Three-dimensional acoustic propagation effects induced by the sea ice canopy.

This work examines three-dimensional (3D) propagation caused by interaction with the sea ice canopy using an approximate normal mode/parabolic equation hybrid model. The effects of horizontal refraction are assessed through comparison of two-dimensional (2D) and 3D solutions for the modal amplitudes and depth-averaged transmission loss. The following 3D effects are described: diffraction of sound into shadow zones behind ice keels, horizontal defocusing of sound behind ice keels, and horizontal focusing of sound that has propagated between ice keels. A statistical analysis shows that the 3D solution is characterized by 20% greater variance in the depth-averaged transmission loss than the 2D solution.