Neutrino Telescope Array (NTA) - Towards Survey of Astronomical $\nu_\tau$ Sources

The Earth-skimming $\nu_{\tau}$ method allows for huge target mass and detection volume simultaneously. In part motivated by IceCube PeV astro-neutrino events, the planned NTA observatory has three site stations watching the air mass surrounded by Mauna Loa, Mauna Kea, and Hualalai on Hawaii Island, plus a site station at the center watching the lower night sky. Sensitivities equivalent to $> 100$ km$^3$ water and pointing accuracy of $< 0.2^\circ$ can be achieved with Cherenkov-fluorescence stereoscopic observation for PeV-EeV neutrinos that is almost background-free. With design based on experience from Ashra-1 and the goal of clear discovery and identification of astronomical $\nu_\tau$ sources, a new international collaboration is being formed.