Three centuries of weather observations on board of Danish ships: First results from ROPEWALK (Rescuing Old data with People's Efforts: Weather and climate Archives from LogbooK records)

ROPEWALK, funded by the AP Møller Mærsk Fund, is a joint initiative of the Danish National Archive and the Danish Meteorological Institute, which aims at digitizing and transcribing all weather observations in Danish ship journals and logbooks stored in the Danish National Archive, consisting of more than 750 shelf metres beginning as early as the 1680s. With the exception of the Napoleonic wars, the data is complete.

The archive keeps ship journals over large parts of the Northern Atlantic, with two regions of particular interest, Greenland and the Øresund:

The Greenlandic Trade Company had a monopoly for commerce with the colony of Greenland for nearly 200 years. The company conducted these "Greenland Voyages" to western Greenland several times per year, starting as early as 1721 and through the 1930s. Weather observations from these voyages often include detailed sea ice observations.

Every ship passing the sound or belts in Denmark had to pay for passage between 1426 and 1857. To ensure payment, Danish war ships were placed at strategic locations in Øresund and Great Belt. Weather observations on board of these ships (some as often as every half hour) go back to the end of the Little Ice Age.

Up to roughly 1750, the data consists of diary-like daily notes in free text. However, starting already in the 1710s, observations are recorded as numbers in preprinted tables. We have scanned and transcribed this latter dataset, which took 13 person-years, resulting in 2.1 million images covering more than 2.5 TB of data. We then constructed a data model, trained a machine learning algorithm and conducted metadata enhancement and quality control, the latter both in an automatised way and (in a subproject by means of an app we constructed) with the help of pupils in the final grades of Danish primary schools. Free text data will be considered later.

We are now able to present first results. When the project is finished, all transcribed data will be made publicly available for future research or reanalysis projects.