Rough surfaces created back-reflected internal waves

Internal wave beams do not propagate long distances in the ocean, and we hypothesize that dissipation upon reflection contributes to scattering wave energy. We study how boundary roughness in our tank experiments affects the reflection coefficient: the ratio of the outgoing energy flux to the incoming energy flux through a surface near the reflection region. We measure the velocity field using particle image velocimetry and determine the energy flux using the work of Lee et al. (Phys. Fluids, 26, 2014). The wave beams are separated using the Hilbert transform method of Mercier et al. (Phys. Fluids, 20, 2008) to calculate the contributions from the incoming wave beam and any harmonic waves. We find high energy dissipation rates (small reflection coefficients) for steep boundary angles or when the boundary is roughened. We also find significant wave energy reflected back from the boundary towards the generation site under these same conditions.