Fig. 1. Measurement platform of optical-electrical signals of underwater streamer discharge

Fig. 2. Development of positive primary streamer discharge in water

Fig. 3. Waveforms and shadow images of secondary streamer in water

Fig. 4. Waveforms and shadow images of secondary streamer in water

Fig. 5. Reillumination process of primary streamer in water

Fig. 6. Varying trend of underwater positive streamer versus applied voltage

Fig. 7. Geometric structure and mesh generation of two-dimensional axisymmetric model of needle-to-plane electrode

Fig. 8. Waveforms of applied voltage in simulation model

Fig. 9. Electric field distribution of 20 kV positive secondary streamer during propagation period

Fig. 10. Development characteristics of positive secondary stream under different rising time of applied voltage

Fig. 11. Development characteristics of positive secondary streamer under the effect of micro-convex structure of electrode surface

Fig. 12. Electric field distribution of streamer branching channel under different micro-convex structures of electrode surface

Fig. 13. Branching channel velocity versus time under different micro-convex structures of electrode surface