Atmospheric turbulence profiling with SLODAR using multiple adaptive optics wavefront sensors

The slope detection and ranging (SLODAR) method recovers atmospheric turbulence profiles from time averaged spatial cross correlations of wavefront slopes measured by Shack-Hartmann wavefront sensors. The Palomar multiple guide star unit (MGSU) was set up to test tomographic multiple guide star adaptive optics and provided an ideal test bed for SLODAR turbulence altitude profiling. We present the data reduction methods and SLODAR results from MGSU observations made in 2006. Wind profiling is also performed using delayed wavefront cross correlations along with SLODAR analysis. The wind profiling analysis is shown to improve the height resolution of the SLODAR method and in addition gives the wind velocities of the turbulent layers

Status of the TMT site evaluation process

The Thirty Meter Telescope (TMT) is currently acquiring site characterization data at ve candidate sites. The site testing equipment includes instruments for measuring the seeing and seeing proles, meteorological conditions, cloudiness, precipitable water vapor, etc. All site testing equipment and data have gone through extensive calibrations and verications in order to assure that a reliable and quantitative comparison between the candidate sites will be possible. Here, we present an update on the status of the site selection work, the equipment characterizations and the resulting accuracies of our site selection data

Site selection and characterization for giant telescopes

I describe the procedures used during the different phases of site testing for astronomical telescopes, that is, during the pre-selection of candidate sites, on-site testing (site selection), the site decision itself and characterization of the telescope site once the decision has been made. Many of the important parameters for astronomical night-time telescopes and some of the methods that can be used to determine these parameters are described. There appear to be no fundamental differences between the methods used for telescopes in the 5 to 10 meter range and telescopes with diameters larger than 10 meters, although specific differences certainly exist

Open questions in site characterization and turbulence parameter measurements

With the development of increasingly larger and more complex telescopes and instrumentation, site testing and characterization efforts also increase in both magnitude and complexity. This happens because the investment into larger observatories is higher and because new technologies, such as adaptive optics, require knowledge about parameters that did not matter previously, such as the vertical distribution of turbulence. We present examples of remaining questions which, to date, are not generally addressed by "standard" site characterization efforts, either because they are technically not (yet) feasible or because they are impractical. We center our observations around the experience gained during the Thirty Meter Telescope (TMT) site testing effort with an emphasis on turbulence measurements, but our findings are applicable in general to other current and future projects as well

CELT site testing program

The California Extremely Large Telescope, CELT, is a proposed 30-m telescope. Choosing the best possible site for CELT is essential in order to extract the best science from the observations and to reduce the complexity of the telescope. Site selection is therefore currently one of the most critical pacing items of the CELT project. In this paper, we first present selected results from a survey of the atmospheric transparency at optical and infrared wavelengths over the southwestern USA and northern Mexico using satellite data. Results of a similar study of South America have been reported elsewhere. These studies will serve as the pre-selection criterion of the sites at which we will perform on-site testing. We then describe the current status of on-site turbulence evaluation efforts and the future plans of the CELT site testing program

The Thirty Meter Telescope site testing robotic computer system

The Thirty Meter Telescope (TMT) project is currently testing six remote sites as candidates for the final location of the telescope. Each site has several instruments, including seeing monitors, weather stations, and turbulence profile measuring systems, each of which is computer controlled. As the sites are remote (usually hours from the nearest town), they requires a system that can control the operations of all the varied subsystems, keep the systems safe from damage and recover from errors during operation. The robotic system must also be robust enough to operate without human intervention and when internet connections are lost. It is also critical that a data archiving system diligently records all data as gathered. This paper is a discussion of the TMT site testing robotic computer system as implemented

High-accuracy differential image motion monitor measurements for the Thirty Meter Telescope site testing program

Differential image motion monitors (DIMMs) have become the industry standard for astronomical site characterization. The calibration of DIMMs is generally considered to be routine, but we show that particular care must be paid to this issue if high-accuracy measurements are to be achieved. In a side by side comparison of several DIMMs, we demonstrate that with proper care we can achieve an agreement between the seeing measurements of two DIMMS operating under the same conditions to better than ±0.02 arc sec

Thirty Meter Telescope astrometry error budget

The Thirty Meter Telescope (TMT) with its first-light multi-conjugate adaptive optics system, NFIRAOS, and high-resolution imager, IRIS, is expected to take differential astrometric measurements with an accuracy on the order of tens of micro arcsec. This requires the control, correction, characterization and calibration of a large number of error sources and uncertainties, many of which have magnitudes much in excess of this level of accuracy. In addition to designing the observatory such that very high precision and accuracy astrometric observations are enabled, satisfying the TMT requirements can only be achieved by a careful calibration, observation and data reduction strategy. In this paper, we present descriptions of the individual errors sources, how and when they apply to different astrometry science cases and the mitigation methods required for each of them, as well as example results for individual error terms and the overall error budgets for a variety of different science cases

The Thirty Meter Telescope site testing system

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 C^2_n 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 C^2_n 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