Three‐dimensional deformation mapping of a dike intrusion event in Sakurajima in 2015 by exploiting the right‐ and left‐looking ALOS‐2 InSAR

One of the limitations of the interferometric synthetic aperture radar (InSAR) is its one‐dimensional measurement capability. Although three‐dimensional (3‐D) deformation can be studied if there are three or more measurements with different viewing geometries, it has not been executed because almost all SAR data are acquired using a right‐looking geometry. For the Sakurajima volcanic activity on 15 August 2015, ALOS‐2 conducted SAR observations from four different viewing directions, ascending/descending and right‐/left‐looking, enabling the retrieval of 3‐D deformation data only from the InSAR results. We have retrieved 3‐D deformation with high precision and resolution by a weighted least squares approach. Expansive deformation of over 10 cm has been observed with standard errors of 0.8, 3.4, and 0.7 cm for east‐west, north‐south, and up‐down components, respectively. It is inferred that a dike of 1.7 × 10 6 m 3 volume intruded beneath the Showa crater at a depth of 0.4–1.2 km.