Short-Range Signatures of Explosive Sounds in Shallow Water Used for Seabed Characterization

Small explosions were used as sound sources in the Seabed Characterization Experiment conducted in spring 2017 in the New England Mud Patch, a shallow-water region with a depth of approximately 75 m. The sources were U.S. Navy Signal Underwater Sound (SUS) Mk 64 charges, which contained 31.18 g of the explosive 2,4,6-Trinitrophenylmethylnitramine, commonly referred to as Tetryl. Source recordings were obtained by two hydrophones deployed from the same ship that deployed the SUS. The recordings were analyzed for bubble period, energy spectral density, and the variability of these parameters, and compared to previous results from the literature, including the prediction of a historic spectral model, and a new semiempirical time-domain model assembled using measured data from the literature. The new model describes the source level measurements in the 25–275-Hz band and in the 400-Hz octave band to within 0.5 dB, and agrees with similar measurements from the literature to within 0.6 dB. The standard deviation of the band-limited source levels was found to be about 1 dB, some of which is ascribed to uncertainty and variation in the source-to-receiver distance. The observed source level variation is similar to previously reported values.