Fig. 1. Coordinate systems for single photon double collision scattering

Fig. 2. Flow chart of photon simulated motion

Fig. 3. Backscattering echo signal of bubble under different distances

Fig. 4. Backscattering echo signal of bubble under different bubble densities

Fig. 5. Backscattering echo signal of bubble under different bubble thicknesses

Fig. 6. Backscattering echo signal of bubble with different bubble sizes

Fig. 7. Backscattering echo signals with different bubble target characteristrics

Fig. 8. Experimental system design

Fig. 9. Laser backscattering signal intensities under (a) different bubble distances and (b) different bubble thicknesses

Fig. 10. Peak echo amplitude of water body under different bubble thicknesses and different densities

Fig. 11. Laser backscattering signal intensities of water body under (a) various bubble distances, (b) different bubble densities and (c) different bubble thicknesses

Fig. 12. Variation of laser backscattering signal of water body at different distances. (a) Signal peak amplitude; (b) pulse width