Laboratory‐scale simulation of under‐ice reflectivity at low frequencies

Abstract

Under‐ice reflectivity is dominated by sea ice ridges, long, randomly spaced, randomly oriented rubble piles of broken ice. The effective low‐frequency shear and compressional velocities of these formuations have been estimated to be between 1100–1700 and 2700–3400 m/s, respectively (Diachok, Proceedings International Congress on Acoustics, 1986). To be consistent with these estimates, Lucite, a readily available and easily machined material, for which Vs = 1260 m/s and Vp = 2600 m/s was used to construct laboratory scale analogs of sea ice ridges situated on a thin plate. Both parallel and randomly oriented ridge models were construtted, and the effects of ridge elasticity and orientation on under‐ice reflectivity (amplitude and phase) were examined for 0.67 < ka < 6 (k = wavenumber and a = mean depth). Initial reflection coefficient data at the lowest frequencies are approximately consistent with Twersky's predictions for reflectivity from both hard and soft half‐cylinders on a soft boundary. Higher fre...