Three-dimensional primary acoustic field characterization for a seismic airgun array

Abstract

The Littoral Acoustic Demonstration Center conducted the Source Characterization Study in 2007 (SCS07) to measure the 3-D acoustic field of a seismic airgun array in the Gulf of Mexico. Three moorings with sensitive and desensitized hydrophones at different depths were deployed as well as hydrophones suspended from a ship, while a seismic source vessel shot specified lines. Hydrophone positions were measured. Peak pressures, RMS sound pressure levels (SPL), sound exposure levels, total shot energy spectra, one-third octave band analyses, and source directivity studies are used to characterize the field. Summary results are first calculated for each hydrophone. These are then combined to give isopleths for azimuthal cuts at 0, 45, 90 degrees, etc., for the spatial domain measures. Plots for each solid angle bin give these and frequency measures analyzed versus range. Zero-to-peak pressures directly under the array go from 210 dB for depths less than 200 m down to 195 dB at 1200 m. At 2000 m horizontal range the pressures go from 160 dB near the surface to 175 to 180 dB at 1200 m. RMS SPL is about 5 dB smaller. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]