Estimation of Depth and Charge Weight for a Shallow Underwater Explosion Using cut off Frequencies and Ray-Trace Modeling

Abstract

In this paper we utilized an additional forward model to estimate the detonation depth using normal modes (cutoff frequencies) to estimate the detonation depth and net explosive weight. With detonation depth the net explosive weight for a shallow underwater explosion could also be determined. The hydroacoustic wave propagation in shallow channel was confirmed via ray-tracing method. We found cutoff frequencies of the reflection off the ocean bottom to be 8.5 Hz, 25 Hz, and 43 Hz while the cutoff frequency of the reflection off the free surface to be 45 Hz including 1.01 Hz for the bubble pulse, and also found the cutoff frequency of surface reflection to well fit the ray-trace modeling. Our findings led us to the net explosive weight of the ROKS Cheonan to be approximately 136 kg TNT at a depth of about 8 m within an ocean depth of around 44 m.