Pressure and particle velocity measurements from a broad band source at ranges 1–10 km

Abstract

The IVAR system (Intensity Vector Autonomous Recorder) is a bottom deployed system developed for first-use in the Sediment Characterization Experiment (SCE17), conducted on the New England Mud Patch [40°28’ N, 70°35’ W] in spring 2017. IVAR continuously and coherently records four channels of acoustic data, three from a tri-axial accelerometer embedded in a neutrally buoyant sphere (diameter 10 cm) and one from an omnidirectional hydrophone positioned 10 cm above the centroid of the sphere positioned 1.2 m above the seafloor. The connection of these measurements to understanding seabed properties as part of SCE17 has been discussed previously. Here, emphasis is placed on documenting pressure and particle velocity signals as these quantities evolve with range from a broad band explosive source (Mk64 SUS charge). We explore the phase relation between pressure and components of particle velocity through study of active (in phase) and reactive (out of phase) intensity, as well as corresponding non-dimensional indices of the acoustic vector field, and discuss how these are influenced by propagation conditions. The work has relevance to both the ongoing geoacoustic studies from SCE17 as well as to studies on the sensitivity of fish to acoustic particle velocity generated by explosions.The IVAR system (Intensity Vector Autonomous Recorder) is a bottom deployed system developed for first-use in the Sediment Characterization Experiment (SCE17), conducted on the New England Mud Patch [40°28’ N, 70°35’ W] in spring 2017. IVAR continuously and coherently records four channels of acoustic data, three from a tri-axial accelerometer embedded in a neutrally buoyant sphere (diameter 10 cm) and one from an omnidirectional hydrophone positioned 10 cm above the centroid of the sphere positioned 1.2 m above the seafloor. The connection of these measurements to understanding seabed properties as part of SCE17 has been discussed previously. Here, emphasis is placed on documenting pressure and particle velocity signals as these quantities evolve with range from a broad band explosive source (Mk64 SUS charge). We explore the phase relation between pressure and components of particle velocity through study of active (in phase) and reactive (out of phase) intensity, as well as corresponding non-dimensional...