  In this article, the structure of semiclassical measures for solutions to the
linear Schr\"{o}dinger equation on the torus is analysed. We show that the
disintegration of such a measure on every invariant lagrangian torus is
absolutely continuous with respect to the Lebesgue measure. We obtain an
expression of the Radon-Nikodym derivative in terms of the sequence of initial
data and show that it satisfies an explicit propagation law. As a consequence,
we also prove an observability inequality, saying that the $L^2$-norm of a
solution on any open subset of the torus controls the full $L^2$-norm.
