Spectral changes in snapping shrimp sounds between dusk and dawn

We report continuous time acoustic recordings of snapping shrimp dominated ambient noise at two shallow water locations on Oahu, Hawaii: Kilo Nalu Observatory and Coconut Island. We are able to resolve novel spectral changes in the ambient noise during sunrise and sunset by using higher sampling rates than have been previously employed. Also, we show that there is a significant difference in spectral levels depending on the time window used in its calculation. Spectral levels calculated over a time scale on the order of seconds to minutes can be different on the order of ∼3–6 dB from those calculated over a week. This is important for harbor security applications in which potential events of interest may occur on the scale of minutes. Previously reported ambient noise spectra averaged over the course of a week or more may not be appropriate for these scenarios and likewise the design of acoustic harbor security systems.