Development of Portable SAR for Detection of Volcano Deformation: Application of SAR Interferometry to the Repeated Observation Data

Abstract

Synthetic aperture radar (SAR), which transmits radar waves from the ground, can detect crustal deformation with high spatial and temporal resolution. To obtain crustal deformation data useful for evaluating volcanic activity, we are developing a portable SAR that can conduct repeated observations without being fixed to the site under Project B of the Integrated Program for Next Generation Volcano Research and Human Resource Development. We named this SAR sensor: SAR for crustal deformation with portable equipment (SCOPE). SCOPE detects crustal deformation over a wide area by repeating observations at several points, which differs from the general ground-based SAR (GB-SAR). SCOPE has four observation types: GB-SAR, car-borne SAR, cart-borne SAR, and man-borne SAR, which are used to conduct such mobile observations efficiently. This study performed repeated observations with a 1-day interval using GB-SAR and car-borne SAR and obtained high coherence and reasonable phase distribution. When using the man-borne SAR type, moderate coherence was obtained. However, focusing on the SAR image was insufficient, and an inappropriate phase slope appeared in the interferogram, suggesting that improvements in the observation and analysis methods remained. We also investigated the temporal persistence of coherence when applying SAR interferometry to the SCOPE data. Sufficient coherence was obtained to detect crustal deformation in sparsely vegetated areas for a data pair at a 1-year interval. Even in densely vegetated areas, sufficient coherence was obtained from the data pair at intervals of several months. These results show that SCOPE has high potential for detecting crustal deformation based on repeated observations.