Starting with a Memorandum of Understanding (MOU) with the California Extremely Large Telescope (CELT) group in FY 2002, NOAO has played a major collaborative role in evaluating candidate sites for TMT, and in developing the methodology for site testing and data analysis. These sites would also be suitable for other telescopes with similar requirements. The initial list of candidate sites was narrowed by investigations of logistical issues such as land ownership, as well as by a series of remote sensing studies that have used satellite data to quantify the number of clear nights and the precipitable water vapor for each site. Each prime candidate site has also been modeled using computational fluid dynamics to investigate the boundary layer turbulence over the site under various wind speeds and directions.

In-situ site testing equipment has been developed, and multiple copies have been purchased and assembled. This equipment includes weather stations, differential image motion monitors (DIMMs) capable of recording integrated seeing through the upper atmosphere and ground-layer, and multi-aperture scintillation sensors (MASS) capable of mapping turbulence profiles above candidate sites. Weather stations, DIMM and MASS units were deployed on five candidate sites; three in northern Chile and one each in Baja California (Mexico) and on Mauna Kea (Hawaii). Observations for the survey have now been completed on four of the five sites; data are in the process of being written up for publication. Additional information on site testing can be found at the NOAO Sites Group website.