Observations of 11 to 12.5 kHz sea ice pulse reflections around 50–55 deg grazing angle in the Beaufort Sea from summer 2016 to summer 2017

Abstract

Beaufort Sea ice has acoustic characteristics that change across time and space. This research aims to quantify sea ice scattering statistics with the goal of using them to predict physical ice characteristics. Over the time between summer 2016 and summer 2017, ice and ocean surface scattering in the 11–12.5 kHz frequency range between grazing angles 50 deg and 55 deg was studied using the navigation systems for a seven mooring 150-km radius acoustic array. Surface scattering has five primary epochs: open water (OW), early ice formation (IF) occurring for a few weeks, ice solidification (IS) occurring again for a few weeks, ice thickening (IT) occurring for about six months, and eventually, ice melting (IM) occurring for 1.5 to 2 months. Important changes in acoustic scattering behavior occurs between these epochs, here expressed in terms of the moments of reflected intensity, intensity probability density function, and pulse time spread. The eras of most considerable change in the observables belong to transition epochs of IF, IS, and IM. These results are interpreted physically and qualitatively in terms of the notions of partially and fully saturated wave fields, an incoherent Kirchhoff-like approximation for the rough surface, and a thin elastic layer reflection coefficient model.