Browsing by Author "Perera, S."

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    An integrated MASS/DIMM monitor based on a low-noise CCD detector
    (2015) Guesalaga Meissner, Andrés Rodrigo; Osborn, J.; Sarazin, M.; Neichel, B.; Perera, S.; Wilson, R.; Wizinowich, Peter
    We propose a novel design for a turbulence profiler. Using a single detector, images of the pupil (scintillation) and stars (image motion) are formed in the detector plane. The instrument is called FASS (Full Aperture Scintillation Sensor), as it uses the full aperture of the telescope. Different processing strategies are evaluated, including spatial segmentation and Fourier analysis. The different approaches are tested via simulation and on-sky data from two telescopes and compared to profiles obtained with the Durham Stereo-SCIDAR monitor. Overall, simulations shows that the method is more accurate that the classical MASS configuration, but it is shown that the photon noise plays an important role in the accuracy of the method, imposing stringent requirements on the pixel size, which must be significantly smaller than the speckle size formed from turbulence close to the ground (Fresnel law for speckle size).
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    FASS: a turbulence profiler based on a fast, low-noise camera
    (2021) Guesalaga, A.; Ayancan, B.; Sarazin, M.; Wilson, R. W.; Perera, S.; Le Louarn, M.
    The measurement of the atmospheric optical turbulence with a new scintillation profiler is described and demonstrated. The instrument, FASS (Full Aperture Scintillation Sensor), uses new fast and low-noise detectors to record and process sequences of scintillation images. Statistical processing of these data is based on the calculation of power spectra of intensity in annular pupil zones over the angular coordinate. The angular power spectra are used to measure the optical turbulence intensity of 14 layers located at logarithmically spaced distances from 0.3 to 25 km. The reference functions relating turbulence strength to the angular power spectra are computed by numerical simulation. Measurement of the ground-later turbulence and total seeing with FASS is possible when the detector is conjugated to a negative (below ground) distance. Results of measurement campaigns at Paranal are reported, documenting a good agreement of turbulence profiles measured by FASS with two other instruments, SCIDAR and MASS.