Fig. 1. Muon energy spectrum (a) and muon flux spectrum (b) at different depths in rocks

Fig. 2. Imaging results of materials with different density contrasts (a), average density at azimuth angles with a zenith angle of 20° (b)

Fig. 3. Diagram of volcano model (a) and the position of the detectors in a volcano top view (b)

Fig. 4. Opacity distribution of volcanic model obtained by detector 1 (a), detector 2 (b), detector 3 (c) and detector 4 (d)

Fig. 5. After considering the background noise, the opacity distribution of volcanic model obtained by detector 1 (a), detector 2 (b), detector 3 (c) and detector 4 (d)

Fig. 6. Density distribution of volcanic model obtained by detector 1 (a), detector 2 (b), detector 3 (c) and detector 4 (d)

Fig. 7. After considering the background noise, the density distribution of volcanic model obtained by detector 1 (a), detector 2 (b), detector 3 (c) and detector 4 (d)

Fig. 8. Diagram of the gold mining model

Fig. 9. Imaging results of gold mines of different scales at a depth of 600 m underground(a) Opacity distribution, (b) Density distribution

Fig. 10. After considering the background noise, imaging results of gold mines of different scales at a depth of 600 m underground(a) Opacity distribution, (b) Density distribution