Parabolic Equation Modeling of a Seismic Airgun Array

The numerical modeling of seismic airgun sources, with a specific emphasis on the impact of sound on the marine ecosystem, is a challenging problem. In this paper, the simplified range-independent isovelocity problem, set up as part of the International Airgun Modelling Workshop, is solved using the parabolic equation (PE). The acoustic pressure and particle acceleration are computed including the arrival time series and source energy level in decidecade bands for ranges spanning from 30 m to 30 km. The particle acceleration is computed by taking the spatial first-order finite difference of the pressure on the PE computational grid (∼1/16th wavelength). The two significant challenges this problem poses to the PE solution are the very large bandwidth (5–4500 Hz) and the computational accuracy required for time-series and particle acceleration computations. Each of the metrics outlined in the statement of the problem is computed and presented. In addition to computing the required fields, the 17-gun volumetric array is placed in a 3-D ocean environment in deep water in the Gulf of Mexico, with peak sound pressure computed out to 30 km and the band integrated sound exposure level ( $L_{E,p}$ ) computed to 400 km.