Bubble pulse arrival time calculations to determine SUS charge detonation depths

Abstract

As part of the New England Seamount Acoustics (NESMA) project in 2023, experiments were conducted over the Atlantis II Seamount. A total of 216 Signal Underwater Sound (SUS) broadband explosives (150 1.1 oz and 66 1.8 lb net explosive weight) were deployed at multiple locations and two different design depths around the seamount. An acoustic recorder (SoundTrap ST4300), with four hydrophone channels of varying sensitivities, was deployed during each of the SUS events to record the signals generated by the explosives. The recorded signals include arrivals corresponding to the shock wave, subsequent bubble pulses and reflections from the sea surface and sea floor. The time between the first arrival and the bubble pulse was used to calculate the depth at which each SUS charge detonated. The resulting SUS detonation depths from the bubble pulse calculation were compared with depths obtained from surface and bottom reflections to assess the accuracy of the bubble pulse method. A comparison of the results from the two methods shows that using the bubble pulse interval to calculate the SUS detonation depth is reasonable and can be used in propagation models. [Work supported by Office of Naval Research Code 322OA and TFO.]