  We show here that the standard physical model used by Vriend et al. to
analyse seismograph data, namely a non-dispersive bulk propagation, does not
apply to the surface layer of sand dunes. According to several experimental,
theoretical and field results, the only possible propagation of sound waves in
a dry sand bed under gravity is through an infinite, yet discrete, number of
dispersive surface modes. Besides, we present a series of evidences, most of
which have already been published in the literature, that the frequency of
booming avalanches is not controlled by any resonance as argued in this
article. In particular, plotting the data provided by Vriend et al. as a table,
it turns out that they do not present any correlation between the booming
frequency and their estimate of the resonant frequency.
