Scattering of internal gravity waves by inhomogeneities

Internal gravity waves are scattered by inhomogeneities, such as background currents and bottom topography. Scattering modifies the wave's length and direction of propagation and in doing so, redistributes energy across wavenumbers and frequencies. When inhomogeneities are large relative to the waves, scattering reduces to a spectral diffusion process. Prior work on spectral diffusion considers only current-induced scattering via Doppler shift of the wave frequency. We generalise the diffusion framework to account for all large-scale inhomogeneities. This includes current-induced effects other than Doppler shift, and entirely different mechanisms such as scattering on bottom topography. We support our results with ray tracing simulations and analytical solutions.