  Earth-skimming neutrinos are those which travel through the Earth's crust at
a shallow angle. For Ultra-High-Energy (E > 1 PeV; UHE) earth-skimming tau
neutrinos, there is a high-probability that the tau lepton created by a
neutrino-Earth interaction will emerge from the ground before it decays. When
this happens, the decaying tau particle initiates an air shower of relativistic
sub-atomic particles which emit Cherenkov radiation. To observe this Cherenkov
radiation, we propose the Trinity Observatory. Using a novel optical structure
design, pointing at the horizon, Trinity will observe the Cherenkov radiation
from upward-going neutrino-induced air showers. Being sensitive to neutrinos in
the 1-10,000 PeV energy range, Trinity's expected sensitivity will have a
unique role to play filling the gap between the observed astrophysical
neutrinos observed by IceCube and the expected sensitivity of radio UHE
neutrino detectors.
