Rescuing historical sea level data using a citizen science platform

Tide gauge records provide the main source of data behind the study of sea level change over the past 200 years. However, our understanding of changes in mean sea levels, tides and extremes is limited by the length of the records available. A large amount of potential data exists in libraries and archives across the world in the form of historical tidal ledgers and charts that have never been converted into digital data suitable for use in scientific studies. The Intergovernmental Oceanographic Commission’s Global Sea Level Observing System (GLOSS) has been encouraging organisations to locate, catalogue and digitise such material.

Unfortunately, the processes required to extract usable data from charts and ledgers is slow, laborious work. Promising attempts have been made to automate this using optical character recognition, but these are often hindered by changes in document formats, and hard to decipher handwriting, particularly in older records.

A possible solution is to use online citizen science platforms such as Zooniverse that bring together scientists and volunteers in projects as diverse as searching for supernovae, identifying whale sounds, transcribing manuscripts from the archives of natural history museums, and helping train algorithms that analyse images of cancer cells. Last year, 5.25 million rainfall observations from the UK were digitised in a few weeks by about 16,000 volunteers.

Here we present a citizen science project to digitise 16,000 images of ledgers recording 15-minute observations of sea level from North West England that is currently in progress. We describe the process the volunteers undertake, the lessons learnt from early testing, and an overview of the results obtained so far. Finally, we discuss some potential extensions of the project, including the possibility of using the platform to digitise tidal charts.