The Impact of Ocean Sound Dynamics on Estimates of Signal Detection Range

This work examines the impact of the dynamic soundscape on estimates of the signal detection area (DA) of passive acoustic monitoring stations. The range of signal detection was investigated at three site locations of the Comprehensive Nuclear-Test-Ban Treaty Organization International Monitoring System (CTBTO IMS). Transmission loss to each hydrophone was computed using the OASIS Peregrine parabolic equation model for a source within the upper 300 m of the water column to be consistent with the hypothesized location of vocalizing baleen whales. Seasonal, monthly, and daily soundscape measurements were incorporated into the sonar equation to estimate the variability in signal DA as a function of sound level and time As a comparison, the seasonal analysis was repeated with a constant noise level to quantify the extent of variability due solely to changes in the seasonal sound speed profile. The greatest DA variability was observed at the Wake Island location in the Pacific Ocean where only a maximum of 18% of the 71 to 85% difference in DA estimates across seasons was attributable to changes in the sound speed profile. Differences in the daily DA estimate distributions as a function of frequency and location illustrate the impact of local sound field dynamics on the overall soundscape and the resulting signal detection range.