$H$-type foliations $(\mathbb{ M},\mathcal{ H},g_{ \mathcal{ H}})$ are studied in the framework of sub-Riemannian geometry with bracket generating distribution defined as the bundle transversal to the fibers. Equipping $\mathbb{ M}$ with the Bott connection we consider the scalar horizontal curvature $\kappa_{ \mathcal{ H}}$ as well as a new local invariant $\tau_{ \mathcal{ V}}$ induced from the vertical distribution. We extend recent results on the small-time asymptotics of the sub-Riemannanian heat kernel on quaternion-contact (qc-)manifolds due to A. Laaroussi and we express the second heat invariant in sub-Riemannian geometry as a linear combination of $\kappa_{ \mathcal{ H}}$ and $\tau_{ \mathcal{ V}}$. The use of an analog to normal coordinates in Riemannian geometry that are well-adapted to the geometric structure of $H$-type foliations allows us to consider the pull-back of Kor\'{ a}nyi balls to $\mathbb{ M}$. We explicitly obtain the first three terms in the asymptotic expansion of their Popp volume for small radii. Finally, we address the question of when $\mathbb{ M}$ is locally isometric as a sub-Riemannian manifold to its $H$-type tangent group.
Categories: math.DG