Between February and April 2009 a number of ultrasonic anemometers, temperature probes and dust sensors were
operated inside the CTIO Blanco telescope dome. These sensors were distributed in a way that temperature and
3 dimensional wind speeds were monitored along the line of sight of the telescope. During telescope operations,
occasional seeing measurements were obtained using the Mosaic CCD imager and the CTIO site monitoring MASS-DIMM
system. In addition, also a Lunar Scintillometer (LuSci) was operated over the course of a few nights inside the
dome. We describe the instrumental setup and first preliminary results on the linkage of the atmospheric conditions
inside the dome to the overall image quality.
Coastal mountains at Canada's northern tip possess many of the desirable properties that make the Antarctic glacial
plateau attractive for astronomy: they are cold, high, dry, and in continuous darkness for several months in winter.
Satellite images suggest that they should also benefit from clear skies for a fraction of time comparable to the best mid-latitude
sites, and conventional site-selection criteria point to good seeing. In order to confirm these conditions, we are
testing three mountain sites on northwestern Ellesmere Island, in Nunavut. On each we have installed a compact,
autonomous site-testing station consisting of a meteorological station, a simple optical/near-infrared camera for sensing
cloud cover, and - at one site - a more advanced all-sky viewing camera. The systems were deployed by helicopter and
run on batteries recharged by wind (a compact methanol fuel cell is under study as a supplementary power source).
Effective two-way communications via the Iridium satellite network allows a limited number of highly compressed
images to be transferred. The full-winter dataset is stored at the site on flash-drives, thus requiring a return visit to
retrieve, but day-to-day station performance can be assessed using telemetry and a computer model. Based on site-testing
results, the plan is to select one site for the addition of a seeing monitor and a small but scientifically productive
telescope.
The Thirty Meter Telescope (TMT) project has been collecting data on five candidate sites since 2003. This paper
describes the site testing portion of the TMT site selection program and the process and standards employed
by it. This includes descriptions of the candidate sites, the process by which they were identified, the site
characterization instrument suite and its calibration and the available results, which will be published shortly.
All Sky Cameras were deployed at all Thirty Meter Telescope (TMT) candidate sites. The images gathered
by these cameras were used to assess the cloud statistics for each site. We describe two methods that were
developed to do this, a manual method based on inspection of blue and red movies, and an automated method
based on photometric analysis of the images.
Light pollution can create difficulties for astronomers attempting to observe faint objects in the night sky. Light
from a local small town can be just as intrusive as light from a large city in the distance. As the population
of the Earth increases, light pollution will become more of a problem, even in remote areas. The Thirty Meter
Telescope site testing program has measured light pollution at the candidate sites by using all sky cameras;
an analysis procedure enhances the all sky camera images to make the determination of the effects of the light
pollution. This paper summarizes the light pollution analysis procedure and current results, which are that light
pollution is currently unimportant for TMT to select a site for the final telescope location.
Seeing stability is an important criterion of site characterization. Two sites, with the same seeing statistics, could in
principle differ in their temporal stability and hence have their observatories perform differently. Temporal variability
can, however, be defined in several ways, all of which may determine the performance of the observatories in different
manner. In this paper, we propose three methods to measure variability each focusing on different applications: Selection
(maximization of observation time), Image quality (seeing variation within a given integration time) and finally
Scheduling (prediction of seeing fluctuation on a given time scale). We apply these methods to the seeing of the TMT
candidate sites to determine their stability properties.
One of the main tools used in the TMT site testing campaign is the turbulence profiler MASS. We describe
empirical investigations and a side by side comparison of two MASS systems which were performed in order to
identify the accuracy of MASS turbulence data and its dependence on the instrument calibration. The accuracy
of the total seeing delivered by the TMT MASS systems is found to be better than 0"05. The combination of
MASS and DIMM allows to observe the seeing within the first few hundred meters of the atmosphere and can be
used to investigate possible correlations with meteorological parameters measured close to the ground. We also
compare the detection of clouds and cirrus by means of MASS data (LOSSAM method) with measurements of
the thermal emission of clouds using a net radiation sensor. These methods are compared with the visual cloud
detection using all sky cameras.
The All-Sky camera used in the LSST and TMT site testing campaigns is described and some early results are shown. The All-Sky camera takes images of
the entire visible hemisphere of sky every 30s in blue, red, Y and Z filters giving
enhanced contrast for the detection of clouds, airglow and the near-infrared.
Animation is used to show movement of clouds. An additional narrow band filter
is centered on the most prominent line of the sodium vapor lamp spectra and is used to monitor any man-made light pollution near the site. The camera also
detects aircraft lights and contrails, satellites, meteor(ite)s, local light polluters,
and can be used for stellar extinction monitoring and for photometry of transient
astronomical objects. For outreach and education the All-Sky camera can show
wandering planets, diurnal rotation of the sky, the zodiacal light, and similar
astronomical basics.
The Thirty Meter Telescope (TMT) site testing team are developing a suite of instruments to measure the atmospheric and optical characteristics of candidate TMT sites. Identical sets of robotically operating instruments will be placed at each candidate site. The fully developed system will comprise of a combined MASS/DIMM. a SODAR, tower mounted thermal probes and a portable DIMM. These instruments have overlapping altitude coverage and provide a measure of the C2n profile from the ground up with sufficient resolution to make conclusions about the ground layer and high altitude turbulence characteristics. The overlapping altitude coverage is essential to ensure consistency between these very different instruments. In addition to checking for consistency in the overlap regions, procedures are being used to cross check between instruments, i.e. the calculation of the isoplanatic angle from both the MASS and DIMM and that the integrals of the C2n profiles from the MASS, SODAR and 30m tower gives the same r0 value as measured by the DIMM.
We discuss a variation of the traditional DIMM system in which we employ a continuous drift mode readout technique giving a maximum of nearly 300 samples per second.
Findings of our major equipment testing campaigns and first field deployment are presented that demonstrate our progress in developing a rigorous approach to site testing.
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