Processing seismic source transients to quantify ecosystem impact

Abstract

Modeling of acoustic field metrics for transient seismic signals in ocean environments is required for the regulatory and resource management purposes. The validation by calibrated measurements is a critical step to assess model’s accuracy. The talk discusses acoustic metrics derived from the field data collected in the Northern Gulf of Mexico. The purpose of the experiment was to characterize 3-dimemsional field of the industrial seismic exploration array. Received Sound Pressure Levels of direct arrivals showed a large variability (up to 50 dB re 1 μPa) for a fixed distance between source and receiver indicating that the distance cannot be used as a single parameter to derive meaningful exposure thresholds. However, the far-field primary acoustic field variations with distance along the true acoustic path for a narrow angular bin are accurately predicted using a simplified model of the theoretical monopole source in free space. The source level of a monopole depends on radiation direction. The different acoustic metrics show robust relationships. As distance between source and receiver increases, the direct arrival may not be present (shadow zone). In this case more comprehensive propagation modeling is required. [Research funded by the Sound and Marine Life Joint Industry Programme.]