collected by ERS-1/2 are used for testing. Tiepoints with varying grid intervals have been used for co-registration. The results indicate that there is no single optimum grid interval for tiepoint grid but the grid with 8×8, coresponding to 205*34 pixels, always result in either best or very good in terms of both RMS and the coherence of interferograms.