Instruments and Methods Glacier velocities from time-lapse photos: Technique development and first results from the Extreme Ice Survey (EIS) in Greenland

Abstract

Automated digital cameras were installed in May-June 2007 beside major West Greenland marine-terminating glaciers as part of the Extreme Ice Survey (EIS). EIS cameras began imaging the lowest 4 km2 of the glacier at hourly intervals throughout sunlit periods of the year. This study presents the development of techniques for quantifying glacier velocity from a single camera perspective. A Multi-Image/Multi-Chip matching procedure yields higher matching skill than conventional matching, and facilitates false-match rejection via a clustering scheme. The matching of motionless on-land features facilitates compensating camera motion. Ray projection to a known terrain elevation allows the assigning of scale to convert pixel displacements to velocity units. With the 10.2-megapixel camera system, velocities on relatively fast glaciers can be resolved at distances up to ∼ 4 km. At a distance of 2 km, a demonstrated precision of ∼ 0.5 pixels yields a ∼ 0.5 m footprint size. Daily velocities indicate progressive multi-day velocity accelerations associated with calving. Deceleration trends are associated with the regrowth of resistive stress after major calving. The higher observation frequency available to terrestrial photogrammetry indicates higher observed intra-seasonal velocity range than observable by the at-best weekly satellite snapshots.