Investigating UV nightglow within the framework of the JEM-EUSO Experiments Frej-Eric Salomon Emmoth Space Engineering, master's level 2020 Luleå University of Technology Department of Computer Science, Electrical and Space Engineering Investigating UV nightglow within the framework of the JEM-EUSO Experiments Master Thesis Space Engineering, Instrumentation and Spacecraft Author: Frej-Eric Salomon Emmoth Supervisors: Dr. Toshikazu Ebisuzaki Chief Scientist at Computational Astrophysics Laboratory, RIKEN & Dr. Marco Casolino Team Leader, EUSO Team, Research Scientist at RIKEN Examiner: Dr. Johnny Ejemalm Senior Lecturer, Lule˚aUniversity of Technology Acknowledgements I would like to first extend my most sincere gratitude to Dr. Ebisuzaki and Dr. Casolino for giving me the opportunity to do my thesis at RIKEN within the JEM-EUSO Collaboration and their invaluable help during my time there. I am also very grateful for the people at the laboratory, many of whom I today consider my friends, who made my stay in Japan so much better. I look forward to once again see the mountains of Nagano. I next want to give thanks to my family and friends for their constant support and encourage- ment. And especially to my brothers and my girlfriend who were always there to give me a push in the right direction. I am lucky to be surrounded by such great people. Lastly, I want to express my gratitude to everyone for their patience with me, with special thanks to my supervisors and my examinator in this regard. Thank you. Abstract The main mission of the JEM-EUSO (Extreme Universe Space Observatory) Collaboration is to observe Cosmic Rays. These high energy particles come from a variety of sources and bombard the Earth all the time. However, the higher the energy, the lower the flux, and par- ticles with an energy above 1018 eV (called Ultra High Energy Cosmic Rays or UHECRs) are so sparse that just a few might hit the atmosphere in a year. When CRs, and UHECRs, hit the atmosphere they cause what is called Extensive Air Showers, EAS, a cascade of secondary particles. This limits the effectiveness of ground based observatories, and that is where the JEM-EUSO Collaboration comes in. The goal is to measure UHECRs, by observing the fluo- rescence of the EAS from space. This way huge areas of the atmosphere can be covered and both galactic hemispheres can be studied. Since the JEM-EUSO instruments are telescopes measuring in the near UV range, a lot of other phenomena can be observed. One of these applications is UV nightglow. Airglow in general are lights in the sky which are emitted from the atmosphere itself, while nightglow is simply the nighttime airglow. There are many uses of airglow, and one of these is as a medium to observe atmospheric gravity waves. The aim of this thesis is to investigate how a space-based photon counting telescope, such as those of the JEM-EUSO Collaboration, can be used to measure disturbances in the terrestrial nightglow, to identify atmospheric gravity waves. To accomplish this, a theoretical basis for these interactions was explored and a simple scenario was built to explore the plausibility of measuring UV nightglow modulations. The aim was to see what variables would affect a mea- surement, and how important they were. Along side this, a calibration was conducted on one of the JEM-EUSO Collaborations instru- ments, the EUSO-TA (EUSO-Telescope Array). The goal in the end was to try and measure the night sky, to complement the calculations. The investigation showed that the conditions during the measurement are very important to the measurement. This includes things like background intensity, nightglow activity, and mag- nitude/shape of the modulations. Of more importance though are the parameters which can be actively changed to improve the measurement, the most important of which is measurement time. It was concluded that a measurement of the nightglow modulation should be, under the right conditions, possible to do with a currently operating instrument, the Mini-EUSO, or sim- ilar instrument. The calibration of the EUSO-TA involved a series of repairs and tests, which highlighted some strengths and weaknesses of the instrument. However, the calibration itself produced few work- able results that in the best case scenario reduced the focal surface to an unevenly biased 2-by-2 Elementary Cell square. Unfortunately this would not be sufficient to do proper measurements with, but the process did point out shortcomings with the then involved sensors, as well as some problematic aspects of the software operating the instrument. Abbreviations List of abbreviations commonly used: AGN : Active Galactic Nuclei AGW : Atmospheric Gravity Wave ASIC : Application Specific Integrated Circuit BW : Bandwidth CPU : Central Processing Unit EAS : Extensive Air Shower EC : Elementary Cell EM : Electromagnetic JEM-EUSO : Joint Exploratory Mission Extreme Universe Space Observatory FD : Fluorescence Detector FS : Focal Surface FoV : Field of View FWHM : Full Width at Half Maximum GBR : Gamma Ray Burst GD : Ground Detector GTU : Gate Time Unit GZK : Greisen-Zatsepin-Ku'min HBI : Herzberg I HVPS : High Voltage Power Supply IR : Infrared ISS : International Space Station JEM : Japanese Experiment Module LED : Light Emitting Diode LEO : Low Earth Orbit LIDAR : Light Detection And Ranging MAPMT : Multi-Anode PMT MLT : Mesosphere-Lower Thermosphere OI5577 : Atomic Oxygen 5577 A˚ PAO : Pierre-Auger Observatory PCE : Photon Collection Efficiency PDM : Photon-Detection Module PMMM : Polymethyl-Methacrylate PMT : Photon Multiplier Tube SNR : Signal-to-Noise Ratio SR : Supernova Remnants SSD : Solid State Drive TA : Telescope Array UHECR : Ultra High Energy Cosmic Rays UV : Ultra Violet Contents 1 Introduction 1 1.1 Thesis Subject . 1 1.2 Thesis Scope . 1 2 Cosmic Rays 3 2.1 Ultra High Energy Cosmic Rays - UHECR . 4 2.1.1 Extensive Air Showers . 5 2.1.2 Current Experiments . 9 2.2 The JEM-EUSO Project . 12 2.2.1 Past and Current Projects . 14 2.2.2 Future Projects . 17 2.3 The Mini-EUSO . 21 2.3.1 Optics, Focal Surface, and Data Acquisition System . 22 2.3.2 Acquisition and Usage . 25 2.4 The EUSO-TA . 27 3 Nightglow 31 3.1 The Herzberg I Bands . 32 3.2 The OI5577 Green Line . 38 3.2.1 Comparison of OI5577 and HBI emission rate . 42 3.3 Atmospheric Gravity Waves . 44 3.3.1 Modulation of Airglow . 45 3.4 Ultraviolet Background . 46 3.5 Measurement Noise . 48 4 Measurement of Nightglow 49 4.1 Method and Analysis . 49 4.1.1 Expected Modulation of Herzberg I bands . 49 4.1.2 Geometry of Measurement . 52 4.1.3 Estimating Photon Counts . 54 4.1.4 Constructing a Scenario . 56 4.1.5 Applying the Scenario . 57 4.1.6 Effects of Measurement Noise . 57 4.2 Results of the Estimation . 58 4.2.1 Singel Pixel . 58 4.2.2 The Scenario . 59 4.2.3 Full Frame . 60 5 Calibration of the EUSO-TA focal surface 64 5.1 Method of Calibration . 64 5.1.1 Initial Complications . 65 5.1.2 Mapping the Frame . 66 5.1.3 Mechanical Problems . 67 5.1.4 Orientation of the ECs . 70 5.1.5 Differences between ECs . 71 5.1.6 Differences between Pixels . 72 5.1.7 Reordering och ECs . 73 4 5.2 Results of the Calibration . 74 6 Conclusions 76 6.1 Discussion . 77 6.2 Future Work . 77 1 Introduction This Master Thesis deals with using the Mini-EUSO space telescope, and similar instruments, to measure the modulations in ultraviolet nightglow in the lower thermosphere induced by Atmospheric Gravity Waves (AGWs). This work is a part of the larger JEM-EUSO Collaboration, an international cooperation which aims to broaden the understanding of the universe at large, but more specifically our understanding of Ultra High Energy Cosmic Rays. This thesis is divided in to two parts, one theoretical and one practical. The theoretical part contains the background and framework for the physics describing the phenomena of nightglow and how it can be used, while the practical part contains a description of the calibration process of the EUSO-TA instrument and measurements done at the Wako Campus of RIKEN, Saitama, Japan. This whole project was facilitated by the Computational Astrophysics Laboratory at the RIKEN research institute main campus, who provided the tools, facilities, and assistance necessary to complete these tasks. 1.1 Thesis Subject The main topic of this thesis is an investigation and estimation of measuring nightglow and the intensity modulations that occur due to atmospheric gravity waves breaking in the upper atmosphere. This is done within the framework of a photon counting instrument, the Mini-EUSO space telescope and therefore the focus lies on ultraviolet nightglow from the Herzberg I system. The goal is to investigate the feasibility and extent to which these modulations can be measured. The Mini-EUSO is currently mounted on the ISS (International Space Station) and is pointed in nadir direction, which affects the amount of light measurable from nightglow. This is combined with a process of practical calibration with a similar instrument, the EUSO-TA, and a test measurement. 1.2 Thesis Scope Since the subjects of airglow and atmospheric gravity waves are quite broad on their own, the scope of this thesis has to be limited. The focus lies in investigating how the Mini-EUSO will measure modulations in the UV nightglow and establishing the signal-to-noise ratio to make these measure- ments possible, and as such these are the goals of this thesis: • Identify and estimate the relevant parameters of nightglow emissions. • Investigate the effect of AGWs on UV nightglow. • Estimate the UV background for a nadir pointing instrument in orbit.