Die versyfering van historiese kosmiese straal-data = The digitization of historic cosmic-ray data
Du Plessis, Tjaard
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Due to the research on cosmic-rays in the 1930's, the Carnegie Institute in Washington DC instigated the construction of cosmic-ray observation centers around the world. Cosmic-ray activity was recorded using the model C cosmic-ray ionization chamber which uses a Lindemann electrometer. The shadow of the electrometer needle was projected onto a continuously moving strip of 60 mm photographic paper. Hour markers were recorded by dimming the lamp for three minutes at the start of each hour, while also grounding the ionization chamber. By grounding the ionization chamber the electrometer needle was returned to the zero position. Six ionization chambers were built and installed at six stations around the world. Approximately 114 station-years of data were recorded. Photographic paper moved about 25 mm an hour giving approximately a 25 km strip of photographic record. It is important to digitize these recordings in order to preserve them for further study of cosmic-rays from this time period. The digitizing of cosmic-ray recordings involves the process of transforming the recording image into numbers. Binarizing these recordings will also preserve it in a clear format enabling future research. This study is an attempt to prove that these historic cosmic-ray recordings can be digitized by using image processing techniques. Each foreground element of the recordings; the hour markers, calibration lines and data sequence is segmented. By using these segmented images, the recordings are digitized into meaningful numbers. The study begins with a brief introduction on cosmic-rays as they are recorded today, and how they were recorded before the 1950's. Important events in the area of cosmicrays, ground level enhancements (GLE's), are also introduced. Four of these GLE's were only recorded by the old model C cosmic ray ionization chambers. To show that it is indeed possible to digitize the historic cosmic-ray recordings, two research methodologies are used: A literature study of image processing techniques thought to be helpful in segmenting the foreground elements of the recordings and experimentation with these techniques. Experimentation is the primary research methodology. Existing techniques are used and adapted to segment the foreground elements of the recordings. New techniques are also developed. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully digitize the historic cosmic-ray recordings. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured and future studies are introduced. In the end it is indeed shown that historic cosmic-ray recordings can be digitized by implementing image processing techniques.