Variation in low-frequency estimates of sound levels based on different units of analysis

Abstract

The measurement and analysis of underwater sound is a complicated process because of the variable durations of contributing sources and constantly changing water column dynamics. Because the ambient sound distribution does not always follow a Gaussian structure and may be nonstationary in time, analysis over an extended period is required to accurately characterize the data. Utilizing recordings from the Indian Ocean, the temporal variation in ambient sound including transient signals was examined using multiple processing window lengths and subsampling intervals. Results illustrate the degree of uncertainty in sound levels based on different units of analysis. The average difference between sound level estimates in the 10-30 Hz band due to subsampling was 2 dB and as high as 4 dB. The difference in the full band (5-110 Hz) was as high as 6 dB. Longer averaging windows (200 vs 60 s) resulted in larger variations over different subsampling intervals. This work demonstrates how sampling protocols within a single dataset can influence results and acknowledges that comparative studies at the same location but with different sampling protocols can be substantial if signal processing parameters are not statistically accounted for to confirm interpretation of results and observed trends.

Quantitative Soundscape Analysis to Understand Multidimensional Features

“…Studies often fail to clearly report metric input parameters critical to the determination of the final metric value; ambiguities in reporting can make replicating study methodologies difficult, and can lead to erroneous comparisons. For example, different methods of 1 https://goosocean.org/index averaging have yielded differences in final metric results of over 10 dB in previous works (Merchant et al, 2012;Hawkins et al, 2014). Some methodology descriptions are so vague it is nearly impossible to determine averaging times, integration windows, and exactly which metric is being calculated (McKenna et al, 2016).…”

Sound exposure level as a metric for analyzing and managing underwater soundscapes

“…Peak sound pressure level is associated with immediate physiological injury to tissues (Halvorsen et al, 2012b). The sound pressure level varies with the averaging time, which makes it difficult to obtain repeatable values between research teams or methods, especially when analyzing the effects of impulsive sound sources (Madsen, 2005;Hawkins et al, 2014). SEL is associated with fatigue injury through the equal energy hypothesis that states the effects on hearing are the same for the same total energy (Eldredge and Covell, 1958).…”