The Mini-EUSO (Mini - Extreme Universe Space Observatory) is an instrument for observation of ultra-high energy cosmic rays (UHECR) from space. It is designed to observe Earth from the international space station (ISS) in the ultra-violet (UV), visible (VIS) and near-infrared (NIR) light ranges. The UV sensor is the main sensor, designed and built by the EUSO collaboration. The visible and near-infrared sensors are secondary sensors. These are two cameras, FMVU-13S2C-CS and CMLN-13S2M-CV, from Point Grey Research Inc. The near-infrared light camera has a phosphor coating on the sensor to convert from near-infrared light to visible light, which is detectable by the camera's CCD. This thesis deals with the calibration and evaluation of the secondary sensors. This is done by first evaluating the bias and dark current for both cameras. After which a calibration is done using the light measurement sphere, located at the National Instituteof Polar Research (NIPR) in Midori-cho, Tachikawa-shi, Japan. Due to the low sensitivity of the near-infrared light camera, an evaluation of its ability to see celestialobjects are also performed. It is found that the visible light camera has a high bias with values around 5 ADU (Analog-to-Digital unit), but almost non-existing dark current, with mean values below 1 ADU. The visible light camera has good sensitivity for all the colors: red, green and blue. However, it is most sensitive to green. Due to this, it is easy to saturate the pixels with too much light. Therefore, saturation intensity was also examined for the shutter times of the visible light camera. This is found to be between 900μWm-2sr-1 and 1·107μWm-2sr-1, depending on color and shutter time. The near-infrared light camera is the opposite; it has a low bias with values below 1 ADU and a high dark current. The values of the dark current for the near-infrared light camera are highly dependent on the temperature of the camera. Mean values are below 1 ADU for temperatures around 310K, but mean values of almost 2 ADU at temperatures around 338K. The sensitivity of the near-infrared light camera is very low, therefore, the only way to detect a difference between the light levels of the light measurement sphere was to use a high ADC amplication gain. With this it was found that there is a power-law behavior, values between 1.33 and 1.50, of the relationship between pixel values and light intensity. This is likely due to the phosphor coating used to convert to visible light. When trying to detect celestial objects, the faintest object detected was Venus with a magnitude of less than -4.

Extragalactic charged particles, each with energies rising up to and beyond 1 Joule, have been studied for almost a century. Yet, no precise evidence have proven to show where they might originate from as their energy levels rise above the current familiar acceleration sources in outer space. The highly energetic particles have been given the name Ultra-High Energy Cosmic Rays (UHECR) and investigations of particle properties such as primary energy, mass composition and direction can be made through indirect measurements of the interaction between the UHECR and Earth's atmosphere. The considered interaction induces an Extensive Air Shower (EAS) which emits fluorescent light in the Ultraviolet (UV) range. The probability of detecting such events is, however, as low as a few particles per km2 per century. Making observations more sufficient therefore requires larger detection volumes. By introducing the Mini-EUSO instrument, a telescope of which the main purpose is to measure the UV-light radiated from the Earth in the wavelength range of 300-400 nm, allows just for this. To be accommodating the International Space Station and targeting Earth in the nadir direction, the Mini-EUSO instrument will allow for a higher exposure to the interactions than what is currently available. The use of two Fresnel lenses provides the instrument with a large field of view (±22o) and the detections are made through multiple photomultiplier tubes. The scope of this thesis is to evaluate the main detector of the Mini-EUSO instrument (i.e. the UV-detector) through ground-based tests. The procedures involved in the evaluation have consisted of; validating the statistical distributions of the signals, implementing dark field and flat field calibrations, and radiations measurements with three kinds of radiation sources. The data from the tests were provided during two periods and the visualization was made by adapting an already existing piece of code, using Python and ROOT Cern, to perform step by step procedures such that all operations are overlooked properly. The analysis showed that the implementation of the dark field and flat field procedures improved the original image significantly. It also showed that both the lower and higher photon count values in a pixel indeed gave the expected statistical behaviours, with a Poissonian distribution for low values and a Gaussian distribution for higher values. The flat fielding screen did however show unknown fluctuations in the emitted light and further tests have to be implemented to assure its functionality. Under proper covering, almost no dark current was found, however, observation tests showed that the borders of the Multi-Anode Photomultiplier Tubes (MAPMTs) gave higher photon count values than the center part even when they were emitted with Lambertian light.

The main mission of the JEM-EUSO (Extreme Universe Space Observatory) Collaborationis 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 particles with an energy above 1018eV (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 theJEM-EUSO Collaboration comes in. The goal is to measure UHECRs, by observing the fluorescence 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 measurement, and how important they were. Along side this, a calibration was conducted on one of the JEM-EUSO Collaborations instruments, the EUSO-TA (EUSO-Telescope Array). The goal in the end was to try and measurethe 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 magnitude/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 similar 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 workable 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.

Under the name EUSO, or Extreme Universe Space Observatory, are multiple instruments where some are currently under design or construction and others have concluded their mission. The main goal they have in common is to detect and analyse cosmic rays with very high energies by using the Earth's atmosphere as a detector. One instrument is called Mini-EUSO, will be placed on the international space station during 2019, and its engineering model is currently being used to collect data and test the function of different components. The engineering model differ from the full scale instrument, and it is also possible to use it for other purposes as well. In this thesis, some of the collected data is used to analyse and compare the engineering models specification to the full Mini-EUSO instrument, with focus on field of view, inert areas on the sensor and its general function. Objects, such as stars, meteors and satellites were also detected, and used in the tests. In addition a short test regarding the possibility to use the instrument to detect plastic residing in the ocean is made, by utilizing fluorescent properties of the plastics. The thesis came to the conclusion that some adjustments needed to be made on the engineering model, but also that the specifications of it was within expected ranges. Several of the objects found can also be used to improve detection algorithms. In addition, the preliminary tests regarding plastic detection in the ocean, have positive results.