Transmission loss of surface-reflected ray arrivals underneath seasonally varying sea ice in the Canada Basin during 2016-2017.

Abstract

During the 2016-2017 Canada Basin Acoustic Propagation Experiment, an ocean acoustic tomography array with a radius of 150 km measured the impulse responses of the ocean every 4 hr at a variety of ranges and bearings using broadband signals with center frequencies from 172.5 to 275 Hz. Ice-profiling sonar data showed a gradual increase in ice draft over the winter with daily median ice drafts reaching maxima of about 1.5 m and daily standard deviations reaching maxima of about 1.2 m. The travel-time variability of early, resolved arrivals from refracted-surface-reflected rays with lower turning depths below 500 m was reported in a previous paper [Worcester et al. (2023). J. Acoust. Soc. Am. 153, 2621-2636]. Here, the transmission loss of these same ray arrivals is analyzed. The transmission loss was lowest when open water was present and increased as the ice draft increased. The excess transmission loss per surface reflection, defined as the increase in transmission loss relative to open water conditions, increased with center frequency and surface grazing angle. The combination of transmission loss measurements for resolved ray arrivals and ice drafts from the ice-profiling sonars provides an excellent dataset for testing ice-scattering models.