Figure 1. Experimental set-up of current muographic observation system.

(a) A profile of residual gravity and topography sliced along the dotted line in (b) is derived from Bouguer anomalies of an assumed density of 2.0 g cm⁻³ and trend removal of upward-continuation of 500 m (ref. 19) based on the gravity data set obtained for the published map. (b) The topographic map of Satsuma–Iwojima volcano shows the location of the muon detector (indicated by Mu). A topographic profile along the A–B line was created to support muographic images.(c) A schematic view of the detector was used for the present observation. It consists of five lead plates supported by stainless steel plates and six layers of scintillation PSPs. Scale bar 1 m. The inset shows the layout of the PSP consists of adjacent scintillator strips, which together form a segmented plane. (d) Close-up map of the summit area of the cone in the box on the map labelled as (b). This enlarged map shows newly created inner crater between 1997 and 2003 (blue, green and orange lines). The grey line on the map corresponds to the A–B line shown in (b).