In the processing of interferometric SAR data, a number of experiences have been reported in the literature and various methods for the processing are available. Among the factors crucial to the accuracy of altitude mapping is the phase unwrapping process, which recovers the absolute phase value from the wrapped phase image. In this paper. sensitivity studies of the unwrapped phase error and the height inversion error are described using the simulated interferometric SAR images first. Then, the phase unwrapping algorithms are applied to real SAR data (JERS-1 SAR Mt. Unzen data), and it is found that the accurate height is obtained by the branch-cut method even though the large phase noise of JERS-1 SAR data due to a long revisit time (44 days). Next, the data of Mt. Unzen obtained by interferometry using the SAR data taken after the eruption is compared with the DEM (Digital Elevation Model) data of the same scene taken before the eruption. The result shows the consistency with the height changes which was as found by geological survey after the eruption, and it is found that the JERS-1 SAR data can extract the topographic changes by differential SAR interferometry.
