Distribution of groups identified by analysis of NIRS3 data on cylindrical projection maps. Left panels: distribution of the two groups obtained at 3σ confidence level; right panels: distribution of the various groups obtained at 2σ confidence level. Distribution maps of the groups obtained for July 11, 2018 are in (a) and (b); (c) and (d) are the distribution maps of the groups obtained for July 19, 2018; and (e) and (f) are the distribution maps of the groups obtained for October 30, 2018. The spatial resolutions are 40, 20, and less than 10 m px⁻¹, respectively. Group #4 reported in green in panels b and d could be affected by uncertainties of thermal correction.