Rescuing 100 Years of Data from the Toronto and Agincourt Magnetic Observatories

Abstract:

We have an ongoing project to digitize a geomagnetic record that began in the 1840s at the Toronto magnetic observatory, on what is now the campus of the University of Toronto. As the city of Toronto grew, the observatory was relocated to Agincourt in 1898, and finally to Ottawa in 1968. The record provides a rare opportunity for high resolution study of geomagnetic phenomena far into the past and over a long time scale. The magnetograms, originally recorded on photographic paper, were transferred to 35mm film in the 1980s. We are now converting these film copies to digital images and devising algorithms for unsupervised extraction of the time series data contained therein. Using the digital images, we are able to extract data with a time resolution of approximately 15 seconds, a magnetic resolution of approximately 0.1 nT, and 24-bit quantization. Spectra computed from the extracted time series are characteristic of spectra computed from current digital instruments, indicating that the extracted data are of high quality. Unsupervised extraction is important for reproducibility and because there are in excess of 32,000 images totalling about 500Gb of computer storage. However, given that perfect extraction performance is impossible due to varying image quality, artefacts such as hand-written notes, and quirks of the recording device, we are developing a semi-supervised approach to ensure data quality.