  The pattern of oscillation parameters emerging from current experimental data
can be further elucidated by the observation of matter effects. In contrast to
planned experiments with conventional neutrino beams, atmospheric neutrinos
offer the possibility to search for Earth-induced matter effects with very long
baselines. Resonant matter effects are asymmetric on neutrinos and
anti-neutrinos, depending on the sign of $\Delta m^2$. In a three-generation
oscillation scenario, this gives access to the mass hierarchy of neutrinos,
while the size of the asymmetry would measure the admixture of electron
neutrinos to muon/tau neutrino oscillations (the mixing angle $\Theta_{13}$).
The sensitivity to these effects is discussed after the detailed simulation of
a realistic experiment based on a massive detector for atmospheric neutrinos
with charge identification. We show how a detector, which measure and
distinguish between $\nu_\mu$ and $\bar{\nu}_\mu$ charged current events, might
be sensitive to matter effects using atmospheric neutrinos, provided the mixing
angle $\Theta_{13}$ is large enough.
