Experimentally determining the reflection coefficient for reflecting internal waves*

Determining the energy flux of an internal wave from the experimentally measured velocity field was made possible by the work of Lee et al. (Lee et al., Phys. Fluids, 26, 2014). This method is used in our work to measure the amount of energy dissipated when internal waves reflect from sloping boundaries by computing the reflection coefficient: the ratio of the outgoing energy flux to the incoming energy flux through a surface near to the reflection region. We account for viscous decay so that we can quantify the losses in the reflected wave due only to boundary processes and harmonic generation. We compare our experimental results to numerical simulations of the Navier-Stokes equations in the Boussinesq limit where the energy flux is known from the pressure and velocity fields. There is good agreement between our experimental and numerical simulation data, and we find that there are high rates of energy dissipation during reflection process. We also find that there is a wave reflected back from the boundary towards the generation site when either the boundary is rough or the angle of the boundary is close to the angle of the internal wave beam.