UC Santa Barbara

Atmospheric acoustic signals produced by crashing ocean waves may be highly variable from sub-hourly to seasonal time scales. Specifically, low-frequency acoustics (below 20 Hz) known as infrasound have been reported near coastlines under variable ocean conditions such as significant wave height, wave period, swell direction, locations of crashing surf, and style of breakers (e.g., Garcés et al. [2003], Aucan et al. [2006], Le Pichon et al. [2004]). Here, we use infrasound and seismic data collected at Coal Oil Point Reserve in Santa Barbara, California, to investigate how the ambient acoustic wave-field is perturbed by variable surf and ocean conditions. Data collection involved one principal infrasound sensor (September 2022–July 2023), complemented by four temporary infrasound arrays of varying geometries: 1) January 11, 2023; 2) January 12–19, 2023; 3) July 10, 2023; 4) October 17–23, 2023. Each array included video recordings, and the latter two arrays involved broadband seismometers as well. We find that distinct groups of surf infrasound signals are produced throughout 10 months of data, and that the amplitudes of these signals are correlated with offshore significant wave height and local wind speed. We estimate source locations of surf infrasound using array-based and network-based processing methods and find a correspondence with expected locations of breaking waves as seen in video footage. We highlight the opportunity to monitor the littoral sea surface state using infrasound and seismic records.