Durham E-Theses Some meteorological parameters aecting the image quality of the William Herschel telescope on La Palma Azzaro, Marco How to cite: Azzaro, Marco (1996) Some meteorological parameters aecting the image quality of the William Herschel telescope on La Palma, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/5165/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk 2 MSc Thesis Some meteorological parameters affecting the image quality of the William Herschel Telescope on La Palma MARCO AZZARO DECEMBER 1996 Abstract Understanding of the factors which limit the image quahty of a ground based tele• scope is still an interesting challenge despite the effort devoted to the problem since the early days of optical astronomy. At the Roque de los Muchachos observatory, on the island of La Palma (Canary Islands) this problem has been studied as part of a programme aimed to improve the optical performance of the biggest instrument at the observatory, the anglo-dutch William Herschel Telescope. The programme comprises a range of studies to investigate the possible factors deteriorating the image quality at the telescope. This thesis forms part of the meteorological studies of this programme and it is based on the data collected by a meteorological station recently installed at the observatory. In particular, phenomena such as wind direction, wind speed, pointing direction of the telescope dome relative to the wind direction, air and soil temperatures, relative inter• nal/external temperatures, barometric pressure and humidity have been investigated and the relationship between these and the image quality at the telescope has been analyzed. The image quality is found to be particularly sensitive to the wind direction and the internal differences in temperatures. The season of the year also seems to have an influence on the image quality. In the conclusions, suggested further avenues of investigation are given. UNIVERSITY OF DURHAM Department of Physics MSc THESIS Some meteorological parameters affecting the image quality of the William Herschel Telescope on La Palma The copyright of this thesis rests with the author. No quotation from it should be published without the written consent of the author and information derived from it should be acknowledged. Author Marco Azzaro December 1996 6 OCT 1897 Contents INTRODUCTION 5 1 The seeing problem 5 1.1 Light distortion 5 1.2 Diffraction hmit 6 1.3 Seeing definition and terminology 7 1.4 The importance of image quality 7 2 Means of reducing the image size 9 2.1 Observe from outside the atmosphere 9 2.2 Site selection 9 2.3 Control of local seeing 10 2.4 Postprocessing of images 10 2.5 Active optics 10 2.6 Adaptive optics 11 3 The Half-arcsecond programme 11 3.1 General aim and plans 11 3.2 Meteorology investigation 13 4 Importance of meteorology 13 5 Earlier attempts at seeing investigation 14 6 The structure of this thesis 14 INSTRUMENTS AND DATA 17 1.1 The meteorological station, general characteristics 17 1.2 Characteristics of the sensors 20 1.2.1 Anemometers 20 1.2.2 Hygrometers 20 1.2.3 Thermometers 20 1.2.4 Solarimeter 21 1.2.5 Surface wetness sensor 21 1.2.6 Dust monitor 21 1.2.7 Barometer 21 1.2.8 Dewpoint meter 22 1.2.9 The Vaisala station 22 1.2.10 Alarms ' 22 1.3 Telescopes safety limits 23 1.4 Assessment of data quahty 24 1 1.4.1 Wind 24 1.4.2 Humidity 25 1.4.3 Temperature 25 1.4.4 Solar radiation 25 1.4.5 Surface wetness 25 1.4.6 Dust 25 1.4.7 Pressure 25 1.4.8 Dewpoint 26 1.4.9 Power supplies 26 1.4.10 Data transmission 26 1.4.11 Occasional malfunctions 26 1.5 Meteorological data format and storage 27 1.6 The seeing data 27 1.6.1 The detector system 27 1.6.2 Seeing data collection 27 1.6.3 Seeing data quality 28 1.7 The computer programs used in this work 29 1.7.1 Programs for instrument quality control 29 1.7.2 Programs for seeing investigation 29 COMPARISONS WITH OTHER STATIONS 31 2.1 Foreword 31 2.2 The comparison with the Nordic Optical Telescope data 31 2.3 The comparison with the Transit Circle data 32 2.4 Meteorological implications of the differences 33 METEOROLOGY AND SEEING 35 3.1 Foreword 35 3.2 Wind/seeing 36 3.2.1 Wind direction and seeing 36 3.2.2 Wind speed and seeing 37 3.3 Angle between telescope azimuth and wind direction/seeing 38 3.4 LocalAir-Soil-Borehole temperature/seeing 39 3.5 Difference between soil and air temperature/seeing 40 3.6 Difference between local temperature and internal temperature/seeing . 