= Focusing power of internal-wave reflection
{title2=$\gamma$}
For an <internal gravity wave> ray at angle $\theta$ to the horizontal reflecting from a slope at angle $\alpha$, conservation of tangential <wavenumber> gives
$$
\gamma=\frac{k_{\rm reflected}}{k_{\rm incident}}
=\frac{\sin(\theta+\alpha)}{\sin(\theta-\alpha)}.
$$
At a <subcritical internal-wave reflection>, $\gamma>1$: the reflected wavelength shortens and its wavelength-averaged <energy density> increases by $\gamma^2$.
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