Unlocking the Past: A review of digital processing of historical aerial and satellite stereo analog imagery for geoscience applications

Dramatic changes have occurred over the past century in many parts of the planet due to natural factors and intensifying human activities. Understanding these changes is critical for quantifying long-term environmental trends and modelling future conditions. A vast, underexploited resource for such analysis lies in historical aerial and satellite stereo imagery captured with analogue cameras from the early 1900s to the early 2000s. Originally acquired for military and mapping purposes, the stereoscopic nature of historical images offers a unique potential to reconstruct 3D Earth surface changes across the 20th century. Recent advances in photogrammetry and computer vision have greatly enhanced this potential. Despite the early recognition of their value, these datasets remain underexploited due to challenges related to: fragmented and inaccessible archives, digitisation and associated costs, and a lack of scalable, automated processing solutions. This review addresses these challenges by analysing 198 studies that digitally process historical aerial and satellite stereo imagery for orthoimage and DEM generation. We provide an overview of accessed archives, processing strategies, and software pipelines. We discuss emerging tools and advanced image-matching algorithms that are improving automation and georeferencing and highlight how historical imagery can support a wide range of geoscientific applications, from climate change to urban development. Finally, we emphasise the urgent need to unlock these archives and develop efficient, reproducible workflows to preserve and exploit this irreplaceable remote sensing dataset before physical degradation or institutional neglect makes it inaccessible. Information about the dataset and analysis scripts can be found in the README file, or on the dataset webpage.