Photogrammetric methods applied to Svalbard glaciers: accuracies and challenges

Use of digital images is expanding as a tool for glacier monitoring, and small-format time-lapse cameras are increasingly being used for glacier monitoring of fast-flowing glaciers. Stereoscopic imagery is preferable since it yields direct displacement results but stereo photogrammetry has more requirements regarding geometry in set-up and control points, as well as the additional cost of another complete camera system. We investigate a combination of methods to achieve satisfactory control of accuracy with resulting significant day-to-day velocity variations ranging from 1.5-4 m day(-1) made at a distance of 2 km. Validation of results was made by comparing different methods, partly using the same image material, but also in combination with aerial and satellite images. Monoscopic results can also be used to gain continuity in a stereo data set when geometry or visibility is poor. We also explore the use of ordinary photographs taken from airliners for compilation of orthoimages as a potential low cost method for detection of sudden changes. The method, showing some tens of metres accuracy, was verified for monitoring velocities and front positions during a glacier surge and was also used to validate monoscopic time-lapse images.