Adaptive binarization of legacy ionization chamber cosmic ray recordings

Abstract

In the 1930s, the Carnegie Institute in Washington DC initiated the construction of cosmic ray observation centres around the world. Cosmic ray activity was recorded using the model C cosmic ray ionization chamber which uses a Lindemann electrometer. Seven of these chambers were constructed at seven stations around the world. These chambers recorded cosmic ray data by projecting the shadow of the electrometer needle 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. The photographic paper moved about 25 mm an hour. Approximately 114 station-years of data was recorded between 1935 and 1960 (Hardy, 2006). It is important to digitize these recordings in order to preserve the data for further study of cosmic rays from this time period. This digitization process consists of binarizing digital images of the photographic strip to extract the cosmic ray data. By binarizing these images the data is recorded in an easily usable format for future research. This study focuses on extraction of the cosmic ray data using an adaptive binarization method that is able to cope with a wide variety of images, ranging from images that are almost too bright to distinguish the data lines from the background, to images that are too dark to distinguish the data lines at all. This study starts off with a brief explanation of cosmic rays, how these were recorded before the 1950s and how the rays are recorded today. Two research methodologies were used to create a method to adaptively binarize and extract data from the historic cosmic ray recordings. A literature study of image processing techniques was conducted, focusing specifically on popular adaptive document binarization methods. During the experimental phase of this study, these methods or parts thereof were applied to the data to determine which techniques would give the most accurate results. Experimentation is the primary research methodology. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully binarize and extract the historic cosmic ray data as well as the temperature of the electrometer while recording. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured by comparing the resulting data graph to the original. The conclusion of this study is that an adaptive method can be applied to historical recordings of cosmic ray activity to extract numerical data from a wide variety of images without any additional user input.