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Abstract. Stretching time series further in the past with the bestpossible accuracy is essential to the understanding of climate change impactsand geomorphological processes evolving on decadal-scale time spans. In thefirst half of the twentieth century, large parts of the polar regions werestill unmapped or only superficially so. To create cartographic data, anumber of historic photogrammetric campaigns were conducted using obliqueimagery, which is easier to work with in unmapped environments as collocatingimages is an easier task for the human eye given a more familiar viewingangle and a larger field of view. Even if the data obtained from suchcampaigns gave a good baseline for the mapping of the area, the precision andaccuracy are to be considered with caution. Exploiting the possibilitiesarising from modern image processing tools and reprocessing the archives toobtain better data is therefore a task worth the effort. The oblique angle ofview of the data is offering a challenge to classical photogrammetric tools,but the use of modern structure-from-motion (SfM) photogrammetry offers anefficient and quantitative way to process these data into terrain models. Inthis paper, we propose a good practice method for processing historicaloblique imagery using free and open source software (MicMac and Python) andillustrate the process using images of the Svalbard archipelago acquired in1936 by the Norwegian Polar Institute. On these data, our workflow provides5 m resolution, high-quality elevation data (SD 2 m for moderate terrain)as well as orthoimages that allow for the reliable quantification of terrainchange when compared to more modern data.

Precise DEM extraction from Svalbard using 1936 high oblique imagery