40 3.7 Difference between internal temperature and mirror temperature/seeing 41 3.8 Atmospheric pressure/seeing 41 3.9 Humidity/seeing 42 CONCLUSIONS 43 4.1 Validity of results 43 4.2 Conclusions . .' 43 4.2.1 Wind effect 44 4.2.2 Seasonal effect 44 4.2.3 Internal temperature differences effect 45 4.2.4 General conclusions 46 4.3 Possible further investigations 46 DETAILS OF THE CALIBRATION OF THE BAROMETER 49 A.l Foreword 49 A.1.1 Temperature barometric error 50 A. 1.2 Gravity corrections 51 A.1.3 Corrections for differences in height 53 A.2 The Transit Circle Mercury barometer 55 A. 3 Programs and correction coefficients 55 INSTRUMENTAL DAMAGE CAUSED BY BAD WEATHER 57 B. l Ice accretion 57 B.2 Solar panel care 58 B.3 Strong winds 58 B. 4 Other meteorological factors causing damage 59 SOURCE CODES FOR DATA REDUCTION PROGRAMMES 61 C. l Explanation 61 BIBLIOGRAPHY 63 LIST OF ABBREVIATIONS Declaration I presently state that the work presented in this thesis has not been previously sub• mitted for any degrees or other qualifications at this or other University. All of it is original except where reference to the work of other persons is made, and of my own with the following exception: the seeing data used through the analysis have been provided by N. O'Mahony; the schematic layouts of the Casella meteorological station in Chapter 1 have been pro• vided by A. Osborne and the Casella Co.; the geographic maps of La Palma and the Observatory site of the Introduction and Chapter 1 have been provided by the Instituto de Astrofisica de Canarias. Marco Azzaro The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. Acknowledgments It is a pleasure to thank J.M. Breare and J.A. Smith for their support during these two years of work and N. O'Mahony for providing part of the data used and good hints and information. Many thanks to A. Osborne and K. Kolle for their advice about the meteorological station. Many thanks to C. Moreno for his software support and to M.W. Asif and N. Walton for cleaning up my english. Many thanks to M. Bontempo, L. Morrison, all the CAMC personnel, C. Benn and all the NOT personnel, who made me available very valuable meteorological data. Many thanks to my colleagues and all the Observatory staff for the friendly atmosphere which helped me so much for this research work. FRANCIA •IHBM MARRUECOS ISIAS CANAWAS ft ^ A R G E L I A AHARA. CCIDECTAL 1.085 MAURITANIA Vermra tfslmsi Praia di •Juan/Uslid e LomaOa^Grand spindolB untaide/JutiMez urtMvrfe la Calga OhtaSr Guindaste Punta de^Se^^ e de los Muc icfi'ri-'la.C Punle~d^-Jdi''PSJifos\ unta Saling^ a Santa Lucia ancna Vmagcarasl HI^NTE Punta, da I, Catatina Punta g anta'C'ruz da/la Palma / Morro Neara SViiiin^dli a de San Carlos Punta da •Juan^Graje liaj! / s/Comaletes •^f«r=l?V.m--#l?aso sTT _ L PALMA n Borond uBia\Malpais Playa del Perdl tienta de las Hoia 'XatitmttJi ilmico Punta-del re/Ias Rnin Hn Snn S/m/in 1.094 9 /a Barque ta q'ue& de ISiaras Roque y Punta\pa los Gulnbho tba'4|| •il'-V'! ••j^;Vi«f;: mfadelo^'Poquas , .-.Hi .fWoiMttnn Jjunii'de Ugalate as Laieias i:7 / —/Los.hoques. de^naga Punta Vuilta de Punta L I Guincho Caleh del Ahdon, Pun'taMalpique>r:f.mr JMIa Malpais ) X^Sn^e/:/ Fuen^ali^tj INTRODUCTION 1 The seeing problem The present work has been carried out as a part of the project, called the Half-arcsecond Programme, to improve the imaging quality of the three anglo-dutch telescopes of the Isaac Newton Group (referred to as ING in this thesis) on La Palma, in particular the largest of these, the 4.2 m William Herschel Telescope (WHT).