  The current work experimentally studies the complex interaction between
underwater explosion (UNDEX) bubbles and a free surface. We aim to reveal the
dependence of the associated physics on the key factor, namely, the
dimensionless detonation depth $\gamma$ (scaled by the maximum equivalent
bubble radius). Four typical bubble behavior patterns are identified with the
respective range of $\gamma$: (i) bubble bursting at the free surface, (ii)
bubble jetting downward, (iii) neutral collapse of the bubble, and (iv)
quasi-free-field motion. By comparison of the jet direction and the migration
of the bubble centroid, a critical value of $\gamma$ is vital for ignoring the
effects of the free surface on UNDEX bubbles. Good agreements are obtained
between the experimental data and the unified theory for bubble dynamics by
Zhang et al. Additionally, the dependence of the pressure signals in the flow
field on $\gamma$ is investigated. The peak pressure, impulse, and energy
dissipation in the UNDEX are investigated.
