Turbulence and wind speed profiles for simulating the TMT
T. Travouillon1,a, M. Sch¨ ock2, S.G. Els3, R. Riddle1, W. Skidmore1, B. Ellerbroek1, and G.
1Thirty Meter Telescope Observatory Corp
1200 E. California Blvd, Pasadena, CA, USA
2TMT Observatory Corporation, Victoria, BC, Canada
3AURA-NIO, Cerro Tololo Inter-American Observatory, La Serena, Chile.
Abstract. The site testing campaign of the Thirty Meter Telescope gathered an extensive amount
of turbulence profiles. This data is modeled to describe the statistical characteristics of each site and
act as ”standard atmospheres” for use in AO simulations.
In this paper, we present a new database of turbulence profiles gathered for the Thirty Meter
Telescope (TMT) project . The data represents to date, the largest comparable study of
different astronomical sites. The data covers the five TMT candidate sites and the test location
of Mt Palomar in California. Three sites in Chile were studied, namely Cerro Tolar, Armazones
and Tolonchar as well as two sites in the Northern hemisphere: San Pedro Martir On the
Mexican peninsula of Baja California and Mauna Kea 13 North located to the North the
ridge of Mauna Kea in Hawaii. These data, were taken with identical sets of equipments on
each site, making them perfectly comparable. The dataset, which will be described in more
details in the next section is used as a reference to determine the expected performance of the
TMT adaptive optics system (AO), NFIRAOS.
As we will show in Sec. 3, defining standard profiles is not a straight forward problem. In
an ideal world, performance simulations should be run on individual cases, using individual
turbulence profiles and site characteristics. However, such a scenario is often not possible as the
runtime of the simulations are long and can only be realistically done a finite sets of conditions.
For this reason, we need to reduce the number of cases to be run by using standard sets of
cases, usually involving median profiles or an accepted range of percentiles. The difficulty is
that there are many ways to define ”median profiles”. Indeed, taking the median value of
each turbulence layer to reconstruct a median profile doesn’t equate to the selection of profile
with median seeing due to the non linear addition of turbulence. We therefore present several
options that have been considered for use in the simulation of TMT performances.
2 The data set
The goal of the TMT site testing campaign was to measure a series of atmospheric parameters
at 5 preselected locations based on a satellite study . To carry out a proper selection, two
criteria were thought of being vital. First, that the site study spanned a period of time which
was long enough to be considered statistically meaningful, hence avoiding bias due to low
number statistics, seasonal variability and unusual climatic behavior. The second criterion, was
to measure the parameters of interest with the same suite of instruments to avoid, instrumental
effects and limitations. In addition, some cross calibration campaigns were carried out to not
1st AO4ELT conference, 03001 (2010)
© Owned by the authors, published by EDP Sciences, 2010
This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial
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the original work is properly cited.
Article published by EDP Sciences and available at http://ao4elt.edpsciences.org or http://dx.doi.org/10.1051/ao4elt/201003001