Cooperative Institute for Research in Environmental Sciences

Application of Wave Interferometry to Experimental Investigation of Infragravity Waves off New Zealand

Nikolay Zabotin (1,2), Oleg Godin (2,3), Anne Sheehan (4,2), Zhaohui Yang (4,2), and John Collins (5)

(1) Department of Electrical and Computer Engineering, University of Colorado, (2) CIRES, University of Colorado, (3) NOAA Earth System Research Laboratory, Physical Sciences Division, (4) Department of Geological Sciences, University of Colorado, (5) Woods Hole Oceanographic Institution, Woods Hole, MA

In the course of the Marine Observations of Anisotropy Near Aotearoa (MOANA) Seismic Experiment, bottom pressure sensors (differential pressure gauges), along with broadband ocean bottom seismometers, were deployed off both east and west coasts of the South Island of New Zealand at approximately 100 km spacing and at water depths from 550 m to 4680 m. We use the year-long, continuous records of pressure at 30 locations on the seafloor to study the total energy, spectral structure, coherence, and directivity of infragravity waves (IGWs) in the 0.5–30 mHz frequency range. We have developed a technique that allows one to compensate for wave dispersion in evaluating the cross-correlation function of a random wave field. When applied to the seafloor pressure data, the technique drastically reduces the signal averaging times necessary for emergence of deterministic features and allows for accurate passive measurements of IGW travel times and directivity. The reduction in the averaging time makes it possible to study dynamics on the IGW field, including seasonal variations of the directionality, and helps to constrain possible IGW generation mechanisms.