  It has recently been suggested that the neutrino mass hierarchy can be
experimentally determined from the oscillation pattern of atmospheric neutrinos
passing through the Earth by measuring the two-dimensional arrival pattern of
neutrinos in energy and zenith angle, in the energy regime of about 3-20 GeV.
ORCA (Oscillation Research with Cosmics in the Abyss) is a study addressing the
feasibility of such a measurement employing the deep-sea neutrino telescope
technology developed for the KM3NeT project. In the following, the underlying
physics and resulting experimental signatures will be discussed and some
aspects of the ongoing simulation studies presented. A preliminary sensitivity
estimate derived from a simplified study strongly indicates that an exposure of
at least 20 Mton-years will be required to arrive at conclusive results.
