The best observing sites in the world, judged on the basis of a combination of atmospheric stability and transmission are of two types, isolated high mountains in temperate oceans (e.g. Mauna Kea, La Palma) or coastal mountain ranges near to a cold ocean with stable sub-tropical anti-cyclone conditions (coasts of Chile, USA, Namibia). Continental mountain sites (e.g. in USA, Uzbekistan, China, South Africa) appear not to be as good as the former. Specialized sites (e.g. South Pole, Chajnantor) have or are being developed, and others (e.g. Stratosphere, Greenland Ice-cap) have received some discussion, see ESO Search for potencial sites (ESPAS).

ESO have stated that they will consider sites anywhere on Earth for their OWL telescope. Our evaluation is that the best examples of the two type of sites defined above are Mauna Kea and the Atacama region of Northern Chile and it is unlikely that superior sites will be found elsewhere. We have however, via AURA, initiated contacts with ESO in order to prevent duplication of effort.

Mauna Kea is well developed and there is an extensive data set containing many of the relevant site parameters. However the actual site availability is likely to be highly constrained, while the environmental impact of a 30m - 50m telescope may be a real issue.
"Non-traditional" trades such as wind protection verses intrinsic image quality, which have not been a factor in the construction of telescopes to date, will be necessary.

Chile has several well-developed sites (Cerro Tololo, Cerro Pachon, Cerro Las Campanas, Cerro La Silla, Cerro Paranal) and Cornell is investigating high altitude peaks that protrude from the altiplano near the Chajnantor MMA site. All extant sites were selected with a different set of criteria to those necessary for a 30-50m telescope, and for which as yet untested sites may prove superior. More so than any existing telescope, the NBT will rely on the use of Adaptive Optics to correct the incoming wavefront so that near diffraction-limited imagery will be possible over a narrow field. This will require careful, and extensive, measurements of the height, strength and variability of the turbulent layers in the atmosphere, and measurement of the outer scale of turbulence. We will also need measurements of the extent of the Sodium layer, since it is likely that the Adaptive Optics will use Sodium D-line lasers.

This then leads to:

a)undertaking an analysis of available Mauna Kea sites, perhaps only one site available, in the context of the NBT.