Reconstruction of former glacier surface topography from archive oblique aerial images

• Published in: Geomorphology
• Main Authors: Midgley, Nicholas G., Tonkin, Toby N.
• Other Authors: Nottingham Trent University, University of Derby
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2017
• Subjects: Structure-from-Motion (SfM); Glacier change; Oblique aerial imagery; Sure-type glaciers; Svalbard; Arctic; Norway; glacier; Norwegian Polar Institute
• Online Access: https://doi.org/10.1016/j.geomorph.2017.01.008; https://repository.derby.ac.uk/download/6e48d9f25731da5a2167edf9a44245a771da36c5f55353eb772e51252854143a/2263852/1-s2.0-S0169555X16306626-main.pdf; https://repository.derby.ac.uk/download/c66e95f032df6c733aa37b1245896da7aee22f62703e8b2b89a4b9771103a03c/1689/license.txt

Archive oblique aerial imagery offers the potential to reconstruct the former geometry of valley glaciers and other landscape surfaces. Whilst the use of Structure-from-Motion (SfM) photogrammetry with multiview stereopsis (MVS) to process small-format imagery is now well established in the geosciences, the potential of the technique for extracting topographic data from archive oblique aerial imagery is unclear. Here, SfM-MVS is used to reconstruct the former topography of two high-Arctic glaciers (Midtre and Austre Lovénbreen, Svalbard, Norway) using three archive oblique aerial images obtained by the Norwegian Polar Institute in 1936. The 1936 point cloud was produced using seven LiDAR-derived ground control points located on stable surfaces in proximity to the former piedmont glacier termini. To assess accuracy, the 1936 data set was compared to a LiDAR data set using the M3C2 algorithm to calculate cloud-to-cloud differences. For stable areas (such as nonglacial surfaces), vertical differences were detected between the two point clouds (RMS M3C2 vertical difference of 8.5 m), with the outwash zones adjacent to the assessed glacier termini showing less extensive vertical discrepancies (94% of M3C2 vertical differences between ± 5 m). This research highlights that historical glacier surface topography can be extracted from archive oblique aerial imagery, but accuracy is limited by issues including the lack of camera calibration, the quality and resolution of the archive imagery, and by the identification of suitable ground control. To demonstrate the value of historical glacier surfaces produced using oblique archive imagery, the reconstructed glacier surface topography is used to investigate evidence of a potential former surge front at the high-Arctic valley glacier, Austre Lovénbreen — a glacier identified to have potentially exhibited surge-type behaviour during the Neoglacial. A surface bulge of ~ 15–20 m is resolved on the 1936 model; however, when compared with the now deglaciated former subglacial ...