'unlocking the Archive': Using Digital Photogrammetry of Modern Airborne Aerial Photography for Analysis of Historic Aerial Photographs to Extend the Record of Glacier Mass Balance Change on the Antarctic Peninsula

Changes to glacier fronts and ice shelves and glacier acceleration are well documented, but there are almost no data on mass changes for the more than 400 glaciers on the Antarctic Peninsula. Satellite data have been used to calculate change over the last 3 decades, but methods to quantify this over longer timescales have eluded researchers. However there is an archive of aerial photography dating back to the 1940s, this has been largely ignored due to the range of technical problems associated with deriving quantitative data from historic imagery and the lack of ground control data. This presentation demonstrates how advances in photogrammetric processing and capture of modern aerial photography has allowed this archive to be 'unlocked'.

Accurate photogrammetric reconstruction from aerial photographs traditionally requires known ground control points acquired in the field; however, in remote and inaccessible areas, such as the Antarctic Peninsula, this is often impossible. A method for providing control for historic photos without fieldwork, by linking them to a newly acquired, highly accurate photogrammetric model adjusted through direct kinematic GPS positioning of the camera has been applied to a number of glaciers across the Antarctic Peninsula.

This presentation will outline the photogrammetric workflow and associated errors to highlight the suitability of this technique and demonstrate the data that can be obtained. Accurate measurements of surface elevation change on glaciers on the Antarctic Peninsula over a 70 year time span have enabled quantification of spatial and temporal patterns of change. The results show a general trend of glacier retreat, but with thinning of the glacier terminus marginally offset by accumulation in the upper areas of the glacier. The use of this technique opens up possibilities for ‘unlocking the archive’ in other remote glacial areas where historic aerial photography exists but the collection of ground control points is limited.