Normalized and asynchronous mirror alignment for Cherenkov telescopes |
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| Affiliation: | 1. ETH Zurich, Institute for Particle Physics, Otto-Stern-Weg 5, 8093 Zurich, Switzerland;2. University of Geneva, ISDC Data Center for Astrophysics, Chemin d’Ecogia 16, 1290 Versoix, Switzerland;3. Universität Würzburg, Institute for Theoretical Physics and Astrophysics, Emil-Fischer-Str. 31, 97074 Würzburg, Germany;4. TU Dortmund, Experimental Physics 5, Otto-Hahn-Str. 4, 44221 Dortmund, Germany;1. Centre National de la Recherche Scientifique, LPP UMR 7648, Ecole Polytechnique - Université Pierre et Marie Curie Paris VI - Observatoire de Paris, Route de Saclay Palaiseau 91128, France;2. Université d’Orléans, Observatoire des Sciences de l’Univers en région Centre, UMS 3116, Centre Nationale de la Recherche Scientifique, LPC2E UMR 7328, 3A Av. de la Recherche Scientifique, Orléans 45071, France;3. Uppsala Universitet, Institutet för Rymdfysik, Ångströmlaboratoriet, Lägerhyddsvägen 1, Låda 537, Uppsala 751 21, Sverige;1. KTH Royal Institute of Technology, Department of Physics, Stockholm 106 91, Sweden;2. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, Stockholm 106 91, Sweden;3. Department of Physical Science, Hiroshima University, Hiroshima 739–8526, Japan;4. Max Planck Institut for Physics, Munich D-80805, Germany;5. University of Geneva, Geneva CH-1211, Switzerland;1. ITeDA (CNEA, CONICET, UNSAM), Buenos Aires, Argentina;2. Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), Buenos Aires, Argentina;1. A. Alikhanyan National Lab (Yerevan Physics Institute), 2 Alikhanyan Brothers, Yerevan 0036, Armenian;2. National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow 115409, Russian Federation |
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| Abstract: | Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and as they are composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment is a challenge. Here we present a computer vision based star tracking alignment method, which also works for limited or changing star light visibility. Our method normalizes the mirror facet reflection intensities to become independent of the reference star’s intensity or the cloud coverage. Using two CCD cameras, our method records the mirror facet orientations asynchronously of the telescope drive system, and thus makes the method easy to integrate into existing telescopes. It can be combined with remote facet actuation, but does not require one to work. Furthermore, it can reconstruct all individual mirror facet point spread functions without moving any mirror. We present alignment results on the 4 m First Geiger-mode Avalanche Cherenkov Telescope (FACT). |
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