Tuning, validation, and uncertainty estimates for a sound exposure model

Abstract

To tune and validate the performance of an acoustic model, sound signals were transmitted from a calibrated source, at varied mid-range frequencies, and received on a moored acoustic recording package at the edge of Tanner Bank near the Southern California Anti-Submarine Warfare Range (SOAR). The acoustic monitoring package was constructed of three calibrated Acousonde recorders. Source levels (SL) were measured at 1.8 meters from the source using a Bioacoustic Probe. Signals recorded on the Acousondes and the Bioacoustic Probe were processed to measure transmission loss (TL) and its variability. Measurements were compared with estimates of TL calculated from the Navy Standard Parabolic Equation (NSPE) acoustic model using a first guess geoacoustic bottom based on the literature. Other model inputs included bathymetry from the U.S. Coastal Relief Model, and sound speed profiles from Expendable Bathythermographs (XBT) and the Navy Coastal Ocean Model. Using data garnered from previous studies of the bottom sediment and sub-layer near the Southern California Offshore Range, variations of a geoacoustic model were constructed and input into the NSPE model. TL from all model runs were then analyzed across all frequencies to determine the best fit geoacoustic model to use with NSPE when applying it near SCORE for acoustic predictions. Research was funded by the United States Navy Chief of Naval Operations Environmental Readiness Division (CNO/N45).