Extraction of Disaster Area from Satellite Image by combining Machine Learning and Image Processing Technology

In recent years, heavy rain which frequently occurred in various places in Japan have been caused severe damage. It is important to identify the damaged area for disaster recovery and reconstruction. In this study, we focus on the optical satellite images that are easy to process and interpret, and extract the damaged area by combining a land cover classification method using machine learning and an additive color mixture method. As the results, it is possible to visually express the land cover changes before and after the disasters in a specific category and to extract the damaged area from the optical satellite image

Higher-order modulations in the skyrmion-lattice phase of Cu2_2OSeO3_3

Using small angle neutron scattering, we have investigated higher-order peaks in the skyrmion-lattice phase of Cu$_2$OSeO$_3$, in which two different skyrmion lattices, SkX1 and SkX2, are known to form. For each skyrmion-lattice phase, we observed two sets of symmetrically inequivalent peaks at the higher-order-reflection positions with the indices $(110)$ and $(200)$. Under the condition where the SkX1 and SkX2 coexist, we confirmed the absence of the scattering at $\mathbf{Q}$ positions combining reflections from the two phases, indicating a significantly weak double-scattering component. Detailed analysis of the peak profile, as well as the temperature and magnetic-field dependence of the peak intensity, also supports the intrinsic higher-order modulation rather than the parasitic double scattering. The two higher-order modulations show contrasting magnetic-field dependence; the former $(110)$ increases as the field is increased, whereas the latter $(200)$ decreases. This indicates that, in Cu$_2$OSeO$_3$, skyrmions are weakly distorted, and the distortion is field-dependent in a way that the dominant higher-order modulation switches from $(110)$ to $(200)$ under field. Monte Carlo simulations under sweeping external magnetic field qualitatively reproduce the observed magnetic-field dependence, and suggests that the higher-order modulations correspond to the superlattices of weak swirlings appearing in the middle of the original triangular-latticed skyrmions.Comment: 13 pages, 14 figure